Choline-oxalic acid DES extracts molecular-weight-controlled collagen peptides from sturgeon skin

The demand for collagen peptides is rapidly growing across nutraceutical, cosmetic, and biomedical industries due to their diverse bioactivities. Traditional extraction methods often involve harsh chemicals or enzymes, leading to high costs, environmental concerns, and limited control over peptide molecular weight. Utilizing fish processing by-products, such as sturgeon skin, offers a sustainable source, but requires innovative, green extraction technologies. Deep eutectic solvents (DESs) present a promising alternative, offering tunable properties and reduced environmental impact, addressing the need for efficient and controlled peptide production from underutilized biomass.

Researchers developed and optimized a deep eutectic solvent (DES) system for extracting collagen peptides from sturgeon skin, which contains 78.28% protein and 63.47% collagen. They compared three choline-based organic-acid DESs, identifying choline-oxalic acid as the most effective. Optimized extraction conditions were 70 °C, a solid-to-liquid ratio of 1:80, and a reaction time of 2 hours. Peptide products were characterized using UV-Vis and FT-IR spectroscopy to confirm their collagen-derived nature, and molecular simulation was employed to elucidate the extraction mechanism. Isopropanol was used for downstream peptide recovery.

The choline-oxalic acid DES demonstrated superior extraction performance, achieving an extraction rate of 98.45% under optimized conditions. This system produced lower-molecular-weight peptide fractions compared to choline-lactic acid and choline-acetic acid DESs. Crucially, extraction time allowed for precise molecular-weight control: a 2-hour treatment primarily generated collagen polypeptides in the 1-10 kDa range, while extending the reaction to 4 hours predominantly yielded oligopeptides in the 0.5-1 kDa range. For recovery, isopropanol achieved a high precipitation efficiency of approximately 92% at an extract-to-solvent ratio of 1:6. UV-Vis analysis confirmed a characteristic collagen peptide absorption band near 230 nm, and FT-IR spectra showed typical amide I (~1630 cm-1) and amide III (~1240-1300 cm-1) bands. Molecular simulation provided mechanistic insights: > Oxalic acid competed for backbone hydrogen bonding, and chloride ions interacted with hydroxyproline residues (Hyp-Cl- radial distribution peak at 0.328 nm), collectively promoting collagen swelling, triple-helix loosening, and controlled depolymerization.