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In order to identify biomarkers of lipid deterioration in grass carp (Ctenopharyngodon idella) muscle during cold storage, the lipid profile change of the grass carp muscle stored at 4 ℃ for different periods (3, 6, and 9 d) was investigated by UPLC-Q Exactive HF-X. Multivariate statistical analysis and one-way ANOVA were used to screen the differential lipids during the cold storage, and then to enrich the metabolic pathways involved in the differential lipids through the KEGG database. The results showed that the pH in grass carp muscle decreased gradually, while the thiobarbituric acid reactive substance, total free fatty acid content, and volatile base total nitrogen increased gradually, reaching 0.82 µg/kg, 168.22 µg/10 g and 23.63 mg/100 g, respectively, on the 9 d of cold storage. A total of 1265 lipid molecules belonging to 5 categories and 35 subclasses were identified in the chilled grass carp muscle. Glycerol phospholipids (GP) and glycerol esters (GL) were the main components of lipids in grass carp muscle. There was no significant difference in lipid profile between grass carp muscle refrigerated for 3~6 days (P>0.05), but there were significant changes in lipid composition when refrigerated for 9 days. Fatty acyl (FA) and sphingolipids (SP) were the major different lipids in the early stage of refrigeration (3~6 days), and GP was the main lipids with significant changes in the late stage of refrigeration (6~9 days). A total of 20 different lipid molecules were screened from multivariate statistical difference analysis, and they were mainly glycerol ester and glycerol phospholipid, among which PE (16:1e/22:6) showed significant differences (P

To explore the different extraction methods and traditional refining process of squid visceral fish oil and its quality changes, the deep-sea squid viscera from the Equator, Argentina, and the North Pacific were used as raw materials in this study. Firstly, different organic reagent extraction methods and compound methods were used to extract fish oil from Argentine squid viscera. The method with the highest oil yield and best quality was selected for refining three types of crude squid visceral oil. The sensory morphology, physicochemical indicators, fatty acid composition and volatile flavor compounds of three types of crude and refined squid visceral oils were analyzed. The results showed that the oil extraction method of the No.6 solvent assisted freeze-thaw was the best, with a yield of 12.90%, and the physical and chemical indexes of squid visceral oil after refining were significantly improved. The peroxide value, insoluble impurities, color difference value, acid value, moisture and volatiles, and anisidine values were significantly reduced (P

Low salt dry-curing (LSD), as a healthier pre-treatment for the preservation of fishery products, is a potential technique substitute for excessively salty curing. The regulatory effects of 2 % and 3 % LSD on the quality evolution through an intrinsic correlation between microbiota succession and flavour precursors of refrigerated grass carp fillets were investigated in this study. The results showed that the LSD pre-treatment was effective in promoting proteolysis, free amino acid and fatty acid metabolism with the microbiota succession and quality evolution. Compared with unpre-treated samples, the 3 % LSD pre-treatment effectively extended the shelf life by 10 days within the acceptable quality attributes. Not only did the LSD pre-treatment lead to catalytic microbiota succession and inhibitive spoilage substance production but it also improved the flavour precursors, which are taste-active amino acids and polyunsaturated fatty acids (PUFAs). Moreover, considerable correlations between quality attributes, taste-active amino acids, PUFAs and microbiota were obtained.

Low-temperature preservation is an important storage method for grass carp. Although low temperature can not completely inhibit the activity of enzymes in fish, it can significantly decrease the activity of enzymes and inhibit the growth and reproduction of microorganisms in fish, thereby prolonging the shelf life of fish. When the storage temperature is relatively low, the quality and taste of grass carp are not easily lost, thereby delaying its spoilage. In response to the national development plan of the cold chain circulation in the "14th Five-Year Plan", it is necessary to delay the shelf life of grass carp and reduce the quality change of grass carp through effective preservation technology. This paper summarizes the effects of low-temperature preservation of grass carp on microbial and enzyme activities and reviews the principles and methods of several common low-temperature preservation methods of grass carp (cooling preservation, ice temperature preservation, micro-freezing preservation, frozen preservation, modified low-temperature preservation, compound preservation and new preservation technology), and their application in grass carp preservation, preservation effect. This study aims to provide a reference for low-temperature grass carp preservation and find a more practical and economical way of grass carp preservation.

Structured lipids are a new class of lipids recombined by combining fatty acids with special physiological functions at specific positions on the triglyceride backbone. Enzymatic catalyzed synthesis of structured lipids has attracted attention due to its mild reaction conditions, low energy consumption, simple separation and purification process, and the ability to synthesize functional fatty acids at specific acyl positions. However, with the increase of use times of lipases in industry, the catalytic activity of lipase decreases significantly, resulting in a decrease in the production of target structural lipids. This paper reviews the structure change, activity change and decreasing catalytic activity mechanisms of lipase-catalyzed synthesis of structured lipids in China and outside China in recent years. It found that the decrease of enzyme activity is mainly due to the destruction of the catalytic active center by strong or weak intermolecular interaction. This study provides a reference for solving the technical bottleneck of reducing lipase activity in the enzymatic synthesis of structured lipids.