Antibacterial properties of oil extracts of black soldier fly larvae reared on bakery waste

Farming black soldier fly larvae (BSFL) has become an emerging agricultural sector for upcycling food waste into a biomass of high-quality protein and oil. Depending on the chemical composition of the food waste, the oil extracted from BSFL can reach high levels of lauric acid, a natural antimicrobial compound. We hypothesised that feeding bakery waste provides adequate carbohydrate substrate to enhance the lauric acid synthesis of BSFL, thereby providing antibacterial activity against E. coli in vitro. In a 12-day long feeding trial, we reared BSFL either on a ground corn-based control substrate (n=6) or a substrate based on bread waste sourced from a local bakery in Hong Kong (n=6). We studied the growth performance, crude fat content, gas chromatography-based fatty acid profile, and agar well diffusion-based antibacterial activity of oil samples extracted from the larvae. The BSFL reared on the bakery waste had a higher average weight, similar crude fat content, and higher lauric acid content compared to the control larvae. In the antibacterial activity test, the bakery waste-based oil samples had bigger inhibition zones than the control oil samples. Our results indicate that locally sourced bread waste is a suitable substrate for farming BSFL, providing a sustainable alternative for waste management. The inclusion of the locally produced BSFL oil as a feed ingredient for the local livestock farming sector might be an avenue to achieve circular economy, however, the effects on animal health and productive performance warrant further in vivo experiments.