j food proce ng 2001

8/12/2019 j Food Proce Ng 2001

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MASS TRANSFER IN PACIFIC HAKE (Merluccius australis)PACKED IN REFRIGERATED MODIFIED ATMOSPHERER. SIMPSON', S. ALMONACID and C. ACEVEDO

Departamento de Procesos Qufmicos,Biotecnoldgicos, y AmbientalesUniversidad Tkcnica Federico Santa MariaCasilla 110-VValparaiso, CHEEAccepted for Publication August 22 , 2001

ABSTRACTThe objective of this research was to develop, and experimentally validatea u l l y mathematical model, to predict mass transfer phenomena in Pacific Hake(Merluccius australis) packed in refngerated modified atmosphere.A mathematical model to predict mass transfer of CO,, 0 . N2 and watervapor was developed and validated. The di fis io n model was developed utilizingF ic ks second law, considering fis h fillet as an infinite sl b and applied to

Pacific Hake lean ish species) under rejhgeration conditions. CO, difu sivi tyof Pacific Hake was determined by an inverse procedure at OC and resulted ina value of 5.19 x 10 [m2/s] that is in accordance with values reported in theliterature. However, postmortem variations of pH could affect solubility anddifusivity of CO, n fish muscle.

INTRODUCTIONPacific Hake Merlucciusaustralis) is a valuable and very perishable exportgood to seafood companies from the Northern and Southern coast of PacificOcean. Because international markets are a long distance away, Pacific Hake ismainly transported by air in a costly manner. One of the technologies that havebeen explored to significantly extend the shelf-life of refrigerated Pacific Hakeis Modified Atmosphere Packaging (MAP). The ultimate target is to extendshelf-life to be able to export Pacific Hake, and related products (salmon fillets),using low cost transportation methods ( i.e ., by m aritime freightage).

I Towhom correspondenceshould be addressed. EL: 56-32-654302;FAX: 56-32-654478; E-mail:ricardo. impsonapqui.utfsm.cl

Journal of Food Process Engineering 24 (2001) 405-421. All Righis Resewed.Copyrighi 2001 by Food Nutrition Press, Inc.. Trumbull, Conneciicui. 405


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406 R. SIMPSON, S . ALMONACID and C. ACEVEDO

The increased demand for seafood products and the rapid growth ofaquaculture (SUBPESCA 1999) has motivated and forced a constant improve-ment of process conditions, and to pursue total quality assurance. Deteriorativeeffects could be controlled or minimized through an adequate packagingmaterial, additionally; shelf-life can be extended if such packaging modeconsiders Modified Atmosphere Packaging (MAP). MAP has been studied inseveral products, where, normally it has proven to be very efficient in terms ofshelf-life extension (Penney et al 1994; Parry 1995; Pastoriza et al. 1996).Modified Atmosphere Packaging (MAP), in conjunction with refrigeration,has doubled shelf-life of fresh fish (Brody 1996). Pastoriza e? al. (1996)reported a shelf-life of 3 weeks when Hake fillets were stored at 2C underconcentrations of 40% through 60% CO,, cons idering a normal shelf-life, of 5to 10days. As reported by Fey and Regenstein (1982) 1% of potassium sorbatecombined with modified atmosphere (60% C0,/20% 0,/20% N, at 1C) wereable to extend shelf-life and preserve sensory quality for almost a m onth. Nuiiez(2000) was able to extend shelf-life of Pacific Hake fillets from 6 to 10 daysunder refrigerated MAP.MAP systems require several considerations due to side effects caused bythe interaction of headspace and food product. This is because food product andheadspace conform a dynamic system, in which gas exchange is related tointrinsic factors like food product type, freshness, microbial load, lipid content,package permeability and also to extrinsic factors like temperature and storagetime (Lioutas 1988).Research studies using mathematical modeling for MAP systems havecentered their efforts on postharvest fruits and vegetables (Lee et al. 1991;Morales-Castro e?al. 1994; Fishman el al. 1995; Talasila and Cameron 1997;Lakakul et al 1999). Some models have been proposed for simulating gasconcentration evolution over time. These m odels account for fruit or vegetablerespiration and gas transport across the films. Some of these models are limitedto estimate the equilibrium concentration inside the package. This b reakthrough,although valid, can only be applied to biological materials with respiration. andnot to food items where the gas diffusion is the main transport mechanism.Some authors have studied the transport problem. Bertola ef al. (1990) usedFicks second law for a MAP system (CO, and air) applied to tom ato, andMannapperuma et al. (1991) utilized the transport equation, including a firstorder chemical reaction, applied to apples stored in a MAP system.The determination ofphysical properties from transient m easurements is anattractive technique both from the experimental and methodological points ofview. The apparatus needed is simple, and experimental procedures are done ina short period of time. Moreover, during the test, the specimen is subjected toa transient state that reflects the working condition of most app lications (Milanoet al . 1991).


