1

NEW APPARATUS SIMPLIFIES DESIGN OF MODIFIED ATMOSPHERE PACKAGING USING PERFORATED FILMS

By

AYMAN ABDELLATIEF

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA

2007

2

© 2007 Ayman Abdellatief

3

To my friends and family whose support helped made this possible

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ACKNOWLEDGMENTS

I show my appreciation to my advisor Dr. Bruce Welt whose support made this project

possible. I am grateful to my committee members Dr. Murat O Balaban for his guidance and Dr.

David W Hahn and his graduate student Leia Coffey for their assistance. I thank my colleague

Fernando Vargas for his guidance and friendship. I express my gratitude to Steve Feagle whose

technical expertise was very valuable for this research.I show my sincere appreciation to the

University of Florida and the Agricultural and Biological Engineering Department for their

funding and support.

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TABLE OF CONTENTS Page

ACKNOWLEDGMENTS ...............................................................................................................4

LIST OF TABLES...........................................................................................................................7

LIST OF FIGURES .........................................................................................................................9

NOMENCLATURE ......................................................................................................................12

ABSTRACT...................................................................................................................................14

CHAPTER

1 INTRODUCTION ..................................................................................................................16

Modified Atmosphere Packaging ...........................................................................................16 Mathematical Modeling of Modified Atmosphere Packaging ...............................................16

Permeation Theory ..........................................................................................................16 Modeling of Modified Atmosphere Packaging ...............................................................18

2 DETERMINING THE NECESSITY OF PERFORATIONS FOR COMMERCIALLY PACKAGED PRODUCE.......................................................................................................21

Introduction.............................................................................................................................21 Respiration.......................................................................................................................21 Permeation.......................................................................................................................22 Ideal Storage Conditions .................................................................................................23 Objectives ........................................................................................................................24

Materials and Methods ...........................................................................................................24 Headspace Analysis.........................................................................................................24 Oxygen Transmission Rates of the Package ...................................................................25 Product Respiration Rates ...............................................................................................25

Results and Discussion ...........................................................................................................26 Headspace........................................................................................................................26 Respiration and Package Oxygen Transmission Rate .....................................................26 Example of How to Calculate Respiration Rate from Respiration Data .........................29

3 METHOD FOR MEASURING THE OXYGEN TRANSMISSION RATE OF PERFORATED FILMS..........................................................................................................31

Introduction.............................................................................................................................31 Theory..............................................................................................................................32 Oxygen Transmission Rate (OTR) Measurements..........................................................35

Non-perforated films ................................................................................................35 Perforated films ........................................................................................................36

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Fiber optic oxygen sensor ........................................................................................36 Materials and Methods ...........................................................................................................37

Measurement of Samples ................................................................................................38 Recalculating Diffusion Coefficients ..............................................................................39 Results and Discussion ....................................................................................................39

4 NEW APPARATUS SIMPLIFIES DESIGN OF MODIFIED ATMOSPHERE PACKAGING WITH PERFORATED FILMS......................................................................42

Introduction.............................................................................................................................42 Materials and Methods ...........................................................................................................42

Broccoli Package OTR....................................................................................................43 Modified Atmosphere Package Design with Perforations ..............................................43

Results and Discussion ...........................................................................................................44 Headspace of Commercially Packaged Broccoli ............................................................44 Respiration of Broccoli....................................................................................................44 Broccoli Package OTR....................................................................................................46 Broccoli Package Performance Data ...............................................................................46 Prediction of OTR Package using Design Equation........................................................48

5 CONCLUSIONS ....................................................................................................................49

APPENDIX

A RESPIRATION DATA FOR THE FIVE RESPIRING PRODUCTS ...................................52

B OXYGEN TRANSMISSION RATE OF PRECISION ORIFICES.......................................82

C BROCCOLI PACKAGE DATA ............................................................................................88

REFERENCES ..............................................................................................................................90

BIOGRAPHICAL SKETCH .........................................................................................................93

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LIST OF TABLES

Table page 1-1 Gas Permeabilities of various polymers used in Modified Atmosphere Packaging

(Robertson 1993). ..............................................................................................................18

2-1 Headspace data from bagged samples. ..............................................................................26

2-2 Oxygen respiration coefficients .........................................................................................28

2-3 Required OTR at design temperature and desired O2 level ..............................................29

3-1 Oxygen diffusion coefficient in air calculated from precision orifices and Perry’s Chemical Engineering Handbook ......................................................................................40

4-1 Respiration coefficients for oxygen and carbon dioxide for broccoli................................46

A-1 Rutabaga respiration data 15ºC..........................................................................................52

A-2 Rutabaga respiration data 8ºC............................................................................................54

A-3 Rutabaga respiration data 1ºC............................................................................................56

A-4 Sweet Potato respiration data 15ºC....................................................................................58

A-5 Sweet Potato respiration data 8ºC......................................................................................60

A-6 Sweet Potato respiration data 1ºC......................................................................................62

A-7 Squash respiration data 15ºC .............................................................................................64

A-8 Squash respiration data 8ºC ...............................................................................................66

A-9 Squash respiration data 1ºC ...............................................................................................68

A-10 Squash and Zucchini respiration data 15ºC .......................................................................70

A-11 Squash and Zucchini respiration data 8ºC .........................................................................72

A-12 Squash and Zucchini respiration data 1C...........................................................................74

A-13 Turnip respiration data 15ºC..............................................................................................76

A-14 Turnip respiration data 8ºC................................................................................................78

A-15 Turnip respiration data 1ºC................................................................................................80

B-1 OTR of precision orifices at 15, 23, and 30°C...................................................................82

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C-1 Commercially Packaged Broccoli Head Space Samples ...................................................88

C-2 Broccoli Respiration Data..................................................................................................89

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LIST OF FIGURES

Figure page 1-2 Atmosphere of packaged tomatoes over time. The top curve indicates the CO2

concentration while the bottom curve indicates the oxygen concentration over time.......20

2-1 Actual data logger results for sample shipment from commercial producer to University of Florida..........................................................................................................24

2-2 Unsteady state respiration data for Rutabaga at 15°C, % vs time. ....................................27

2-3 Unsteady state respiration data for Rutabaga at 15°C, cc/g vs time. .................................27

3-1 Typical apparatus for measuring OTR using coulometric method....................................32

3-2 Unsteady state measurement of headspace over time........................................................33

3-3 Schematic Profile of OTR chamber...................................................................................38

3-4 Plot used to determine OTR of hole/perforation 249µm hole at 300C. .............................39

3-5 OTR of holes vs. temperature ............................................................................................40

4-1 Unsteady state respiration data for Broccoli at 4°C % vs time..........................................45

4-2 Unsteady state respiration data for Broccoli at 4°C cc/g ...................................................45

4-2 Plot used to determine OTR of hole/perforation at 40C. ...................................................47

4-3 Broccoli packages reaching steady state............................................................................47

A-1 Rutabaga 15ºC, % vs time .................................................................................................53

A-2 Rutabaga 15ºC, cc/g vs time ..............................................................................................53

A-3 Rutabaga 8ºC, % vs time....................................................................................................55

A-4 Rutabaga 8ºC cc/g vs time .................................................................................................55

A-5 Rutabaga 1ºC, % vs time....................................................................................................57

A-6 Rutabaga 1ºC, cc/g vs time ................................................................................................57

A-7 Sweet Potato 15ºC, % vs time............................................................................................59

A-8 Sweet Potato 15ºC, cc/g vs time ........................................................................................59

A-9 Sweet Potato 8ºC, % vs time..............................................................................................61

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A-10 Sweet Potato 8ºC, cc/g vs time ..........................................................................................61

A-11 Sweet Potato 1ºC, % vs time..............................................................................................63

A-12 Sweet Potato 1ºC, cc/g vs time ..........................................................................................63

A-13 Squash 15ºC, % vs time .....................................................................................................65

A-14 Squash 15ºC, cc/g vs time..................................................................................................65

A-15 Squash 8ºC, % vs time .......................................................................................................67

A-16 Squash 8ºC, cc/g vs time....................................................................................................67

A-17 Squash 1ºC, % vs time .......................................................................................................69

A-18 Squash 1ºC, cc/g vs time....................................................................................................69

A-19 Squash and Zuchini 15ºC, % vs time.................................................................................71

A-20 Squash and Zuchini 15ºC, cc/g vs time..............................................................................71

A-21 Squash and Zuchini 8ºC, % vs time...................................................................................73

A-22 Squash and Zuchini 8ºC, cc/g vs time................................................................................73

A-23 Squash and Zuchini 1ºC, % vs time...................................................................................75

A-24 Squash and Zuchini 1ºC, cc/g vs time................................................................................75

A-25 Turnips 15ºC, % vs time ....................................................................................................77

A-26 Turnips 15ºC, cc/g vs time.................................................................................................77

A-27 Turnips 8ºC, % vs time ......................................................................................................79

A-28 Turnips 8ºC, cc/g vs time...................................................................................................79

A-29 Turnips 1ºC, % vs time ......................................................................................................81

A-30 Turnips 1ºC, cc/g vs time...................................................................................................81

B-1 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 100 µm 15°C............................................................82

B-2 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 153 µm 15°C............................................................82

B-3 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 205 µm 15°C............................................................83

B-4 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 249 µm 15°C............................................................83

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B-5 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 100 µm 23°C............................................................84

B-6 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 153 µm 23°C............................................................84

B-7 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 205 µm 23°C............................................................85

B-8 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 249 µm 23°C............................................................85

B-9 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 100 µm 30°C............................................................86

B-10 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 153 µm 30°C............................................................86

B-11 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 205 µm 30°C............................................................87

B-7 -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 249 µm 30°C............................................................87

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NOMENCLATURE

A area of package (cm2)

Ah .area of hole (cm2)

c1 gas concentration inside package

c2 gas concentration outside package

J diffusive flux of gas through package (cm3/cm2/s)

Jh diffusive flux of gas through perforation (cm3/cm2/s)

L package thickness (mil)

Lh perforation thickness (cm)

OTRnon perf oxygen transmission rate (cc/cm2/day) for non-perforated package

OTR perf oxygen transmission rate (cc/day) for perforated package

2inOp partial pressure of oxygen inside package

2outOp partial pressure of oxygen outside package

2inCOp partial pressure of carbon dioxide inside package

2outCOp partial pressure of carbon dioxide outside package

2inNp partial pressure of nitrogen inside package

2outNp partial pressure of nitrogen outside package

p1 partial pressure of gas inside package

p2 partial pressure of gas outside package

−−

P gas permeability coefficient (cc-mil/cm2/day)

2OP−−

oxygen permeability coefficient (cc-mil/cm2/day)

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2COP−−

carbon dioxide permeability coefficient (cc-mil/cm2/day)

2NP−−

nitrogen permeability coefficient (cc-mil/cm2/day)

Rh radius of perforation (cm)

2OR respiration rate of oxygen (cc/g/day)

2COR respiration rate of carbon dioxide (cc/g/day)

S Henry’s Law gas solubility coefficient

t time (days)

V volume of package (cc)

W weight of product in package (g)

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering

NEW APPARATUS SIMPLIFIES DESIGN OF MODIFIED ATMOSPHERE PACKAGING USING PERFORATED FILMS

By

Ayman Abdellatief

May 2008

Chair: Bruce Welt Major: Agricultural and Biological Engineering The overall objective of this project was to design a modified atmosphere package for

respiring produce using perforated films. Respiration was measured for sliced rutabaga, sweet

potato, squash, squash and zucchini mixture, and turnips. Samples were stored in closed jars at 1,

8, and 15°C. Rutabaga consistently followed a hyperbolic decay trend at all three temperatures.

The other products showed hyperbolic decay at the highest temperature but shifted to a linear

trend at lower temperatures. Oxygen transmission rate of the commercial package of each

product was measured and respiration rate of each product was determined at the recommended

temperature and atmosphere of storage to assess the necessity of perforations to the package. It

was determined that turnips were the only product that did not require perforations in its

packaging.

A new apparatus using a fiber optic oxygen sensor was developed to measure OTR of

perforated films. OTR of holes of 100, 153, 205, and 249 μm were measured at 15, 23, and 30°C.

As diameter increased OTR increased and as temperature increased OTR decreased for a

particular diameter. Consistent and reproducible measurements using precision orifices provided

confidence that the device could be applied to perforations in plastic films, which are not as

easily characterized.

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Packages of broccoli were designed using polyethylene film (2.5 mil thick) with an area

of 1050 cm2. A 13.5 gage drill tool was used to perforate packages. Unsteady state methods were

used to measure respiration rate of broccoli at 4°C. Ten packages were stored at 4°C and allowed

to reach steady state. Required OTR to maintain package at average steady state O2

concentration was calculated using experimentally derived respiration rate and literature values,

which were of similar orders of magnitude. Package OTR was measured in two parts, a non-

perforated portion and a perforated portion. Non-perforated OTR was measured in the typical

way at 20 and 30°C. OTR at 4°C was determined by extrapolation of the Arrhenius temperature

sensitivity relationship. Perforated film OTR was measured at 4°C using our new apparatus.

