Mathematical model and electronic system for real-time O2 control in storage boxes: Development and validation under fluctuating temperatures

Modified atmosphere storage containers with gas-permeable membranes are effective in reducing post-harvest losses, mainly at low temperatures but become ineffective in controlling O₂ and CO₂ at temperatures above 3 °C. This study aimed to develop a method to control O₂ in a storage box. This method uses a diffusion tube, that blocks air from entering the box but allows for air exchange when an air blower is activated. The blower ON frequency (BOF) was modelled as a function of temperature, considering the type and amount of produce, blower properties, tube dimension, and the O₂ setpoint. The effects of temperature and gas composition on respiration rate kinetics were analysed with Michaelis-Menten and Arrhenius equations. The model was used to program the microcontroller to control the blower. Validation was performed using a 190 L box containing 25 kg of broccoli. The developed model maintained the desired O₂ concentration under fluctuating temperatures. The BOF values ranged from 25.6 to 549.2 s h⁻¹, for temperature fluctuations between 4 and 23 °C. The time required to reach the 3% O₂ in the box differed depending on the blower's state. With the blower turned ON from the beginning, it took 24.9 h. However, when the blower was initially turned OFF, it took 11.1 h. Despite temperature changes, the system maintained O₂ at 3.8 ± 0.29% and CO₂ at 14.4 ± 0.66%. The system is promising for commercial use and best suited for CO₂ tolerant produce because it requires a separate mathematical model and control mechanism.