Comprehensive Analysis of Adsorption–Desorption Isotherms, Drying Kinetics, and Nutritional Quality of Black Soldier Fly (Hermetia illucens) Larvae

Abstract

Black soldier fly larvae (BSFL) are gaining attention as an alternative protein source in food and feed, promoting a circular economy, particularly in their dried form. In the literature, monitoring the behavior of larvae in a humid environment has not been established under different conditions of temperature and relative humidity as well as the quality of dried larvae is not always correlated to the conditions of drying. Therefore, this study comprehensively analyses the adsorption–desorption isotherms, drying kinetics, and subsequent quality changes of dried BSFL. Sorption isotherms were assessed at 40, 50, 60, and 70 °C using the gravimetric method, followed by mathematical modelling and determination of thermodynamic variables. Thin-layer drying kinetics were studied in a forced-air oven at the same temperatures, with a subsequent proximate analysis of the dried larvae. Among eight sorption isotherm models evaluated, the Peleg model provided the best fit, revealing type II sorption isotherms with an optimal storage water activity of 0.38. The Page model accurately described the drying kinetics of BSFL across all temperatures. Moisture diffusion coefficients ranged from 6.15 × 10^–11 to 2.63 × 10^–10 m²/s, with an activation energy of 48.66 kJ/mol. The dried larvae displayed impressive protein levels, varying from 39.67 ± 0.28% to 45.29 ± 0.07%, exceeding the minimum requirements set in the global insect production industry. Higher drying temperatures significantly impacted the proximate composition, reducing larvae quality. These findings underscore the potential of BSFL as a valuable protein source and enhance the understanding of their sorption behavior and quality attributes during drying. This study contributes to the optimization of drying conditions for improving the quality of BSFL as a sustainable protein alternative.