Multiscale modeling of RQ-DCA storage of different pear cultivars using a hybrid physics-based stochastic approach

Abstract

During respiratory quotient based dynamic controlled atmosphere (RQ-DCA) storage, the oxygen concentration in the room is reduced until the RQ measured in the air of the room (RQair) increases above a predefined threshold. This increase in RQ indicates an increased extent of fermentation within the fruit. Because of internal gas gradients, the oxygen concentration inside the fruit is lower than that of the storage atmosphere and, hence, the RQ value in the fruit (RQfruit,max) is larger than RQair. Moreover, due to biological variability and fluctuations in the storage conditions, both RQfruit,max and RQair vary. Currently, no information exists about how the RQ measured in the atmosphere correlates with the RQ value inside the fruit, and how representative this RQair is for all fruit inside the room. In this article, we investigated how variability affects the critical RQair threshold in RQ-DCA. Hereto we used a multiscale stochastic reaction-diffusion model to compute gas transport within pears of three different cultivars, ‘Cepuna’, ‘Conference’ and ‘Queen’s Forelle’. Biological variability in diffusion and respiration parameters and fluctuations in cool room conditions were taken into account by performing Monte-Carlo simulations. The results showed large variations in both RQfruit,max and RQair. The effect of cool room filling degree on both RQ values was negligible, while variations in fruit material properties (pear size, tissue gas diffusivity and respiration kinetics) showed to be of high importance. However, as RQair increased before fermentation started to dominate, the underestimation and variability of RQair did not inhibit a proper detection of hypoxia inside the fruit within the room. This finding indicates that RQair is a proper parameter to control DCA storage of various cultivars. Due to differences in fruit properties, the RQ-response varied between the cultivars. ‘Cepuna’ requires the highest O2 (0.61 kPa) to prevent fermentation, while ‘Conference’ and ‘Queen’s Forelle’ can be stored at lower O2 (0.33 and 0.22 kPa, respectively). The results obtained in this research can be used to optimize RQ-DCA storage of each cultivar.