Total measured OTR was calculated by adding perforated OTR and non-perforated OTR.

Perforation region accounted for the majority of the OTR. Measured OTR agreed well with

required calculated values of OTR suggesting the new apparatus is a valuable tool for designing

modified atmosphere packaging of fresh produce using perforated films.

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CHAPTER 1 INTRODUCTION

Modified Atmosphere Packaging

Consumer demand for fresh and convenient foods has led to the growth of modified

atmosphere packaging (MAP) as a technique to improve product image, reduce waste, and

extend the shelf life of a wide range of foods (Martinez-Ferrer et al., 2002). Many fresh products

reduce respiration rate due to reduced oxygen concentration and increased carbon dioxide

concentration, which increases shelf life (Lee et al., 1991). Modified atmospheres must not be

too deficient in oxygen in order to avoid anaerobic respiration that can rapidly damage plant

tissue, cause fermentation, and produce off flavors (Kader et al., 1989). Additionally, high

concentrations of CO2 can also injure plant tissues. Therefore, packaging with oxygen

transmission rates that match desired respiration requirements are necessary in order to achieve

optimal shelf-life results. Recommended atmospheres for various fruits and vegetables can be

found in the literature (Mannapperuma et al., 1989, Saltveit, 1985).

Mathematical Modeling of Modified Atmosphere Packaging

Permeation Theory

Permeation of a gas through a polymer film is a combination of diffusion and solubility.

A gas will diffuse through a polymer film at a constant rate if a constant concentration gradient is

maintained across the film. The diffusive flux, J, of a gas in a polymer is the amount (Q) passing

through a surface of area (A) normal to the direction to the direction of flow during time (t), i.e.

AtQJ = (1-1)

The diffusive flux of a gas through a film is directly proportional to the concentration

gradient, ⎟⎠⎞

⎜⎝⎛∂∂Lc , across a surface of thickness L)(∂ and is given by Fick’s first law:

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Lc-DJ

∂∂

= (1-2)

Once steady state is achieved equation (1-2) can be integrated from the concentration of

one surface c1 to the opposite surface c2 across a film of thickness X and is given by:

)c(c D- L J 21 −= (1-3)

which can be re-arranged to

L)c(c D

J 12 −= (1-4)

The right hand side of equation (1-1) can be substituted for the diffusive flux J which

yields.

L)c(c D

AtQ 12 −= (1-5)

At sufficiently low concentrations Henry’s law can be applied and is expressed as

p S c = (1-6)

Where S is the solubility coefficient and p is the partial pressure of the gas. Equation 6 can

be substituted into equation (1-5) which gives.

L)p(p S D

AtQ 12 −= (1-7)

The product D S is the permeability coefficient and is represented by the symbol P.

Yielding

Lp)(P

AtQ

__Δ

= (1-8)

Which can be rearranged to

p)(A t L QP

__

Δ= (1-9)

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Four assumptions were made in the derivation of the permeability coefficient. The

assumptions are that diffusion is at steady state, the concentration gradient is linear though the

polymer, diffusion takes place in only one direction, and D and S are independent of

concentration (Robertson 1993). The gas permeability of various polymers used in modified

atmosphere packaging is shown in Table (1-1) (Robertson 1993)..

Table 1-1. Gas Permeabilities of various polymers used in Modified Atmosphere Packaging

Polymer N2 O2 CO2 (P_O2/P_N2) (P_CO2/P_O2) (P_CO2/P_N2)30°C 30°C 30°C

Low Density Polyethylene 4910 14200 91000 2.9 6.4 18.5High Density Polyethylene 698 2740 9040 3.9 3.3 13.0Polypropylene ----- 5940 23800 ----- 4.0 -----Poly( vinyl chloride) 103 310 2580 3.0 8.3 25.0Polystyrene 749 2840 22700 3.8 8.0 30.3Nylon 6 25.8 98.2 413 3.8 4.2 16.0Poly( ethylene terephthlate) 12.9 56.8 395 4.4 7.0 30.6Poly( vinylidene chloride) 2.43 13.7 74.9 5.6 5.5 30.9

Mean 3.9 5.8 23.5

(cc-mil)/(m2day-atm)

Modeling of Modified Atmosphere Packaging

To maintain a desired atmosphere within a package, rates of gas permeation for a particular

gas through the package must match the respiration rate of that gas for that product. At any time

the rates of changes in the concentrations of O2, CO2, and N2 per unit volume of free gas space

can be expressed as (Wiley, 1994):

( )V

WRLV

ppAPdt

dp22out2in22 OOOOO −

−=

−−

(1-10)

( )V

WRLV

ppAPdt

dp22out2in22 COCOCOCOCO −

−=

−−

(1-11)

( )

LVppAP

dtdp

2out2in22 NNNN −=

−−

(1-12)

Where [O2], [CO2], and [N2] are the concentrations of O2, CO2, and N2 respectively; 2OP−−

,

2COP−−

, and 2NP−−

are the permeabilities of the film to O2, CO2, and N2; A is the area of the film; L

19

is the thickness of the film 2O

R , and2COR , the rates of consumption of O2 and production of CO2

respectively; W is the weight of the produce; and V is the headspace volume of the package.

When the system reaches steady state, the concentration of the gases do not change with

time, equations (1), (2), and (3) simplify to

( )L

ppAPWR 2out2in2

2

OOO

O

−=

−−

(1-13)

( )

LppAP

WR 2out2in2

2

COCOCO

CO

−=

−−

(1-14)

2out2in NN pp = (1-15)

Many attempts have been made to mathematically model the gas atmosphere in a

modified atmosphere package. Equations (1-10, 1-11) were simulated numerically by Henig and

Gilbert (1975) for packaged tomatoes while Hayakawa et. al. (1975) solved them analytically

using Laplace Transforms (Figure 1-2) also for tomatoes.

Many respiring products have respirations rates too high for the oxygen transmission rates

of most commercially available packaging material. For these products it is necessary to

perforate the packages to increase oxygen transmission rate to a sufficient level. Diffusion of

oxygen through air is about six orders of magnitude greater than permeation through

polyethylene films commonly used in packaging. Even a small hole can greatly increase oxygen

transmission rate of packaging material.

To be able to design a modified atmosphere package for respiring produce, respiration rate

of the product must be known at the desired gas composition and storage temperature. Once

respiration rate is known, a suitable packaging material must be selected. If there is no

commercially available packaging material with sufficient oxygen transmission rate, then it

becomes necessary to incorporate perforations. Therefore it becomes necessary to measure

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oxygen transmission rate of the perforated material. Unfortunately most of the methods used to

measure oxygen transmission rate of packaging materials are not suitable for films with

perforations.

Figure 1-2. Atmosphere of packaged tomatoes over time. The top curve indicates the CO2 concentration while the bottom curve indicates the oxygen concentration over time

The objectives of this work were threefold. The first was to determine the respiration rates

of sliced Rutabaga, Sweet Potato, Squash, Squash and Zucchini, and Turnips at optimal storage

conditions and to assess the necessity of value added perforations to the commercial packaging

for each product. The second was to develop a method to determine the oxygen transmission

rates (OTR) of perforated packaging films. The third was to demonstrate the design of a

modified atmosphere package with perforations using the new method and apparatus developed

to measure the OTR of perforated films.

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CHAPTER 2 DETERMINING THE NECESSITY OF PERFORATIONS FOR COMMERCIALLY

PACKAGED PRODUCE

Introduction

Fresh produce is particularly challenging to package because products contain living

tissues that require adequate gas exchange to remain fresh. Produce respiration rate is one of the

best measures for prediction of shelf life. Generally, lower respiration rate translates into longer

shelf life. Rate of respiration typically varies with oxygen concentration and inversely with

carbon dioxide concentration. The goal of MAP is to design a package that provides an optimal

level of oxygen and carbon dioxide transmission to match reduced respiration rate requirements

of the produce.

Respiration

Respiration in fruits and vegetables can be described by the following chemical reaction

(Ryall and Pentzer, 1979; 1982):

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (2-1)

Attempts have been made to model respiration of fruits and vegetables with Michaelis

Menten type kinetics with competitive inhibition of oxygen consumption by the production of

carbon dioxide (Lee et al., 1991; Hagger et al., 1992).

Lowering the O2 level around fresh fruits and vegetables reduces their respiration rate in

proportion to the O2 concentration, but a minimum of about 1-3% O2 is required depending on

the commodity. Otherwise respiration will shift from aerobic to anaerobic. The glycolytic

pathway replaces the Krebs cycle as the main source of energy for the plant tissues. Byproducts

such as acetaldehyde and ethanol are formed which give off flavors and spoil the product (Kader,

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1986). Injuring fruit and vegetable tissue by slicing generally increase the respiration rate 3 to 5

fold. The respiration rate also increases 2 to 3 fold as the product ages. (Laties, 1978).

Permeation

To maintain a desired atmosphere within a package, rates of gas permeation through the

package must match respiration demands of products. This steady state relationship is described

by Equation (2-2) (Robertson, 1993).

LpAPWR Δ

= (2-2)

where W is the weight of produce, R is the respiration rate of produce (amount of gas)/(weight of

produce x time)), P is the gas permeation coefficient for the gas of interest through the

particular plastic at a specified temperature (amount of gas x film thickness/(area of film x gas

partial pressure difference on either side of the film x time), A is the area of the plastic package,

pΔ is partial pressure difference and L is film thickness.

Oxygen transmission rate (OTR) is often measured for particular films. OTR is related to

permeability, P , via Equation (2-3).

LΔpPOTR perfnon ⋅

= (2-3)

OTR is often measured using 100% oxygen as the test gas, which provides the maximum

driving force for oxygen transmission (1 atm), and higher analytical resolution. OTR

requirements may be predicted for air by combining Equations (2-2) and (2-3) by rearranging to

form Equation (2-4).

⎟⎠⎞

⎜⎝⎛

−=

20.9100

)pA(0.21RWOTR

inside

(2-4)

23

Where R is respiration rate of produce, W is the weight of the produce in the package, A is

package area, and pinside is the desired partial pressure of oxygen inside the package.

Ideal Storage Conditions

Determination of ideal storage conditions (temperature and gas compositions) for products

requires extensive experimentation under controlled conditions. Often, ideal conditions vary

considerably for any particular product and may be a function of produce size, geometry,

cultivar, season, etc. Therefore, ideal conditions are better described as ideal ranges of

conditions and therefore, package designs tend to be conservative. The following conditions for

produce items related to those studied here were found in the literature:

Rutabagas. Rutabagas should be stored in an atmosphere of approximately 5% CO2 and >

5% O2 between 1 and 3 °C for maximum shelf life (Gorny, 1997).

Sweet Potato. Sweet Potatoes should be stored in an atmosphere of approximately 6.5%

CO2 and > 12% O2 between 0 and 4 °C for maximum shelf life

(http://usna.usda.gov/hb66/147freshcutvegetables.pdf).

Squash . Squash is highly perishable and should not be stored for more than 2 weeks.

Optimal storage conditions are 5 to 10°C at 95% RH (Hardenburg et al., 1986). Lower oxygen

atmospheres are of no beneficial use for Squash (Leshuk and Saltveit, 1990; Mencarelli et al.,

1983). Squash is susceptible to chilling injury at temperatures below 50C. (Ryall and Lipton,

1979).

Zucchini. Sliced zucchini develops water soaked areas (chilling injury) at 0°C and brown

discoloration between 5 and 10°C, which increases with storage duration. Zucchini slices can be

dipped in solutions of CaCl2 alone or with NaOCl. Calcium treatments reduce development of

24

decay and total microbial growth, and ascorbate loss. Optimal storage conditions for zucchini are

0.25% to 1% oxygen at 0 to 5°C (Gorny, 1997).

Turnips. Turnips can be held 4 to 5 mo at 0 °C (32 °F) with 90 to 95% RH. An ideal

atmosphere has not been determined for turnips 6 (http://usna.usda.gov/hb66/140turnip.pdf).

Objectives

The objectives of this work were to verify performance of commercially produced MAP

packages and to assess necessity for cost-adding film perforations used to produce certain fresh-

cut product packages.

Materials and Methods

Headspace Analysis

Bagged product samples were shipped to the University of Florida via overnight delivery

in insulated packaging equipped with two freezer cold packs. Several shipments contained

temperature recorders that showed product enroute approximately 18 hours with temperatures

generally between 4 and 10°C (Figure 2-1).

Figure 2-1. Actual data logger results for sample shipment from commercial producer to University of Florida.

Upon arrival at our laboratory, products were placed in a 1-3°C controlled environmental

chamber for about 24 to 48 hours prior to use. A dab of silicone sealant was applied to each bag

upon arrival in order to create a septum through which a needle was inserted to sample achieved

headspace gas compositions of product samples. A headspace analyzer (Pack Check, Mocon,

25

Inc., Minneapolis, MN) was used to determine oxygen and carbon dioxide concentrations in

sample headspaces. Table 2-1 shows results of headspace measurements.

