Physicochemical properties of zinc chelating purified components by different method of tilapia scraps protein hydrolysate

Tilapia scraps were hydrolyzed by neutral protease and flavourzyme, and the hydrolysate was fractionated through ultrafiltration membranes with a range of molecular weight cutoffs(MWCO)of 10 ku, to yield the fraction EH10K with MW distribution<10 ku.The zinc chelating salts(CH-0)was produced by EH10K chelating with ZnSO₄.CH-Ⅰ and CH-Ⅱ were the purified components from CH-0 by using 95% ethanol and dialysis(FW=500 u)respectively.The formation of Zn²⁺ chelating salts of hydrolysate was confirmed by the UV-VIS spectra.The physicochemical properties of CH-0, CH-Ⅰ and CH-Ⅱ were analysed and their free radical scavenging activities were evaluated also.The results showed that CH-0 contained 71.86% of protein(on dry basis), 16.08% of Zn, CH-Ⅰ and CH-Ⅱ were 75.94% and 14.49%, 78.83% and 12.20% respectively.The gel chromatography results showed that CH-Ⅰand CH-Ⅱ had three same main absorption peaks compared to CH-0 but had little impurity peaks.The contents of Asp, Glu, Gly, Lys, Arg and His in CH-Ⅱ were high than those of CH-Ⅰ, and all were high than those of CH-0.The content of essential amino acid and branched chain amino acid in CH-Ⅱ were high than that in CH-Ⅰ.CH-0, CH-Ⅰ and CH-Ⅱ showed evident radical scavenging activity in a dose-dependent manner with the IC₅₀ values for hydroxyl radical and 1, 1-diphenyl-2-pycrylhydrazyl(DPPH)radical being 9.08 and 6.07, 8.27 and 3.76, 6.90 and 3.27 mg/mL respectively.The superoxide radical scavenging activity of EH10K was 69.27% at 10.00 mg/mL, CH-0, CH-Ⅰ and CH-Ⅱ showed no effect on superoxide radical scavenging but to promote the oxidation.