Khe V. Chau

Modelling O2 and CO2 exchange for development of perforation- mediated modified atmosphere packaging

Perforation-mediated modified atmosphere packaging relies on the use of macro perforations or tubes to control the O2 and CO2 exchange and create the desired atmosphere inside an otherwise gas-tight package. In this work, the O2 and CO2 exchange through a single tube was studied. DiAerent temperatures (5‐20∞C) and tube dimensions (length from 9 to 17 mm and diameter from 6 to 30 mm) were tested. O2 and CO2 mass transfer coeAcients were determined according to a lumped mass transfer capacitance model that yielded a good description of the gas transfer. Temperature in the range tested did not show a significant eAect on the mass transfer coeAcients. A multiplicative non-linear equation was found to yield a good prediction of the dependence of the O2 mass transfer coeAcient on tube diameter and length. The ratio between the CO2 and O2 mass transfer coeAcients, an important parameter in the design of MAP, was 0.81 and none of the factors tested influenced its value. ” 2000 Elsevier Science Ltd. All rights reserved.

Maintaining optimal atmosphere conditions for fruits and vegetables throughout the postharvest handling chain

Optimal controlled and modified atmospheres (CA and MA) for fresh produce vary according to the specie, its maturity or ripeness stage, the temperature, and the duration of exposure. However, individual lots of produce are typically handled for different times and at different temperatures during storage, transportation, and retail display. In this paper, we review some of our previous work showing the potential for using different atmospheres for mangoes (Mangifera indica L.) and strawberries (Fragaria � /ananassa Duchesne) depending on the anticipated storage length and temperature. Since it would be desirable, especially for produce transported over extended distances, as in marine transport, to maintain optimal atmosphere conditions throughout the postharvest handling chain, we also describe our procedure for designing a combination CA/MAP system that involves first designing the MAP for a particular commodity that will produce an optimal atmosphere for retail display conditions, then selecting a CA that will interact with the MAP to produce the optimal atmosphere within the packages during transportation at a lower temperature. An example of the design procedure is given from our work with fresh-cut kale (Brassica oleracea var. acephala DC.). Another example of this proposed MAP/CA system deals with its application to mixed load transportation of strawberries and snap beans (Phaseolus vulgaris L.). # 2002 Elsevier Science B.V. All rights reserved.

Modelling respiration rate of shredded Galega kale for development of modified atmosphere packaging

Abstract The design of modified atmosphere packaging (MAP) for fresh-cut produce requires an adequate model for prediction of respiration rate as a function of both temperature and gas composition. In this work, the O2 consumption and CO2 production rates of shredded Galega kale were studied. The storage temperatures used were 1, 5, 10, 15 and 20 °C. The atmospheres tested were all combinations of 1, 5 and 10% v/v O2 plus 0, 10 and 20% v/v CO2 with the balance being N2, as well as ambient air. Temperature was the variable with the greatest influence on respiration rate and the effect of gas composition increased with temperature. The dependence of respiration rate on gas composition was well described by a Michaelis–Menten type equation with uncompetitive CO2 inhibition. The respiratory quotient (RQ) was found to be constant for the range of temperatures and gas compositions tested and was equal to 0.93±0.01. The constants of the Michaelis–Menten equation increased exponentially with temperature. The change over time of respiration rate of leaves exposed to air at 20 °C was also analysed. It was observed that respiration rate decreased with time and that the ratio between the respiration rate of shredded and intact leaves was approximately constant in the period tested and equal to 2.8.

Effects of Gas Concentrations and Temperature on O2 Consumption of Strawberries

The O2 consumption rate of strawberries was determined at 16 combinations of O2 and CO2 and at three levels of temperature in the ranges of 1 to 20%, 0 to 30%, and 5 to 20° C, respectively. Influence of temperature, O2 concentration, and CO2 concentration on O2 consumption rate was studied and an empirical model was developed for O2 consumption rate as a function of these three variables. The O2 consumption rate decreased significantly with a decrease in temperature and O2 levels. Especially at low O2 concentrations, CO2 had a lesser effect on O2 consumption rate. The O2 consumption rate decreased with an increase in CO2 concentration at higher levels of O2.

