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 degrees 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 degrees 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.