Intensifying Biovalorization of Squid Pen Waste to Produce β-Chitin and Bioactive Peptides through Co-Lactic Acid Fermentation and Enzymatic Post-Treatment

This study demonstrates the effective biovalorization of squid pen waste (SPW) to produce high-purity β-chitin and other valuable biomolecules following the biorefinery concept. Symbiotic colactic acid fermentation (Co-LAF) cultivated in mature coconut water was used to deproteinize SPW. The optimal conditions were 4% sugar content, 10% inoculum, and 12.5-fold liquid-to-solid ratio. This process not only deproteinized SPW into crude chitin but also provided a lactic acid yield of 20.26 ± 0.25 g/L and a soluble protein yield of 105 ± 3.6 mg/g-SPW with antioxidant activity toward the DPPH radical (54.2 ± 2.3 μmol-Trolox equivalent (TE)/g-protein). Crude chitin was post-treated using alkaline protease (10 U/mg-crude chitin), resulting in the maximum deproteinization of 98.1 ± 1.1%, a β-chitin yield of 28.2 ± 1.3%, and a soluble protein yield of 374.85 ± 2.1 mg/g-crude chitin with antioxidant activity (25.01 ± 0.28 μmol-TE/g-protein). The final β-chitin retained crystallinity (75.7%) and ∼100% degree of acetylation. These results suggest that Co-LAF and enzymatic post-treatment can effectively valorize SPW, potentially making a significant contribution to sustainable waste valorization.