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Objective: Bioactive peptides with an inhibitory effect on dipeptidyl peptidase-IV (DPP-IV) were prepared from pearl mussel muscle. Methods: Two-step enzymatic hydrolysis was adopted and enzymatic hydrolysis conditions were optimized. Fractions with in vitro DPP-IV inhibitory activity were concentrated by ultrafiltration, and purified by SuperdexTM peptide 10/300 GL gel filtration column chromatography and reverse phase-high performance liquid chromatography (RP-HPLC). DPP-IV inhibitory peptides were purified from the enzymatic hydrolysate and their amino acid sequences were identified by liquid chromatography-tandem mass spectrometry. Results: Both neutral protease and alkaline protease could effectively hydrolyze pearl mussel muscle. After concentration using a 3 kDa cut-off ultrafiltration membrane, the DPP-IV inhibition rate of the enzymatic hydrolysate reached 67.4%. After separation by gel filtration column and purification by RP-HPLC, 6 active peptides were obtained, whose sequences were FNAPAM, FIPNY, IYNPPTPF, LAMPYP, FFVVMP and LAGMP, respectively. Furthermore, the interactions between these peptides and DPP-IV were analyzed by molecular docking. Conclusion: Our present study provides a theoretical reference for the effective utilization of fish processing byproducts as raw materials for functional food production.

This study investigated the effects of different concentrations (0.1%, 0.3%, 0.5%, 0.8% and 1.0% by mass relative to shrimp meat) of hyaluronic acid (HA) on the gel and physicochemical properties of surimi made from Litopenaeus vannamei. The results showed that adding a certain amount of HA improved the textural characteristics, gel strength, brightness and whiteness of shrimp surimi gel, promoted the transformation of free and immobilized water into bound water, and increased the water-binding characteristics and water-holding capacity. Rheological analysis showed that addition of a certain amount of HA improved the storage moduli of shrimp surimi, but low concentrations of HA could have adverse effects on the apparent viscosity. Chemical force analysis showed that ionic bonds first decreased and then increased, while hydrogen bonds exhibited the opposite trend with the addition of HA. An appropriate amount of HA could improve hydrophobic interactions but the formation of disulfide bonds from sulfhydryl oxidation was also inhibited by HA. Moreover, HA could interact with shrimp surimi proteins, inhibit the formation of protein polymers, change the conformation of proteins, and promote the transformation of the secondary structure of proteins from α-helix to β-structure and random coil. The microstructure of shrimp surimi gel was improved by adding an appropriate amount of HA, becoming more uniform and denser. Among all samples with different levels of HA, shrimp surimi gel with the addition of 0.8% HA had the highest hardness, gumminess, chewiness, gel strength, storage modulus and the densest microstructure, and its water-holding capacity significantly improved when compared with that of the control group (P < 0.05). However, the textural characteristics, gel strength, water-holding capacity and storage modulus of shrimp surimi gel with 0.1% HA were lower than those of the control group, and the microstructure was looser.

In order to investigate the quality changes of Crassostrea gigas during cold storage at 0 and 4 ℃, the changes in the visual appearance of different tissues (adductor muscle, mantle, gills and visceral mass) during cold storage were observed. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to analyze the changes of total proteins in oyster tissues. The degradation of myosin heavy chain (MHC), actin, paramyosin (PM) and tropomyosin (TM) in adductor muscle was identified by Western blotting. The activity of endogenous serine protease and cathepsin B was measured using fluorescent spectrum. The quality change of adductor muscle during cold storage was evaluated in terms of its pH, K value and texture properties. The results showed that during cold storage, the texture of adductor muscle changed from tight to soft. Western blotting showed that MHC in adductor muscle began to degrade on days 3 and 1 for 0 and 4 ℃, respectively, indicating that low temperature is beneficial to reduce the rate of protein hydrolysis. However, PM, TM and actin did not change obviously. The activity of serine protease and cathepsin B in adductor muscle first rose and then decreased during cold storage. After cold storage for 11 days, the pH decreased from an initial value of 6.79 to 6.52 and 5.84 for 0 and 4 ℃, respectively. The K value exceeded the second degree of freshness range (40%) on days 9 and 5 for 0 and 4 ℃, respectively. The hardness and chewiness of adductor muscle peaked on day 1 and then decreased gradually, and elasticity decreased with storage time. The degradation of MHC in adductor muscle was most remarkable and closely related to the deterioration of oyster quality during cold storage. This study can provide a theoretical reference for oyster cold storage and preservation.

In order to improve the utilization of Haliotis discus hannai mantle, collagen purified from it was hydrolyzed by trypsin and pepsin to prepare angiotensin I-converting enzyme (ACE) inhibitory peptides. The hydrolysate was purified by sequential ultrafiltration, SuperdexTM peptide 10/300 GL gel filtration chromatography and high performance liquid chromatography (HPLC). Three ACE inhibitory peptides, SGEVGQ, QRGPAGAQGPQ and GPPGPAGAR, were obtained . Among them, GPPGPAGAR had the highest ACE inhibitory activity with a half maximal inhibitory concentration (IC50) of 177.1 μmol/L. Molecular docking results showed that GPPGPAGAR mainly acted on the S1 active pocket of ACE and the inhibitory mode was similar to that of lisinopril. GPPGPAGAR still showed high ACE inhibitory activity after simulated gastrointestinal digestion. This study will provide a reference for deep processing of abalone mantle and the development of ACE inhibitory peptides.

This study was conducted in order to explore the changes in muscle quality of sea bass during cold storage. The physiological and biochemical changes of fish meat during storage at 4 ℃ were evaluated in terms of its pH, total bacterial count, total volatile basic nitrogen (TVB-N) content, K value and texture. Morphological changes of muscle were evaluated by Masson staining and immuno-histochemical staining. The enzymatic activity of matrix metalloproteinases (MMPs) was determined by hydrolyzing fluorescent peptide substrates. The results showed that the pH of sea bass muscle decreased firstly and then increased during cold storage. The total bacterial count, TVB-N content and K value increased with storage time, and exceeded the threshold on the 8th day. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that there was little change in the protein composition in sea bass muscle after 6 days of storage, while the myosin heavy chain was significantly degraded on the 8th day. Masson staining and immuno-histochemical staining of type I collagen showed that the endomysium was gradually degraded during storage. On the 12th day, an evident gap between type I collagen and muscle fibers was observed. The activity of MMPs increased significantly with storage time while the hardness of fish muscle decreased gradually. Hence, the softening of fish muscle during cold storage is closely related to collagen decomposition, and type I collagen degradation by MMPs may be the major reason for muscle softening after fish death.

Aquatic products are favored by consumers because of their delicious 1381- and rich nutrition, which belong to the allergic food recognized by the Food and Agriculture Organization of the United Nations and the World Health Organization, and they may be contaminated by foreign allergens during processing, transportation and storage, resulting in increasingly serious food safety problems caused by aquatic food allergy, which seriously restricts the development of the aquatic industry. Therefore, identifying the allergens in aquatic food and using appropriate detection techniques to detect and monitor them are conducive to preventing the occurrence of aquatic food allergies and diseases. In this paper, the main allergens in aquatic food, as well as the research progress of nucleic acid detection technology based on gene level, immunoassay technology based on protein level and mass spectrometry detection technology were summarized, which provided a theoretical basis for enriching the comprehensive understanding of aquatic allergens and their detection methods. [ABSTRACT FROM AUTHOR]