portable water activity measurement system...

Portable Water Activity Measurement System

Operator’s Manual

METER Group, Inc.

Version: July 19, 2017 — 07:03:59

Pawkit

METER Group, Inc.2365 NE Hopkins Court

Pullman WA 99163

Phone: 509-332-5601Fax: 509-332-5158

Website: www.metergroup.comEmail: [email protected] or

[email protected]

TrademarksAquaLab is a registered trademark of METER Group, Inc.

c©2017 METER Group, Inc.

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Pawkit CONTENTS

Contents

1 Introduction 11.1 Customer Support . . . . . . . . . . . . . . . . . . . . 11.2 About This Manual . . . . . . . . . . . . . . . . . . . 11.3 Warranty . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . 2

2 About the Pawkit 32.1 Pawkit Instrument Specifications . . . . . . . . . . . . 32.2 How the Pawkit Works . . . . . . . . . . . . . . . . . . 42.3 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . 42.4 Getting Started . . . . . . . . . . . . . . . . . . . . . . 4

2.4.1 Components of your Pawkit System . . . . . . 42.5 Preparing for Operation . . . . . . . . . . . . . . . . . 5

3 Water Activity Theory 63.1 Moisture Content . . . . . . . . . . . . . . . . . . . . . 63.2 Water Activity . . . . . . . . . . . . . . . . . . . . . . 63.3 Water Potential . . . . . . . . . . . . . . . . . . . . . . 83.4 Sorption Isotherms . . . . . . . . . . . . . . . . . . . . 9

4 Getting Started 114.1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Sample Preparation and Placement . . . . . . . . . . . 12

4.2.1 Sample Preparation . . . . . . . . . . . . . . . 124.2.2 Sample Placement . . . . . . . . . . . . . . . . 13

4.3 Taking Measurements . . . . . . . . . . . . . . . . . . 154.4 Turning Pawkit off . . . . . . . . . . . . . . . . . . . . 184.5 Sampling Precautions . . . . . . . . . . . . . . . . . . 184.6 Pawkit and Temperature . . . . . . . . . . . . . . . . . 19

5 Cleaning and Maintenance 205.1 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5.1.1 Cleaning Supplies . . . . . . . . . . . . . . . . 205.2 Maintenance . . . . . . . . . . . . . . . . . . . . . . . 21

5.2.1 Sensor Filter Cleaning/Replacement . . . . . . 215.2.2 Thermopile Sensor Cleaning . . . . . . . . . . . 235.2.3 Chamber Cleaning Instructions . . . . . . . . . 23

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CONTENTS Pawkit

5.2.4 Battery Replacement . . . . . . . . . . . . . . . 24

6 Verification and Calibration 276.1 Verification Standards . . . . . . . . . . . . . . . . . . 276.2 Steps to Verify Calibration . . . . . . . . . . . . . . . 28

7 Support and Repair 317.1 Repair Costs . . . . . . . . . . . . . . . . . . . . . . . 327.2 Loaner Service . . . . . . . . . . . . . . . . . . . . . . 32

8 Further Reading 338.1 Water Activity Theory & Measurement . . . . . . . . 33

9 Declaration of Conformity 55

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Pawkit 1 INTRODUCTION

1 Introduction

Welcome to the Pawkit Water Activity Measurement system. ThePawkit allows you to make quick measurements of water activity toensure the safety of your product. We hope you find the contents ofthis manual useful in understanding your instrument and maximizingits benefit to you.

1.1 Customer Support

If you ever need assistance with your Pawkit, have any questions orfeedback, there are several ways to contact us. METER has Cus-tomer Service Representatives available to speak with you Mondaythrough Friday, between 7 am and 5 pm Pacific time.

Note: If you purchased your Pawkit through a distributor, pleasecontact them for assistance.

Email:[email protected] or [email protected]

Phone:509-332-5601

Fax:509-332-5158

If contacting us by email or fax, please include as part of your mes-sage your instrument serial number, your name, address, phone, faxnumber, and a description of your problem or question.

1.2 About This Manual

This manual includes instructions for setting up your Pawkit, verify-ing the calibration of the instrument, preparing samples, and main-taining and caring for your instrument. Please read these instruc-tions before operating your instrument to ensure that the instrument

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1 INTRODUCTION Pawkit

performs to its full potential.

1.3 Warranty

The Pawkit has a 30-day satisfaction guarantee and a one-year war-ranty on parts and labor. Your warranty is automatically validatedupon receipt of the instrument.

1.4 Seller’s Liability

Seller warrants new equipment of its own manufacture against de-fective workmanship and materials for a period of one year from thedate of receipt of equipment.

Note: We do not consider the results of ordinary wear and tear,neglect, misuse, accident and excessive deterioration due to corro-sion from any cause as defects.

The seller’s liability for defective parts shall in no event exceed thefurnishing of replacement parts Freight On Board the factory whereoriginally manufactured. Material and equipment covered herebywhich is not manufactured by Seller shall be covered only by thewarranty of its manufacturer. Seller shall not be liable to Buyer forloss, damage or injuries to persons (including death), or to propertyor things of whatsoever kind (including, but not without limitation,loss of anticipated profits), occasioned by or arising out of the instal-lation, operation, use, misuse, nonuse, repair, or replacement of saidmaterial and equipment, or out of the use of any method or processfor which the same may be employed. The use of this equipment con-stitutes Buyer’s acceptance of the terms set forth in this warranty.There are no understandings, representations, or warranties of anykind, express, implied, statutory or otherwise (including, but with-out limitation, the implied warranties of merchantability and fitnessfor a particular purpose), not expressly set forth herein.

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Pawkit 2 ABOUT THE PAWKIT

2 About the Pawkit

The Pawkit is designed to be a simple, rapid and portable systemfor measurement of water activity. It is easy to use, durable, andrequires little maintenance.

2.1 Pawkit Instrument Specifications

Sensor Type: Capacitance Sensor

Water Activity Range: 0.00to1.00 aw

Water Activity Accuracy: ±0.02

Water Activity Resolution: 0.01

Sample Temperature Accuracy: ±0.2 ◦C

Sample Temperature Resolution: 0.1 ◦C

Read Time: 5 min

Sample Dish Capacity: 7.5 mL Recommended (15 mL Full)

Operating Environment: 4 to 50 ◦C; 0 to 90% Relative Humidity(non-condensing)

Case Dimensions: 6.6 x 10.7 x 2.0 cm

Weight: 115 g (4 oz)

Case Material: Stainless Steel and Valox 325 Plastic

Display: 6-digit Custom LCD with Symbols

Data Communications: NA

Power: 2 to 3 Volt 16 mm coin cell batteries (Three Years)

Warranty: 1 year parts and labor

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2 ABOUT THE PAWKIT Pawkit

2.2 How the Pawkit Works

The Pawkit uses a capacitance humidity sensor to measure the wateractivity of a sample. The sensor converts the humidity value into aspecific capacitance, which is then measured electronically by the cir-cuit. This signal is then translated by the software and displayed aswater activity on the instrument screen. At equilibrium, the relativehumidity of the air in the chamber is the same as the water activityof the sample.

2.3 Accuracy

The Pawkit is accurate to ±0.02 aw. For many applications, this ac-curacy is more than adequate. If you require higher accuracy in yourmeasurements, we recommend you use METER’s AquaLab water ac-tivity meter, which is a lab-grade, bench-top instrument that has anaccuracy of ±0.003 aw, and measures based upon the chilled-mirrordew point method. Contact METER for more details.

2.4 Getting Started

2.4.1 Components of your Pawkit System

Your Pawkit should have been shipped to you with the followingitems:

• Pawkit main unit

• Operator’s Manual

• Quick Start Guide

• Certificate of Analysis

• Calibration Certificates

• Anti-Skid Pad

• Durable carrying case

• 60 disposable sample cups with lids

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Pawkit 2 ABOUT THE PAWKIT

• Spare sensor filters

• Reusable stainless steel cup

• Two vials each of the following verification standards:

2.33 mol/kg NaCl (0.920 aw)

6.00 mol/kg NaCl (0.760 aw)

13.41 mol/kg LiCl (0.250 aw)

• AquaLab cleaning kit

2.5 Preparing for Operation

To ensure that your Pawkit operates correctly and consistently, al-ways place it on a level surface when measuring. This mitigatesthe risk of sample material spilling inside the instrument. To avoidinaccurate readings, place your Pawkit in a location where the tem-perature remains fairly stable. This location should be well awayfrom air conditioner and heater vents, open windows, outside doors,refrigerator exhausts, or other items that may cause rapid tempera-ture fluctuation.

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3 WATER ACTIVITY THEORY Pawkit

3 Water Activity Theory

Water is a major component of foods, pharmaceuticals, and cosmet-ics. Water influences the texture, appearance, taste and spoilage ofthese products. There are two basic types of water analysis: moisturecontent and water activity

3.1 Moisture Content

The meaning of the term moisture content is familiar to most people.It implies a quantitative analysis to determine the total amount ofwater present in a sample. There are two primary methods for deter-mining moisture content: loss on drying and Karl Fisher titration,but you can also use secondary methods such as infrared and NMR.Moisture content determination is essential in meeting product nu-tritional labeling regulations, specifying recipes and monitoring pro-cesses. However, moisture content alone is not a reliable indicator forpredicting microbial responses and chemical reactions in materials.The limitations of moisture content measurement are attributed todifferences in the intensity with which water associates with othercomponents.