Oxygen Transmission Rates of the Package

Two samples from the front panel of the package of each product were prepared by cutting

a 100 cm2 sample films using a standard cutting die and razor knife. Film sample were then

mounted into the oxygen transmission rate analyzer (Oxtran 2/20, Mocon, Inc., Minneapolis,

MN).

Product Respiration Rates

Product respiration rates were measured using an unsteady-state method (Lee et al., 1991;

Hagger et al., 1992). Briefly, a given amount of product is placed in hermetically sealed jars and

changes in headspace gas compositions are monitored over time. Empirical curves are fitted to

gas versus time data and mathematical derivatives of these curves (instantaneous slopes), provide

respiration rates as a function of gas composition.

One liter mason jars were used for unsteady-state respiration experiments. Holes were

drilled (about ½ inch) into mason jar lids to accommodate a rubber septum. Prior to conducting

respiration experiments, product densities were measured via water displacement in the jars

(Table 1). Product densities were used to calculate head space gas volume from the difference

between container volume and sample volume.

Nine Samples of each product (ca. 125 g) were placed in each jar. For “Squash and

Zucchini” samples, about half was squash and half was zucchini, by weight. Lids were placed

firmly on jars and holes were sealed with rubber septa. Three samples of each product were

placed in controlled environmental chambers set at 1, 8, and 15°C. Oxygen and carbon dioxide

concentrations were measured periodically using the headspace analyzer (Pac-Check, Mocon,

26

Inc., Minneapolis, MN). Samples stored at 15, 8 and 1°C were measured about every 2 hours, 4

hours, and 12 hours, respectively.

Results and Discussion

Headspace

Sample headspace data proved to be highly variable, as seen by relatively large standard

deviations in Table 2-1. However, data appear to be in desirable ranges.

Table 2-1. Headspace data from bagged samples.

Item Mean S.D. Mean S.D. (g/cm3) S.D.Rutabaga 8.30 3.16 10.81 2.22 1.00 0.001Sweet Potato 11.17 5.88 9.41 5.34 0.95 0.015Squash 15.51 1.20 7.51 1.22 0.88 0.008Squash and Zucchini 13.45 1.38 8.71 1.19 0.90 0.040Turnips 7.46 2.69 11.32 2.10 0.90 0.012

O2 (%) CO2 (%) Density

Means and standard deviations for headspace data are from 10 samples. Average density values and standard deviations calculated from 3 samples.

Respiration and Package Oxygen Transmission Rate

Changes in carbon dioxide and oxygen concentrations with time showed approximately

linear or hyperbolic trends. Squash and Zucchini at 15°C, Rutabaga at 15 and 8°C and Turnips

at 15 and 8°C showed nonlinear behavior. For oxygen, a hyperbolic decay function was used to

fit data using non-linear regression (Equation 2-5):

tbabyy+

+= 0 (2-5)

Where y is oxygen concentration, t is time and y0, a, and b are coefficients. For carbon

dioxide, a hyperbolic function was used to fit data using a non-linear regression (Equation 2-6):

tbatyy+

+= 0 (2-6)

27

Where y is carbon dioxide concentration, t is time and y0, a, and b are coefficients. Figure

2-2 shows changes in gas compositions for Rutabaga at 15°C. Measured data and fitted curves

are shown in Figure 2-6 and fitted curve coefficients are provided in Table 2-2.

Figure 2-2. Unsteady state respiration data for Rutabaga at 15°C, % vs time.

Figure 2-3. Unsteady state respiration data for Rutabaga at 15°C, cc/g vs time.

28

Some products could be reasonably approximated as linear for changes in oxygen and

carbon dioxide with time. These data were fitted with Equation 2-8.

baty += (2-7)

Where y is either oxygen or carbon dioxide concentration, x is time and a, and b are

coefficients. Table 2-2 provides coefficients for all products at all temperatures for oxygen. Data

fitted with Equation 2-8 are indicated with the term, “Linear” in the yo column of Table (2-2).

Table 2-2. Oxygen respiration coefficients Temp yo(0C) cc/g a b R2

Rutabaga 15 -1.0916 2.4305 1.9985 0.98958 -0.7373 2.0799 3.6545 0.99071 -2.8446 4.1162 38.0157 0.9899

Sweet Potato 15 -2.7040 4.0357 2.1200 0.99088 -3.8433 5.1709 5.4468 0.99581 Linear -0.3174 1.3313 0.9958

Squash 15 -2.6889 4.0052 3.7000 0.99618 Linear -0.4957 1.3398 0.98771 Linear -0.1733 1.3536 0.9839

Squash and Zuchinni 15 -0.5543 1.899 1.3609 0.99218 Linear -0.4589 1.3403 0.99521 Linear -0.1595 1.3456 0.9934

Turnips 15 -1.2961 2.5458 3.3636 0.97088 -0.7443 1.9545 6.5762 0.98321 Linear -0.0618 1.1130 0.9704

Rates of respiration for both oxygen and carbon dioxide were calculated from the

mathematical derivatives of the non-linear regression functions. Cases where gas compositions

changed linearly with time suggested that respiration rate was not a strong function of gas

composition under the specific test conditions and these were considered to be a constant equal

to the slope of the fitted curve. Rates of oxygen consumption were similar to carbon dioxide

evolution, suggesting respiration quotients, RQ, of about unity for all products. Therefore,

further calculations were based solely on oxygen consumption. Table (2-3) provides additional

29

data used to estimate average rates of oxygen consumption at apparently “desirable” package

oxygen levels for each product at each temperature.

Table 2-3. Required OTR at design temperature and desired O2 level Product weight OTR

Design T Desired O2 Film Area in package Film OTR RequiredItem 0C (%) (cm2/bag) (g) (cc/day/bag) (cc/day/bag)

Rutabaga 3.0 8.0 817.48 454 25 44Sweet Potato 3.0 12.0 794.29 568 39 232Squash 5.0 10.0 719.78 340 38 100Squash and Zuchinni 5.0 10.0 752.00 340 38 100Turnips 3.0 7.5 785.97 340 29 24

The respiration rates were then calculated at the desired temperature and oxygen

concentration and compared to the OTR of the film at the desired temperature. Table 2-3

indicates that the packages for all the products except for turnips do not have a high enough OTR

to meet the respiration requirements at the design temperature and desired O2 level and therefore

perforations are necessary.

Example of How to Calculate Respiration Rate from Respiration Data

For rutabaga, design temperature is 3°C and desired O2 level is 8%. It would be ideal to

conduct respiration studies at design temperature, but if data are not available they may be

inferred from the Arrhenius temperature sensitivity relationship. Oxygen respiration rate at 8%

headspace oxygen must be calculated at 1, 8 and 15°C. Then, oxygen respiration rate at 3°C

may be calculated from the Arrhenius relationship.

Using 15°C for demonstration, time to reach the desired O2 level may be estimated from

the O2% - time curve (Figure 2-2). The Figure shows that it takes approximately 1 day to reach

8% O2 at 15°C. Time can be substituted into the mathematical derivative of equation (2-6), which

is given by

( )2tbab

dtdy

+−

= (2-8)

30

Substituting time and coefficients given in Table 2-2 yields

( ) daygcc54025.0

19985.19985.1*4305.2

2 −−=

+−

=dtdy

Following the same procedure for 8 and 1°C gives oxygen respiration rates of

-0.20067 and -0.07155 cc/g/day, respectively. Arrhenius temperature sensitivity is given by

Equation 2-9

T11047

O 38.969R2

−

= e (2-9)

where T is the absolute temperature in Kelvin. Substituting design temperature 276.15 K into

Equation 2-9 gives

daygcc09650.0R

2O −=

Multiplying 2OR by the weight of the product in the package from Table 2-3 gives

44 cc/day. An OTR of 44 cc/day is required to maintain a 454 g package of rutabaga at

3°C and 8% O2. OTR of commercial package for Rutabaga measured in this experiment is 25

cc/day from Table 2-3.

31

CHAPTER 3 METHOD FOR MEASURING THE OXYGEN TRANSMISSION RATE OF PERFORATED

FILMS

Introduction

Few commercially available films have sufficiently high oxygen transmission rates for

packaging of respiring products. Many fruits and vegetables, such as strawberries and mangos

have high respiration rates which makes it difficult to supply sufficient oxygen through

packaging films without perforations. Films with perforations on the order of 40 to 250 µm are

generally referred to as micro-perforated films. Design of packages using micro-perforated films

has been difficult due to lack of methods capable of properly measuring OTR of films with

perforations. OTR of micro-perforated film depends on temperature dependant factors including

permeability of the film, perforation geometry, film thickness, and number of perforations in a

given area of film.

Difficulties measuring OTR of perforated films with traditional approaches is evident.

Figure 3-1 shows the coulometric approach that is the basis of instrumentation supplied by

Mocon, Inc. (Minneapolis, MN). The figure shows a test where oxygen would permeate from

right to left through the sample film mounted in the middle.

Test films split the test chamber into two halves. An oxygen containing gas (test gas)

flows on one side while an oxygen free gas (carrier gas) flows on the other. This system works

well for film samples without perforations since slight variations of pressure on either side of the

sample do not significantly alter measurements. However, when perforations exist, variations in

pressure cause gas to flow freely from one side to the other, which directly affects

measurements. It is difficult to imagine how this approach could be designed to work reliably for

perforated films.

32

Figure 3-1. Typical apparatus for measuring OTR using coulometric method.

Figure 3-2 shows an alternative method for measuring OTR, which requires headspace

sampling over time. Actual experiments often require removal of multiple samples from a single

test specimen. Without perforations, each sampling changes headspace volume, which affects

the measurement. With perforations, each sample draws new gas into the headspace, changing

gas compositions, thus affecting subsequent samples

To overcome these difficulties, a new approach was developed using a fluorescence based

fiber optic sensor that is capable of continuously measuring gas within the test apparatus without

removing or consuming gas and without a need for continuously flowing gases.

Theory

Attempts to predict transmission rates of gases through perforated films have been made.

Emond et al., (1991) and Fonseca et al., (1996) used empirical models to describe diffusion of

gases through perforated films. Fishman et al., (1996) modeled transmission rates of gases using

33

Fick’s law of diffusion, while Hirata et al., (1996) used Graham’s law of diffusion. Renault et al.,

(1994a) modeled diffusion of gas through perforated films with Maxwell Stefans law. Ghosh and

Anantheswaran (1998) determined that models based on Fick’s law were in closest agreement

with experimental data.

Figure 3-2. Unsteady state measurement of headspace over time

Oxygen transfer rate of perforated film depends on two mechanisms including

permeation of oxygen through the base film and diffusion of oxygen through the perforation.

Total flow through the film was described by Fishman et al. (1996) as:

hh AJJAF += (3-1)

Where A is the total area of the film, J is the flux of oxygen through the film, Ah is the total area

of the holes, and Jh is the flux of gas through a unit area of a hole.

Permeation of gas through the film is given by:

L

)p(pPJ 21 −−=

−−

(3-2)

Air

Film

Perforation

34

Where P is the permeability of the film, L is film thickness, pi is partial pressure of oxygen

inside the package and pA is partial pressure of oxygen in the atmosphere surrounding the

package.

Diffusion of oxygen through perforations should obey Fick’s Law:

h

21h L

)pD(pJ

−−= (3-3)

Where D is the diffusion coefficient of gas in air through the perforation and Lh is the diffusion

path length. If the distance between perforations is much greater than the radius of the

perforation than Lh can be approximated by the model employed by Meidner and Mansfield

(1968) and Nobel (1974) for stomatal resistance.

hh RLL += (3-4)

Where Rh is the radius of the hole. Combining equations (3-1), (3-2), (3-3), and (3-4) yields

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

++−=

−−

h

hA RL

DALPAp)(pF (3-5)

To achieve a stable, steady state gas composition in packaged produce gas transfer must equal

respiration rate at the desired gas composition. Unsteady state methods as described by Lee et al.,

(1991) can be used to determine the respiration rate at the desired gas composition. Once the

respiration rate is known the area of the package, the number and size perforations, and the

weight of the product can be determined. Setting the respiration rate of the product equal to the

gas transmission rate through the film (3-5) yields

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

++−=

−−

h

hOA RL

DALPA)p(pwR

2in (3-6)

35

The term ⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

++

−−

h

h

RLDA

LPA is the total OTR of the package and (3-6) reduces to the steady state

design equation for a modified atmosphere package of fresh produce.

perfOA )OTRp(pwR2in

−= (3-7)

Oxygen Transmission Rate (OTR) Measurements

Non-perforated films

Ghosh and Anantheswaran (1998) reviewed four methods used to determine OTR. These

methods include (1) manometric (ASTM D1434, 1995), (2) volume (ASTM D1434, 1995), (3)

coulometric sensor method (ASTM D3985, 1995) and (4) concentration increase methods

(Landrock and Procter 1952; Moyls et al., 1992).

