In-Depth Characterization of Black Soldier Fly Larvae Reared on Phenolic-Rich Agro-Industrial Substrates

Black soldier fly (Hermetia illucens) larvae (BSFL) represent a sustainable protein source for animal feed, efficiently converting organic waste into high-value biomass. This study aimed to valorize agricultural by-products (apple, potato, and red beetroot peels) as rearing substrates to obtain larvae enriched with bioactive phenolic compounds, while evaluating their nutritional, functional, and safety characteristics. Larvae were reared on diets with varying inclusion levels of each peel’s by-products. Proximate analysis showed that the substrate type and inclusion level significantly (p < 0.05) influenced larval composition, with consistently high protein and variable ash and fat contents. Colorimetric measurements indicated that phenolic-rich diets, particularly apple by-products, promoted cuticle darkening, reflecting the impact of dietary phenols on pigmentation. Functional properties were also modulated by the substrates: 2% potato peel yielded the highest phenolic content, while 20% apple peel produced the highest flavonoid concentration, both enhancing antioxidant capacity across CUPRAC-Cupric Ion Reducing Antioxidant Capacity, ABTS-2,2′-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid, and DPPH-1,1-diphenyl-2-picrylhydrazyl assays. Rheological analysis confirmed desirable non-Newtonian, shear-thinning behavior, suggesting improved technological quality. Mycotoxin testing revealed low Aflatoxin B1 but variable Zearalenone levels, highlighting the influence of substrate composition on toxin metabolism. Overall, agricultural by-products can produce enriched BSFL with enhanced nutritional and antioxidant properties, as long as the substrate choice and inclusion levels are carefully optimized for safety.