Efficient and green extraction of sturgeon skin gelatin using hydrated choline-glycine deep eutectic solvent

Abstract

ABSTRACT Conventional gelatin extraction from fish skin usually requires acid/alkali pretreatment and long hot-water extraction, which increases processing complexity and may affect gelatin quality. In this study, choline-based deep eutectic solvents (DESs), including choline–urea, choline–glycerol, and five choline–amino acid DESs, were screened for the direct extraction of gelatin from sturgeon skin without conventional acid/alkali pretreatment. Among the tested DESs, choline–glycine ([Ch][Gly]) showed the best extraction performance and was selected for further evaluation by controlling hydration level and extraction conditions. Under the optimized conditions using hydrated [Ch][Gly] containing 10 wt% water at 80°C for 2 h with a solid-to-liquid ratio of 1:100, the hydroxyproline-based extraction efficiency reached about 90%. Using ethanol as the antisolvent (DES-to-antisolvent ratio 1:5, standing at 4°C for 16 h), the hydroxyproline-based gelatin precipitation recovery exceeded 90%. The DES-extracted gelatin showed an amino acid composition typical of collagen-derived gelatin, met transparency standards, and exhibited a gel strength of 135 g Bloom. Overall, hydrated [Ch][Gly] provides a promising DES-based alternative for valorizing sturgeon skin by-products into gelatin, although solvent recovery and recyclability require further evaluation.