| Grey mullet(Mugil cephalus),a type of actinopterygii widely distributed in China's southeast coastal,especially in Zhejiang and Guangdong province,has been one of the important upper economic fish in China.Because grey mullet contains high content of protein,it would be of great importance in producing canned foods and special bioactive peptides.In our study,hydrolysis parameter of grey mullet protein was studied.In addition,in vitro antioxidant activities and functional characteristics of the hydrolysates were investigated.The hydrolysates were purified by gel chromatography and Reverse phase HPLC,obtaining some fractions which were analysed for their antioxidant activity.The purpose of this work was to provide some useful information for deep processing of grey mullet and improving its addes value.The main results obtained in this work are as follows:1.The assays for the nutritional composition of grey mullet's muscle indicated that it contains 18.12%protein and 9.14%fat;the fat content in gut of grey mullet(24.78%)is higher.The amino acid composition of its protein was of an excellent balance.The content of hydrophobic amino acids which had been reported to contribute greatly to the potency of antioxidant peptides,was found to be high.In addition,grey mullet is rich in unsaturated fatty acids,the content of bioactive polyunsaturated fatty acids(PUFA)is 34.3%.Ethyl acetate was found to be the most suitable solvent for defatting the mullet power with the highest degreasing rate(84.83%)and lowest protein loss(14.95%).The colour and flavour of defatted mulet meat were also improved,lipid peroxidation degree reduced.Furthmore,defatted the mullet power improved effectively the antioxidant activity of hydrolysates.2.Five commercial enzymes were screened for hydrolysis of the defatted grey mullet meat.The neutrase hydrolysate exhibited the best DPPH radical scavenging activities and the highest soluble protein content.The molecular weight of hydrolysates mostly was below 14kDa.On the basis of single factor experiments,the hydrolysis conditions were optimized by using response surface methodology(RSM):a ratio of enzyme to substrate 5.8:1(activity unit of enzyme/mg of substrate),pH 7.3,51 ?,3.5 h.The DPPH scavenging rate of hydrolysate obtained under the optimal conditions(HGM-2)was determined to be 60.19%±0.57,which was well matched with the value(59.16%)predicted by the RSM model.3.The in vitro antioxidant activity and function characteristics of hydrolysate obtained under the optimized hydrolysis conditions(HGM-2)were evaluated.The results showed that HGM-2 possessed marked DPPH radical scavenging activity(IC50 value,0.786 mg/mL),superoxide anion radical scavenging activity(IC50 value,1.294 mg/mL),hydroxyl radical scavenging activity(IC50 value,4.69 mg/mL),ferric reducing power(absorbance of 1.462 at 2.5 mg/mL),metal chelating activity(71.7%at 2.5 mg/mL),and anti-lipid peroxidation ability.In addition,HGM-2 exhibited better foaming capacity,solubility and emulsion properties at differert pH when compared to GM,however its emulsion stability performance was reduced.4.The research on the separation and purification of grey mullet hydrolysates showed that the molecular weight of most peptides in HGM-2 was below 10 kDa,and more than 50%of peptides was below 3 kDa.Then,HGM-2 was separated into four fractions(F1-F4)by Sephadex G-25.The results showed that fraction F4 had the strongest antioxidant activity.Fraction F4 was purified by RP-HPLC,obtaining six fractions(B1-B6).Fraction B4 was found to possess the highest DPPH scavenging ratio(80.42%±2.26 at 0.5 mg/mL).Analysis of fraction B4 by analytical RP-HPLC indicated it was separated into two fractions,namely B4-1 and B4-2,the molecular weight of which being 452.3434 and 339.2600 Da,respectively. |
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