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Optimizing the physicochemical properties of microwave-cooked meat needs a better understanding of the mechanisms responsible for protein changes. This paper explored the causes of aggregation of the denatured fish protein in ready-to-eat food by determining the changes in sarcoplasmic and myofibril proteins, which includes the effects of different microwave power levels (300, 600, and 900 W) and heating times (0-60 s) on the aggregation kinetics and physiochemical properties. The determination of aggregation kinetics that accurately describes microwave cooking characteristics is crucial for the optimization of operating parameters, performance improvement of the cooked food system, and product quality. The aggregation rate and turbidity of proteins increased with increasing microwave power and time. A negative correlation was observed between the protein solubility and microwave power and time. Protein aggregation induced by microwave showed a reliable and reproducible characterization of particle size distributions. At longer microwave heating time or higher microwave power, these protein particles formed larger aggregates. [ABSTRACT FROM AUTHOR]

Abstract: The effects of chitosan coating enriched with lemon and thyme essential oils on the physicochemical, microbiological, and quality changes of grass carp fillets during 2 °C storage were determined during 16 days of storage. The pH, total volatile basic nitrogen, thiobarbituric acid reactive substances, color, texture, sensory quality, total viable count, psychrotrophic bacteria, pseudomonads, Shewanella putrefaciens, Enterobacteriaceae, and lactic acid bacteria counts were analyzed. The results indicated that chitosan coating (1.5%) incorporated with lemon or thyme essential oils (0.5%) maintained higher hardness and retarded the oxidation of lipid and protein. The most effective treatment was chitosan coating (1.5%) enriched with lemon and thyme essential oils (0.25 and 0.25%) together, which maintained the color and texture properties, and reduced the microorganisms counts. The results suggested that the synergized use of lemon and thyme essential oils increased the efficiency of chitosan coating, maintained fish fillets quality and extended its shelf life to 16 days. Practical applications: The commercial value of fresh fish fillets is lost in a few days. Many methods have been used to inhibit the spoilage caused by microorganisms, retard the degradation of protein, and extend the shelf life of fish fillets. As an alternative to chemical and synthetic preservatives, many studies are currently focused on using natural products to improve the quality of fish products. This study reports that chitosan coating incorporated with lemon and thyme essential oils together is a promising edible coating for use in commercial applications for prolonging the shelf life of fish fillets. [ABSTRACT FROM AUTHOR]

The physical properties and nanostructure of fish skin gelatin with and without whey protein isolate (WPI) were investigated. The addition of low concentrations of WPI (1 and 3%, w/v) into fish gelatin decreased the gel strength and textural properties. The addition of 5% WPI did not significantly influence textural properties but increased the melting and gelling temperatures of fish skin gelatin and improved the appearance of gelatin gels. X-ray diffraction indicated that a higher degree of crystallinity with an ordered structure or ordered structure snippets occurred with increasing WPI concentrations in line with the slight decrease in the loss factor (tan δ) with time sweeps. Fish gelatin had a spherical nanostructure, and a homogeneous nanostructure was observed in gelatin with 3% WPI. The addition of 5% WPI led to large aggregates in gelatin gels. The results indicated that whey protein could affect the nanostructure of fish skin gelatin gels and thus change their gelation properties and texture in food and pharmaceutical applications. [ABSTRACT FROM PUBLISHER]

BACKGROUND Collagen has a wide range of applications in food, biomedical and pharmaceutical products. RESULTS The collagens in grass carp ( Ctenopharyngodon idella) skin and swim bladder were extracted using acetic acid and pepsin. Higher yield of pepsin-soluble collagen ( PSC) was obtained from skin (178 g kg−1) than from swim bladder (114 g kg−1). Not surprisingly, yields of PSC from skin and swim bladder were also higher than those of acid-soluble collagen ( ASC) from the same organs (89 and 51 g kg−1). Sodium dodecyl sulfate polyacrylamide gel electrophoresis ( SDS-PAGE) profiles showed that ASC and PSC were type I collagens, with PSC containing a higher proportion of α components than ASC. Fourier transform infrared spectra revealed that ASC and PSC were very similar in their protein secondary structures. Scanning electron micrographs showed that the collagens had a spongy structure, with more pores being obtained in swim bladder than in skin collagens. The collagens showed high solubility in the acidic pH range. However, their solubility decreased in the presence of NaCl at concentrations above 20 g kg−1. CONCLUSION Collagens were successfully extracted from the skin and swim bladder of grass carp. These fish by-products could serve as an alternative source of collagens for a wide variety of applications in the food and nutraceutical industries. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Protein derived from grass carp ( Ctenopharyngodon idella ) skin was hydrolyzed by using Alcalase to obtain antioxidant peptides. Three antioxidant peptides were isolated from the protein hydrolysate and their amino acid sequences were determined to be Pro-Tyr-Ser-Phe-Lys (640.74 Da), Gly-Phe-Gly-Pro-Glu-Leu (618.89 Da) and Val-Gly-Gly-Arg-Pro (484.56 Da). The three purified peptides exhibited high scavenging activity on DPPH radical (IC 50 2.459, 3.634 and 6.063 mM, respectively), hydroxyl radical (IC 50 3.563, 2.606 and 4.241 mM, respectively) and ABTS radical (IC 50 0.281, 0.530 and 0.960 mM, respectively) in a dose-dependent manner. In addition, all peptides also effectively inhibited the peroxidation in linoleic acid model system. The high activity of purified peptides was attributed to the small sizes and the peculiar amino acid residues within their peptide sequences. Results indicated that the novel peptides isolated from grass carp skin possess potent antioxidant activities and might be used for food preservation and medicinal purposes. However, more detailed studies are required to explore their antioxidant abilities in vivo . [ABSTRACT FROM AUTHOR]