3.2 Water Activity

Water activity is a measure of the energy status of the water in asystem, and thus is a far better indicator of perishability than watercontent. Figure 1 shows how the relative activity of microorganisms,lipids and enzymes relate to water activity. While other factors, suchas nutrient availability and temperature, can affect the relationships,water activity is the best single measure of how water affects theseprocesses. Researchers measure the water activity of a system byequilibrating the liquid phase water in the sample with the vaporphase water in the headspace and measuring the relative humidityof the headspace. In the Pawkit, place a sample in the sample cupthat fits underneath the Pawkit. Inside the sensor block is a capac-itive humidity sensor. Changes in the electrical capacitance of thepolymide layer of the sensor occur as the relative humidity of the

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Pawkit 3 WATER ACTIVITY THEORY

Figure 1: Water Activity Diagram adapted from Labuza

chamber changes. The Pawkit computes the relative humidity of theheadspace by monitoring the change in electrical capacitance. Whenthe water activity of the sample and the relative humidity of the airare in equilibrium, the measurement of the headspace humidity givesthe water activity of the sample.

In addition to equilibrium between the liquid phase water in thesample and the vapor phase, the internal equilibrium of the sampleis important. If a system is not at internal equilibrium, one mightmeasure a steady vapor pressure (over the period of measurement)which is not the true water activity of the system. An example of thismight be a baked good or a multi-component food. Initially out ofthe oven, a baked good is not at internal equilibrium; the outer sur-face is at a lower water activity than the center of the baked good.One must wait a period of time in order for the water to migrateand the system to come to internal equilibrium. It is important toremember the restriction of the definition of water activity to equi-librium.

Temperature Effects

Temperature plays a critical role in water activity determination.

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Most critical is the measurement of the difference between sampleand capacitance sensor temperature. Best accuracy is therefore ob-tained when the sample is near chamber temperature.

3.3 Water Potential

Some additional information may be useful for understanding whatwater activity is and why it is such a useful measure of moisturestatus in products. Water activity is closely related to a thermody-namic property called the water potential, or chemical potential (µ)of water, which is the change in Gibbs free energy (∆G) when waterconcentration changes. Equilibrium occurs in a system when (µ) isthe same everywhere in the system. Equilibrium between the liquidand the vapor phases implies that (µ) is the same in both phases.It is this fact that allows us to measure the water potential of thevapor phase and use that to determine the water potential of the liq-uid phase. Gradients in (µ) are driving forces for moisture movement.

Thus, in an isothermal system, water tends to move from regionsof high water potential (high aw) to regions of low water potential(low aw). Water content is not a driving force for water movement,and therefore can not be used to predict the direction of water move-ment, except in homogeneous materials.

Factors In Determining Water Activity

The water activity of the water in a system is influenced by factorsthat effect the binding of water. They include osmotic, matric, andpressure effects. Typically water activity is measured at atmosphericpressure, so only the osmotic and matric effects are important.

Osmotic Effects: Osmotic effects are well known from biology andphysical chemistry. Water is diluted when a solute is added. Ifthis diluted water is separated from pure water by a semi-permeablemembrane, water tends to move from the pure water side throughthe membrane to the side with the added solute. If sufficient pressureis applied to the solute-water mixture to just stop the flow, this pres-sure is a measure of the osmotic potential of the solution. Addition

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Pawkit 3 WATER ACTIVITY THEORY

of one mole of an ideal solute to a kilogram of water produces anosmotic pressure of 22.4 atm. This lowers the water activity of thesolution from 1.0 to 0.98 aw. For a given amount of solute, increasingthe water content of the systems dilutes the solute, decreasing theosmotic pressure, and increasing the water activity. Since microbialcells are high concentrations of solute surrounded by semi-permeablemembranes, the osmotic effect on the free energy of the water is im-portant for determining microbial water relations and therefore theiractivity.

Matric Effects: The sample matrix affects water activity by phys-ically binding water within its structure through adhesive and cohe-sive forces that hold water in pores and capillaries, and to particlesurfaces. If cellulose or protein were added to water, the energy sta-tus of the water would be reduced. Work would need to be done toextract the water from this matrix. This reduction in energy statusof the water is not osmotic, because the cellulose or protein concen-trations are far too low to produce any significant dilution of water.The reduction in energy is the result of direct physical binding ofwater to the cellulose or protein matrix by hydrogen bonding andvan der Waal forces. At higher water activity levels, capillary forcesand surface tension can also play a role.

3.4 Sorption Isotherms

Relating Water Activity to Water Content

Changes in water content affect both the osmotic and matric bindingof water in a product. Thus a relationship exists between the wateractivity and water content of a product. This relationship is calledthe sorption isotherm, and is unique for each product. Besides beingunique to each product, the isotherm changes depending on whetherit was obtained by drying or wetting the sample. These factors needto be kept in mind if one tries to use water content to infer thestability or safety of a product. Typically, large safety margins arebuilt into water content specifications to allow for these uncertainties.

While the sorption isotherm is often used to infer water activity from

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water content, one could easily go the other direction and use the wa-ter activity to infer the water content. This is particularly attractivebecause water activity is much more quickly measured than watercontent. This method gives particularly good precision in the centerof the isotherm. In order to infer water content from water activity,one needs an isotherm for the particular product. METER sells anIsotherm Generator called the AquaLab Vapor Sorption Analyzer oryou can also have METER run the isotherm for a fee.

For example, if one were to monitor the water content of dried potatoflakes, one would measure the water activity and water content ofpotato flakes dried to varying degrees using the standard drying pro-cess for those flakes. An isotherm would be constructed using thosedata, and the water content would be inferred using the measuredwater activity of samples and that isotherm.

We cannot overemphasize the importance of the concept of wateractivity for foods, pharmaceuticals, and cosmetics. Water activity isa measure of the energy status of the water in a system. More impor-tantly, the utility of water activity in relation to microbial growth,chemical reactivity, and stability over water content has been shown.

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Pawkit 4 GETTING STARTED

4 Getting Started

Operation of the Pawkit is very simple. Once you have ensuredthat you have a stable working environment, you are ready to beginsampling. The following is a description of the features and operationof the instrument.

4.1 Features

Figure 2: Pawkit Features Top

Figure 3: Pawkit Features Bottom

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4 GETTING STARTED Pawkit

4.2 Sample Preparation and Placement

Your Pawkit system comes with 60 disposable plastic sample cupsand one stainless steel sample cup. If you run out, you can purchaseadditional cups from METER.

4.2.1 Sample Preparation

Take special care when preparing the sample in order to get thebest readings possible. Always follow the bulleted guidelines whenpreparing samples.

• Make sure that the sample to be measured is homoge-neous. Multi-component samples (e.g., muffins with raisins)or samples that have outside coatings (like deep-fried, breadedfoods) can be measured, but may take longer to equilibrate.Samples like these may require additional preparation (crush-ing or grinding) to obtain a representative sample.

• Completely cover the bottom of the cup with the sam-ple, if possible. The Pawkit is able to accurately measurea sample that leave small spaces of the cup bottom exposed.For example, raisins only need to be placed in the cup and notflattened to cover the bottom. A larger sample surface areaincreases instrument efficiency by shortening the time neededto reach vapor equilibrium.

• Fill the cup no more than half-full of the sample. ThePawkit does not require a large sample size to make its reading.As long as the sample covers the bottom of the cup and thesample is representative of the product you wish to measure,you should be able to make accurate readings. If the samplecup is too full, you risk contaminating the sensor, which canlead to inaccurate readings.

• Make sure that the rim and outside of the sample cupare clean. Wipe any excess sample material from the rimof the cup with a clean tissue. Material left on the rim or theoutside of the cup can be transferred to subsequent samples andmay affect the accuracy of your readings. The rim of the cup

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forms a vapor seal with the sensor. Any sample material lefton the cup rim may prevent this seal and contaminate futuresamples.

• If you are reading a sample at a later time, put thesample cup disposable lid on the cup to restrict watertransfer. To seal the lid, place tape or ParafilmTMcompletelyaround the cup/lid junction. It is necessary to seal the cup ifit is going to be a long time before you make the measurement.

4.2.2 Sample Placement

1. Open the Pawkit by holding the case near the LCD with onehand and pulling down on the plastic sensor cover tab with theother hand.

The sensor cover rotates and snaps into the open position.

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2. Place your prepared sample cup onto a level surface.

Next, place the opened Pawkit onto the prepared sample cup.The cup fits under the sensor into a recess in the bottom of thePawkit.

A correctly positioned cup results in the Pawkit being level onthe bench when sitting on the cup and the sensor cover legs.Ensure the cup is entirely within the recess. Otherwise, thePawkit may not be level on the bench and the cup might notmake a vapor seal with the sensor.

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3. Once you have the Pawkit properly positioned over the samplecup, you are now ready to take readings.

4. To close the instrument, reverse the opening procedure. Withone hand holding the case near the LCD pull down on theplastic sensor cover tab with the other hand and rotate until itsnaps into the closed position covering the sensors.

4.3 Taking Measurements

1. Make sure the sample cup is positioned as described in theSample Placement section.

2. Press the left button (I) to turn on the instrument. It displaysthe last reading taken. This allows you to begin a measurementand leave without having to attend the instrument throughoutthe measurement. If it is already on, proceed to the next step.

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3. Press button I to begin the water activity measurement. TheLCD display resets to 0.00aw.

Note: Pressing button I any time during a measurement restartsthe water activity measurement.

4. Once the measurement process has been started, the Pawkitbegins to display water activity measurements as well as tem-perature after five seconds updating the display every secondthereafter. During this time you are be able to see that it ismeasuring by looking at the “sunburst” icon to the right of thewater activity value. As it measures, you may see the “beams”of the sunburst move from left to right.

