Valorization of seasonal agri-food leftovers through insects

Most of the leftovers from agricultural productions and industrial processing of vegetables are currently discarded as waste, augmenting production costs and environmental impacts. Black soldier flies (BSF) are non-pest insects that can grow on various types of organic materials. The larvae initially act as fast and efficient bioconverters, before being further valorized as biomass rich in proteins, fats and chitin. The aim of the present study was to exploit the potential of BSF prepupae reared on vegetable leftovers with high seasonality, and to obtain compounds with high added value and further industrial and agronomic uses such as food/feed, soil improver or fuel. The optimization of BSF rearing substrates based on different leftovers combinations was performed through a Mixture Design approach. Initially, a database was built detailing the availability, seasonality and nutrient composition of the vegetable by-products. According to the seasonal availability of the agri-food leftovers, three main groups were identified: annual, summer and autumn mixtures, in order to promote the exploitation of the highest quantity of leftovers. This approach allowed the obtainment of statistically reliable correlations (R2 > 0.75) between the employed leftovers and the content of lipid and nitrogen compounds (protein and chitin) of the BSF prepupae. In particular, a mixture of vegetable leftovers available in autumn that included legume (25 wt%), cereal (20 wt%) and vegetable (25 wt%) wastes proved to be the best combination in terms of insect growth (-25% development time compared to the control group) and nutritional composition. The chemical composition of the insect biomass allowed the identification of potential applications with high added value, such as food ingredients (protein and fats) or nutraceuticals (chitin). The identification of the optimal parameters to ensure the greatest possible efficiency would promote the scale-up of BSF rearing to an industrial level.