Effects of different blanching treatments on microbiological profile and quality of the mealworm (Tenebrio molitor)

Safety and quality of edible insects are among the primary aspects which heavily affect edible insect acceptance by the consumers. In this study, the effects of different blanching treatments on the microbiological profile, pH and colour of mealworm larvae were evaluated. The effect of 10 combinations of temperature (50, 60, 70, 80 and 90 °C) and time (2.5 and 5 min) were compared to fresh larvae and oven cooked larvae (10 min at 150 °C). Moreover, the effect of 24 h starvation on the microbiological profile was evaluated. Total viable aerobic count, Enterobacteriaceae, staphylococci, yeasts and moulds, lactic acid bacteria, aerobic bacterial endospores, Escherichia coli, Bacillus cereus, Listeria monocytogenes and Salmonella spp. were determined. Starvation only marginally affected the microflora, furthermore, in all samples E. coli, B. cereus, L. monocytogenes and Salmonella spp. were never detected. A blanching treatment at 60 °C for 5 min seems to be the lower time-temperature combination in order to achieve a significant decrease of microbial loads. Blanching treatments also played a role in pH and colour modifications: larvae blanched at least at 60 °C stopped browning, possibly in relation to an enzymatic inhibition. Among the tested blanching treatments, 60 °C for 5 min seems to be the most feasible application in order to achieve the fixed goals. Lower temperature or time combinations were unable to reduce microbial loads or stop the browning effect, on the other hand, higher temperatures did not allow to improve the product quality and microbiological parameters.