Modified atmosphere packaging for mixed loads of horticultural commodities exposed to two postharvest temperatures

A procedure to maintain desired levels of O2 and CO2 inside packages that are exposed to different surrounding temperatures was designed and tested. This procedure included the design of packages for a high temperature, ambient atmosphere conditions simulating retail display conditions and the use of a controlled atmosphere (CA) environment surrounding the packages at a lower temperature simulating storage or transport conditions. To test the concept, strawberries and snap beans were held at 7°C for 4 days and 19°C for 2 days to simulate mixed storage:transport and retail display at these respective temperatures. The strawberries were stored in jars fitted with a short tube to modify the interior atmosphere; snap beans were stored in commercially available, semipermeable plastic bags. Both package types were placed in a CA of 14.8% O2 plus 8.3% CO2 at 7°C followed by storage in air at 19°C. Under these conditions, it was possible to maintain atmospheres that were close to the desired atmospheres for the products at both temperatures.

Development of perforation-mediated modified atmosphere packaging to preserve fresh fruit and vegetable quality after harvest

The use of perforations as a means of obtaining large size containers suitable for modified atmosphere packaging (MAP) would greatly enhance the applicability of this technology for storage and distribution of fresh and minimally processed products. General concepts of MAP, and advantages and drawbacks of using perforations to achieve it are discussed. Products for which perforated packages can be used are listed. The variables that affect this type of package are presented and the methodology for designing an adequate package is described and illustrated with the case study of shredded cabbage.

Modeling of heat conduction in elliptical cross section : II. Adaptation to thermal processing of shrimp

The quality of processed shrimp is partly determined by microbiological and textural attributes, and yield loss is economically important. Temperature is the most important variable that affects the above. A mathematical model was developed for the prediction of temperature distribution during cooking of shrimp. To develop the model, experimental cross-sectional areas of shrimp at different segments were compared with circular and elliptical cross-sectional area assumptions, and the circular cross-sectional area assumption was found to be a valid assumption for the model for its simplicity. The model used a finite difference approach with non-capacitance surface nodes (NCSN), and assumed variable thermal conductivity, specific heat, density, as well as changes in dimensions due to shrinkage. The mathematical model accurately predicted the temperature distribution in shrimp.

Modified Atmosphere Packaging Under Varying Surrounding Temperature

A mathematical model was developed to predict temperature and gas concentrations in modified atmosphere packages exposed to variable surrounding temperatures. Experiments were conducted with strawberries under constant and variable surrounding temperatures to validate the model for both conditions. For a constant surrounding temperature condition of 15.2° C, the mathematical model closely predicted the CO2 concentrations in the packages, whereas the O2 concentrations were underpredicted. For a variable surrounding temperature condition of 12 h at 18.6° C, followed by 48 h at 4.2° C, then 12 to 20 h at 18.6° C, temperatures and O2 concentrations predicted by the model closely agreed with the experimental data. The CO2 concentrations in some of the packages were slightly underpredicted. Natural variation in respiration rate between batches of the product caused the slight disagreement between experimental and model-predicted results. The mathematical model can be used not only to determine the package specifications for a given product and given surrounding temperatures, but also to predict the amount of time required for the packaging system to attain the designed optimum conditions.

Modeling of heat conduction in elliptical cross section : I. Development and testing of the model

Abstract A finite difference procedure for heat conduction in elliptical cylinders using heat flow lines was developed. This method reduces the elliptical heat transfer problem from 3 to 2-dimensional for finite length, and from 2 to 1-dimensional for infinite length. Temperature predictions were very close to experimental results. Conditions in which elliptical cross section can be approximated by circular cross-section were determined. For this, an equal cross-sectional area, and an equal surface area-to-volume ratio of the elliptical and circular cross sections were considered. The equal circular cross-sectional area approach closely predicted the center temperature only at low ellipse eccentricities (e

A Predictive Model on Moisture and Yield Loss in Phosphate-Treated, Cooked Tiger Shrimp (Penaeus monodon)

Abstract Physical properties of shrimp are economically important, and affected by size of shrimp, pre-treatments, used cooking time and temperature, cooling methods and other processing conditions during thermal processing. Phosphates are commonly used in shrimp industryto reduce moisture and yield losses in processing. Isothermal experiments were conducted to measure the changes in yield loss and moisture content of shrimp after treatment with sodium tripolyphosphate (STP) solutions, 3-cooking temperatures (75, 85,95), 3-cooking times (3.4, 2.1, 1.6 mins), and 2-cooling methods (direct ice slush and indirect ice slush). All these processing conditions were found to have a significant effect on yield and moisture losses (p < 0.001). The experimental data observed for yield and moisture loss as affected by cooking temperature/time, and STP solutions were fitted to nonlinear polynomial equations. These data were used in a mathematical model of temperature distribution to predict the yield loss of shrimp in thermal processing. The model predictions and experimental results showed close agreement. This mathematical model can be used to determine the yield loss of STP-treated shrimp for different processing conditions provided that the experimental yield loss data for different conditions are available.