A mathematical model was developed from experimental measurements to describe the evolution of the O 2 , CO 2 and ethylene in a modified atmosphere packaging system for Cavendish bananas. The respiration and ethylene production in the fruits were experimentally obtained from a closed system method and then represented by Michaelis-Menten equations of enzyme kinetics. The gas transfer through the packaging was described by a Fick's diffusion equation, and the temperature dependence was represented based on the Arrhenius law. The model was validated by packaging the fruit in perforated bags of polypropylene and low density polyethylene at 12°C for a period of 8 days. With the developed model it was possible to satisfactorily describe the experimental evolution of the gas content in the headspace of the packages, obtaining coefficients of determination (R 2 ) of 0.93 for the O 2 levels, 0.90-0.91 for the CO 2 levels, and 0.89-0.93 for the ethylene levels.

A proper description of the respiration and ethylene generation is important in the development of package systems for the preservation of fresh fruits and vegetables. In this work, a model based on both Michaelis-Menten and chemical kinetics equations was developed and assessed in order to describe the respiration and ethylene generation of avocado (Persea americana cv. Hass) and feijoa fruits (Acca sellowiana Berg) from experimental data obtained at different temperatures by a closed system method. The temperature effect in both processes was described using Arrhenius-type relationships. After this, avocadoes and feijoas were packed in perforated low-density polyethylene (LDPE) and polypropylene (PP) bags for 8 days at 12°C and 80% RH to validate the usefulness of the model to describe the gas evolution in modified atmosphere packaging (MAP). For avocado fruits, respiration rates of 2680-3030 cm 3 kg-1 d-1 were obtained at 24°C and normal atmosphere, and 3650-4230 cm 3 kg-1 d-1 for feijoa fruits. As for ethylene production rates, at 24°C were obtained values of 3.11 cm 3 kg-1 d-1 for avocado and 0.50 cm 3 kg-1 d-1 for feijoa. At 6°C, respiration and ethylene production rates were up to 6 times lower. It was possible to describe properly the ethylene generation using a Michaelis-Menten simple equation and the respiration rates using a Michaelis-Menten uncompetitive kinetics for both fruits with coefficients of determination above 0.9 in each case. The overall model was validated in the MAP test being possible to predict successfully the O 2 , CO 2 and C 2 H 4 levels inside the packages.

ResumenEl objetivo de este trabajo fue determinar la cinética de inactivación de la enzima peroxidasa y la cinética del color y textura en tubérculos de papa criolla (Solanum tuberosum grupo phureja) sometidos a escaldado mediante agua a 80°C, 90°C y vapor saturado a 93°C. Los coeficientes de transferencia de calor para el escaldado en agua oscilaron entre 214 y 230 W °C -1 m -2 mientras que para vapor saturado fueron en promedio 84.5 W °C -1 m -2 . A diferentes tiempos de precocción el tubérculo de papa criolla presentó una zona en donde ocurrió pardeamiento enzimático, hecho que fue modelado según la cinética de Michaelis-Menten y otra zona en donde el cambio de color disminuyó debido a la inactivación enzimática que correspondió a una cinética de primer orden, de manera similar al comportamiento de la textura. La inactivación de la enzima peroxidasa obedeció al mecanismo de Lumry-Eyring.Palabras clave: modelación de procesos, Solanum tuberosum grupo phureja, cambio de color, textura, peroxidasa AbstractThe objective of this work was to determine the inactivation kinetics of peroxidase enzyme and the change in color and texture in golden potato tubers (Solanum tuberosum phureja group) exposed to blanching with water at 80°C, 90°C and to saturated steam at 93°C. The heat transfer coefficients for the blanch water ranged between 214 and 230 W °C -1 m -2 while for saturated steam they showed an average of 84.5 W °C -1 m -2 . At different pre-cooking times the golden potato tuber showed an area that developed enzymatic browning, which was fitted to the Michaelis-Menten kinetic model and another area where the color change decreased due to enzyme inactivation, which corresponded to first order kinetics, in a similar way as the texture behavior. The inactivation of peroxidase enzyme followed the Lumry-Eyring mechanism.

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