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MASS TRAN SFER IN MO DIFIED ATMO SPHERE PACKAGING 407

Moisture Proteins Lipids N.N.E.79.98 17.82 0.32 0.6680.9 16.2 1.3 0.5

81.71 16.56 0.68

Many papers have been published on the subject of determining d iffusivity.The main difference between the methodology to be examined in this paper, andsteady state approaches, lies in the experimental simplicity. A successfulvalidation of this new procedure would represent a powerful tool for diffusivityestimation.The objective of this research study was to develop a general mathematicalmodel to predict the dynamic changes on headspace (CO,, N,, 0 and moisturecontent) of Pacific Hake fillets packed under modified atmosphere.

Ash Source1.22 a1.1 b

1 Ol C

MATHEMATICAL MODELThe gas composition of the headspace could change due to several aspectssuch as production and/or demand of volatile substances by microorganisms.However, in this model this aspect was not considered. Even though it is betterto consider the aforementioned effect, specially if we are dealing with seafoodproducts, (high microorganisms load), a MAP refrigerated system minimizesmicrobial growth, and under these conditions it is safe to simplify the mathemat-ical model. According to Simpson ef al. (2001) using maximum values for

oxygen dem and, microbial loads over l@ CFU /g) have a m easurable effect onheadspace gas composition. On the other hand, microbial loads over lo5(CFU /g) reflects a product that is ended in terms of shelf-life and simulation hasno meaning.Given that Pacific Hake is a lean fish with a high moisture content (Tablel), the oxygen consum ption due to oxidation was considered negligible.


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408 R. SIMPSON, S. ALMONACID and C. ACEVEDO

FILM

The mathematical model was built for MAP systems, considering: (1) lowfat food material considered as an infinite slab shape, 2) a flexible package(plastic tray and film), (3) a gas mixture containing N,, 0, nd CO,. Themathematical model renders that headspace gas variation through time isproduced by gas sorption from food material and package permeability (Fig. 1).

,CKACE

FIG. 1 . SCHEMATIC DIAGRAM

Diffusion and Sorption of O,, CO, and N, by Food MaterialFicks second law, considering fish fillet as an infinite slab:Variation of gas concentration within the food material was estimated using

=.( )tAccording to Carslaw and Jeager (1959), for a parallelepiped with onedimension less than six times to the other two the body can be considered as aninfinite slab shape.Gas diffusion is rather slow when compared with convective transfer fromheadspace through the product surface (high Biot mass number). Bertola et al.(1990) reported a Biot mass number of 652 for convective transfer of CO intomatoes packed under MAP. Biot mass numbers over 40 are required toconsider convectivemass transfer negligible. The concentration on the fish fillet


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MASS TRANSFER IN MODIFIED ATMOSPHERE PACKAGING 409

was considered in equilibrium with headspace and can be described by Henry'slaw.