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Note: The final water activity measurement is not be displayeduntil the instrument beeps and the sunburst icon disappearsfrom the screen.

If you receive an error code of 9.99 at any time during theprocess, it indicates that the sensor has failed and that theinstrument needs to be serviced. Refer to Section 7 for instruc-tions on how to return your Pawkit for repair.

Note: DO NOT lift or move the instrument during the mea-surement. You risk contaminating the chamber and breakingthe chamber vapor seal and invalidates the water activity mea-surement.

5. After five minutes, the instrument displays the final water ac-tivity and beep five times. The sunburst disappears when thewater activity reading is finished.

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Note: We recommend you record the reading value before pro-ceeding.

At this point you can either restart the measurement by press-ing button I again or end the measurement procedure.

6. Remove the sample cup by lifting the Pawkit. Lift the Pawkitstraight up as shown to avoid spilling the sample cup. Thesample may now be discarded or covered with a lid if it is tobe re-measured at a later time.

4.4 Turning Pawkit off

To turn off the Pawkit, leave it idle for more than five minutes, andit shuts off automatically. If the Pawkit has automatically shut itselfoff, pressing the “I” button wakes up the instrument and display thelast water activity measurement.

Remember to close the lid before storing the case.

4.5 Sampling Precautions

Long exposure to a variety of volatile substances or to samples withwater activities near 1.00 can shift the sensor calibration. Therefore,

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always remove samples as soon as the Pawkit is finished sampling(beeps) to avoid damage to the sensor. If a sample is accidentallyleft in the chamber for an extended period of time, be sure to checkthe calibration when you next use the instrument.

If sensor damage occurs, the instrument displays an error code of9.99 on the screen. Refer to Section 7 for further instructions on howto return your Pawkit for repair.

4.6 Pawkit and Temperature

The Pawkit makes its most accurate measurements when the sampleand instrument temperatures are within 1 ◦C. If the sample is toowarm, the thermometer icon on the left of the screen appears.

You see the “mercury” go up the thermometer and pop out of thetop, and the instrument beeps, indicating that the sample tempera-ture is too high and there is danger of condensing water in the samplechamber and on the sensor. If you get this warning while sampling,remove the Pawkit, place the cup lid on the sample and wait until ithas reached ambient temperature before attempting to read again.

If your sample is colder than the ambient temperature of the Pawkit,the accuracy of your reading after five minutes may be questionable.Wait until the sample temperature is similar to that of the Pawkit.

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5 CLEANING AND MAINTENANCE Pawkit

5 Cleaning and Maintenance

5.1 Cleaning

The accuracy of your Pawkit is dependent on keeping your instru-ment clean. Dust and sample debris can contaminate the samplingchamber, and must therefore be regularly cleaned out. To clean yourinstrument, carefully follow the instructions in this Section.

5.1.1 Cleaning Supplies

Your new instrument comes with the compact AquaLab CleaningKit that contains all the materials needed to clean the instrument forabout a year. If you need to purchase a new cleaning kit, please con-tact us by phone at 509-332-5601 or at [email protected] offers two sizes of cleaning kits. The larger cleaning kit isprimarily used for benchtop units and the compact is more useful forthe handheld. The following supplies are included in the compactcleaning kit.

• Swab (a thin plastic rod)• Steam Distilled Water• Cleaning Solution• Kimwipe R© Strips• Sample Cup with Charcoal Pellets• Cleaning Procedure Information Card

Note: Wash your hands with soap and water and/or use clean labgloves before starting the cleaning procedure. This prevents oils fromcontaminating the cleaning materials, the sample chamber and/orthe sensors.

Here are four tips for keeping your Pawkit clean.

1. First, watch the instructional AquaLab Pawkit and Lite clean-ing video at http://www.aqualab.com/education/aqualab-pawkit-lite-cleaning-video/ to see step-by-step instructions on how toclean your Pawkit.

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Pawkit 5 CLEANING AND MAINTENANCE

2. Use only a soft cotton cloth to clean the LCD. Tissues canscratch the plastic, causing damage.

3. Use moist Kimwipes or soft cotton cloth to clean the rest ofthe outer case.

4. Begin each step cleaning the chamber and thermopile sensorusing a new Kimwipe strip wrapped around the plastic swabincluded in your kit. If you have spilled sample material onthe sensor filter and it does not come off replace the filter asexplained in the next section. It is important that contamina-tion of this filter is minimized, as the relative humidity of thesample is measured via the filter.

5.2 Maintenance

5.2.1 Sensor Filter Cleaning/Replacement

You may periodically need to replace the porous white humiditysensor filter if it becomes dirty. To remove the sensor filter use aknife or needle point to gently pry up the edge of the filter. YourPawkit shipped with three spare filters and you can order more bycontacting METER through email at [email protected] orby phone at 509-332-5601.

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Figure 4: Removal of Filter

Caution: The capacitance humidity sensor below the filteris extremely fragile, Do not touch it.

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5.2.2 Thermopile Sensor Cleaning

The lens of this sensor must be free of all dirt and lint to be accurate.

1. WASH–using a Kimwipe tissue moistened with cleaning solu-tion or isopropyl alcohol to clean the thermopile sensor.

2. RINSE–using a new Kimwipe moistened with steam distilledwater to rinse the cleaning solution from the sensor.

3. DRY–use a dry Kimwipe to help remove any moisture remain-ing from the cleaning process.

5.2.3 Chamber Cleaning Instructions

Wrap a new Kimwipe strip around the end of the swab (included inthe cleaning kit) and moisten it with cleaning solution or isopropylalcohol.

1. WASH–clean the surrounding chamber area with the moistKimwipe. The chamber area, especially where the cup seals,must be free of all contamination.

2. RINSE–repeat the steps above using a new Kimwipe strip moist-ened with steam distilled water.

3. DRY–repeat steps above again, this time using a dry Kimwipestrip to remove any moisture remaining from the cleaning pro-cess.

Note: Do NOT reuse Kimwipes.

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5.2.4 Battery Replacement

The Pawkit uses two Lithium-ion battery cells that should lastfor several years. If the battery charge is low, you may see alow-battery indicator icon appear in the lower right corner ofthe screen

Note: An occasional low battery indication does not mean thebattery needs replacing.

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Follow steps 1 through 4 to replace the battery.

1. Remove the Pawkit bottom by unscrewing the two screws.

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2. Separate the stainless steel top and elastomer (which containsthe batteries) from the white plastic bottom.

3. Remove the old Lithium-ion batteries. Replace with new CR1632or equivalent 3V lithium coin cells. Make sure to orient thebatteries so the positive (+) contact is facing down into the

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elastomer pocket. Make sure the two small springs which makecontact between the (+) battery terminal and the circuit boardare in place.

4. Replace the circuit board/plastic bottom in the elastomer top.Tighten the two screws to complete the assembly of the Pawkit.

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Pawkit 6 VERIFICATION AND CALIBRATION

6 Verification and Calibration

The Pawkit takes water activity measurements by measuring thechange in electrical properties of a special polymer held between twoelectrodes. Due to the nature of the capacitance humidity sensor, it isimportant to verify the AquaLab water activity calibration againstknown standards to guarantee optimal performance and accuracy.METER recommends verification daily, once per shift or before eachuse. METER also recommends annual factory calibration to main-tain optimal performance.

6.1 Verification Standards

The Pawkit uses four calibration standards: 6.00 mol/kg NaCl (0.760aw), 13.41 mol/kg LiCl (0.250 aw), and 2.33 mol/kg NaCl (0.920 aw).You received a small supply of these standards with your instrument.These standards are specially prepared salt solutions at specific con-centrations for constant and accurate water activity measurements.They have been produced under a strict quality assurance regime,and their accuracy is verified by an independent third party instru-ment. They are very accurate, easy to use, and readily available fromMETER. Most importantly, they greatly reduce preparation errors.Because of these reasons, we recommend using these standards forthe most accurate calibration of your Pawkit. The verification stan-dards are shelf-stable for one year.

If these standards are not available you can make a saturated SodiumChloride (NaCl) slurry with a water activity value of 0.75 aw. Tomake a salt slurry of NaCl add water until the salt can absorb nomore water, as evidenced by the presence of free liquid. The slurryshould take the shape of the cup and flow when tipped with theamount of free liquid at a minimum.

Note: To avoid inaccurate water activity readings, verification stan-dards should be used once immediately after opening and not storedin sample cups for repeated use.

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6 VERIFICATION AND CALIBRATION Pawkit

6.2 Steps to Verify Calibration

1. Take a vial of the 0.760 aw NaCl standard and empty the entirecontents of the vial into a sample cup. Place the Pawkit overthe sample cup as described in the Sample Placement section.

2. Press the left button (I) to take a reading. If it is reading thecorrect water activity ±0.02, your Pawkit needs no adjustmentfor this standard. Skip to step 9.

3. If the first reading was not the correct water activity (±0.02),clean the Pawkit according to the instructions in Section 5 andtake a second reading. If it is reading the correct water activity±0.02, your Pawkit needs no adjustment at this time and youmay now skip to step 9. If it is not reading correctly, continueto the next step.

Note: An error code of 9.99 at any time during the process in-dicates that the sensor has failed and that the instrument needsto be serviced. Refer to Section 7 for shipping instructions.

4. Once the reading is finished, the right button (II) activates.Button II is only active until the Pawkit shuts itself off. Pressit once to get the Calibration Mode screen.

