Ozonation at low-pressures: relationship between reaction kinetics and physical properties of grains, control of egg and larvae phases of Zabrotes subfasciatus, inactivation of aspergillus flavus, and quality analysis
Authors:   , Sitoe Eugénio da Piedade Edmundo 
Published: July 2024

The use of ozone gas (O 3 ) has achieved satisfactory results in controlling insect pests, inactivating fungi, and maintaining the quality of stored grains. The ozonation of grains in a closed system at low-pressures is also a promising strategy for packaged products. The objectives of this study were the following: (i) to evaluate the effect of the low-pressure ozone injection system, establishing the relationship between the reaction kinetics and physical properties of the grains; (ii) to evaluate the effect of ozone gas injections on the control of egg and larval phases of Zabrotes subfasciatus (Boh.) and inactivation of Aspergillus flavus in bean grains; and (iii) to evaluate the quality of beans exposed to ozone or oxygen and stored for 180 days. The study was carried out in three stages. First, the low-pressure ozone injection system was evaluated to determine the physical properties of the grains and to determine possible quality changes in common beans, cowpeas, popcorn, corn, paddy rice and polished rice. For this purpose, 5.0-kilogram samples of grains were exposed to ozone or oxygen (control) at low pressures in a 70-liter hypobaric chamber. The ozone exposure was preceded by the reduction of the internal chamber pressure to 500 hPa. Then, ozone was injected until the pressure inside the chamber reached 1000 hPa. In the study, an ozone concentration of 32.10 mg L -1 was applied at a flow rate of 1 L min -1 . The second step evaluated the effect of the ozone gas injections on the control of new-insect emergence from the egg and larval stages of Z. subfasciatus (Boh.) and on the inactivation of A. flavus in bean grains. Ozone was applied to 5.0 kg of bean grains at 61.37 mg L -1 and a flow rate of 1 L min -1 in 1, 4, 7, and 10 injections. Oxygen was used as the control, injected at a flow rate of 1 L min -1 . The injection escalation occurred at regular intervals of 2 h and 15 min. The third stage assessed the effect of ozone (treatment) or oxygen (negative control) administered in 10 injections on the technological properties, phenolic compounds, and antioxidant capacity of beans stored for 180 days. Five samples of 1.0 kg of bean grains were packaged in low-density polypropylene bags to evaluate the effect of the treatments during storage. The packages were stored in a chamber at 25°C and 60±5% relative humidity. The quality of the beans treated with ozone oroxygen and the control (untreated grain) was determined after 180 days of storage by analyzing the technological properties, phenolic compounds, and antioxidant capacity. The results of the first stage made it clear that the physical properties of the grains were affected by the reaction kinetics of the ozone gas during the low-pressure injection process. Ozone depletion was faster in polished rice and slower in common beans. The half-life of ozone gas in different grains ranged from 17.8 to 52.9 and 16.4 to 52.9 minutes outside and inside the package, respectively. Low-pressure ozone gas injection had no effect on the grain quality characteristics. The low-pressure ozone concentration of 32.10 mg L -1 caused mortality of 99.45 and 73.06 of S. zeamais in popcorn and corn, 92.10% of C. maculatus in cowpea and 100% of Z. subfasciatus in common bean. In the second phase, it was observed that the ozonation of beans at low-pressures in 10 injections provided the creation of a modified atmosphere inside the packaging that was efficient in controlling 100% of egg and larval phases of Z. subfasciatus, implying in less mass loss, and inactivation of 70% of A. flavus. In the third step, it was found that the application of ozone in 10 injections did not change the chemical composition, color, cooking properties, and level of antioxidant capacity of the grains. All treatments showed a decrease in the phenolic compound content and antioxidant capacity during storage. This study concludes that the application of ozone at low pressure is a promising technology for insect-pest control and fungal inactivation without affecting the commercial quality of the grains. Keywords: Hypobaric chamber. Ozonation. Pest insects. Bean Quality.