Mechanical Processing of Hermetia illucens Larvae and Bombyx mori Pupae Produces Oils with Antimicrobial Activity

SIMPLE SUMMARY: Insect rearing and processing are widely studied to provide solutions to the increasing demand for proteins caused by a growing human population. It has been demonstrated that insect meal can be introduced into the feed ratio of livestock and its exploitation can limit the environmental impact of animal husbandry. When their ecological footprint is analyzed, insects are considered “biorefineries” able to generate multiple economic outputs for the food industry. Fat and antimicrobial peptides contained in the insect oil can represent important resources to treat animal diseases, e.g., allowing to reduce antibiotic overuse. In this paper we focused on two insects exploitable both for protein and oil production: the black soldier fly larvae (BSFL) and the domestic silkworm. As the diet regimen remarkably affects the fat composition of the insects, both BSFL and silkworm larvae were reared on plant-based diets. Silkworms were fed mulberry leaves, while BSFL were reared on a diet composed of leftover vegetables and fruit, in the perspective of their bioconversion and valorization. The best technique to maximize the oil extraction yield was defined for BSFL and applied to the silkworm pupae. An antimicrobial activity of the oil against some bacterial species was demonstrated in both insects and compared. ABSTRACT: The aim of this work was to develop processing methods that safeguard the quality and antimicrobial properties of H. illucens and B. mori oils. We adopted a vegetable diet for both insects: leftover vegetables and fruit for H. illucens and mulberry leaves for B. mori. First, alternative techniques to obtain a good oil extraction yield from the dried biomass of H. illucens larvae were tested. Traditional pressing resulted to be the best system to maximize the oil yield and it was successfully applied to B. mori pupae. Oil quality resulted comparable to that obtained with other extraction methods described in the literature. In the case of B. mori pupae, different treatments and preservation periods were investigated to evaluate their influence on the oil composition and quality. Interestingly, agar diffusion assays demonstrated the sensitivity of Gram-positive Bacillus subtilis and Staphylococcus aureus to H. illucens and B. mori derived oils, whereas the growth of Gram-negative Pseudomonas aeruginosa and Escherichia coli was not affected. This study confirms that fat and other active compounds of the oil extracted by hot pressing could represent effective antimicrobials against bacteria, a relevant result if we consider that they are by-products of the protein extraction process in the feed industry.