Mass transfer through tray walls was considered negligible and wasrepresented by the following equation:

S O = L t 26 X (3)

Normally, before packing, food products are in equilibrium with air.Therefore, the gas concentration within food material is equal to air partialpressure of each gas. The initial condition was defined, assuming that the gasconcentration was homogeneous inside the food material, and equal to the airpartial pressure.PAc=- O < X < L , t = OH

The gas sorption by the product was estimated by:6C

[El,= M8rAnd the mean gas concentration in the food product was calculated by:

M

(4)


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Experimental studies have dem onstrated that Pacific Hake fillets lose weightwhen packed under refrigerated MA P, in an amount less than 3 (Nuiiez 2000),therefore, the mass of the product w as considered constant during storage.Moisture Mass Transfer on Food Product

Headspace gas composition varies during storage time in a complexmanner. Due to several mechanisms, gases flow from the food material throughheadspace and vice versa. Some mechanisms for this transport are: (1) productdecomposition generates many volatile compounds that migrate from foodmaterial through headspace, (2) desorption of other gases dissolved in theproduct, 3) food dehydration, etc. Within these ways, m oisture transfer is themost important mechanism in terms of headspace gas composition.Normally, headspace in MAP applications is very small and reachessaturation rapidly (equilibrium between water activity and relative humidity ofheadspace), also, part of the evaporated water condenses and the packagesurface gets wet with small droplets with a water activity close to 1. Given thatthe weight losses were considered negligible the resistance that controls thedehydration mass transfer process was located on the surface. The moisturemass transfer on food surface was expressed as

To validate this assumption, Pacific Hake fillets were packed in a rigidmaterial with air (to attain constant volume and pressure within headspace), andmoisture content variation was measured with an HOBO H8 ogger for RH.From Eq. 7 a mass balance was established and solved analytically, thenlinearized to get the following expression:

Experimental data were fitted using Eq. 8 and a correlation coefficient of-0.99was obtained. Then a mass transfer coefficient of 4.54 x [mol/s m2atm] was estimated. Water activity was measured using a Rototronic


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AWVC 2101. The Antoine equation (Perry and Green 1997) was used tocorrelate vapor pressure of pure water against temperature.Mass Transfer Through Packaging Material

The molar fluxes of CO,, 0 N, and water vapor through the packagingmaterial were calculated with the typical equations of permeability as follows:

Gases Composition Variation on HeadspaceThe mass (moles) changes within headspace will modify the PV term(pressure by volume). Given that CO,, 0 N, and water vapor could beconsidered as ideal gases, this estimation was done using the ideal gasesequation, and the variation of the PV term on the headspace, was obtainedthrough mass balance per each component.The variation of the PV term in headspace has two extreme situations: (1)Isobaric expansion or com pression of headspace, that corresponds to a 100%flexible packaging material, or, (2) pressure change at constant volume, thatcorrespond to a rigid packaging material like a tin container for canned foods.Packaging m aterials used for MA P applications are classified between these twoextremes, because they are norm ally made of a plastic tray (rigid or sem i rigid)and a flexible film. Therefore, the mathematical model was solved for these twoextreme situations and then compared and analyzed against experimental data.The following differential equations considered both cases, variable volume

(with constant pressure), and variable pressure (with constant volume),respectively:


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412 R. SIMPSON. S. ALMONACID and C. ACEVEDO

In the first case, the gas composition i is calculated by c, = 100( v , / V ) , where the headspace volume is calculated by V = vHW+ vHCo2+vHo2 v,,; in the second case this is done using ci = 100 (pH,/P), wherethe headspace pressure is calculated by P = pHW+ pHCa + pHoZ+ pHN2.Numerical Calculations

The mathematical model was solved using a numerical m ethod. Differentialequations were solved using an explicit finite difference scheme. T he meanconcentration inside the food material was estimated using the trapezoidal ru le.Numerical calculations were done with Microsoft Excel 97, in a Pentium Icomputer of 350 Mhz and 64 MB of RAM.

MATERIALS AND METHODSSample Preparation

Pacific Hake was aseptically prepared to attain fillets of 300 [g] and 1.5[cm] of width. Then, they were packed utilizing an ILPRA FOOD PACK modelBASIC V/G. he gas mixture was provided by AGA Co. (Santiago, Chile), thePP/EVOH/PP trays and 82 [p ] PET/(PP/EVOH/PP) film were provided byEmpack Co ., Santiago, Chile. Information related topackage characteristics andpermeabilities were also provided by Empack Co. (Table 2). Samples werestored at OC in a REV CO refrigerator model REL 5004VI4.

