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Oysters, favored as a delicious seafood by people worldwide, contain various nutritional components, especially proteins. In this work, the immunoregulatory peptides were isolated and purified from oyster enzymatic hydrolysate by utilizing anion exchange chromatography and RP-HPLC, and were identified via LC-MS/MS. A proliferation assay, a phagocytosis assay, and TNF-a production, NO production and IL-6 production assays were used to examine the immunoregulatory effects of the two identified peptides.The results indicate that the peptides, DNSIAMESMK (P1) and LLQLGSGR (P2), increased the proliferation rate of macrophages, TNF-a and NO production, IL-6 production, and the phagocytosis ability, but to different degrees; P2, with more hydrophobic amino acids, was more potent than P1. This suggested that these peptides might be potential candidates for developing immunoregulatory functional foods and nutraceuticals.

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Previous studies have found that UV-C irradiation activated endogenous acid protease (EAP) in shrimp heads. Aiming at understanding the effect of UV-C irradiation on the activation of EAP and improving the utilisation of EAP, the effect of UV-C irradiation on the enzymatic properties and conformation of EAP was investigated. The enzymatic properties of EAP were unaltered after UV-C irradiation, and the optimum pH, temperature, and NaCl concentration were 3, 60°C, and 0.5 mol/L, respectively. Ca 2+ and Mg 2+ activated the enzyme. The molecular weight of the purified endogenous acid protease (P-EAP) was 32 kDa. UV-Vis, FTIR, circular dichroism, and fluorescence spectroscopy indicated that the increase in enzyme activity by UV-C irradiation was related to an increase in tryptophan and hydrogen bonding, implying that it may be the change in the spatial structure of the protein that caused the activation of the enzyme. Results revealed that UV-C irradiation can be used to activate proteases and provide a reference for enhancing the enzymatic activity of other enzymes from shrimp heads.

Pinctada martensii muscle proteins were separated into water-soluble, salt-soluble and insoluble protein fractions. The salt-soluble protein fraction was the most abundant, comprising approximately 66.3% of the protein, followed by the water-soluble and insoluble protein fractions in decreasing order. sodium dodecyl sulphate polyacrylamide gel electrophoresis profiles showed that 35-and 97-kDa peptides represented the highest proportions of the water-soluble and salt-soluble protein fractions, respectively. The three protein fractions contained high levels of flavourful amino acids (Glu, Asp, Ala and Lys), with the water-soluble protein fraction having the highest level (47.1%). The size exclusion chromatography profiles of the watersoluble and salt-soluble protein pancreatin hydrolysate demonstrated no significant differences in the molecular weight distributions in the >20 000, 5000-10 000 and 2000-5000 Da fractions, while those of the insoluble protein pancreatin hydrolysate were different. In conclusion, the results provided some basic information that would contribute to the utilisation of these protein fractions.Keywords Pancreatin hydrolysate, Pinctada martensii, salt-soluble protein, sodium dodecyl sulphate polyacrylamide gel electrophoresis, water-soluble protein.