Comparison of hot air and vacuum drying for yellow mealworm (Tenebrio molitor): Effect of oxygen, vacuum and temperature in drying kinetics, browning reaction and quality deterioration

• Mechanism of drying rate differences in yellow mealworms was elucidated. • Vacuum drying reduced PPO activity, lipid oxidation and Maillard reaction. • Prolonged low temperature hot air drying leads to abnormal accumulation of α-DCs. • High-temperature short-time drying improve the quality retention of yellow mealworms. Drying is required to prolong the shelf life of yellow mealworms, but hot air drying methods expose them to oxygen, which affects their quality. Therefore, further studies on the mechanism of oxygen's effect on the drying process of yellow mealworms are necessary. In this study, yellow mealworms were dried using two methods: hot air drying with oxygen and vacuum drying without oxygen, at three different temperatures. After the drying process, we analyzed the drying kinetics, color, products of the Maillard reaction, and browning-related qualities of the dried yellow mealworms. Compared to hot air-drying yellow mealworms, vacuum-drying yellow mealworms increased the soluble protein content by 54.05% - 69.29% and decreased the malondialdehyde content by 42.30% - 63.61%. Hot air drying caused severe browning under all conditions, leading to a decrease in chromaticity. Both drying methods caused a decrease in free amino acid content to varying degrees, which was more severe at 55°C and 65°C. With the exception of glyoxal, all Maillard reaction products were higher in hot air-drying yellow mealworms. The results indicate that vacuum drying promotes the drying rate of yellow mealworms at low temperatures through the puffing effect and pressure difference. We also found that during aerobic drying, increasing the temperature reduces the content of α-dicarbonyl compounds, thereby attenuating the overall Maillard reaction. Compared with vacuum drying, oxygen promotes protein denaturation and lipid oxidation, thereby facilitating the Maillard reaction. This study provides a theoretical basis and technical guidance for the dry processing of yellow mealworm and the development of high value insect protein products.