Source: EMPACK Co. 1999


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Headspace composition (CO, and 3 was measured with a PBIDANSENSOR CheckMate 9900 O2/CO, equipment, water vapor with an HOBOH 8 logger for RH, and N, by difference. All headspace measurements weredone in triplicate utilizing destructive samples.Mathematical Model Validation

The validation experiment was similar to one reported by Simpson et al.(2001), where gelatin (using a water solution) was packed under M AP. Henrysconstant was estimated assuming that gases are solubilized in the aqueousfraction of the product. Gases effective diffusivity in the polymer wereestimated by the Klein expression:

D = D, exp - b e (12)

Henrys constants and gases diffusivities in water were obtained fromGeankoplis 1 982) and Brown (1959, respectively.To validate the mathematical model, experimental data were comparedagainst simulated data. As an acceptance criterion, a Roots Means Square (RMS)

lower than 5 % was used (Bizot 1983).2

ARMS=@]100Henrys Constant and CO, Diffusivity Determination

Henrys constant and CO, diffusivity were determined by transient indirectmethod measuring headspace gases composition. Experimental data were fittedusing the minimum square error criterion through the solver subroutine(Microsoft Excel 97). Samples (30) of Pacific Hake fillets were packed on 40[ v/v] CO, and tested in triplicate during a 192 F] period.O 2 (when oxidation is negligible) and N, sorption were neglected whencompared with CO,, mainly because their solubilities (taking solubilities in wateras a reference) are in the following ratio 70:2:1 (C0,:02:N3. Simpson et al.(2001) demonstrated that 0, and N, variations (neglecting oxidation reactionsand interfering microorganisms) in headspace are directly related to volumechange, and not to the change of gas mass, which one is approximately constant,depending on packaging permeability. Zhao and Wells (1999 , demonstrated that


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Iar iable volum e

Veriable press ureb

N, absorption in packed meat was negligible. In regards to the aforementionedinformation only the absorption by CO, was considered to determine therespective physical properties.In terms of parameter validation, experimental data (initial value of 30 [%v/v] C02, 12 [% v/v] 0 and 58 [% v/v NJ were compared w ith simulated datafor CO, hrough the RMS riterion.RESULTS AND DISCUSSIONS

Mathematical Model ValidationUnder the conditions of this research study, the proposed mathematicalmodel or variable volume and constant pressure were in good agreementwith experimental results (RMS< 5 ) . However, the variable volume modelobtained a lower % RMSwhen compared with the variable pressure model (Fig.2).

4240E

32 15 1 150 200 250 3

Time [h ]FIG. 2 EXPERIMENTAL AN D SIMULATED DATA (MODEL AT VAR IABLEVOLUME/CONSTANT PRESSURE AND VARIABLE PRESSUREXONSTANTVOLUME) OF CO, COMPOSITION IN HEADSPACE


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MASS TR ANSFER IN MODIFIED ATMOSPHERE PACKAGING 415

5FE 45eu)

The mass transfer process can be divided in two different stages, first atransient period (0-100 h) and then a constant period similar to controlledatmosphere. The equilibrium period is reached when food product is saturatedwith CO,. Both models (variable volume and variable pressure) reach theequilibrium at the same time, but concentration differs from 1 to 3 [ /v].Other packaging materials could be best represented by a variable pressuremodel (different rigidity and/or permeability). The following results anddiscussions are referred to the model solved considering variable volume (withconstant pressure).Good agreement between experimental and simulated data was found. Thecalculated RMS were 1.96%, 1.72%, 1.24% and 3.58 for CO,, O,, , andwater vapor, respectively. Figures 3 and 4 ogether with the calculated RMSdemonstrate that the mathematical model is valid as well as the assumptionsmade to build it.

