Instant controlled pressure-drop assisted pressing for defatting and dewatering of yellow mealworm larvae: process study and optimisation

Abstract

Insects are gaining interest as a sustainable and highly nutritious source of proteins and lipids for food and feed production sectors. Insect bio-refinery includes lipid extraction by pressing, dewatering, microbiological decontamination, and protein fractionation. The present study is experimenting the use of instant controlled pressure-drop (DIC), an emerging technology, for treating yellow mealworms and evaluating its combined effects on insect bio-refinery steps. A preliminary study allowed identifying the optimal hydraulic pressing conditions for Tenebrio molitor larvae. Then, establishing an experimental design with DIC operative parameters of the saturated dry steam absolute pressure and treatment time ranging between (0.15 and 0.45 MPa) and (15 and 35 s), respectively, allowed identifying the DIC impact as a pretreatment on different larvae properties. It was possible to identify the optimal pressing parameters at 6 MPa, 60 °C, 2 cm of thickness, and 0.15 mm/s as initial piston speed. Moreover, DIC performed at 0.15 MPa for 25 seconds stood as an efficient killing method. Thanks to the changes in the membrane’s structure it provokes, DIC treatment modified larvae properties, ensured a partial expulsion of the matter (up to 0.47 g/g dry basis (db)), and resulted in larval expansion (up to 67%) which resulted in a decrease in the apparent density. As for the chemical properties, the larvae and larvae juice colours were found to become lighter as we increased the treatment conditions, which might be caused by the inactivation of oxidative enzymes. Moreover, severe DIC operative parameters decreased the pressing yields from 68 to 55%, possibly caused by protein aggregation and denaturation phenomena that prevent molecules from coming out by pressing. However, the water activity and moisture, lipid, and protein contents remained unaffected.