Selective Extraction of Collagen Peptides with High Purity from Cod Skins by Deep Eutectic Solvents

This paper reports an efficient and eco-friendly extraction and separation method of collagen peptides from cod skins based on a nascent class of green and sustainable deep eutectic solvents (DESs). Six kinds of DESs were designed and synthesized. On the basis of the principle of high extraction efficiency and high purity, choline chloride–oxalic acid was selected as the optimal extraction solvent. In the process of collagen peptides purification, ethanol was the optimal precipitation reagent due to the low toxicity. Afterward, single factor experiments proved that the extraction efficiency and purity of collagen peptides were influenced by the molar ratios of choline chloride–oxalic acid, extraction temperature, reaction time and solvent-to-solid ratio. Under the optimal conditions, higher and lower molecular weight collagen peptides were obtained. The values of their respective extraction efficiencies were up to 91.57% and 96.01% and the corresponding purity was up to 93.14% and 100%, respectively. Finally, UV–vis and Fourier transform infrared spectrometry were utilized to study the extraction mechanism. The results from this study demonstrate that choline chloride–oxalic acid is a green, efficient and promising solvent for extracting collagen peptides from cod skins.