Quality properties of salt-fermented mealworms (Tenebrio molitor larvae) with added millet

Abstract

Mealworms, edible insects, have attracted attention as a sustainable alternative protein source. This study introduces an insect-based product obtained by fermentation. Fresh mealworms were fermented for 30 days in four different conditions: whole unground mealworms (WM), whole unground mealworms with millet (WMM), ground mealworms (GM), and ground mealworms with millet (GMM). The presence of millet in WMM and GMM resulted in lower pH (4.62 and 4.27) and sugar contents (2.33 and 2.03°Bx) and higher titratable acidity (0.96 and 1.25%), compared to WM and GM (5.57 and 5.54, 3.10 and 3.07°Bx, 0.41 and 0.42%). Grinding increased total nitrogen, amino acidic nitrogen, nitrogen degradation ratio, and volatile basic nitrogen levels in GM and GMM. Particularly GM and GMM showed a significant increase in free amino acid contents from 19.20 g/kg in unfermented raw mealworms to 69.51 and 62.59 g/kg, respectively. Regarding volatile compounds, WMM (200.80 and 410.42) and GMM (311.50 and 997.75) exhibited higher relative peak areas of acetic acid and ethanol than WM (25.50 and 4.32) and GM (22.90 and 86.65), whereas WM (233.22) and GM (565.27) had higher butanoic acid than WMM (51.75) and GMM (93.34). These results indicate that adding millet promotes protein fermentation, and the grinding imparts new flavors through accelerated protein degradation while reducing undesirable aromas.