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.

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A novel cold-adapted and salt-tolerant α-amylase gene (amy175) from Antarctic sea ice bacterium Pseudoalteromonas sp. M175 was successfully cloned and expressed. The open reading frame (ORF) of amy175 had 1722 bp encoding a protein of 573 amino acids residues. Multiple alignments indicated Amy175 had seven highly conserved sequences and the putative catalytic triad (Asp244, Glu286, and Asp372). It was the first identified member of GH13_36 subfamily which contained QPDLN in the CSR V. The recombinant enzyme (Amy175) was purified to homogeneity with a molecular mass of about 62 kDa on SDS-PAGE. It had a mixed enzyme specificity of α-amylase and α-glucosidase. Amy175 displayed highest activity at pH 8.0 and 25°C and exhibited extreme salt-resistance with the maximum activity at 1 M NaCl. Amy175 was strongly stimulated by Mg2+, Ni2+, K+, 1 mM Ca2+, 1 mM Ba2+, 1 mM Pb2+, 1 mM sodium dodecyl sulphate (SDS), and 10% dimethyl sulfoxide (DMSO) but was significantly inhibited by Cu2+, Mn2+, Hg2+, 10 mM β-mercaptoethanol (β-ME), and 10% Tween 80. Amy175 demonstrated excellent resistance towards all the tested commercial detergents, and wash performance analysis displayed that the addition of Amy175 improved the stain removal efficiency. This study demonstrated that Amy175 would be proposed as a novel α-amylase source for industrial application in the future.

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