Both manometric and volume methods rely on the same type of apparatus. Neither

approach is appropriate for perforated films, so these are only briefly described here. A sample

is mounted in a gas transmission cell to form a sealed semibarrier between two chambers. One

chamber contains test gas at a specific high pressure, and the other chamber at a lower pressure

receives the permeating gas. In the Manometric method the lower pressure chamber is evacuated

and transmission of the gas through the film is indicated by an increase in pressure. In the

volume method the lower pressure chamber is maintained at atmospheric pressure and the gas

transmission is indicated by a change in volume.

The coulometric method Figure 3-1 involves mounting a specimen as a sealed semi-

barrier between two chambers at atmospheric pressure. One chamber is purged with a non-

oxygen containing carrier gas such as nitrogen, and the other chamber is purged with oxygen

containing test gas, which is typically air (21% oxygen) or 100% oxygen. Oxygen permeates

through the film into the carrier gas, which is then transported to a coulometric sensor. Oxygen

36

is consumed in a process that generates an electric current proportional to the amount of oxygen

flowing to the sensor in a given time period.

The concentration increase method is an unsteady state method whereby the chamber is

sealed with a semi-barrier and is initially purged with an oxygen free gas such as nitrogen.

Oxygen diffuses through the barrier and the concentration of oxygen is measured over time. The

most common method used to measure the oxygen concentration is a gas chromatograph, which

requires removal of gas samples from the test chamber (Figure 3-2).

Perforated films

The volume and manometric methods involve a pressure differential which would cause

gas to flow through perforations, rendering these methods unsuitable for OTR measurements of

perforated films. The coulumetric method has basic physical limitations (Johnson and Demorest

1997) and becomes impractical for very high OTRs even without perforations due to costly

sensor consumption. Perforations create additional challenges due to practical difficulties of

avoiding non-diffusional gas flow through perforations.

The approach developed in this work is an enhancement of the typical concentration

increase method. This approach is superior to other methods since the measurement does not

rapidly consume the sensor, the sensor does not consume gases involved in the measurement, the

apparatus does not require consumption of constantly flowing gases, and the approach does not

create or rely upon pressure differentials.

Fiber optic oxygen sensor

Sensors based on oxygen quenching fluorophores are commercially available. Typically

fluorophores are suspended in sol gel complex and mounted at the tip of a fiber optic probe.

Oxygen probes available from Ocean Optics Inc. (Dunedin, Fl) use a fluorescing ruthenium

complex. For durability, probes may be mounted in steel shafts of varying diameter in a manner

37

that resembles hypodermic needles. For this work 18 gauge probes were used (Model FOXY

18G, Ocean Optics Inc, Dunedin, Fl). A pulsed blue LED sends light, at 475 nm, onto an optical

fiber. The optical fiber carries the light to the probe tip, which excites the flourophore causing an

emission at ~600 nm. Excitation energy is also transferred to oxygen molecules in non-radiative

transfers. Therefore oxygen decreases or quenches the fluorescence signal (Kautsky 1939).

Florescent energy is collected by the probe and carried through the optical fiber to spectrometer.

Degree of fluorescence quenching relates to the frequency of collisions, and therefore

concentration, pressure and temperature of the oxygen-containing media. A fluorescence

quenching based sensor was selected for use in this method primarily because it can measure

oxygen concentration without consuming oxygen. Other methods require removal of gas from

the system or consumption of oxygen, which directly affects the measurement.

Materials and Methods

The apparatus for measuring OTR was divided into in three parts, which, in this case, were

fabricated mainly from magnesium metal, which was readily available in our machine shop

(Figure 3-3). The bottom incorporates a transparent plastic window in order to allow for a

magnetic stir bar in the test chamber. The height of the middle section is 5 cm and is a hollow

cylinder with four ports for flushing with nitrogen and compressed air, mounting the fiber optic

oxygen probe, and to provide for a gas outlet valve. The middle also accommodated o-rings for

gas tight seals with top and bottom. The top is a ring with a precise open area of 50 cm2 to

accommodate film samples. Figure 3-3 shows a diagram of the OTR measurement chamber.

38

air

probe

N2

tightening screw

O-ring Groove

Outlet Stream

Plexi Glass Plate

Magnetic Stir Bar

Figure 3-3. Schematic Profile of OTR chamber

Measurement of Samples

Stainless steel disks 0.02 inches thick with precision orifices were procured (FSS-318-cal-

100, 150, 200, 250, Lenox Laser, Glen Arm, MD) and used to test the apparatus since we found

it difficult to repeatedly produce consistent holes with desired geometry in our laboratory. Hole

diameters were 100, 153, 205, and 249µm. Oxygen partial pressure in the chamber was recorded

every 10 seconds using the average of four measurements with the fiber optic oxygen sensing

system. Measurements were made at 150C, 230C, and 300C inside a computer controlled

environmental chamber. From the change in oxygen partial pressure over time, OTR of holes can

be determined with the following Fick’s law based equation for a well stirred volume (Emond,

1992).

V)p(pOTR

dtdp

222 OairOperfO −= (3-8)

This can be integrated from initial time 0 to t and from initial partial pressure 0O2p to

2Op yielding:

39

tV

OTRpppp

ln perf

0OairO

OairO

22

22 =⎟⎟⎠

⎞⎜⎜⎝

⎛

−

−− (3-9)

Recalculating Diffusion Coefficients

Diffusion coefficient of oxygen in air was calculated from OTR of the precision orifices by

setting the term ⎥⎦

⎤⎢⎣

⎡+ h

h

RLDA in equation (3-6) equal to OTR and solving for D, which yields

( )h

h

ARLOTR

D+

= (3-10)

Values calculated from equation 3-10 were compared to the Fuller, Schettler, and Giddings

relation from Perry’s Chemical Engineering Handbook, (Perry and Green 1984) Table 3-1.

Results and Discussion

A plot was made from equation (3-9) and the OTR was calculated by multiplying the slope

by the volume of the chamber. An example of this plot is provided in Figure 3-4 for the case of

the 249µm hole at 30 0C.

y = 2.2701x - 0.0062R2 = 0.9993

0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.02 0.04 0.06 0.08 0.1 0.12

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure 3-4. Plot used to determine OTR of hole/perforation 249µm hole at 300C.

40

Figure 3-5 shows OTR data, at least in duplicate, for all holes at all temperatures. The

figure primarily shows that the apparatus is capable of providing consistent and reliable

measurements. Additionally, the figure shows a surprising tendency for OTR to decrease with

increasing temperature, despite the fact that gas diffusion coefficients are generally known to

increase with temperature. It is likely that reduced gas density at higher temperatures more than

offset increases in gas diffusion coefficients

0100200300400500600700

100 153 205 249

hole diameter (microns)

OTR

(cc/

day)

15 C23 C30 C

Figure 3-5. OTR of holes vs. temperature

Table 3-1. Oxygen diffusion coefficient in air calculated from precision orifices and Perry’s Chemical Engineering Handbook

D_O2

cm2/s 15 23 30Perry's 0.186 0.196 0.204

100 µ m 0.453 0.374 0.282150 µ m 0.331 0.283 0.304200 µ m 0.311 0.241 0.214250 µ m 0.257 0.234 0.231

Temperature 0C

. Table 3-1 shows that the difference between oxygen diffusion coefficients estimated from

Perry’s and the precision orifice decreases with increasing temperature and with increasing

diameter. However, for most modified atmosphere packaging applications, temperatures tend to

be low and temperature variations are much less pronounced, reducing the potential value of this

observed trend. Most importantly however, OTR measurements with precision holes proved to

41

be consistent and reproducible. This provides confidence that this approach can be used to

accurately measure OTR in microperforated packaging films where such microperforations tend

to be dimensionally irregular.

42

CHAPTER 4 NEW APPARATUS SIMPLIFIES DESIGN OF MODIFIED ATMOSPHERE PACKAGING

WITH PERFORATED FILMS

Introduction

In previous chapters respiration rates were measured on five respiring products and a new

method was developed to determine the Oxygen Transmission Rate (OTR) of perforated films.

In this experiment respiration rates on broccoli were measured using the unsteady state method

described in chapter 2. OTR of perforated and non perforated portions of the package were

measured. Non-perforated portions of the package were measured using the Oxtran 2/20 (Mocon

Inc., Minneapolis, MN.) Perforated portions were measured using the method developed in

Chapter 3. Perforated packages of broccoli were designed and gas composition inside packages

was measured periodically until each package reached steady state. OTR was calculated from

equation (3-7) using measured respiration rates and as well as rates from the literature. Predicted

OTR was found to agree well with measured OTR.

Materials and Methods

Head Space Analysis of Commercially Packaged Broccoli

A headspace analyzer (Pack Check, Mocon, Inc., Minneapolis, MN) was used to determine

oxygen and carbon dioxide concentrations in sample headspaces of the prepackaged broccoli.

Headspace gas composition of 14 bags of commercially packaged broccoli was measured.

Respiration Rate of Broccoli

Product respiration rates were measured using an unsteady-state method (Lee et al., 1991;

Hagger et al., 1992). Briefly, a given amount of broccoli was placed in hermetically sealed jars

and changes in headspace gas compositions are monitored over time. Empirical curves are fitted

to gas versus time data and mathematical derivatives of these curves (instantaneous slopes),

provide respiration rates as a function of headspace composition.

43

One liter mason jars were used for unsteady-state respiration experiments. Holes were

drilled (about ½ inch diameter) into mason jar lids to accommodate rubber septa. Prior to

conducting respiration experiments, broccoli density was measured via water displacement.

Broccoli density was used to calculate head space gas volume from the difference between the

container volume and sample volume.

Five Samples of broccoli (ca. 100 g) were placed in each jar. Lids were placed firmly on

jars and holes and were sealed with rubber septa. Samples of broccoli were placed in a controlled

environmental chamber set at 4°C. Oxygen and carbon dioxide concentrations were measured

periodically using the headspace analyzer (Pac-Check, Mocon, Inc., Minneapolis, MN).

Broccoli Package OTR

Broccoli packages were made from polyethylene with a thickness of 2.5 mil (Paragon Film

Inc. Broken Arrow, OK). Oxygen transmission rates of two non-perforated samples 100 cm2

each were measured using the Oxtran 2/20 (Mocon, Inc., Minneapolis, MN) at 200C and 300C.

The Arrhenius Temperature Sensitivity Relationship was used to determine the OTR at 40C.

Total area of the non-perforated region of the package was 1000 cm2. One perforated portion of

the package with an area of 50 cm2 was measured using a device employing a fiber optic oxygen

sensor as described in chapter 3 at 40C.

Modified Atmosphere Package Design with Perforations

Ten bags were designed using polyethylene film with a thickness of 2.5 mil (Paragon Film

Inc. Broken Arrow, OK) and an area of 1050 cm2 (30 cm x 35 cm). Bags were sealed using a

heat sealing machine (Sencorp Systems, Inc. Hyannis, MA). Approximately 110 grams ± 1 gram

of broccoli florets were added to each bag. All bags were perforated once with a 13.5 gage tool.

A headspace analyzer (Pack Check, Mocon, Inc., Minneapolis, MN) was used to determine

oxygen and carbon dioxide concentrations in the headspace of the packaged broccoli.

44

Measurements were made approximately every 12 hours until gas compositions reached steady

state.

Results and Discussion

Headspace of Commercially Packaged Broccoli

Broccoli was found to have a density of 0.815 g/cm3. Fourteen samples were taken with an

average of 5.18 ± 2.41% O2 ranging from 1.32% O2 to 9.06% O2 and 5.86 ± 1.29% CO2 ranging

from 8.4% CO2 to 4.1% CO2.

Respiration of Broccoli

Changes in carbon dioxide and oxygen concentrations with time for broccoli showed

hyperbolic trends. For oxygen, a hyperbolic decay function was used to fit data using non-linear

regression (Equation 4-1):

tbabyy+

+= 0 (4-1)

Where y is oxygen concentration, x is time and y0, a, and b are coefficients. For carbon

dioxide, a hyperbolic function was used to fit data using a non-linear regression (Equation 4-2):

tbatyy+

+= 0 (4-2)

Where y is carbon dioxide concentration, x is time and y0, a, and b are coefficients. Figure

2 shows changes in gas compositions for Broccoli at 4°C. Measured data and fitted curves are

shown in Figures (4-1) and (4-2) and fitted curve coefficients are provided in Table (4-1).

