Pistachios were coated with different chitosan concentrations (0%,1%, and 1.5%) and then packaged under different initial gas compositions (ambient air composition: 21%O2, < 0.1% CO2,78% N2, and 10%O2 + 90%N2) in a closed system under different temperatures (5, 12, and 25 °C) to measure respiration rate. The results showed that with decreasing the initial level of oxygen, the respiration rate decreased, and with increasing temperature, it increased. Also, temperature had a more significant effect on respiration rate than initial O2 concentration, so that for treatment without chitosan coating under ambient air gas composition, the respiration rate increased to 58% with increasing temperature from 5 to 25 °C. To develop the Modified Atmosphere Packaging (MAP) system, the respiration rate and its dependence on gas concentration and temperature was modeled using the Michaelis–Menten (competitive) and Arrhenius models, respectively. After obtaining the O2 and CO2 concentrations under MAP during storage at 5 °C, it was observed that the equilibrium concentration of gases were well predicted by the models for all treatments. But in the case of uncoated treatment under 90%N2 + 10%O2, the model did not adapt well to the changes in O2 and CO2 concentrations in the package and could not predict them accurately. This may be due to the occurrence of anaerobic respiration in the package and its non-consideration in respiration rate modeling. It was concluded that the competitive Michaelis–Menten model with parameters that change with temperature under the Arrhenius equation, predicted the effects of gas concentration and temperature on the respiration rate of chitosan coated fresh pistachio nuts well.

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