5. This screen shows that you are in the calibration mode. Thisone in particular shows that you are ready to adjust calibra-tion upwards for the 0.76 standard. The number in the up-per right corner indicates the water activity measurement thatyour Pawkit just read. Press the II button to scroll throughthe other selections. They are: u76, d76, u25, d25, Sto, u92

28

Pawkit 6 VERIFICATION AND CALIBRATION

and d92. The “u” and “d” before each number stand for “up”or “down” adjustment for each standard. The numbers (25,76, and 92) correspond to the water activity of a verificationstandard (0.76, 0.25, and 0.92 aw). The “Sto” position storesa reading.

6. As an example, if your NaCl reading is lower than it shouldbe, press the II button to scroll to “u76” (“adjust up for 0.76standard”). If it is higher than it should be, scroll to “d76”(“adjust down for 0.76 standard”).

Note: If you accidentally scroll past your desired adjustmentscreen, simply keep pressing the II button until you cycle backto the right screen.

7. Once you have scrolled to the proper screen for calibrationadjustment, press the I button to adjust the value to what itshould be. Each time you press the I button, the value in thecorner changes by an increment of 0.01.

8. When you have it set to the correct value, press the II button toscroll until “Sto” appears in the lower right corner, then pressI. This stores the new value you have set. You then return tothe main screen and begin a new measurement.

Note: If you do not press “Sto” no change is made to the cali-bration of the Pawkit.

9. Verify with a second standard, either the 0.25 standard or the0.92 standard. Choose the one that is closest to the water ac-tivity range of the sample material you are testing. In otherwords, if it is normally higher than 0.76 aw, use the 0.92 stan-dard. If it is normally lower than 0.76 aw, use the 0.25 standard.If the Pawkit measures the second standard correctly (±0.02),begin testing your product. If it does not measure correctly,repeat steps 3 for 8 for the second standard.

10. If you inadvertently enter the calibration routine, keep pressingbutton II until you scroll back to the main screen.

Note: The 0.76 standard adjustment adjusts the calibration in-

29

6 VERIFICATION AND CALIBRATION Pawkit

tercept, while the 0.25 and 0.92 adjusts the slope. Changes inthe intercept are more likely to occur than changes in the slope,so the 0.76 verification check is the most important and shouldbe done more frequently.

Review the graphical representation of the calibration routine in Fig-ure 5.

Figure 5: Calibration Routine Flowchart

30

Pawkit 7 SUPPORT AND REPAIR

7 Support and Repair

Note: If you purchased your Pawkit from one of our internationaldistributors, please contact them. They can provide you with localsupport and service.

When encountering problems with your AquaLab that you are un-able to resolve with the help of this manual, please contact METERCustomer Support at [email protected], 509-332-5601or fax us at 509-332-5158. Please have the serial number and modelof the instrument ready.

All Pawkits returning to METER for servicing must be accompa-nied with a Return Material Authorization (RMA) number. Prior toshipping the instrument, please contact a METER customer supportrepresentative to obtain an RMA.

Shipping Directions

The following steps can help to ensure the safe shipping and pro-cessing of your AquaLab.

1. Pack the Pawkit in its carrying case, securely in its original box.If the original packaging is not available, pack the box mod-erately tight with packing material (e.g. styrofoam peanutsor bubble wrap), ensuring the instrument is suspended in thepacking material. Use a box that has at least two inches ofspace between your instrument and each wall of the box.

2. Include a copy of the RMA form in the shipment. Please verifythe ship to and bill to information, contact name, and problemdescription. If anything is incorrect please contact a METERrepresentative.

3. Tape the box in both directions for added support.

31

7 SUPPORT AND REPAIR Pawkit

Ship to:METER Group, Inc.ATTN: RMA (insert your RMA #)2365 NE Hopkins CourtPullman, WA 99163

7.1 Repair Costs

We repair manufacturer defects and instruments within the one-yearwarranty at no charge. Non-warranty repair charges for parts, laborand shipping are billed to you. An extra fee may be charged for rushwork. METER can provide an estimated repair cost, if requested.

7.2 Loaner Service

METER has loaner instruments available to keep you measuring wa-ter activity while your instrument is being serviced. Please con-tact customer support for pricing and availability of loaners. If yourAquaLab is being serviced under warranty, you qualify for a freeloaner.

32

Pawkit 8 FURTHER READING

8 Further Reading

8.1 Water Activity Theory & Measurement

Bousquet-Ricard, M., G. Qualyle, T. Pharm, and J. C. Cheftel. 1980.Comparative study of three methods of determining water activityin intermediate moisture foods. Lebensm Wiss Technol 13:169-173.

Cazier, J.B., and V. Gekas. 2001. Water activity and its predic-tion: a review. International Journal of Food properties 4(1):35-43.

Chirife, J., G. Favetto, C. Ferro-Fontn, and S.L.Resnik. 1983. Thewater activity of standard saturated salt solutions in the range ofintermediate moisture foods. Lebensm Wiss Technol 16:36-38.

Duckworth, R. 1975. Water relations of foods. Academic Press,New York.

Gmez, R., and J. Fernandez-Salguero. 1992. Water activity andchemical composition of some food emulsions. Food Chem 45:91-93.

Greenspan, L. 1977. Humidity fixed points of binary saturated aque-ous solutions. J Res Nat Bur Stand - A Phys Chem 81A:89-96.

Karmas, E. 1981. Measurement of moisture content. Cereal FoodsWorld 26:332-334.

Kitic, D., D.C. Pereira-Jardim, G.J. Favetto, S.L. Resnik, and J.Chirife. 1986. Theoretical prediction of the water activity of stan-dard saturated salt solutions at various temperatures. Journal ofFood Science 51:1037-1042.

Labuza, T.P., and R. Contreras-Medellin. 1981. Prediction of mois-ture protection requirements for foods. Cereal Foods World 26:335-343.

Labuza, T.P., K. Acott, S.R. Tatini, R.Y. Lee, J. Flink, and W.McCall. 1976. Water activity determination: A collaborative study

33

8 FURTHER READING Pawkit

of different methods. Journal of Food Science 41:910-917.

Marcolli, C., and Th. Peter. 2005. Water activity in polyol/watersystems: new UNIFAC parameterization. Atmospheric Chemistryand Physics 5:1545-1555.

Ninni, L., M.S. Camargo, and A.J.A. Meirelles. 2000. Water ac-tivity in polyol systems. Journal of Chemical and Engineering Data45:654-660.

Prior, B.A. 1979. Measurement of water activity in foods: A re-view. Journal of Food Protection 42:668-674.

Rahman, M.S. and S.S. Sablani. 2001. Measurement of water ac-tivity by electronic sensors. P. A2.5.1-A2.5.4 In R.E.Wrolstad (ed.)Current Protocols In Food Analytical Chemistry. John Wiley &Sons, Inc., New York.

Rahman, M.S., S.S. Sablani, N. Guizani, T.P. Labuza, and P.P.Lewicki. 2001. Direct manometic determination of vapor pressure.P. A2.4.1-A2.4.6. In R.E. Wrolstad (ed.) Current Protocols In FoodAnalytical Chemistry. John Wiley & Sons, Inc., New York.

Reid, D.S., A.J. Fontana, M.S. Rahman, S.S. Sablani, T.P. Labuza,N. Guizani, and P.P. Lewicki. 2001. Vapor pressure measurementsof water p. A2.1.1-A2.5.4. In R.E. Wrolstad (ed.) Current ProtocolsIn Food Analytical Chemistry. John Wiley & Sons, Inc., New York.

Reid, D.S. 1976. Water activity concepts in intermediate moisturefoods. p. 54-65. In R. Davies, G.G. Birch, and K.J. Parker (ed.)Intermediate Moisture Foods. Applied Science Publishers, London.

Richard, J., and T.P. Labuza. 1990. Rapid determination of thewater activity of some reference solutions, culture media and cheeseusing a dew point method. Sci. des Aliments 10:57-64.

Roa,V., and M.S. Tapia de Daza. 1991. Evaluation of water activitymeasurements with a dew point electronic humidity meter. Lebensm

34


Wiss Technol 24:208-213.

Rodel, W. 2001. Water activity and its measurement in food. P.453-483. In E. Kress-Rogers, and C.B. Brimelow (ed.) Instrumenta-tion and sensors for the food industry. CRC Press LLC, Boca Raton,FL.

Roos, K.D. 1975. Estimation of water activity in intermediate mois-ture foods. Food Tech 29:26-30.

Scott, V.N., and D.T. Bernard. 1983. Influence of temperature onthe measurement of water activity of food and salt systems. Journalof Food Science 48:552-554.

Snavely, M.J., J.C. Price, and H.W. Jun. 1990. A comparison ofthree equilibrium relative humidity measuring devices. Drug Dev.Ind. Pharm. 16:1399-1409.

Stamp, J.A., S. Linscott, C. Lomauro, and T.P. Labuza. 1984. Mea-surement of water activity of salt solutions and foods by several elec-tronic methods as compared to direct vapor pressure measurement.Journal of Food Science 49:1139-1142.

Stoloff, L. 1978. Calibration of water activity measuring instrumentsand devices: Collaborative study. Journal of the Association of Of-ficial Analytical Chemists 61:1166-1178.

Troller, J.A. 1983. Methods to measure water activity. Journal ofFood Protection 46:129-134.

Troller, J.A., and J.H.B Christian. 1978. Water Activity and Food.Academic Press, New York.

