Impact of Thermal and High-Pressure Treatments on the Microbiological Quality and In Vitro Digestibility of Black Soldier Fly (Hermetia illucens) Larvae

SIMPLE SUMMARY: While facing climate change and natural resource scarcity, ensuring sufficient, nutritious, safe, and affordable protein sources to a fast-growing feed demand becomes increasingly challenging. The emerging insect sector has the potential to improve the circularity of the agri-food chain thanks to their ability to upcycle industrial organic wastes into valuable biomass that can be included as a feed ingredient for livestock. The black soldier fly is considered one of the most promising insect species for its large-scale production due to its ability to be reared in a wide variety of organic substrates. However, more information is required regarding the suitability of agri-food by-products and processing techniques to ensure the quality of the final insect-derived products for large-scale production. The present study showed that breweries’ by-products are a suitable source of substrate for the development of black soldier fly larvae as an ingredient for both ruminant and non-ruminant livestock feed. High-pressure processing showed no clear improvement in terms of decontamination capacity and digestibility in comparison to heating treatment, resulting in a less cost-effective process for large-scale production of black soldier fly larvae. ABSTRACT: Black soldier fly larvae (BSFL) are gaining importance in animal feeding due to their ability to upcycle low-value agroindustry by-products into high-protein biomass. The present study evaluated the nutritional composition of BSFL reared on brewer’s by-product (BBP) and the impact of thermal (90 °C for 10/15 min) and high-pressure processing (HPP; 400/600MPa for 1.5/10 min) treatments on the microbial levels and in vitro digestibility in both ruminant and monogastric models. BBP-reared BSFL contained a high level of protein, amino acids, lauric acid, and calcium, and high counts of total viable counts (TVC; 7.97), Enterobacteriaceae (7.65), lactic acid bacteria (LAB; 6.50), and yeasts and moulds (YM; 5.07). Thermal processing was more effective (p < 0.05) than any of the HPP treatments in reducing TVC. Both temperature of 90 °C and pressure of 600 MPa reduced the levels of Enterobacteriaceae, LAB, and YM below the detection limit. In contrast, the application of the 400 MPa showed a reduced inactivation (p < 0.05) potential. Heat-treated samples did not result in any significant changes (p > 0.05) on any of the in vitro digestibility models, whereas HPP showed increased and decreased ruminal and monogastric digestibility, respectively. HPP did not seem to be a suitable, cost-effective method as an alternative to heat-processing for the large-scale treatment of BSFL.