Chitin from Hermetia illucens exuviae: A sustainable biopolymer yielding composition-defined functional oligomers...

In this study, we demonstrate that larval and pupal exuviae from the black soldier fly (Hermetia illucens) provide a high-purity, structurally defined source of α-chitin suitable for conversion to bioactive chitooligosaccharides (COS). Life-stage-resolved extraction yielded α-chitin of 98.8 % purity (dry basis) with source-dependent differences. Pupal exuviae gave higher chitin yield (23.4 ± 1.8 % vs 19.2 ± 1.3 %), greater crystallinity (Segal CrI 80.4 ± 1.7 % vs 76.2 ± 1.3 %), and higher thermal stability, whereas larval material retained a more porous and chemically accessible surface. After structural characterization, the streams were combined to generate a standardized feedstock for COS production. Heterogeneous deacetylation produced chitosan with a degree of deacetylation (DDA) of 90-92 % and controlled nitrous acid-mediated depolymerization generated water-soluble COS with a narrow low-DP distribution (DP 2-6, predominantly DP 2-4). COS exhibited dose-dependent antioxidant activity, achieving 0.83-0.90 of the l-ascorbic acid response at 1 mg mL^-1 across DPPH, ABTS, and H₂O₂ assays, with ferric reducing power of 4.30 mmol Fe²⁺ L^-1. In HL-60 cells, COS were non-cytotoxic up to 200 μg mL^-1, suppressed H₂O₂-induced reactive oxygen species by ~99 %, and lowered protein carbonyls and malondialdehyde toward near-baseline levels. Together, the findings establish a structure to function pathway linking exuviae source, chitin architecture and COS composition to intracellular antioxidant protection. This circular valorization of exuviae supports the development of composition-defined chitin-based polymers for applications in antioxidant surface coatings, drug delivery interfaces, and wound care hydrogels.