Functional biofortification of black soldier fly (Hermetia illucens) larvae through Spirulina and flaxseed-enriched substrates for enhanced nutritional and oxidative stability

Abstract Black soldier fly larvae (BSFL) efficiently convert organic waste into nutrient-rich biomass, but their nutritional value depends strongly on substrate composition. This study evaluated whether supplementing fruit- and vegetable-based substrates with Spirulina (5% DM), flaxseed meal (7% DM), or their combination could enhance BSFL growth performance and biochemical quality. Four diets were tested: an unsupplemented control (T 0 ), Spirulina (T 1 ), flaxseed (T 2 ), and Spirulina + flaxseed (T 3 ). Larval performance improved progressively with enrichment. Final dry mass increased from 268 ± 2.9 g (T 0 ) to 311 ± 3.4 g (T 3 ), while waste-reduction rate rose from 60.6 to 66.6% and bioconversion efficiency from 18.1 to 20.7% ( ). Crude protein increased from 43.97 ± 0.15% DM in T 0 to 47.37 ± 0.09% DM in T 3 , accompanied by a reduction in crude lipid from 25.43 to 22.20%. Fatty-acid profiles shifted markedly: lauric acid decreased (40.0 to 33.4%), α -linolenic acid rose from 1.50% to 5.70%, and total unsaturated fatty acids increased from 29.1 to 37.3% ( ). Pigment and antioxidant levels were enhanced in enriched groups, with carotenoids, TPC, DPPH, and FRAP all showing significant increases. Larval oil oxidative stability improved accordingly, as peroxide value decreased from 4.56 to 2.63 meq O 2 ⋅ kg −1 and TOTOX from 17.5 to 10.4. Mineral concentrations also increased, particularly Ca, P, Fe and Zn, reaching maximum values in T 3 . Microbiological counts remained within safe limits and were lower in supplemented treatments. Overall, Spirulina and flaxseed enrichment produced BSFL with superior nutritional composition, improved fatty-acid balance, stronger antioxidant capacity, and more stable lipids, indicating strong potential for application in sustainable aquafeed formulations.