0 40

0* imulated C 0 2SimulatedN2Experimental C 0 2

Henry's Constant and CO, DiffusivityCO, iffusivity for Pacific Hake fillets at OC was estimated to be 5.19 x

lO- O [m2/s]. The fitted data obtained from the inverse procedure is shown inFig. 5 . Henry's constant was estimated to be 12.76 [atm kg/mol]. Good

g 40

55

Experimental N2-


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16

f 12E88 4

C8 8

0

0 - 0 0 0

-S imula ted 0 2Simulated H2O

0 Experimental 0 2Experimental H 2 0

0 50 100 f50 200 250 300Time [h]

FIG. 4 EXPERIMENTAL AN D SIMULATED DATA OF 0, ND WATER VAPORCOMPOSXTION IN HEADSPACE FOR MATHEMATICAL MODEL VALIDATION

45

f 40Eg 35cu8 30

25

-Simulated C 0 2Experimental C 0 2

0 50 f 0 0 15 200T ime [h ]

FIG. 5. FITTED EXPERIMENTAL DATA TO OBTAIN HENRYS CONSTANT ANDCOZ DIFFUSIVITY IN PACIFIC HAKE


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MASS TRAN SFER IN MOD IFIED ATMOSPHER E PACKA GING 417

Diffusivity [m ]Apple' 3 . 2 8 ~ 1 0 . ~Tomatob 2 . 3 0 ~ 1 0 - ~Water' 2 . 0 9 ~ 1 0 ' ~

agreement was found when these values were compared with values reported inthe literature (Table 3). The validation experiment for these coefficientspresented a RMS of 4.13% and the graphic representation is shown in Fig. 6.

Henry's Constant [atm kg/mol]Meat (OC; pH 5.5)d 23.33Brine (OC; 0.5 M)' 14.98Water (OC)' 12.99

8o .imulated C 0 2

Simulated 0 2Simulated N2Experimental C 0 2

x Experimental 2Experimental N20Q 30

P-il: - = - . = - - -.x... *...___.._....... . _ _ _ . _ _ . .=1

0 50 100 15 2 25Time [h ]

FIG. 6. EXPERIM ENTAL AND SIMULA TED DATA O F CO,, 0, ND N, TO VALIDATEHENRY'S CONSTANT A CO, DIFFUSIVITY IN PACIFIC HAKE


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HHRkLMNnPPPRRMSSTtVVXP

Henry's constant [atm kg/mol]Relative moisture in headspace [%]Mass transfer coefficient [mol/s m2 atm]Width [m]Food mass [kg]Number of experimental valuesmolesHeadspace pressure [atrn]Saturated water vapor pressure at system temperature [ a m ]Partial pressure [atm]Ideal gas constantRoots Means SquareSimulated valueAbsolute temperature [ K]Time [s ]Headspace volume [m3]Partial volume [m3]Distance in x direction [m]permeability [molls m a m ]

Sub indicesAirCarbon dioxideFoodFilmHeadspaceNitrogenOxygenPackageSolutionTrayWaterInitial value (t = 0)

REFERENCESBERTOLA, N., CHAVES, A . and ZARITZKY, N.E. 1990. Diffusion ofcarbon dioxide in tomato fruits during cold storage in modified atmosphere.Intern. J. Food Sci. Technol. 25 318-327.


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BIZOT, H. 1983. Using the G.A.B. model to construct sorption isotherms. InPhysical Properties of Foods, (R. Jowitt. ed.) pp. 43-54, Elsevier AppliedScience Pub., London.BRODY , A.L. 1996. Envasado de pescado y marisco en atmbsferas modifica-das. In Envasado de Alimentos en Atmdsferas C ontroladas, Modificadas ya Vacio . A.L. Brody, ed.) pp. 69-77. Acribia Editorial, Zaragoza, Spain.BROWN, G.G. 1955. Operaciones Basicas de la Ingeniena Quimica, p. 542,M a r h S.A. Editorial, Barcelona, Spain.CARSLAW, H.S. nd JAEGER, J.C. 1947. Conduction of Heat in Solids.Second Edition. pp. 123, Clarendon Press, Oxford, U.K.

