Low-pressure ozone injection system: relationship between reaction kinetics and physical properties of grains

The ozonation of grains in a closed system at low pressure is a strategy with the potential for treating packaged products. Research is necessary to characterize the reaction kinetics of ozone in this type of injection system so that it is possible to design chambers and determine the ozone concentrations suitable for commercial-scale applications. The objective of this study was therefore to characterize the low-pressure ozone injection system in relation to the physical properties of the grains and determine possible changes in their quality. Samples (5 kg each) of common beans, cowpea beans, corn, popcorn kernels, paddy rice, and polished rice were exposed to ozone in a 70 L hypobaric chamber. Initially, the internal pressure of the chamber was reduced to 500 hPa. Then, ozone was injected at a concentration of 32.10 g m^-3 at a volumetric flow rate of 1 L min^-1 until reaching a pressure of 1000 hPa. To relate the decomposition of ozone to the grains that were being evaluated, different physical properties were determined, and quality analysis was conducted.

Ozone gas half-life outside and inside the package depended on the grain type. Ozone decomposition was quickest in polished rice and slowest in common beans. The half-life of the different grains ranged from 17.8 to 52.9 and 16.4 to 52.9 min, outside and inside the package, respectively. Considering the physical properties, specific surface (Ss), surface area (SA), and sphericity (φ) exhibited a significant correlation with the decomposition rate constant (k) of ozone. However, the variables volume (V), permeability (K), porosity (ε), and specific mass (ρ) showed no correlation with k.

The physical properties of grain influenced the reaction kinetics of ozone gas during the low-pressure injection process. Ozone gas injection at low pressures did not alter the quality attributes of the grains under study. © 2022 Society of Chemical Industry.