Troller, J.A., and V.N. Scott. 1992. Measurement of water activity(aw)and acidity. p. 135-151. In C. Vanderzant, and D.F. Splittstoesser(ed.) Compendium of Methods for the Microbiological Examinationof Foods. American Public Health Association, Washington, D.C.

35


Van den Berg, C. 1986. Water activity. p. 11-36. In D. MacCarthy(ed.) Concentration and drying of foods. Elsevier Applied SciencePublishers, London.

Van den Berg, C. 1991. Food-water relations: Progress and inte-gration, comments and thoughts. In H. Levine, and L. Slade (ed.)Water Relationships in Foods. Plenum Press, New York.

Van den Berg, C., and S. Bruin. 1981. Water activity and its estima-tion in food systems: Theoretical aspects. p. 1-61. In L.B. Rockland,and G.F. Stewart (ed.) Water Activity: Influences on Food Quality.Academic Press, New York.

Vega-Mercado, H., and G.V. Barbosa-Canovas. 1994. Predictionof water activity in food systems: A review on theoretical models.Revista Espanola De Ciencia Y Tecnologia De Alimentos 34:368-388.

Vega-Mercado, H., B. Romanach, and G.V. Barbosa-Canovas. 1994.Prediction of water activity in food systems: A computer programfor predicting water activity in multicomponent foods. Revista Es-panola De Ciencia Y Tecnologia De Alimentos 34:427-440.

Vos, P.T., and T.P. Labuza. 1974. Technique for measurements ofwater activity in the high aw range. J. Agric. Food Chem. 22:326-327.

Voysey, P. 1993. An evaluation of the AquaLab CX-2 system formeasuring water activity. F. M. B. R. A. Digest No. 124 24-25.

Food Safety and Microbiology

Bei, Z.H., and R.-M.J. Nout. 2000. Effects of temperature, wa-ter activity and gas atmosphere on mycelial growth of tempe fungiRhizopus microsporus var. microcporus and R. microsporus var.oligosporus. World Journal of Microbiology and Biotechnology 16:853-858.

Beuchat, L.R. 1981. Microbial stability as affected by water activity.

36


Cereal Foods World 26:345-349.

Brandt, L. 1996. Bound for success. Controlling water activity givestechnologists the edge in developing safe, shelf-stable foods. FoodFormulating 2:41-48.

Chirife, J., and M.P. Buera. 1994. Water activity, glass transi-tion and microbial stability in concentrated/semimoist food systems.Journal of Food Science 59:921-927.

Chirife, J., and M.P. Buera. 1995. A critical review of some nonequi-librium situations and glass transitions on water activity values offoods in the microbiological growth range. Journal of Food Engi-neering 25:531-552.

Chirife, J., and M.P. Buera. 1996. Water activity, water glass dy-namics, and the control of microbiological growth in foods. CriticalRev. in Food Sci. Nutr. 36:465-513.

Farberm, J.M., F. Coates, and E. Daley. 1992. Minimum water ac-tivity requirements for the growth of Listeria monocytogenes. LettAppl Microbiol 15:103-105.

Franks, F. 1991. Water activity: a credible measure of food safetyand quality? Trends Food Sci Technol March:68-72.

Garcia de Fernando, G.D., O. Diaz, M. Fernandez, and J.A. Or-donez. 1992. Changes in water activity of selected solid culturemedia throughout incubation. Food Microbiology 9:77-82.

Gibson, A.M., J. Baranyi, J.I. Pitt, M.J. Eyles, and T.A. Roberts.1994. Predicting fungal growth: The effect of water activity on As-pergillus flavus and related species. International Journal of FoodMicrobiology 23:419-431.

Goaleni, N., J.E. Smith, J. Lacey, and G. Gettinby. 1997. Effects oftemperature, water activity, and incubation time on production ofaflatoxins and cyclopiazonic acid by an isolate of Aspergillus flavus

37


in surface agar culture. Appl Environ Microbiol 63:1048-1053.

Hardman, T.M. 1988. Water and food quality. Elseiver Press, Lon-don.

Hocking, A.D., and B.F. Miscamble. 1995. Water relations of someZygomycetes isolated from food. Mycological Research 99:1113-1118.

Hocking, A.D., B.F. Miscamble, and J.I. Pitt. 1994. Water re-lations of Alternaria alternata, Cladosporium cladosporioides, Cla-dosporium sphaerospermum, Curvulario lunata and Curvulario pall-escens. Mycological Research 98:91-94.

Houtsma, P.C., A. Heuvelink, J. Dufrenne, and S. Notermans. 1994.Effect of sodium lactate on toxin production, spore germination andheat resistance of proteolytic Clostridium botulinum strains. Journalof Food Protection 57:327-330.

Kress-Rogers, E. 1993. Food quality measurement. Food IndustryNews September:23-26.

Kuntz, L.A. 1992. Keeping microorganisms in control. Food Prod-uct Design August:44-51.

Levine, H., and L. Slade. 1991. Water Relationships in Foods.Plenum Press, New York.

Li, K.Y., and J.A. Torres. 1993. Water activity relationships forselected mesophiles and psychrotrophs at refrigeration temperatureJournal of Food Protection 56:612-615.

Lopez-Malo, A., S. Guerrero, and S.M. Alzamora. 2000. Proba-bilistic modeling of Saccharomyces cerevisiae inhibition under theeffects of water activity, pH, and potassium sorbate concentration.Journal of Food Protection 63:91-95.

Mannheim,C.H., J.X. Liu, and S.G. Gilbert. 1994. Control of waterin foods during storage. Journal of Food Engineering 22:509-532.

38


Marauska, M., A. Vigants, A. Klincare, D. Upite, E. Kaminska, andM. Bekers. 1996. Influence of water activity and medium osmolalityon the growth and acid production of Lactobacillus casei var. alac-tosus. Proceedings of the Latvian Academy of Sciences Section BNatural Exact and Applied Sciences 50:144-146.

Masana, M.O., and J. Baranyi. 2000. Growth/no growth interface ofBrochothrix thermosphacta as a function of pH and water activity.Food Microbiology 17:485-858.

Mattick, K. L., F. Jorgensen, J.D. Legan, M.B. Cole, J. Porter, H.M.Lappin-Scott, and T.J. Humphrey. 2000. Survival and filamentationof Salmonella enterica serovar Enteritidis PT4 and Salmonella enter-ica serovar Typhimurium DT104 at low water activity. Appl EnvironMicrobiol 66:1274-1279.

Mattick, K.L., F. Jorgensen, J.D. Legan, H.M. Lappin-Scott, andT.J. Humphrey. 2000. Habituation of Salmonella spp. at reducedwater activity and its effect on heat tolerance. Appl Environ Micro-biol 66:4921-4925.

Mattick, K.L., F. Jorgensen, J.D. Legan, H.M. Lappin-Scott, andT.J. Humphrey. 2001. Improving recovery of Salmonella entericaSerovar Typhimurium DT104 cells injured by heating at differentwater activity values. Journal of Food Protection 64:1472-1476.

McMeekin, T.A., and T. Ross. 1996. Shelf life prediction: Statusand future possibilities. International Journal of Food Microbiology33:65-83.

Miller, A.J. 1992. Combined water activity and solute effects ongrowth and survival of Listeria monocytogenes. Journal of FoodProtection 55:414-418.

Nakajo, M., and Y. Moriyama. 1993. Effect of pH and water ac-tivity on heat resistance of spores of Bacillus coagulans. Journal ofthe Japanese Society for Food Science and Technology 40:268-271.

39


Nelson, K.A., and T.P. Labuza. 1994. Water activity and foodpolymerscience: Implications of state on arrhenius and WLF modelsin predicting shelf life. Journal of Food Engineering 22:271-289.

Nesci, A., M. Rodrigues, and M. Etcheverry. 2003. Control ofAspergillus growth and aflatoxin production using antioxidants atdifferent conditions of water activity and pH. Journal of Applied Mi-crobiology 95:279-287.

Nolan, D.A., D.C. Chamblin, and J.A. Troller. 1992. Minimal wa-ter activity levels for growth and survival of Listeria monocytogenesand Listeria innocua. International Journal of Food Microbiology16:323-335.

Noorlidah, A., A. Nawawi, and I. Othman. 2000. Fungal spoilage ofstarch-based foods in relation to its water activity (aw). Journal ofStored Products Research 36:47-54.

Park, C.M., and L.R. Beuchat. 2000. Survival of Escherichia coliO157:H7 in potato starch as affected by water activity, pH and tem-perature. Lett Appl Microbiol 31(5):364-367.

Petersson, S., and J. Schnuerer. 1995. Biocontrol of mold growthin high-moisture wheat stored under airtight conditions by Pichiaanomala, Pichia guilliermondii, and Saccharomyces cerevisiae. ApplEnviron Microbiol 61:1027-1032.

Pitt, J.I., and B.F. Miscamble. 1995. Water relations of Aspergillusflavus and closely related species. Journal of Food Protection 58:86-90.

Plaza, P., J. Usall, N. Teixido, and I. Vinas. 2003 Effect of wateractivity and temperature on germination and growth of Penicilliumdigitatum, P. italicum and Geoteichum candidum. Journal of Ap-plied Microbiology 94:549-554.

Quintavalla, S., and G. Parolari. 1993. Effects of temperature, water

40


activity and pH on the growth of Bacillus cells and spore: A responsesurface methodology study. International Journal of Food Microbi-ology 19:207-216.

Rockland, L.B., and G.F. Stewart. 1981. Water activity: Influ-ences on food quality. Academic Press, New York.

