Preparation, Purification, Characterization Of Antioxidant Peptides Derived From Silver Carp Protein And Functional Properties Of Their Glycation Products

In China, silver carp with fast growing and large production is one of the main freshwater fish species. However it is a low market-value resource because of its muddy flavor and many fish bones. Nowerday, the development of silver carp products became to be most popular research area for aquatic researchers, but the researches are still in the early stages. The research objective of this study was to utilize silver carp fish protein and to impove the additional value for this freshwater fish. Antioxidant peptides from silver carp protein by enzymes hydrolysation were prepared. And functional properties and antioxidant acitivities of glycosylated hydrolysates and water-soluble proteins from silver carp were studied.Five common enzymes were used for hydrolysation at the same enzyme activity. The hydrolysis degree and antioxidant activities of hydrolysates were determined. The relativity between the degree of hydrolysis and antioxidant activities were also dicussed. The results showed that the DPPH radical scavenging capacity and reducing power of pepsin hydrolysates were higher than other hydrolysates, and the values were61%and1.6, respectively. There were marked relativity between the degree of hydrolysis and metal-chelating activity (p<0.05)Silver carp peptides were separated by ultrafiltration, gel filtration and reverse phrase high pressure liquid chromatogram. The DPPH radical scavenging capacity, hydroxyl radical scavenging capacity, iron chelating, reducing power and oxygen radical absorbance capacity of fractions were determined. Ten peptides from silver carp myosin and actin were identified by LC-MS/MS, and their antioxidant activities were determined using synthetic peptides. Two pentapeptides (Tyr-Thr-Ile-Gln-Tyr and Asn-Trp-Asp-Asp-Met) showed higher antioxidant activity, and the ORAC values of them were higher than catechin.The Maillard reaction products (MRPs) were prepared at different temperatures and ratios between silver carp protein hydrolysates (SPH) and glucose by Maillard reaction in powdered state, respectively. MRPs possessed a strong2,2-diphenyl-l-picrylhydrazyl (DPPH) radical scavenging activity and reducing power (p<0.05). The hydrolysate and glucose heated with the ratio of2:1at60℃showed high browning intensity and good antioxidant properties (p<0.05). According to the correlation coefficients of variables included in the hydrolysate-glucose system, good correlations were observed among the antioxidant activities and the absorbance at294nm. The results suggested that Maillard reaction has a good potential to improve the antioxidant activity of SPH.Water-soluble proteins (WSP) from silver carp muscle are currently underutilized in China and are discarded into waste streams in surimi processing. In order to utilize WSP resources efficiently, this work investigated the effect of three processing conditions on the physicochemical properties and fuctional properties such as solubility, heat stability, emulsifying activity and foamability of water-soluble proteins from silver carp. The results showed that silver carp water-soluble proteins would suffer huge denaturation and aggregation from40to55℃. Most of silver carp water-soluble proteins precipitated at55℃. Lyophilization could increase surface hydrophobicity of water-soluble proteins, but decrease its solubility and sulfhydryl groups. The functional properties of WSP were greatly affected by pH value, the lowest solubility was observed at pH4.0-5.0.WSP denature easily during thermal processing, leading to the reduction of functional properties. Five different kinds of carbohydrates (i.e., xylose, glucose, galactose, oligoisomaltose, and dextran-10) were used to conjugate with WSP by Maillard reaction. Results suggested that the use of the Maillard reaction improved the solubility, heat stability, and emulsifying properties of WSP.With the increase of molecular weight (MW) of the sugars, the solubility, emulsifying properties, and total sulfhydryl (SH) group of WSP increased, while the surface hydrophobicity decreased. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the five Maillard reaction products (MRPs) showed that xylose reacted easily with WSP than the other four kinds of sugar did. Dextran-10conjugated to WSP could efficiently improve the functional properties of WSP during heat processing.