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Research on hydrolysis of soy protein by Asperigillus oryzae recombinant neutral protease(rNpI) and its hydrolysates' bitterness and antioxidant activity

To study the applications of recombinant neutral protease(rNpI)in Soy Protein Isolate(SPI)hydrolysis,the hydrolysis degree,bitterness and antioxidant activity of SPI hydrolysates(SPIH)were evaluated.After protease digestion,the DH and bitterness of SPIH were assessed.Further more,three different in vitro methods were used to evaluate the antioxidant activities of SPIH,including DPPH radical scavenging activity assay,reducing power assay and Oxygen Radical Absorbance Capacity(ORAC)assay.The results showed that rNpI had relative high efficiency in SPI hydrolysis,the hydrolysis degrees were 7.8%,11.5% and 16.0%,under the E/S ratio of 1 000 U/g,4 000 U/g and 8 000 U/g.For the bitterness evaluation,results showed that the bitterness of SPIH of rNpI was significantly lower than hydrolysates of Alcalase.The antioxidant activities of SPIH were determined by different assays,and the results showed that these SPIH of rNpI had high antioxidant activities.When the E/S ratio was 4 000 U/g,SPIH had high antioxidant activities,the reducing power of 1.0 mg/m L SPIH was 0.34,its DPPH free radical scavenging activity was 80% and the ORAC value was 455 μmol TE/g protein.Ultrafiltration membrane was used to separate SPIH components,and their antioxidant activities were analyzed.Results showed that SPIH-I(molecular weight above 10 ku)had the highest DPPH radical scavenging activity(82.7%),while SPIH-III(molecular weight below 3 ku)had the highest ORAC value(722 μmol TE/g protein).rNpI had high efficiency in SPI hydrolysis.Its SPIH had low bitterness and high antioxidant activity.All these results indicated that the rNpI had good application potentials in food production.