Rockland, L.B., and S.K. Nishi. 1980. Influence of water activityon food product quality and stability. Food Tech 34:42-59.

Saad, R.R. 1992. Effect of water activity on growth and lipids ofxerophilic fungi, Aspergillus repens and Aspergillus amstelodami.Zentralblatt Fuer Mikrobiologie 147:61-64.

Salter, M.A., D.A. Ratkowsky, T. Ross, and T.A. McMeekin. 2000.Modelling the combined temperature and salt (NaCl) limits for growthof a pathogenic Escherichia coli strain using nonlinear logistic regres-sion. International Journal of Food Microbiology 61:159-167.

Santos, J., T.M. Lopez-Diaz, M.C. Garcia-Lopez, M.C. Garcia-Fernandez, and A. Otero. 1994. Minimum water activity for thegrowth of Aeromonas hydrophila as affected by strain, temperatureand humectant. Lett Appl Microbiol 19:76-78.

Sautour, M., A. Rouget, P. Dantigny, C. Divies, and M. Bennsoussan.2001. Prediction of conidial germination of Penicillium chrysogenumas influenced by temperature, water activity and pH. Lett Appl Mi-crobiol 32:131-134.

Seow, C.C., T.T. Teng, and C.H. Quah. 1988. Food preservationby moisture control. Elsevier, New York.

Shebuski, J.R., O. Vilhelmsson, and K.J. Miller. 2000. Effects ofgrowth at low water activity on the thermal tolerance of Staphylo-coccus aureus. Journal of Food Protection 63:1277-1281.

Taoukis, P., W. Breene, and T.P. Labuza. 1988. Intermediate mois-ture foods. Adv Cereal Sci Technol 9:91-128.

41


Tapia de Daza, M.S., Y. Villegas, and A. Martinez. 1991. Mini-mal water activity for growth of Listeria monocytogenes as affectedby solute and temperature. International Journal of Food Microbi-ology 14:333-337.

Tokuoka, K., and T. Ishitani. 1991. Minimum water activities forthe growth of yeasts isolated from high-sugar foods. Journal of Gen-eral and Appied Microbiology 37:111-119.

Torres, R., J. Usall, N. Teixido, M. Abadias, and I. Vinas. 2003.Liquid formulation of the biocontrol agent Candida sake by modify-ing water activity or adding protectants. Journal of Applied Micro-biology 94:330-339.

Ucar, F., and I. Guneri. 1996. The effect of water activity, pHand temperature on the growth of osmophilic yeasts. Turkish Jour-nal of Biology 20:37-46.

Wijtzes, T., P.J. Mcclure, M.H. Zwietering, and T.A. Roberts. 1993.Modelling bacterial growth of Listeria monocytogenes as a functionof water activity, pH and temperature. International Journal of FoodMicrobiology 18:139-149.

Zwietering, M.H., T. Wijtzes, J.C. de Wit, and K.Van’T Riet. 1992.A decision support system for prediction of the microbial spoilage infoods. Journal of Food Protection 55:973-979.

Meat and Seafood

Allen, K., D. Cornforth, D. Whittier, M. Vasavada, and B. Num-mer. 2007. Evaluation of high humidity and wet marinade methodsfor pasteurization of jerky. Journal of Food Science. 72:C351-C355.

Chen, H.C. 1995. Seafood microorganisms and seafood safety. Jour-nal of Food and Drug Analysis 3:133-144.

Clavero, M.R.S., and L.R. Beuchat. 1996. Survival of Escherichia

42


coli O157:H7 in broth and processed salami as influenced by pH, wa-ter activity, and temperature and suitability of media for its recovery.Appl Environ Microbiol 62:2735-2740.

Duffy, L.L., P.B. Vanderlinde, and F.H. Grau. 1994. Growth ofListeria monocytogenes on vacuum-packed cooked meats: Effects ofpH, aw, nitrite and ascorbate. International Journal of Food Micro-biology 23:377-390.

Elgasim, E.A., and M.S. Al Wesali. 2000. Water activity and Huntercolour values of beef patties extended with samh (Mesembryanthe-mum forsskalei Hochst) flour. Food Chem 69(2):181-185.

Gmez, R., andJ. Fernandez-Salguero. 1993. Note: Water activityof Spanish intermediate moisture fish products. Revista EspanolaDe Ciencia Y Tecnologia De Alimentos 33:651-656.

Hand, L. 1994. Controlling water activity and pH in snack sticks.Meat Marketing and Technology May:55-56.

Lee, M.B., and S. Styliadis. 1996. A survey of pH and water ac-tivity levels in processed salamis and sausages in Metro Toronto.Journal of Food Protection 59:1007-1010.

Luecke, F.K. 1994. Fermented meat products. Food Res Intl 27:299-307. Minegishi, Y., Y. Tsukamasa, K. Miake, T. Shimasaki, C. Imai,M.

Sugiyama, and H. Shinano. 1995. Water activity and microflorain commercial vacuum-packed smoked salmons. Journal of the FoodHygienic Society of Japan 36:442-446.

Nunez, F., M.C. Diaz, M. Rodriguez, E. Aranda, A. Martin, andM.A. Asensio. 2000. Effects of substrate, water activity, and temper-ature on growth and verrucosidin production by Penicillium polonicumisolated from dry-cured ham. Journal of Food Protection 63:231-236.

Placido, M. and M.P. Aleman. 2002. Rapid hygrometric method for

43


determing water activity. Ciencia y Tecnologia Alimentaria 3(4):229-235.

Rocha-Garza, A.E., and J.F. Zayas. 1996. Quality of broiled beefpatties supplemented with wheat germ protein flour. Journal of FoodScience 61:418-421

Sabadini, E., M.D. Hubinger, P.-J.d.Sobral, and B.C. Carvalho, Jr.2001. Change of water activity and meat colour in the elabora-tionprocess of dehydrated salted meat. Ciencia e Tecnologia de Ali-mentos 21(1):14-19.

Shimasaki, T., K. Miake, Y. Tsukamasa, M.A. Sugiyama, Y. Minegishi,and H. Shinano. 1994. Effect of water activity and storage tempera-ture on the quality and microflora of smoked salmon. Nippon SuisanGakkaishi 60:569-576.

Untermann, F., and C. Muller. 1992. Influence of aw value andstorage temperature on the multiplication and enterotoxin forma-tion of staphylococci in dry-cured raw hams. International Journalof Food Microbiology 16:109-115.

Williams, S.K., G.E. Rodrick, and R.L. West. 1995. Sodium lactateaffects shelf life and consumer acceptance of fresh Catfish (Ictalu-rus nebulosus, marmoratus) fillets under simulated retail conditions.Journal of Food Science 60:636-639.

Dairy Products

Clavero, M.R.S., and L.R. Beuchat. 1996. Survival of Escherichiacoli O157:H7 in broth and processed salami as influenced by pH, wa-ter activity, and temperature and suitability of media for its recovery.Appl Environ Microbiol 62:2735-2740.

Correia, R., M. Magalhaes, M. Pedrini, A. da Cruz, and I. Clementino.2008. Ice cream made from cow and goat milk: chemical composi-tion and melting point characteristics. Revista Ciencia Agronomica39:251-256.

44


Duffy, L.L., P.B. Vanderlinde, and F.H. Grau. 1994. Growth ofListeria monocytogenes on vacuum-packed cooked meats: Effects ofpH, aw, nitrite and ascorbate. International Journal of Food Micro-biology 23:377-390.

Gmez, R., and J. Fernandez-Salguero. 1993. Note: Water activity ofSpanish intermediate moisture fish products. Revista Espanola DeCiencia Y Tecnologia De Alimentos 33:651-656.

Hand, L. 1994. Controlling water activity and pH in snack sticks.Meat Marketing and Technology May:55-56.

Hardy, J., J. Scher, and S. Banon. 2002. Water activity and hy-dration of dairy powders. Lait 82:441-442.

Lee, M.B., and S. Styliadis. 1996. A survey of pH and water ac-tivity levels in processed salamis and sausages in Metro Toronto.Journal of Food Protection 59:1007-1010.

Luecke, F.K. 1994. Fermented meat products. Food Res Intl 27:299-307.

Malec, L.S., A.S. Pereyra-Gonzales, G.B. Naranjo, and M.S. Vigo.2002. Influence of water activity and storage temperature on lysineavailability of a milk like system. Food Res Intl 35(9):849-853.

Minegishi, Y., Y. Tsukamasa, K. Miake, T. Shimasaki, C. Imai, M.Sugiyama, and H. Shinano. 1995. Water activity and microflora incommercial vacuum-packed smoked salmons. Journal of the FoodHygienic Society of Japan 36:442-446.

Rocha-Garza, A.E., and J.F. Zayas. 1996. Quality of broiled beefpatties supplemented with wheat germ protein flour. Journal of FoodScience 61:418-421.

Shah, N.P., and R.R. Ravula. 2000. Influence of water activity onfermentation, organic acids production and viability of yoghurt and

45


probiotic bacteria. Australian Journal of Dairy Technology 55(3):127-131.

Shimasaki, T., K. Miake, Y. Tsukamasa, M.A. Sugiyama, Y. Minegi-shi, and H. Shinano. 1994. Effect of water activity and storage tem-perature on the quality and microflora of smoked salmon. NipponSuisan Gakkaishi 60:569-576.

Untermann, F., and C. Muller. 1992. Influence of aw value andstorage temperature on the multiplication and enterotoxin forma-tion of staphylococci in dry-cured raw hams. International Journalof Food Microbiology 16:109-115.

