Functional Properties, Antioxidative Activity And Ace-Inhibitory Peptides Preparation Of Silver Carp Protein

The abundant fish resource is the important sources of activated substance like protein or peptide. In China, as the large quantity freshwater farmed fish, silver carp have some defects like less of meat, much of sting and possessing fishy odour, so that it’s cheap in the supermarket. Because of its high yield and low price, silver carp is worth to be developed. It might dissolve the waste of high quality protein, and develop new kinds of functional food. For this purpose, the study carried on with silver carp protein (SCP) as raw material. The first step was about measuring elementary composition and amino acid composition. The second step was proteases screening and the discussing of hydrolysis, what aimed to get silver carp protein hydrolysates (SCPH) in different degree of hydrolysis (DH). After that, functional properties and antioxidative activity of SCPH were analyzed. Finally, optimize hydrolyzation conditions and SCPH prepared in this condition were obtained through response surface method. ACE inhibitory peptides from SCPH were prepare through ultrafiltration and Sephadex column, accompanied with high performance liquid chromatography (HPLC) and amino acid analysis. The main results were as follows:(1) Silver carp muscle was high in protein. The content of protein was determined as91.12%(drybasis) after degreaseing. Moreover, the SCP was high quality protein because of the result showed it rich in essential amino acid like Leucine, Lysine and Valine. In conclusion, SCP could be used for preparing protein enzyme hydrolysis. Alcalase was the most suitable for hydrolysis in the six kinds of proteases (Trypsin, Flavourzyme, Neutrase, Papain, Protamex, Alcalase), it was screened out to hydrolyze SCP. The hydrograph of SCPH hydrolyze showed: The DH increased with time, the hydrolysis rate decreased gradually. DH could be controlled by controlling reaction time, so the SCPH in different DH (4.5%,9.0%,13.5%,18.0%) could be obtained.(2) Compared with SCP, the functional properties of SCPH in different DH were better except oil holding capacity. Meanwhile, pH could affect the solubility and emulsifying property. Specific results were as follows: The solubility of SCP and SCPH can grow up with the increase of DH, the nitrogen solubility index (NSI) of SCPH in different DH improved during pH2.0-10.0, the NSI of SCPH in pH7.0enhanced77.7%of SCP. Water holding capacity increased as DH increasing, the water holding capacity of SCPH in DH18.0%improved37.7%to SCP. Whereas, oil holding capacity decrease as DH increasing. Emulsifying activity index (EAI) and Emulsion stability index(ESI) of SCP were between SCPH in high DH or low DH, the most outstanding emulsifying property of SCPH turns up in DH4.5%, the EAI of SCPH in DH4.5%was determined as58.8%higher than SCP in pH10.0. The foaming ability of SCP and SCPH could reach the best value in DH4.5%, which was20.4%higher than SCP. Good functional properties were the premise that the active peptide could be prepared for foods and food additives.(3) The antioxidative activity of SCPH was obviously better than SCP in four kinds of antioxidant systems. SCPH with DH13.5%exhibits better activities than those with other three DH value in DPPH radical scavenging (DPPH), superoxide radical scavenging and reducing power radical scavenging. The DPPH· inhibition ratio reached the maximal value of39.95%at1.60mg/ml, it’s7.1times of The DPPH· inhibition ratio of SCPH, The reducing power of SCPH in DH13.5% increased10.6times in8mg/ml, and the superoxide anion inhibition ratio of SCPH reaches the maximal value of25.45%, that was6.9times of SCP. SCPH at DH18%with the concentration of2.0mg/mL was found to display the maximal TEAC value of1.31μmol/L,2.4times developed by the TEAC value of SCP. The result showed, the antioxidant activates of SCPH greatly increased after hydrolysis from SCP.(4) On the basis of single factor experiment which taking DH as index, the optimize hydrolyzation conditions was performed by the response surface analysis: pH8.73, T54.7℃,[E]/[S]1.78%. The ACE inhibition ratio of the SCPH prepared with the optimal condition was76.34%. Response surface equation was as follows:Y=71.72+4.80A+5.81B+7.75C-6.31A2-9.78B2-9.12C2+4.68BC(5) The optimize Sephadex column separating situation was take Sephadex G-10as the padding and ultrapure water as the eluent. Three fractions could be collected:SCPH-1, SCPH-2and SCPH-3. The ACE IC50of SCPH-3was0.40mg/ml, that was the most excellent of the three fractions. The HPLC and amino acid analysis of SCPH-3showed the amount of nonpolar amino acid and aromatic amino acid were relatively high, that means SCPH-3has the potential to be development and to put into food and medicine production.