45

Figure 4-1. Unsteady state respiration data for Broccoli at 4°C % vs time

Figure 4-2. Unsteady state respiration data for Broccoli at 4°C cc/g

46

Table 4-1. Respiration coefficients for oxygen and carbon dioxide for broccoli y0 a bcc/g cc/g days R2

O2 -1.7103 3.3538 4.0833 0.9881CO2 0.0490 2.8600 5.8523 0.9789

Broccoli Package OTR

Non-perforated portions of the package had an average OTR of 3900 cc/m2/day at 200C

and 6600 cc/m2/day at 300C. The Arrhenius temperature sensitivity relationship equation (4-3)

suggests an OTR of about 1500 cc/m2/day at 40C.

T4734

10103.99OTR−

×= e (4-3)

Non-perforated portion of the package had a total oxygen transmission rate of 150

ccO2/day. OTR of the perforated region was 570 cc/day calculated from measured data as

described in Chapter 3 as shown in (Figure 4-2). The total OTR of the package was 720cc/day.

Perforated region accounted for about 80% of OTR despite having an area slightly less than 5%

of the package area. This result is expected since the diffusion coefficient is about six orders of

magnitude greater than the permeability coefficient in equation (3-5) for polyethylene. When

total area of all perforations is large enough compared to total package area the permeation term

in equation (3-5) becomes negligible compared to the diffusion term and practically all OTR

comes from the perforations.

Broccoli Package Performance Data

Packages reached an average steady state of 11.6% O2 with a standard deviation of 3.04%

O2 ranging from 6.54% O2 to 14.5% O2. Average CO2 concentration was 4.4% CO2 with a

standard deviation of 0.684% CO2 ranging from 5.5% CO2 to 3.6% CO2. Figure (4-3) shows

broccoli packages reaching steady state.

47

y = 2.3235x + 0.0255R2 = 0.9934

-0.2

0

0.2

0.4

0.6

0.8

1

0 0.1 0.2 0.3 0.4

time (days)

-ln((p

O2a

-pO

2)/(p

O2a

i-pO

2i))

Figure 4-2. Plot used to determine OTR of hole/perforation at 40C.

0

5

10

15

20

25

0.00 20.00 40.00 60.00 80.00 100.00 120.00time (hour)

%O

2, %

CO

2

O2

CO2

Figure 4-3. Broccoli packages reaching steady state

Calculation of Broccoli oxygen consumption rate

Broccoli oxygen consumption rate was calculated at average steady state values and

storage temperature. Figure 1 show that it takes approximately 1.1 days to reach 11.6% O2 at

4°C. Time can be substituted into the mathematical derivative of equation (4-1), which is given

by

48

( )2tbab

dtdy

+−

= (4-4)

Substituting time and coefficients given in Table 4-1 yields

( ) daygcc510.0

1.10833.40833.4*3538.3

2 −−=

+−

=dtdy

Multiplying this value by the weight of the product in the package (110 g) gives a total oxygen

consumption rate of 56 cc/day.

Prediction of OTR Package using Design Equation

Respiration rates calculated from this experiment using the same method described in

Chapter 2 and from the literature (Hagger et al., 1992) were used to estimate actual OTR of the

package. Experimental respiration rate at 4°C and average steady state concentrations was 0.530

ccO2/g/day and the respiration rate derived from the literature was 0.820 ccO2/g/day. Equation 3-

7 suggests OTR values of 630 cc/day and 970 cc/day using our experimental and literature

values respectively. Measured OTR using our new apparatus was 720 cc/day, which agreed well

with predicted values.

49

CHAPTER 5 CONCLUSIONS

Modified atmosphere packaging is a simple and inexpensive way to extend the shelf life of

minimally processed produce. Lower oxygen environments at lower temperatures can

significantly reduce the respiration rate of produce. Headspace oxygen concentration of

packaged produce is dependent on two main factors: the oxygen transmission rate of the

packaging material and the oxygen consumption by the product due to respiration. Oxygen

consumption of the produce at the storage temperature and desired oxygen concentration must

match the oxygen transmission rate of the package to maintain the desired atmosphere. When

designing a modified atmosphere package it is necessary to measure the OTR of the packaging

material selected and the respiration rate of the product.

The unsteady state method is an effective way to measure respiration rates at a specified

temperature over a range of O2 and CO2 concentrations. A hyperbolic decay function fit many of

the products including rutabaga and broccoli indicating a more dramatic decrease in respiration

rates at higher O2 levels. Some products shift from a hyperbolic decay function to a linear

function at lower temperatures suggesting that respiration is not a strong function of oxygen

concentration at these temperatures. This behavior was observed in sweet potato, squash,

zucchini, and turnips. Once respiration rate has been measured at the specified conditions, OTR

necessary to maintain desired O2 level can be calculated from equation (3-7).

Most of the oxygen consumption rates of products measured in this work at the

recommended temperature and O2 level exceeds the oxygen transmission rate of commercially

available packaging material. Perforations in the package are necessary to maintain the desired

O2 level at the storage temperature. Currently the methods commonly used to measure OTR of

packaging material have deficiencies that make them unsuitable for measuring OTR of

50

perforated packages. A new apparatus was developed to overcome these deficiencies. This

method is a variation of the concentration increase method and involves the use of a fiber optic

oxygen sensor to measure oxygen concentration over time. From oxygen concentration data

OTR can be calculated. The new apparatus was used to measure OTR of four calibrated holes

with diameters of 100, 153, 205, and 249 µm, each hole measured at 15, 23, and 30°C. OTR

increased with increasing diameter and decreased with increasing temperature which was not

expected. Decreased OTR with increasing temperature could be due to decreasing gas density

offsetting increase in diffusion coefficients. This trend is not important for modified atmosphere

packaging applications which occur at lower temperatures with less temperature variation.

Consistent and reproducible measurements with precision orifices provide confidence that the

apparatus can be used to measure OTR of micro-perforated films.

A modified atmosphere package was designed for broccoli using the new apparatus.

Broccoli respiration rates were measured using the unsteady state method at 4°C, the optimal

storage temperature for broccoli. Perforated packages were designed for broccoli. Packages were

perforated with a 13.5 gage tool. Package OTR consisted of two parts a perforated portion and a

non perforated portion. Non-perforated OTR was measured using the Oxtran 2/20 (Mocon Inc.,

Minneapolis, MN) at 20°C and 30°C. Arrhenius temperature sensitivity relationship was used to

infer OTR at 4°C. Perforated OTR was measured using the new apparatus. Total OTR was

calculated by adding non-perforated OTR to perforated OTR. Perforated OTR accounted for

80% of total OTR despite having an area twenty times less than the non-perforated region.

Packaged broccoli was then stored at 4°C and headspace composition was allowed to reach

steady state. OTR necessary to maintain the average steady state O2 level was calculated using

both measured respiration rate and respiration rate from the literature and compared. Both

51

calculated OTRs were the same order of magnitude and measured OTR was in between the two.

This suggests the new apparatus is a useful tool for designing a modified atmosphere package for

respiring produce.

52

APPENDIX A RESPIRATION DATA FOR THE FIVE RESPIRING PRODUCTS

Table A-1. Rutabaga respiration data 15ºC time (hours) time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.33 0.000.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.31 0.000.72 0.03 20.6 1.1 1.30 0.070.73 0.03 20.7 1.1 1.29 0.070.75 0.03 20.6 1.3 1.29 0.082.68 0.11 19.7 2.4 1.24 0.152.68 0.11 19.7 2.3 1.22 0.142.70 0.11 19.1 3.0 1.19 0.194.40 0.18 18.4 3.7 1.16 0.234.42 0.18 18.7 3.4 1.16 0.214.43 0.18 17.8 4.3 1.11 0.276.00 0.25 17.4 4.7 1.10 0.306.00 0.25 17.7 4.4 1.10 0.276.02 0.25 16.6 5.6 1.04 0.357.75 0.32 16.6 5.8 1.05 0.377.77 0.32 16.8 5.1 1.04 0.327.78 0.32 15.6 6.8 0.98 0.439.03 0.38 15.6 6.0 0.99 0.389.05 0.38 16.0 5.6 0.99 0.359.07 0.38 14.6 6.9 0.91 0.4310.58 0.44 14.7 6.7 0.93 0.4210.58 0.44 15.2 6.4 0.94 0.4010.60 0.44 13.5 7.8 0.84 0.4917.37 0.72 11.6 8.9 0.72 0.5517.38 0.72 9.89 10.3 0.62 0.6420.37 0.85 10.1 9.9 0.64 0.6320.42 0.85 10.2 9.9 0.63 0.6120.43 0.85 8.95 11.2 0.56 0.7022.82 0.95 9.26 10.6 0.58 0.6722.82 0.95 9.28 10.6 0.58 0.6622.83 0.95 7.54 12.0 0.47 0.7525.52 1.06 8.22 11.4 0.52 0.7225.52 1.06 8.24 11.3 0.51 0.7025.53 1.06 6.61 12.8 0.41 0.8026.83 1.12 7.83 11.8 0.49 0.7326.87 1.12 6.42 13.1 0.40 0.8229.90 1.25 7.21 12.2 0.45 0.7629.92 1.25 5.43 13.6 0.34 0.8534.82 1.45 5.36 13.4 0.33 0.8335.82 1.49 5.98 13.1 0.38 0.8337.45 1.56 4.70 13.8 0.29 0.8637.47 1.56 3.13 15.0 0.20 0.9446.00 1.92 2.79 16.1 0.17 1.0046.02 1.92 3.23 15.0 0.20 0.9546.02 1.92 1.86 17.1 0.12 1.0751.18 2.13 1.74 16.4 0.11 1.0251.23 2.13 1.04 18.1 0.07 1.1353.07 2.21 2.2 16.8 0.14 1.0654.27 2.26 0.358 18.2 0.02 1.1560.28 2.51 0.276 17.5 0.02 1.09

53

0.0

5.0

10.0

15.0

20.0

25.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

% C

O2,

O2

%O2 %CO2

Figure A-1. Rutabaga 15ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time days

cc/g

ccO2/g ccCO2/g

Figure A-2. Rutabaga 15ºC, cc/g vs time

54

Table A-2. Rutabaga respiration data 8ºC times (hours) times (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.31 0.000.00 0.00 21.0 0.0 1.31 0.000.00 0.00 21.0 0.0 1.32 0.004.00 0.17 19.8 2.1 1.23 0.134.00 0.17 20.3 1.7 1.26 0.114.02 0.17 20.0 1.9 1.26 0.127.52 0.31 19.2 2.8 1.19 0.177.57 0.32 18.8 3.3 1.17 0.217.57 0.32 19.0 3.0 1.20 0.199.30 0.39 18.9 3.1 1.18 0.199.32 0.39 18.1 3.9 1.13 0.249.33 0.39 18.5 3.5 1.16 0.2217.72 0.74 15.7 5.6 0.98 0.3517.72 0.74 16.8 4.7 1.04 0.2917.73 0.74 16.3 5.4 1.03 0.3420.82 0.87 14.7 6.5 0.91 0.4020.83 0.87 15.9 5.8 0.99 0.3620.85 0.87 15.5 5.9 0.98 0.3730.20 1.26 12.3 8.4 0.76 0.5230.20 1.26 14.0 7.1 0.87 0.4430.22 1.26 13.3 7.6 0.84 0.4837.73 1.57 10.5 9.6 0.65 0.6037.73 1.57 12.4 8.0 0.77 0.5037.75 1.57 11.6 8.7 0.73 0.5546.32 1.93 9.2 10.5 0.57 0.6546.32 1.93 10.9 8.9 0.68 0.5546.33 1.93 10.0 9.9 0.63 0.6254.55 2.27 7.93 11.1 0.49 0.6954.55 2.27 5.6 12.70 0.35 0.7954.58 2.27 7.09 12.4 0.45 0.7872.93 3.04 6.86 12.0 0.43 0.7572.93 3.04 6.24 10.30 0.39 0.6472.95 3.04 5.77 13.0 0.36 0.8281.00 3.38 3.5 14.20 0.22 0.8881.02 3.38 4.57 13.8 0.29 0.8781.05 3.38 6.18 12.6 0.38 0.78115.83 4.83 2.15 15.1 0.13 0.94115.88 4.83 5.62 13.00 0.35 0.81115.92 4.83 2.89 14.7 0.18 0.93121.23 5.05 1.84 15.3 0.12 0.96162.65 6.78 0.581 16.6 0.04 1.03162.65 6.78 2.40 15.00 0.15 0.93162.67 6.78 0.139 16.9 0.01 1.06

55

0.0

5.0

10.0

15.0

20.0

25.0

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

time (days)