Williams, S.K., G.E. Rodrick, and R.L. West. 1995. Sodium lactateaffects shelf life and consumer acceptance of fresh Catfish (Ictalu-rus nebulosus, marmoratus) fillets under simulated retail conditions.Journal of Food Science 60:636-639.

Fruits and Vegetables

Ayub, M., R. Khan, S. Wahab, A. Zeb, and J. Muhammad. 1995.Effect of crystalline sweeteners on the water activity and shelf stabil-ity of osmotically dehydrated guava. Sarhad Journal of Agriculture11:755-761.

Beveridge,T., and S.E. Weintraub. 1995. Effect of blanching pre-treatment on color and texture of apple slices at various water activ-ities. Food Res Intl 28:83-86.

Clavero, M.R.S., R.E. Brackett, L.R. Beuchat, and M.P. Doyle. 2000.Influence of water activity and storage conditions on survival andgrowth of proteolytic Clostridium botulinum in peanut spread. FoodMicrobiology 17(1):53-61.

Fouskaki, M., K. Karametsi, and N.A. Chaniotakis. 2003. Methodfor the determination of water content in sultana raisins using a wa-ter activity probe. Food Chem 82:133-1337.

46


Gogus, F., C. Cuzdemir, and S. Eren. 2000. Effects of some hydro-colloids and water activity on nonenzymic browning of concentratedorange juice. Nahrung 44(6):438-442.

Hubinger, M., F.C. Menegalli, R.J. Aguerre, and C. Suarez. 1992.Water vapor adsorption isotherms of guava, mango and pineapple.Journal of Food Science 57:1405-1407.

Jimenez, M., M. Manez, and E. Hernandez. 1996. Infuence of wateractivity and temperature on the production of zearalenone in corn bythree Fusarium species. International Journal of Food Microbiology29:417-421.

Khalloufi, S., J. Giasson, and C. Ratti. 2000. Water activity offreeze dried mushrooms and berries. Canadian Agricultural Engi-neering 42(1):51-56.

Kiranoudis, C.T., Z.B. Maroulis, E. Tsami, and D. Marinos-Kouris.1993. Equilibrium moisture content and heat of desorption of somevegetables. Journal of Food Engineering 20:55-74.

Lopez-Malo, A., and E. Palou. 2000. Modeling the growth/nogrowthinterface of Zygosaccharomyces bailii in Mango puree. Journal ofFood Science: 65:516-520.

Makower, B., and S. Myers. 1943. A new method for the determina-tion of moisture in dehydrated vegetables. Proceedings of Instituteof Food Technologists, 4th Conference 156.

Maltini, E., D. Torreggiani, B.R. Brovetto, and G. Bertolo. 1993.Functional properties of reduced moisture fruits as ingredients infood systems. Food Res Intl 26:413-419.

Marin, S., N. Magan, M. Abellana, R. Canela, A.J. Ramos, andV. Sanchis. 2000. Selective effect of propionates and water activ-ity on maize mycoflora and impact on fumonisin B1 accumulation.Journal of Stored Products Research 36:203-214.

47


Marin, S., V. Sanchis, I. Vinas, R. Canela, and N. Magan. 1995.Effect of water activity and temperature on growth and fumonisinB-1 and B-2 production by Fusarium proliferatum and F. monili-forme on maize grain. Lett Appl Microbiol 21:298-301.

Monsalve-Gonzalez, A., G.V. Barbosa-Canovas, and R.P. Cavalieri.1993. Mass transfer and textural changes during processing of applesby combined methods. Journal of Food Science 58:1118-1124.

Pinsirodom, P., and K.L. Parkin. 2000. Selectivity of Celite immobi-lized patatin (lipid acyl hydrolase) from potato (Solanum tuberosumL.) tubers in esterification reactions as influenced by water activityand glycerol analogues as alcohol acceptors. J. Agric. Food Chem.48(2):155-160.

Tapia de Daza, M.S., C.E. Aguilar, V. Roa, and R.V. Diaz de Tablante.1995. Combined stress effects on growth of Zygosaccharomyces rouxiifrom an intermediate moisture papaya product. Journal of Food Sci-ence 60:356-359.

Zeb, A., R. Khan, A. Khan, M. Saeed, and S.A. Manan. 1994. Influ-ence of crystalline sucrose and chemical preservatives on the wateractivity and shelf stability of intermediate banana chips. SarhadJournal of Agriculture 10:721-726.

Zhang, X.W., X. Liu, D.X. Gu, W. Zhou, R.L. Wang, and P. Liu.1996. Desorption isotherms of some vegetables. Journal of the Sci-ence of Food and Agriculture 70:303-306.

Baked Goods and Cereals

Abellana, M., A.J. Ramos, V. Sanchis, and P.V. Nielsen. 2000. Ef-fect of modified atmosphere packaging and water activity on growthof Eurotium amstelodami, E. chevalieri and E. herbariorum on asponge cake analogue. Journal of Applied Microbiology 88:606-616.

Aramouni, F.M., K.K. Kone, J.A. Craig, and D.Y.C. Fung. 1994.Growth of Clostridium sporogenes PA 3679 in home-style canned

48


quick breads. Journal of Food Protection 57:882-886.

Cahagnier, B., L. Lesage, and D. Richard-Molard. 1993. Mouldgrowth and conidiation in cereal grains as affected by water activityand temperature. Lett Appl Microbiol 17:7-13.

Clawson, A.R., and A.J. Taylor. 1993. Chemical changes duringcooking of wheat. Food Chem 47:337-343.

Fleurat-Lessard, F. 2002. Qualitative reasoning and integrated man-agement of the quality of stored grain: a promising new approach.Journal of Stored Products Research 38:191-218.

Gmez, R., J. Fernandez-Salguero, M.A. Carmona, and D. Sanchez.1993. Water activity in foods with intermediate moisture levels: Bak-ery and confectionery products: Miscellany. Alimentaria 30:55-57.

Guynot, M.E., A.J. Ramos, L. Seto, P. Purroy, V. Sanchis, and S.Marin. 2003. Antifungal activity of volatile compounds generated byessential oils against fungi commonly causing deterioration of bakeryproducts.

Harris, M., and M. Peleg. 1996. Patterns of textural changes in brit-tle cellular cereal foods caused by moisture sorption. Cereal Chem73:225-231.

Hope, R., and N. Magan. 2003. Two-dimensional environmental pro-files of growth, deoxynivalenol and nivalenol production by Fusariumculmorum on wheat-based substrate. Lett Appl Microbiol 37:70-74.

Michniewicz, J., C.G. Biliaderis, and W. Bushuk. 1992. Effect ofadded pentosans on some properties of wheat bread. Food Chem43:251-257.

Moreno-Contreras, M.D., A.J. Martinez-Yepez, and R.R. Martinez.2000. Determination of deoxynivalenol (DON) in wheat, barley andcorn and its relationship with the levels of total molds, Fusarium spp.,infestation percentage, and water activity. Archivos Latinoameri-

49


canos de Mutricion. 50(2):183-186.

Phoungchandang, S., and J.L. Woods. 2000. Moisture diffusion anddesorption isotherms for banana. Journal of Food Science 65:651-657.

Ramanathan, S., and S. Cenkowski. 1995. Sorption isotherms offlour and flow behaviour of dough as influenced by flour compaction.Canadian Agricultural Engineering 37:119-124.

Roessler, P.F., and M.C. Ballenger. 1996. Contamination of an un-preserved semisoft baked cookie with a Xerophilic Aspergillus species.Journal of Food Protection 59:1055-1060.

Schebor, C., and J. Chirife. 2000. A survey of water activity andpH values in fresh pasta packed under modified atmosphere man-ufactured in Argentina and Uruguay. Journal of Food Protection63:965-969.

Seiler, D.A.L. 1979. The mould-free shelf life of bakery products.FMBRA Bulletin April:71-74.

Sumner, S.S., J.A. Albrecht, and D.L. Peters. 1993. Occurrenceof enterotoxigenic strains of Staphylococcus aureus and enterotoxinproduction in bakery products. Journal of Food Protection 56:722-724.

Tesch, R., M.D. Normand, and M. Peleg. 1996. Comparison ofthe acoustic and mechanical signatures of two cellular crunchy cerealfoods at various water activity levels. Journal of the Science of Foodand Agriculture 70:347-354.

Weegels, P.L., J.A. Verhoek, A.M.G. de Groot, and R.J. Hamer.1994. Effects of gluten of heating at different moisture contents: I.Changes in functional properties. Journal of Cereal Science 19:31-38.

Beverages, Soups, Sauces, and Preserves

Cardelli, C., and T.P. Labuza. 2001. Application of Weibull Hazard

50


Analysis to the determination of shelf life of roasted and ground cof-fee. Lebensm Wiss Technol 34:273-278.

Carson, K.J., J.L. Collins, and M.P. Penfield. 1994. Unrefined,dried apple pomace as a potential food ingredient. Journal of FoodScience 59:1213-1215.

Cavia, M.M., M.A. Fernandez-Muio, J.F. Huidobro, and M.T. San-cho. 2004. Correlation between Moisture and Water Activity ofHoneys Harvested in Different Years. Journal of Food Science 69:C-368-370.

Durrani, M.J., R. Khan, M. Saeed, and A. Khan. 1992. Devel-opment of concentrated beverages from Anna apples with or withoutadded preservatives by controlling activity of water for shelf stability.Sarhad Journal of Agriculture 8:23-28.

Ferragut, V., J.A. Salazar, and A. Chiralt. 1993. Stability in theconservation of emulsified sauces low in oil content. Alimentaria30:67-69.

