The increase of waste, due to the rise of the world population, renders the use of the black soldier fly (BSF; Hermetia illucens) as agri-food leftover biotransformer very attractive. Indeed, feeding on these substrates, BSF is capable of transforming them into valuable fat, proteins, and chitin. The present study is aimed at evaluating different approaches to the killing of the prepupae in order to assess which is associated with the lowest production of artefacts, notably free fatty acids. Folch extraction method, via an Ultra-Turrax homogeniser, was selected to isolate and analyse prepupal fat. The same method was also applied for a direct grinding method to kill black soldier fly prepupae. The integrity of fat originated from this direct grinding approach to the killing was compared in terms of fatty acid profile with the samples obtained with two other killing procedures, i.e. freezing and blanching. Direct grinding proved to be a better preservative of fat integrity in terms of lowest amount of free fatty acids (about 2.5%) in comparison with freezing (about 15%), but also with blanching (about 10%). Furthermore, the direct grinding is a killing strategy that reduces energetic demand and process time and helps lower analytical costs.

BACKGROUND The total amount of bio‐waste produced annually in the EU by the food and beverage chains is estimated at 37 billion kg. The use of insects for the valorization of by‐products from these value chains may represent a sustainable solution. This study aimed to investigate the by‐products obtained from different food chains and used for the rearing of black soldier fly (BSF) prepupae, and to evaluate the content and profile of the lipid extracted from the prepupae and outline its possible applications. The substrates used in this experiment were: (i) industrial by‐products (brewery spent grains, cows’ milk whey, grape stalks, and tomato peels and seeds) and (ii) by‐products from retailers (bread dough, fish scraps, and spent coffee ground). Fat extracted from prepupae using an adjusted Folch method was used for total lipid content and fatty acid profile. RESULTS The best larval performances were obtained from beer (0.22 gweight per prepupa), tomato (0.19 gweight per prepupa), and cheese (0.14 gweight per prepupa) food‐chain by‐products. The extremely different compositions of the substrates were reflected in the differentiated lipid profile of the BSF prepupae and in the range of ratios between unsaturated and saturated fatty acids, which varied from 0.37 for cows’ milk whey to 1.34 for tomato peels and seeds. CONCLUSION The lipids, proteins, and chitin extracted from prepupae are high‐value bio‐based products that could be used in the feed / food industry or for the development of innovative biomaterials, such as biodiesel. These results suggest that food‐chain by‐products are the best candidates for insect‐bioconversion purposes. © 2020 Society of Chemical Industry

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