% C

O2,

O2

%O2 %CO2

Figure A-3. Rutabaga 8ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

time days

cc/g

ccO2/g ccCO2/g

Figure A-4. Rutabaga 8ºC cc/g vs time

56

Table A-3. Rutabaga respiration data 1ºC times (hours) times (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.33 0.000.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.32 0.0011.17 0.47 19.7 2.3 1.24 0.1511.20 0.47 19.8 2.1 1.23 0.1311.22 0.47 19.9 1.9 1.25 0.1230.55 1.27 17.9 4.0 1.13 0.2530.55 1.27 18.1 3.8 1.12 0.2430.57 1.27 18.4 3.5 1.15 0.2246.73 1.95 16.7 5.2 1.05 0.3346.73 1.95 16.4 5.1 1.02 0.3246.75 1.95 16.7 4.7 1.05 0.2966.95 2.79 15.1 6.6 0.95 0.4266.95 2.79 15.0 6.2 0.93 0.3966.98 2.79 15.0 6.0 0.94 0.3892.22 3.84 13.5 8.0 0.85 0.5192.22 3.84 13.1 8.1 0.81 0.5092.23 3.84 13.2 7.4 0.83 0.46138.97 5.79 12.3 9.1 0.78 0.57138.98 5.79 11.9 8.2 0.75 0.51163.98 6.83 10.5 9.3 0.65 0.58164.00 6.83 11.0 10.1 0.69 0.64164.02 6.83 10.7 9.3 0.67 0.58189.88 7.91 9.10 10.2 0.57 0.63189.90 7.91 9.68 11.6 0.61 0.73189.90 7.91 9.19 10.0 0.58 0.63216.93 9.04 8.49 12.5 0.54 0.79216.97 9.04 7.70 11.0 0.48 0.68216.98 9.04 7.73 11.0 0.48 0.69240.23 10.01 6.43 11.7 0.40 0.73240.25 10.01 7.45 13.4 0.47 0.85240.25 10.01 6.92 11.5 0.43 0.72258.20 10.76 6.65 14.2 0.42 0.90258.20 10.76 5.38 12.3 0.33 0.76258.22 10.76 5.53 12.3 0.35 0.77286.58 11.94 5.34 15.5 0.34 0.98286.62 11.94 4.00 13.2 0.25 0.83286.72 11.95 4.10 13.3 0.25 0.83380.68 15.86 0.554 18.8 0.03 1.19380.72 15.86 0.591 17.3 0.04 1.07380.77 15.87 0.489 16.9 0.03 1.06

57

0.0

5.0

10.0

15.0

20.0

25.0

0.00 5.00 10.00 15.00 20.00

time (days)

% C

O2,

O2

%O2 %CO2

Figure A-5. Rutabaga 1ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 5.00 10.00 15.00 20.00

time days

cc/g

ccO2/g ccCO2/g

Figure A-6. Rutabaga 1ºC, cc/g vs time

58

Table A-4. Sweet Potato respiration data 15ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.30 0.002.28 0.10 19.2 3.1 1.19 0.192.28 0.10 19.4 3.0 1.20 0.192.32 0.10 18.6 4.0 1.15 0.254.37 0.18 17.0 5.6 1.05 0.354.37 0.18 17.3 5.4 1.07 0.334.38 0.18 16.0 7.2 0.99 0.456.83 0.28 14.2 8.8 0.88 0.546.83 0.28 14.8 8.4 0.92 0.526.87 0.29 12.9 10.9 0.80 0.689.00 0.38 11.8 11.6 0.73 0.729.00 0.38 12.5 10.9 0.77 0.679.03 0.38 10.1 14.1 0.63 0.8712.07 0.50 9.38 14.5 0.58 0.9012.07 0.50 8.46 15.4 0.52 0.9512.10 0.50 6.68 18.4 0.41 1.1413.80 0.57 6.75 17.1 0.42 1.0613.80 0.57 7.70 15.3 0.48 0.9513.83 0.58 5.01 20.7 0.31 1.2821.33 0.89 2.09 23.6 0.13 1.4621.33 0.89 1.47 24.6 0.09 1.5221.37 0.89 0.391 28.3 0.02 1.7623.85 0.99 1.02 25.9 0.06 1.6023.85 0.99 0.595 26.9 0.04 1.6625.82 1.08 0.46 27.2 0.03 1.68

59

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.00 0.20 0.40 0.60 0.80 1.00 1.20

time (days)

%O

2, %

CO

2

%O2 %CO2

Figure A-7. Sweet Potato 15ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-8. Sweet Potato 15ºC, cc/g vs time

60

Table A-5. Sweet Potato respiration data 8ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.30 0.004.82 0.20 19.1 3.1 1.18 0.194.83 0.20 18.6 3.7 1.15 0.234.83 0.20 18.8 3.5 1.17 0.229.45 0.39 16.4 5.8 1.01 0.369.47 0.39 15.7 6.8 0.97 0.429.48 0.40 16.2 6.4 1.01 0.4012.55 0.52 14.7 7.5 0.91 0.4612.58 0.52 13.7 8.8 0.85 0.5412.58 0.52 14.4 8.4 0.89 0.5221.83 0.91 9.62 12.4 0.59 0.7721.85 0.91 8.04 14.7 0.50 0.9121.87 0.91 9.28 13.5 0.58 0.8426.65 1.11 7.05 15.0 0.44 0.9326.67 1.11 5.38 17.7 0.33 1.0926.67 1.11 6.75 16.3 0.42 1.0131.27 1.30 4.82 17.5 0.30 1.0831.28 1.30 2.91 20.9 0.18 1.2931.30 1.30 4.64 18.9 0.29 1.1745.27 1.89 0.385 22.4 0.02 1.3845.28 1.89 0.407 23.8 0.03 1.48

61

0.0

5.0

10.0

15.0

20.0

25.0

0.00 0.50 1.00 1.50 2.00

time (days)

%O

2, %

CO

2

%O2 %CO2

Figure A-9. Sweet Potato 8ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.50 1.00 1.50 2.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-10. Sweet Potato 8ºC, cc/g vs time

62

Table A-6. Sweet Potato respiration data 1ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.30 0.009.88 0.41 19.5 2.4 1.21 0.159.90 0.41 19.3 2.6 1.20 0.169.90 0.41 19.2 2.7 1.19 0.1724.53 1.02 17.1 4.8 1.06 0.3024.55 1.02 16.3 5.5 1.01 0.3424.55 1.02 17.2 4.9 1.07 0.3045.68 1.90 12.9 8.8 0.80 0.5445.70 1.90 11.8 9.8 0.73 0.6145.70 1.90 11.8 9.9 0.73 0.6168.40 2.85 7.70 13.5 0.48 0.8468.42 2.85 6.68 14.4 0.41 0.8968.42 2.85 6.75 14.5 0.42 0.9079.38 3.31 5.12 16.0 0.32 0.9979.40 3.31 3.82 17.0 0.24 1.0579.40 3.31 3.79 17.3 0.24 1.0794.68 3.95 1.83 18.9 0.11 1.1794.70 3.95 1.44 19.9 0.09 1.2394.70 3.95 1.17 19.8 0.07 1.23

63

0.0

5.0

10.0

15.0

20.0

25.0

0.00 1.00 2.00 3.00 4.00 5.00

time (days)

%O

2, %

CO

2

%O2 %CO2

Figure A-11. Sweet Potato 1ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 1.00 2.00 3.00 4.00 5.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-12. Sweet Potato 1ºC, cc/g vs time

64

Table A-7. Squash respiration data 15ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.28 0.000.00 0.00 21.0 0.0 1.28 0.000.00 0.00 21.0 0.0 1.29 0.002.23 0.09 20.3 1.6 1.24 0.102.23 0.09 20.2 1.8 1.24 0.112.25 0.09 20.5 1.5 1.25 0.094.33 0.18 18.8 3.0 1.15 0.184.35 0.18 19.3 2.7 1.18 0.164.35 0.18 19.3 2.6 1.18 0.166.78 0.28 17.1 4.7 1.05 0.296.78 0.28 18.0 4.1 1.10 0.256.80 0.28 18.2 4.0 1.11 0.248.97 0.37 15.6 6.3 0.96 0.398.97 0.37 17.5 4.8 1.07 0.298.97 0.37 17.2 5.2 1.05 0.3212.02 0.50 13.8 8.1 0.85 0.5012.02 0.50 16.0 6.4 0.98 0.3912.02 0.50 16.3 6.4 0.99 0.3913.78 0.57 12.7 9.2 0.78 0.5613.78 0.57 15.5 7.2 0.95 0.4413.78 0.57 15.9 7.1 0.97 0.4321.28 0.89 8.7 13.3 0.54 0.8221.30 0.89 14.0 9.7 0.85 0.5921.30 0.89 14.7 9.1 0.90 0.5625.78 1.07 6.30 15.0 0.39 0.9225.80 1.08 13.4 10.2 0.82 0.6225.80 1.08 14.2 10.1 0.87 0.6230.90 1.29 3.94 17.9 0.24 1.1030.90 1.29 13.8 10.6 0.84 0.6544.92 1.87 0.0992 21.5 0.01 1.3244.92 1.87 12.1 12.2 0.74 0.7444.92 1.87 13.70 11.2 0.84 0.6853.08 2.21 11.8 12.8 0.72 0.78

65

0.0

5.0

10.0

15.0

20.0

25.0

0.00 0.50 1.00 1.50 2.00 2.50

time (days)

%O

2, %

CO

2

%O2 %CO2

Figure A-13. Squash 15ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 0.50 1.00 1.50 2.00 2.50

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-14. Squash 15ºC, cc/g vs time

66

Table A-8. Squash respiration data 8ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.29 0.004.75 0.20 20.2 1.6 1.24 0.104.75 0.20 20.2 1.5 1.24 0.094.77 0.20 20.4 1.6 1.25 0.109.40 0.39 19.0 2.8 1.17 0.179.40 0.39 19.0 2.6 1.16 0.169.42 0.39 18.7 2.9 1.15 0.1812.43 0.52 18.3 3.6 1.12 0.2212.45 0.52 17.9 3.7 1.10 0.2312.53 0.52 17.9 3.7 1.10 0.2321.75 0.91 16.0 5.6 0.98 0.3421.77 0.91 15.5 5.8 0.95 0.3621.78 0.91 15.0 6.4 0.92 0.3926.57 1.11 14.7 7.0 0.90 0.4326.57 1.11 13.7 7.4 0.84 0.4526.58 1.11 13.2 8.1 0.81 0.5031.20 1.30 13.5 7.4 0.83 0.4531.22 1.30 12.0 8.0 0.74 0.4931.25 1.30 11.5 8.7 0.71 0.5345.22 1.88 6.1 13.5 0.37 0.8345.22 1.88 9.10 10.6 0.56 0.6545.23 1.88 5.61 12.8 0.34 0.7853.37 2.22 1.8 16.1 0.11 0.9953.37 2.22 6.26 13.1 0.38 0.8053.38 2.22 2.49 17.5 0.15 1.0767.88 2.83 2.43E-02 20.9 0.00 1.2867.88 2.83 0.706 18.3 0.04 1.1267.90 2.83 3.32E-02 20.1 0.00 1.23

67

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

%O

2,C

O2

%O2 %CO2

Figure A-15. Squash 8ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-16. Squash 8ºC, cc/g vs time

68

Table A-9. Squash respiration data 1ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.29 0.009.83 0.41 20.3 1.4 1.24 0.099.83 0.41 20.3 1.3 1.24 0.089.83 0.41 20.4 1.3 1.25 0.0824.42 1.02 19.1 2.7 1.17 0.1724.42 1.02 19.1 2.5 1.17 0.1524.43 1.02 19.0 2.5 1.17 0.1545.65 1.90 17.1 4.3 1.05 0.2645.65 1.90 17.3 4.2 1.06 0.2645.65 1.90 17.6 4.0 1.08 0.2568.35 2.85 15.2 5.5 0.93 0.3468.35 2.85 15.6 5.8 0.96 0.3668.35 2.85 14.5 6.5 0.89 0.4079.33 3.31 13.7 6.7 0.84 0.4179.33 3.31 14.3 6.7 0.88 0.4179.33 3.31 12.8 8.1 0.78 0.5094.60 3.94 11.5 9.0 0.70 0.5594.60 3.94 12.4 8.6 0.76 0.5394.60 3.94 10.2 10.2 0.63 0.63126.62 5.28 7.8 11.2 0.48 0.69126.62 5.28 6.3 11.5 0.38 0.70126.65 5.28 3.7 15.1 0.22 0.93166.83 6.95 0.0569 16.6 0.00 1.02166.85 6.95 1.0 17.6 0.06 1.08166.85 6.95 0.0266 19.6 0.00 1.20

69

0.0

5.0

10.0

15.0

20.0

25.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

%O

2,C

O2

%O2 %CO2

Figure A-17. Squash 1ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-18. Squash 1ºC, cc/g vs time