Gleiter, R.A., H. Horn, and H.-D. Isengard. 2006. Influence of typeand state of crystallization on the water activity of honey. FoodChem 96:441-445.

Hajmeer, M.N., F.M. Aramouni, and E.A.E.Boyle. 2000. Shelf-life of lite syrup after opening and storage at room or refrigeratedtemperature. Journal of Food Quality 23:529-540.

Ibarz, A., J. Pagan, and R. Miguelsanz. 1992. Rheology of clarifiedfruit juices: II. Blackcurrant juices. Journal of Food Engineering15:63-74.

Khalloufi, S., Y. El-Maslouhi, and C. Ratti. 2000. Mathematicalmodel for prediction of glass transition temperature of fruit pow-ders. Journal of Food Science 65:842-848.

Kusumegi,K., T.Takahashi, and M.Miyagi. 1996. Effects of addition

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of sodium citrate on the pasteurizing conditions in Tuyu, Japanesenoodle soup. Journal of the Japanese Society for Food Science andTechnology 43:740-747.

Perera, C.O. 2005. Selected quality attributes of dried foods. DryingTechnology 23:717-730.

Sa, M.M., and A.M. Sereno. 1993. Effect of temperature on sorptionisotherms and heats of sorption of quince jam. International Journalof Food Science & Technology 28:241-248.

Shafi ur-Rahman, M. 2005. Dried food properties: challenges ahead.Drying Technology 23:695-715.

Pharmaceuticals/Cosmetics

Ahlneck, C., and G. Zografi. 1990. The Molecular basis of mois-ture effects on the physical and chemical stabilty of drugs in thesolid state. International Journal of Pharmaceutics 62:87-95.

Bell, L.N., and K.L. White. 2000. Thiamin Stability in Solids asAffected by the Glass Transition. Journal of Food Science 65:498-501.

Cochet, N., and A.L. Demain. 1996. Effect of water activity onproduction of beta-lactam antibiolics by Streptomyces clavuligerusin submerged culture. Journal of Applied Bacteriology 80:333-337.

Constantino, H.R., R. Langer, and A.M. Klibanov. 1994. Solid-Phase Aggregation of Proteins under Pharmaceutically Relevant Con-ditions. Journal of Pharmaceutical Science 83:1662-1669.

Enigl, D.C. 2001. Pharmaceutical stability testing using water ac-tivity. European Pharmaceutical Review 6:46-49.

Enigl, D.C., and K.M.Sorrel. 1997. Water Activity and Self-PreservingFormulas. p. 45-73. In J.J. Kabara, and D.S. Orth (ed.) Preservative-Free and Self-Preserving Cosmetics and Drugs: Principles and Prac-

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tice. Marcel Dekker.

Hageman, M.J. 1988. The Role of Moisture in Protein Stability.Drug Dev. Ind. Pharm. 14:2047-2070.

Heidemann, D.R., and P.J. Jarosz. 1991. Preformulation StudiesInvolving Moisture Uptake in Solid Dosage Forms. PharmaceuticalResearch 8:292-297.

Kontny, M.J. 1988. Distribution of Water in Solid Pharmaceuti-cal Systems. Drug Dev. Ind. Pharm. 14:1991-2027.

Sablani, S.S., K. Al-Belushi, I. Al-Marhubi, and R. Al-Belushi. 2007.Evaluating Stability of Vitamin C in Fortified Formula Using WaterActivity and Glass Transition. International Journal of Food Prop-erties 10:61-71.

Zografi, G. 1988. States of Water Associated with Solids. DrugDev. Ind. Pharm. 14:1905-1926.

Zografi, G., and M.J. Kontny. 1986. The interactions of water withcellulose- and starch-derived pharmaceutical excipients. Pharmaceu-tical Research 3:187-193.

Miscellaneous

Bell, L.N. 1995. Kinetics of non-enzymatic browning in amorphoussolid systems: Distinguishing the effects of water activity and theglass transition. Food Res Intl 28:591-597.

Bell, L.N., and T.P. Labuza. 1992. Compositional influence on thepH of reduced-moisture solutions. Journal of Food Science 57:732-734.

Bell, L.N., and T.P. Labuza. 1994. Influence of the low-moisturestate on pH and its implication for reaction kinetics. Journal ofFood Engineering 22:291-312.

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Bhandari, B., and I. Bareyre, 2003. Estimarion of crystalline phasepresent in glucose crystal-solution mixture by water activity mea-surement. Lebensm Wiss Technol 36:729-733(5).

Brake, N.C., and O.R. Fennema. 1993. Edible coatings to inhibitlipid migration in a confectionery product. Journal of Food Science58:1422-1425.

Dole, M., and L. Faller. 1950. Water sorption by synthetic highpolymers. Journal of the American Chemical Society 12:414-419.

Fernandez-Salguero, J., R. Gmez, and M.A. Carmona. 1993. Wateractivity in selected high-moisture foods. Journal of Food Composi-tion and Analysis 6:364-369.

Juhan, K., and G.K. Byung. 2000. Lipase-catalyzed synthesis oflysophosphatidylcholine using organic cosolvent for in situ water ac-tivity control. Journal of American Oil Chemists’ Society 77(7):701-797.

Lima, J.R., S.D.S. Campos, and L.-A.G. Goncalves. 2000. Rela-tionship between water activity and texture of roasted and saltedcashew kernel. Journal of Food Science and Technology 37(5):512-513.

Lomauro, C.J., A.S. Bakshi, and T.P.Labuza. 1985a. Evaluationof food moisture sorption isotherm equations. Part II: Milk, coffee,tea, nuts, oilseeds, spices and starchy foods. Lebensm Wiss Technol18:118-124.

Lomauro, C.J., A.S. Bakshi, and T.P. Labuza. 1985b. Evaluation offood moisture sorption isotherm equations. Part I: Fruit, vegetableand meat products. Lebensm Wiss Technol 18:111-117.

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Pawkit 9 DECLARATION OF CONFORMITY

9 Declaration of Conformity

Application of Council Directive: 2004/108/EC and 2011/65/EU

Standards to which conformity isdeclared:

EN 61326-1:2013 and

EN 50581:2012

Manufacturer’s Name: METER Group, Inc.2365 NE Hopkins Ct.Pullman, WA 99163 USA

Type of Equipment: water activity meter.

Model Number: Pawkit

Year of First Manufacture: 2007

The undersigned hereby declares on behalf of METER Group, Inc.that the above referenced products, to which this declaration relates,fully conform to the provisions of the Council Directives and stan-dards referenced above.

Michael WadsworthEngineering Director7-9-2015

55

Index

Accuracy, 4Aqualab, 4

BatteryLithium-ion, 24Replacement, 24

Beeper, 17, 19Binding, 8, 9Buttons, 15

to Begin Measurement, 16

Calibration, 19, 27Capillaries, 9Cautions, 22

with Sampling, 18CE Compliance, 55Cleaning, 20Closing the Chamber, 15Cold Samples, 19Contact Information, 1Cosmetics, 6, 10Customer Support, 1, 31

d25, 28d76, 28d92, 29Declaration of Conformity, 55Display

LCD, 16LCD Cleaning, 21

Email, 1, 31Environment, for Sampling, 5Enzymes, and Water Activity, 6Equilibrium, 7

of sample aw and rh, 7

Gibbs Free Energy, 8

Homogeneous, 8Hot Samples, 19Humidity, Related to aw, 4

Inserting Samples, 13

LiCl Standards, 27Lids, for Sample Cups, 13Lipids, and aw, 6Liquid Phase Water, 6Location, for Sampling, 5Loss on Drying, 6Low Battery Indicator, 24

Maintenance, 20, 21Matric Effects, 9Measurement

Taking, 15Time, 17

Microbial Growth, 10Molality, of Calibration Standards,

27Multi-Component Food, 7

NaCl Standards, 27

Off, Turning Off, 18Opening the Chamber, 13Operation, Environment, 5Osmotic Effects, 8

PawkitAccessories, 4Features, 11Operation, 11

56

Pawkit INDEX

Perishability, 6Pharmaceuticals, 6, 10Preparation

for Operation, 5of Samples, 12

Pressure Effects, 8

Quantitative Analysis, 6

ReferencesBaked Goods and Cereals, 48Beverages, Soups,

Sauces, Preserves, 50Dairy Products, 44Food Safety and Microbiol-

ogy, 36Fruits and Vegetables, 46Meat and Seafood, 42Miscellaneous, 53Water Activity Theory & Mea-

surement, 33Regulations, 6Relative Humidity, 6Repair, Costs, 32

SampleInsertion, 13Multi-Component, 12

Sample Cups, 4, 12Filling Level, 12Stainless Steel, 12

Seller’s Liability, 2Sensor

Damage, 19Filter, 21Filter Cleaning, 21Filter Replacement, 21

Sorption Isotherm, 9Specifications, 3Sto, 28

Temperature, 19Effects, 7Effects on Water Activity, 7Equilibrium, 7

Theory, 6Water Activity, 6

Thermodynamic Property, 8Time for Measurement, 17

u25, 28u76, 28u92, 28

Vapor Phase, 6, 8Verification Standards, 5, 27Verification Steps, 28Volatiles, 18

Warranty, 2, 32Water Activity, 6

Effect on Food, 6Microbial Growth, 6Stability Diagram, 7

Water Content, 9Definition, 6versus Water Activity, 6

Water Potential, 8Wet Samples, Cautions, 18

57

portable water activity measurement system...

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