Freezing storage combined with freeze-drying of black soldier fly (Hermetia illucens) larvae to produce oil rich in free lauric acid

Abstract The fat of Hermetia illucens larvae (black soldier fly, BSFL) is a rich source of lauric acid (LA), and its free fatty acid (FFA) form holds valuable potential for applications in food, feed, pharmaceuticals, or cosmetics. This study aimed to establish specific processing conditions of BSFL that naturally promote lipolysis, resulting in a high free LA (FLA) rich oil. Freezing was used for slaughtering, with different times of frozen storage (1, 7 and 14 d). Then, thermal (oven-drying) and non-thermal (freeze-drying) drying processes were compared. Additionally, the impact of 24 h restrictive vs non-restrictive feeding before slaughtering was tested. Free acidity, free fatty acid profile, lipid oxidation (peroxide value, PV; TBARs test) and antioxidant activity (DPPH test) were measured at days 0 and 30 of processing. Freeze-dried samples exhibited higher free acidity (42%) compared to oven-drying (4%), progressively increasing with frozen storage (24% at day 1 vs 51% at day 14). A restricted diet caused up to 60% free acidity. Nevertheless, the FFA profile was similar for both diet conditions, with LA as the major FFA (41% of total FFAs and 27% of total fat). After 30 days of storage, free acidity approached 70%. Oven-drying caused the highest PV (4.5 mEqO 2 /kg), especially after 14 d of frozen storage (>5.0 mEqO 2 /kg) and under restricted diet (6.1 mEqO 2 /kg). Conversely, freeze-drying maintained the lowest PV in all cases (0.6 mEqO 2 /kg). TBARs values mirrored the PV pattern. Antioxidant capacity was lower for freeze-drying compared to oven-drying (46% and 71%, respectively), regardless of frozen storage. Irrespective of the drying method, worse antioxidant activity was observed after restrictive diet. After 30 days of storage, the antioxidant activity decreased for all samples. The proposed strategy of freezing slaughtering, followed by frozen storage and freeze-drying offers a promising approach to naturally obtain a FLA-rich product from BSFL.