70

Table A-10. Squash and Zucchini respiration data 15ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.30 0.002.25 0.09 20.1 1.7 1.24 0.102.25 0.09 20.1 1.6 1.24 0.102.27 0.09 20.1 1.6 1.23 0.104.33 0.18 18.8 2.9 1.16 0.184.35 0.18 18.7 3.0 1.15 0.184.35 0.18 18.8 2.9 1.15 0.186.80 0.28 16.7 5.1 1.03 0.316.80 0.28 17.3 4.6 1.07 0.286.82 0.28 17.3 4.6 1.06 0.288.98 0.37 14.8 6.9 0.91 0.428.98 0.37 15.7 6.3 0.97 0.399.00 0.38 15.7 6.3 0.96 0.3912.00 0.50 13.8 8.3 0.85 0.5112.02 0.50 13.8 8.3 0.85 0.5112.02 0.50 12.3 8.6 0.76 0.5313.78 0.57 10.7 9.7 0.66 0.6013.80 0.58 12.7 9.4 0.78 0.5813.82 0.58 12.7 9.4 0.78 0.5821.32 0.89 4.92 16.2 0.30 1.0021.43 0.89 8.9 13.7 0.55 0.8521.45 0.89 8.88 13.7 0.54 0.8425.80 1.07 1.80 18.0 0.11 1.1125.82 1.08 7.6 15.5 0.47 0.9625.83 1.08 7.62 15.5 0.47 0.9530.72 1.28 6.2 17.1 0.39 1.0630.73 1.28 6.24 17.1 0.38 1.0530.90 1.29 0.4 20.1 0.02 1.2444.90 1.87 4.1 19.7 0.25 1.2244.92 1.87 4.09 19.7 0.25 1.2167.82 2.83 1.64 23.9 0.10 1.4867.83 2.83 1.64 23.9 0.10 1.46

71

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

%O

2,C

O2

%O2 %CO2

Figure A-19. Squash and Zuchini 15ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-20. Squash and Zuchini 15ºC, cc/g vs time

72

Table A-11. Squash and Zucchini respiration data 8ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.28 0.000.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.30 0.004.80 0.20 20.1 1.6 1.23 0.104.80 0.20 20.2 1.5 1.25 0.094.82 0.20 20.2 1.5 1.24 0.099.45 0.39 18.9 2.8 1.15 0.179.45 0.39 19.0 2.7 1.18 0.179.47 0.39 19.1 2.6 1.17 0.1612.52 0.52 18.5 3.3 1.15 0.2012.53 0.52 18.1 3.6 1.11 0.2221.82 0.91 15.4 6.0 0.94 0.3721.82 0.91 15.7 5.7 0.97 0.3521.83 0.91 16.7 5.2 1.02 0.3226.63 1.11 18.8 7.5 1.15 0.4626.65 1.11 14.4 6.5 0.89 0.4026.67 1.11 15.6 6.2 0.96 0.3831.25 1.30 12.3 8.9 0.75 0.5431.25 1.30 12.8 8.5 0.79 0.5331.27 1.30 14.9 7.2 0.91 0.4445.27 1.89 7.61 11.2 0.46 0.6845.27 1.89 8.02 11.3 0.50 0.7045.28 1.89 12.70 9.6 0.78 0.5953.28 2.22 11.80 10.2 0.72 0.6353.27 2.22 3.24 21.4 0.20 1.3253.45 2.23 4.84 14.6 0.30 0.8967.92 2.83 0.125 18.3 0.01 1.1267.93 2.83 0.04 18.9 0.00 1.1767.95 2.83 10.20 12.8 0.63 0.79

73

0.0

5.0

10.0

15.0

20.0

25.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

%O

2,C

O2

%O2 %CO2

Figure A-21. Squash and Zuchini 8ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 0.50 1.00 1.50 2.00 2.50 3.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-22. Squash and Zuchini 8ºC, cc/g vs time

74

Table A-12. Squash and Zucchini respiration data 1C Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.30 0.000.00 0.00 21.0 0.0 1.29 0.000.00 0.00 21.0 0.0 1.29 0.009.85 0.41 20.4 1.3 1.26 0.089.87 0.41 20.4 1.4 1.26 0.099.87 0.41 20.6 1.2 1.26 0.0724.47 1.02 19.2 2.4 1.18 0.1524.47 1.02 19.3 2.4 1.19 0.1524.48 1.02 20.3 1.6 1.24 0.1045.67 1.90 17.5 4.1 1.08 0.2545.67 1.90 17.6 4.0 1.09 0.2545.68 1.90 19.7 2.5 1.21 0.1568.37 2.85 15.6 5.6 0.96 0.3568.37 2.85 15.5 5.7 0.95 0.3568.38 2.85 18.8 3.5 1.15 0.2179.35 3.31 14.4 6.9 0.89 0.4379.35 3.31 14.0 7.1 0.86 0.4479.37 3.31 18.4 4.0 1.13 0.2494.63 3.94 12.7 8.3 0.78 0.5194.65 3.94 12.1 8.7 0.74 0.5494.67 3.94 18.0 4.6 1.10 0.28126.63 5.28 8.4 11.5 0.52 0.71126.67 5.28 6.9 12.5 0.43 0.77126.68 5.28 16.5 6.2 1.01 0.38166.87 6.95 1.7 14.9 0.10 0.92166.87 6.95 0.0704 16.7 0.00 1.03

75

0.0

5.0

10.0

15.0

20.0

25.0

0.00 2.00 4.00 6.00 8.00

time (days)

%O

2,C

O2

%O2 %CO2

Figure A-23. Squash and Zuchini 1ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 2.00 4.00 6.00 8.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-24. Squash and Zuchini 1ºC, cc/g vs time

76

Table A-13. Turnip respiration data 15ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.25 0.000.00 0.00 21.0 0.0 1.25 0.000.00 0.00 21.0 0.0 1.25 0.007.77 0.32 17.5 4.4 1.04 0.267.77 0.32 16.6 5.5 0.99 0.337.78 0.32 17.5 4.4 1.04 0.2617.43 0.73 14.2 7.4 0.85 0.4417.43 0.73 12.6 9.0 0.75 0.5317.45 0.73 13.6 8.1 0.81 0.4820.53 0.86 13.1 8.4 0.78 0.5020.53 0.86 11.5 9.3 0.68 0.5520.57 0.86 12.5 8.5 0.74 0.5022.92 0.95 12.4 8.2 0.74 0.4922.92 0.95 10.6 10.9 0.63 0.6522.93 0.96 11.7 9.8 0.69 0.5826.88 1.12 11.20 9.3 0.67 0.5526.88 1.12 9.15 11.0 0.54 0.6526.90 1.12 10.9 11.0 0.65 0.6529.93 1.25 10.50 9.7 0.63 0.5829.93 1.25 8.25 11.8 0.49 0.7029.95 1.25 11.0 11.5 0.65 0.6834.78 1.45 9.19 10.7 0.55 0.6434.78 1.45 6.74 12.6 0.40 0.7534.82 1.45 8.18 11.8 0.49 0.7037.43 1.56 8.59 10.9 0.51 0.6537.43 1.56 5.98 13.2 0.35 0.7837.47 1.56 7.51 11.9 0.45 0.7145.98 1.92 6.44 12.4 0.38 0.7445.98 1.92 3.53 14.7 0.21 0.8746.07 1.92 5.41 13.4 0.32 0.8051.20 2.13 5.70 12.9 0.34 0.7751.20 2.13 2.43 15.3 0.14 0.9151.22 2.13 4.09 15.1 0.24 0.9066.25 2.76 3.13 15.6 0.19 0.9366.25 2.76 0.672 14.2 0.04 0.8466.28 2.76 1.48 15.9 0.09 0.9470.03 2.92 2.10 15.2 0.13 0.9170.03 2.92 1.02 16.4 0.06 0.97

77

0.0

5.0

10.0

15.0

20.0

25.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

time (days)

% O

2, C

O2

%O2 %CO2

Figure A-25. Turnips 15ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-26. Turnips 15ºC, cc/g vs time

78

Table A-14. Turnip respiration data 8ºC Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.21 0.000.00 0.00 21.0 0.0 1.23 0.000.00 0.00 21.0 0.0 1.21 0.0020.88 0.87 17.1 4.5 0.99 0.2620.92 0.87 16.6 4.9 0.97 0.2920.98 0.87 16.6 5.0 0.96 0.2930.67 1.28 16.0 5.4 0.93 0.3130.68 1.28 15.2 6.3 0.89 0.3730.68 1.28 15.3 6.1 0.88 0.3537.78 1.57 14.8 6.6 0.86 0.3837.80 1.58 14.1 6.8 0.82 0.4037.80 1.58 14.0 7.0 0.81 0.4046.35 1.93 13.8 6.8 0.80 0.3946.37 1.93 12.9 7.6 0.75 0.4446.37 1.93 12.9 7.6 0.74 0.4466.62 2.78 11.5 8.6 0.66 0.5066.63 2.78 10.3 9.4 0.60 0.5566.65 2.78 10.3 9.7 0.59 0.5672.93 3.04 10.8 10.1 0.62 0.5872.95 3.04 11.4 10.7 0.67 0.6372.95 3.04 9.55 10.2 0.55 0.5981.00 3.38 10.0 9.6 0.58 0.5681.02 3.38 8.82 10.4 0.52 0.6181.07 3.38 8.69 10.7 0.50 0.6291.88 3.83 9.04 10.3 0.52 0.6091.90 3.83 7.71 11.1 0.45 0.6591.92 3.83 7.64 11.3 0.44 0.6597.23 4.05 8.55 10.5 0.49 0.6197.23 4.05 7.13 11.6 0.41 0.6797.25 4.05 7.20 11.4 0.42 0.67138.63 5.78 7.19 11.5 0.42 0.66138.67 5.78 5.62 12.4 0.33 0.72138.67 5.78 5.60 12.6 0.32 0.73163.63 6.82 5.36 12.7 0.31 0.73163.65 6.82 3.34 13.7 0.20 0.80189.05 7.88 3.62 13.6 0.21 0.79189.05 7.88 1.74 14.8 0.10 0.86189.08 7.88 2.04 14.7 0.12 0.85215.90 9.00 0.445 16.5 0.03 0.95215.92 9.00 0.260 15.9 0.02 0.93215.95 9.00 1.60 15.1 0.09 0.87

79

0.0

5.0

10.0

15.0

20.0

25.0

0.00 2.00 4.00 6.00 8.00 10.00

time (days)

% O

2, C

O2

%O2 %CO2

Figure A-27. Turnips 8ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 2.00 4.00 6.00 8.00 10.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-28. Turnips 8ºC, cc/g vs time

80

Table A-15. Turnip respiration data 1ºC

Time (hours) Time (days) %O2 % CO2 ccO2/g ccCO2/g0.00 0.00 21.0 0.0 1.18 0.000.00 0.00 21.0 0.0 1.18 0.000.00 0.00 21.0 0.0 1.19 0.0030.58 1.27 18.6 3.1 1.05 0.1730.60 1.28 18.5 2.9 1.04 0.1630.60 1.28 18.3 3.3 1.04 0.1946.77 1.95 17.5 4.0 0.99 0.2346.80 1.95 17.3 4.1 0.97 0.2346.80 1.95 17.1 4.4 0.97 0.2567.02 2.79 16.3 5.1 0.92 0.2967.03 2.79 16.3 5.0 0.92 0.2867.03 2.79 15.8 5.3 0.90 0.3092.23 3.84 15.1 5.9 0.85 0.3392.23 3.84 14.3 6.5 0.81 0.3792.25 3.84 14.9 5.9 0.84 0.33139.00 5.79 14.0 6.6 0.79 0.37139.02 5.79 13.8 7.3 0.78 0.41139.02 5.79 12.9 7.4 0.73 0.42164.02 6.83 12.7 7.6 0.72 0.43164.03 6.83 12.6 7.6 0.71 0.43164.03 6.83 11.5 8.6 0.65 0.49189.93 7.91 11.4 8.5 0.64 0.48189.95 7.91 11.4 8.5 0.64 0.48189.95 7.91 9.92 9.6 0.56 0.54216.02 9.00 10.2 9.1 0.57 0.51216.03 9.00 10.2 9.0 0.57 0.51216.03 9.00 8.49 10.3 0.48 0.58240.28 10.01 9.06 9.7 0.51 0.55240.30 10.01 9.62 9.5 0.54 0.53240.30 10.01 7.40 11.0 0.42 0.62258.25 10.76 8.44 10.5 0.48 0.59258.27 10.76 8.61 10.3 0.48 0.58258.27 10.76 6.34 11.9 0.36 0.67286.60 11.94 7.6 11.1 0.43 0.63286.62 11.94 7.91 10.8 0.44 0.61286.63 11.94 4.88 12.7 0.28 0.72380.73 15.86 2.49 14.1 0.14 0.79380.75 15.86 3.78 13.3 0.21 0.75380.75 15.86 0.522 15.9 0.03 0.90

81

0.0

5.0

10.0

15.0

20.0

25.0

0.00 5.00 10.00 15.00 20.00

time (days)

% O

2, C

O2

%O2 %CO2

Figure A-29. Turnips 1ºC, % vs time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 5.00 10.00 15.00 20.00

time (days)

cc/g

ccO2/g ccCO2/g

Figure A-30. Turnips 1ºC, cc/g vs time

82

APPENDIX B OXYGEN TRANSMISSION RATE OF PRECISION ORIFICES

Table B-1. OTR of precision orifices at 15, 23, and 30°C diameter(µ m) 15 0C 23 0C 30 0C100 308 254 192153 417 357 384205 581 450 400249 618 564 556