Empack Co. 1999. Personal communication. Santiago, Chile.FEY, M. and REGENSTEIN, M. 1982. Extending shelf-life of fresh wet redPacific Pacific Hake and salmon using C02- O2modified atmosphere andpotassium sorbate ice at 1OC. J. Food Sci. 47 1048-1054.Model for gas exchange dynamics in modified-atmosphere packages offruits and vegetables. J. Food Sci. 60(5), 1078-1083.GEANKOPLIS, C. 1982. Procesos de Transpone y Operaciones Unitarias .pp. 729, Continental Editorial, MCxico D.F.

GILL, C.O. 1988. The solubility of carbon dioxide in meat. Meat Sci. 22, 65-71.HUSS, H. 1988. El pescado Fresco: Su Calidad y Cambios de Calidad. Manualde Capacitacibn, F A 0 Collection, pp. 54, Rome.IFOP. 1983. Catalog0 Tecnoldgico. Materias Primas Pesqueras - Chile. pp. 65,Corp. de Foment0 de la Producci6n. Gerencia de Desarrollo. Chile.IFOP. 1998. Boletin informativo SIM N o 42. March, Chile.LAKAKUL, R ., BEAUDRY, R.M. and HERNA NDEZ, R.J. 1999. Modelingrespiration of apple slices in modified-atmosphere packages. J . Food Sci.LEE, D.S., AGGAR, P.E., LEE, J. and YAM, K.L. 1991. Model for freshproduce respiration in modified atmospheres based on principles of enzymekinetics. J. Food Sci. 56(6), 1580-1585.LIOUTAS, T. 1988. Challenges of Controlled and Modified AtmospherePackaging: A Food Company's Perspective. Food Technol. Sept. 78-86.MANNAPPERUMA, J.D., SINGH, R.P. and MONTERO, M.E. 1991.Simultaneous gas diffusion and chemical reaction in foods stored inmodified atmospheres. J. Food Eng. 14 167-183.MILANO, G., SCARPA, F. and BARTOLINI, R. 1991. Identification oftemperature dependent thermophysical properties of insulating materials.Roc . 18 Intern. Congress Refrigeration, pp. 212-221, Montreal.

FISHMAN, S., RODOV, V., PERETZ, J. and BEN-YEHOSHUA, S . 1995.

64(1), 105-110.


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MASS TRANSFER IN MODIFIED ATMOSPHERE PACKAGING 42 1

MORA LES-CASTRO, J., RA O, M .A., HO TCHKISS, J.H. and DOW NING,D.L. 1994. Modified atmosphere packaging of head lettuce. J. FoodProcessing and Preservation 18, 295-304.NU NE Z, C. 2000. Estudio de vidautil en m erluza austral (Merlucciusaustralis)envasada en atmosferas modificadas. Bachelor Thesis, Escuela deAlimentos, U.C.V., Chile.OGRYD ZIAK, D. M . and BROW N, W. D. 1982. Tem perature effects inmodified-atmosphere storage of seafoods. Food Technol. 36 5), 86-96.PARRY, R.T. 995. Introducci6n. In Envasado de 10s Alimentos en Atm6sferaModiJicizdu, (R.T. Parry, ed.) pp. 13-31, A. Madrid Vicente, Editiones,Madrid, Spain.PASTORIZA, L., SAMPEDRO, G. , HERRERA, J . and CABO, M. 1996.Effect of modified atmosphere packaging on shelf-life of ice fresh PacificHake slices. J. Sci. Food Agric. 71, 41-547.PENNEY, N., BELL, R. and CUMMINGS, T. 1994. Extension of the chilledstorage life of smoked blue cod (Parapercis colias) by carbon dioxidepackaging. Intern. J. Food Sci. Technol. 29, 167-178.PERRY, R.H. and GREEN, D.W. 1997. Perrys Chemical EngineersHandbook, 7THEd. pp. 4-15, 13-21. McGraw-Hill Book Co., New York.M . 1992. Tabla de composicion quimica de 10s alimentos chilenos. pp. 14 ,Universidad de Chile, Santiago, Chile.SIMPSON , R., A LMON ACID, S. and ACEVEDO, C. 2001. Development ofa mathematical model for map system applied to nonrespiring foods. J .Food Sci. 66(4), 561-567.

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