Systematic Studies on the Antioxidant Capacity and Volatile Compound Profile of Yellow Mealworm Larvae (T. molitor L.) under Different Drying Regimes

Simple Summary Global population growth will increasingly challenge the food industry sector in the coming years. The yellow mealworm is a promising candidate for production on an industrial scale and it is also the first insect to be approved by EFSA in 2021 under the EU`s Novel Food Regulation. Drying is an important preservation step in the industrial processing of insects but there is limited information on the stability of nutritional, bioactive and sensory components during drying. Thus, this study sought to investigate the impact of different drying procedures (freeze-drying, microwave drying, infrared drying, oven drying and high frequency drying) on the chemical composition, antioxidant capacity and volatile profile of mealworm larvae. To summarize: (1) Mealworm larvae contain considerable amounts of polar or nonpolar extractable antioxidants, whose molecular identity needs to be to be clarified in the future. (2) The drying process was decisive with regard to the extraction efficiency of these antioxidants. The highest antioxidant capacities were found in high-temperature dried larvae, while the extracts obtained from the freeze-dried larvae had the lowest values. (3) The analyses of volatile compounds provide information on the extent to which the Maillard reaction and lipid oxidation occur and indicate relevant changes in the chemical composition during the drying procedure. Deepening the knowledge of process-induced changes of mealworm quality will contribute to improve Tenebrio molitor L. processing technologies, a basic prerequisite for utilizing mealworms as novel food or animal feed in the future. The yellow mealworm (Tenebrio molitor L., Coleoptera: Tenebrionidae) is an edible insect and due to its ubiquitous occurrence and the frequency of consumption, a promising candidate for the cultivation and production on an industrial scale. Moreover, it is the first insect to be approved by EFSA 2021 following the Novel Food Regulation. Industrial production of mealworms necessitates optimized processing techniques, where drying as the first postharvest procedure is of utmost importance for the quality of the final product. The focus of the present study was to analyse the chemical composition, antioxidant capacity, volatile compound profile and colouring of mealworm larvae dried in various regimes (freeze-drying, microwave drying, infrared drying, rack-oven drying and high-frequency drying). Proximate composition and fatty acid profile were similar for all dried larvae. Freeze dried larvae were predominantly marked by lipid oxidation with significantly higher peroxide values, secondary/tertiary oxidation products in the headspace GC-MS profiles and lower antioxidant capacity. High-temperature treatment in the rack oven-and to some extent also infrared or microwave drying-led to mealworm larvae darkening and the appearance of volatile Maillard secondary products such as 2-methylpropanoic acid, 2-/3-methylbutanoic acid and alkylpyrazines. High-frequency drying as a new emerging technology in insect processing was the most cost-effective method with energy costs of solely 0.09 CYRILLIC CAPITAL LETTER UKRAINIAN IE/kg T. molitor L. leading to final larval material characterized by both lipid oxidation and nonenzymatic Maillard-browning.

Automated summary

This study investigated the impact of different drying procedures on the chemical composition, antioxidant capacity, and volatile profile of mealworm larvae. High-temperature treatment led to darkening of mealworm larvae and the appearance of volatile Maillard reaction products. High-frequency drying emerged as a cost-effective method with final larval material characterized by both lipid oxidation and nonenzymatic Maillard-browning.