OTR (cc/day)

y = 1.2571x - 0.0121R2 = 0.9972

-0.05

0

0.05

0.1

0.15

0.2

0.25

0 0.05 0.1 0.15 0.2

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-1. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 100 µm 15°C

y = 1.703x - 0.0072R2 = 0.9997

-0.10

0.10.20.30.40.50.60.70.80.9

0 0.1 0.2 0.3 0.4 0.5 0.6

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-2. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 153 µm 15°C

83

y = 2.3698x + 0.0051R2 = 0.9994

00.05

0.10.15

0.20.25

0.30.35

0.4

0 0.05 0.1 0.15 0.2time (days)

-ln((p

O2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-3. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 205 µm 15°C

y = 2.5236x - 0.0024R2 = 0.9994

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

time (days)

-ln((p

O2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-4. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 249 µm 15°C

84

y = 1.0371x - 0.0083R2 = 0.9962

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.02 0.04 0.06 0.08 0.1 0.12

time (days)

-ln((p

O2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-5. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 100 µm 23°C

y = 1.4554x - 0.0063R2 = 0.9968

-0.020

0.020.040.060.08

0.10.120.140.160.18

0 0.02 0.04 0.06 0.08 0.1 0.12

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-6. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 153 µm 23°C

85

y = 1.837x + 0.005R2 = 0.9992

0

0.05

0.1

0.15

0.2

0.25

0 0.02 0.04 0.06 0.08 0.1 0.12

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-7. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 205 µm 23°C

y = 2.3007x + 0.0007R2 = 0.9996

0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.02 0.04 0.06 0.08 0.1 0.12time (days)

-ln((p

O2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-8. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 249 µm 23°C

86

y = 0.7837x - 0.0137R2 = 0.9992

00.010.020.030.040.050.060.070.080.09

0.1

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14time (days)

-ln((p

O2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-9. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 100 µm 30°C

y = 1.5662x - 0.0407R2 = 0.9955

00.020.040.060.08

0.10.120.140.160.18

0.2

0 0.05 0.1 0.15 0.2

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-10. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 153 µm 30°C

87

y = 1.6342x - 0.006R2 = 0.9975

00.020.040.060.08

0.10.120.140.160.18

0.2

0 0.02 0.04 0.06 0.08 0.1 0.12

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-11. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 205 µm 30°C

y = 2.2701x - 0.0062R2 = 0.9993

0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.02 0.04 0.06 0.08 0.1 0.12

time (days)

-ln((

pO2a

-pO

2)/(p

O2a

-pO

2i))

Figure B-7. -ln((pO2a-pO2)/(pO2a-pO2i)) vs time 249 µm 30°C

88

APPENDIX C BROCCOLI PACKAGE DATA

Table C-1 Commercially Packaged Broccoli Head Space Samples

Sample Number %O2 %CO21 6.07 4.92 1.49 8.43 3.26 5.94 5.7 7.55 8.74 4.46 9.06 4.47 6.78 4.68 5.15 5.69 2.44 6.410 4.6 6.3711 1.32 7.512 3.63 6.713 7.58 5.214 6.71 4.1Average 5.18 5.86Standard Deviation 2.42 1.29

Sample Head Space

89

Table C-2. Broccoli Respiration Data Time (hours) Time (days) %O2 %CO2 ccO2/g ccCO2/g0.00 0.00 20.9 0 1.62 0.000.00 0.00 20.9 0 1.64 0.000.00 0.00 20.9 0 1.67 0.000.00 0.00 20.9 0 1.66 0.003.20 0.13 19.5 1.8 1.53 0.143.22 0.13 19.7 1.5 1.52 0.123.22 0.13 19.7 1.6 1.57 0.133.22 0.13 19.5 1.7 1.55 0.146.37 0.27 18.2 2.5 1.41 0.196.37 0.27 18.1 2.8 1.42 0.226.38 0.27 18.3 2.5 1.46 0.206.38 0.27 18 2.5 1.43 0.2014.93 0.62 15.4 4.3 1.19 0.3314.93 0.62 15 4.5 1.18 0.3514.97 0.62 15.6 4.6 1.25 0.3714.97 0.62 14.6 4.3 1.16 0.3424.82 1.03 13.1 5.8 1.01 0.4524.82 1.03 12.5 6.7 0.98 0.5324.83 1.03 11.2 6.2 0.89 0.4924.87 1.04 12 6.3 0.96 0.5037.82 1.58 10.5 7.4 0.81 0.5737.82 1.58 9.49 7.8 0.74 0.6137.83 1.58 8.69 8.1 0.69 0.6537.83 1.58 7.79 8.7 0.62 0.6949.72 2.07 8.00 9.0 0.62 0.7049.72 2.07 6.84 9.0 0.54 0.7149.73 2.07 6.04 10.6 0.48 0.8564.98 2.71 5.45 10.8 0.42 0.8364.98 2.71 3.98 12.4 0.31 0.9765.00 2.71 2.98 12.6 0.24 1.0165.03 2.71 1.92 13.5 0.15 1.0773.10 3.05 4.94 11.4 0.38 0.8873.10 3.05 2.63 13.2 0.21 1.0373.12 3.05 1.47 13.6 0.12 1.0980.28 3.35 0.596 14.3 0.05 1.1487.97 3.67 1.69 14.3 0.13 1.1187.97 3.67 0.253 15.1 0.02 1.1887.98 3.67 0.000427 15.8 0.00 1.26100.03 4.17 0.000354 15.5 0.00 1.20

90

REFERENCES

Emond, J.P. 1992. Mathematical modeling of gas concentration profiles in perforation-generated modified atmosphere bulk packaging. Ph.D. Thesis, University of Florida.

Emond, J.P., Castaigne, F., Toupin, C.J. and Desilets, D. 1991.Mathematical modeling of gas exchange in modified atmosphere packaging. Trans. ASAE. 34(1), 239-245.

Fishman, S., Rodov, V. and Ben-Yehoshua, S. 1996. Mathematical model for perforation effect on oxygen and water vapor dynamics in modified atmosphere packages. Journal of Food Science 61(5), 956-961

Fonseca, S.C., Oliviera, F.A.R. and Chau, K.V. 1996. Oxygen and carbon dioxide exchange through a perforation, for development of perforated modified atmosphere bulk packages. Poster presented at Ann. Mtg., June 22-26, Institute of Food Technologists, New Orleans, LA.

Ghosh, V. and Anantheswaran, R.C. 2001. Oxygen Transmission Rate through Micro-Perforated Films: Measurement and Model Comparison. J. Food Process Engineering. 24.

Gorny, J.R. 1997. A summary of CA and MA requirements and recommendations for fresh-cut (minimally processed) fruits and vegetables. Vol 5, Fresh-cut Fruits and Vegetables and MAP. J. Gorny (ed) Davis CA, pp. 30-67.

Hagger P.E., D.S. Lee, K.L Yam 1992. ‘Application of an Enzyme Kinetics Based Respiration Model to Closed System Experiments For Fresh Produce ’ Journal of Food Process Engineering 15, 143-157.

Hardenburg, R.E., A.E. Watada and C.Y. Wang. 1986. The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA Agric. Hdbk No. 66, Washington, DC.

Hayakawa, K., Y.S. Henig and S.G. Gilbert. 1975. Formulae for Predicting Gas Exchange of Fresh Produce in Polymeric Film Package. Journal of Food Science. 40: 186.

Henig, Y. S., and Gilbert, S. G., 1975. Computer Analysis of the Variables Affecting Respiration and Quality of Produce Packaged in Polymeric Films. Journal of Food Science Vol. 40, No. 5, 1033-1035

Hirata, T., Makino, Y., Ishikawa, Y., Katusara, S. and Hasegawa. 1996. A theoretical model for designing a modified atmosphere packaging with a perforation. Trans. ASAE. 39(4), 1499- 1504.

Johnson, B. and Demorest, R. 1997. Testing, permeation and leakage. In The Wiley Encyclopedia of Packaging, (A. Brody and K. Marsh, eds.) pp. 895-901, John Wiley & Sons, New York.

Kautsky, H. (1939) Quenching of luminescence by oxygen. Trans. Faraday Soc., 35, 216-219.

91

Kader, A. A. 1986. Biochemical and physiological basis for effects of controlled and modified atmosphere packaging on fruits and vegetables. Food Technol. 34(3):51-54

Kader, A. A., Zagory, D., and Kerbel, E. L. 1989. Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food Sci. 28(1): 1-30.

Landrock, A.H. and Procter, B.E. 1952. The simultaneous measurement of oxygen and carbon dioxide permeabilities of packaging materials. Tappi. 35(6), 241-246

Laties, G.G. 1978. The development and control of respiratory pathways in slices of plant storage organs. 1978. In Biochemistry of Wounded Plant Tissues, Ed. G. Kahl (ed.), pp. 421-466. Berlin: Walter de Gruyter.

Lee D.S., P.E. Hagger, J. Lee, and K.L. Yam 1991. ‘Model for Fresh Produce Respiration in Modified Atmosphere Based on Principle of Enzyme Kinetics’ Journal of Food Science Vol. 56 No. 6, 1580-1585.

Leshuk, J.A. and M.E. Saltveit. 1990. Controlled atmospheres and modified atmospheres for the preservation of vegetables. In: M. Calderon (ed) Food Preservation by Modified Atmospheres, pp. 315-352

Mannapperuma, J.D., Zagory, D., Singh R. P., and Kader, A. A. 1989. Design of polymeric packages for storage of fresh produce. Proceedings 5th Controlled Atmosphere Research Conference, vol. 2, Wenatchee, Washington, p. 225.

Martinez-Ferrer, M., Harper, C., Perez-Muntoz, F., and Chaparro, M. 2002. Modified Atmosphere Packaging of Minimally Processed Mango and Pineapple Fruits. Journal of Food Science Vol. 67, No. 9, 3365-3371.

Meidner, H., and Mansfield, T. A, 1968. Physiology of Stomata. McGraw – Hill Book Co. New York.

Mencarelli, F., W.J. Lipton and S.J. Peterson. 1983. Response of ‘zucchini’ squash to storage in low-O2 atmospheres at chilling and non-chilling temperatures. J. Amer. Soc. Hort. Sci. 108: 884-890.

Moyls, L., Hocking, R., Beveridge, T. and Timbers, G. 1992. Exponential decay method for determining gas transmission rate of films. Trans. ASAE. 35(4), 1259-1265

Nobel, P. S. 1974. Introduction to Biophysical Plant Physiology. W.H. Freeman and Company, San Francisco

Perry, R.H. and Green D., Perry’s Chemical Engineer’s Handbook, 6th ed., McGraw-Hill International Editions, New York, 1984, 3-285.

Renault, P., Souty, M. and Chambroy, Y. 1994a. Gas exchange in modified atmosphere packaging. 1: A new theoretical approach for microperforated packs. Intern. J. Food Sci. Technol. 29, 365-378.

92

Renault, P., Souty, M., Houal, L. and Chambroy, Y. 1994b. Gas exchange in modified atmosphere packaging. 2: Experimental results with strawberries. Intern. J. Food Sci. Technol. 29, 379-394.

Robertson, Gordon L. 1993. Food Packaging Principles and Practice. New York, Marcel Dekker, Inc. pgs 75-77

Ryall, A. L. and W.J. Lipton. 1979. Handling, transportation and storage of fruits and vegetables. Vol. 1. Vegetables and melons. A VI, Westport CT.

Ryall, A. L. and Pentzer, W.T. 1979. Handling Transportation of Fruits and Vegetables and Melons, Vol. 1. Vegetables and Melons, 2nd ed. AVI Publishing CT.

Ryall, A. L. and Pentzer, W.T. 1982. Handling Transportation of Fruits and Vegetables and Melons, Vol. 2. Fruits and Tree Nuts, 2nd ed. AVI Publishing Co., Westport, CT.

Saltveit, M.E. 1985. A summary of CA requirements and recommendations for vegetables. Controlled atmospheres for storage and transport of perishable agricultural commodities. Blankenship, S. M. (Ed), Report No 126. Department of Horticultural Science, North Carolina State University, Raleigh, North Carolina, USA.

Wiley, R. C. 1994. Some Biological and Physical Principles Underlying Modified Atmosphere Packaging. In Minimally Processed Refrigerated Fruits and Vegetables, pg 183 – 225. Chapman & Hall Inc. New York.

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BIOGRAPHICAL SKETCH

I was born in Bellows Falls Vermont and went to elementary, middle, and high school in

the city of Tampa, Florida. My undergraduate studies were done in chemical engineering with a

minor in material science at the University of Florida. Upon completion of my undergraduate

studies I did one tour of duty in the US Navy. After completing my time in the US Navy I did my

masters in Agricultural and Biological Engineering specializing in Packaging Science with a

minor in Food Science also completed at the University of Florida.