Study On Quality And Antioxidant Activity Of Raw Sauce From Rice Dregs

Rice dreg protein(RDP),the major byproduct with rich protein produced from rice starch syrup companies,is a kind of high quality vegetable protein resource.In our previous work,rice dreg was applied as the main brewing raw material to fermented sauce for many years.Preliminary results had shown that RDP sauce fermented by single-strain had certain antioxidant activity,and fermentation by multi-strain improved the utilization ratio of RDP in the sauce.In the paper,the quality and antioxidant activity of RDP sauce by multi-strain were investigated on the basis of previous studies to clarify the ways of strain combination for RDP sauce fermentation.The main contents and results are as follows:The basic physical and chemical components,sensory quality,amino acids and volatile components were used as the main indexes to evaluate the RDP sauce.Qualities of RDP sauce fermented by different strains were determined and the results showed that sensory qualities of RDP sauce reached standards of the first class soy sauce in National Standard,among them the sample fermented by three-strain(A.oryzae,A.niger and Z.rouxii)was the best,with the highest amount of amino nitrogen and total free amino acids by 1.17 g/100 m L and 41.8 g/L(P<0.05)respectively.The results of the volatile components showed that RDP sauce fermented by three-strain contains the most volatile substances,reaching 1074.79 ng/m L(P<0.05),which increased 1.5 times than that fermented by A.oryzae only,of which the content of 4-VG and HEMF were significantly improved,increased by 25 times and 3 times respectively.In addition,RDP sauce fermented by three-strain also contained 71.1 ng/m L anti-cancer D-Limonene(P<0.05).Fermentation temperature significantly affected the sensory quality and the content of amino nitrogen and total nitrogen of RDP sauce,and the optimum fermentation temperature was 35 and 40? ?.Reducing power and DPPH radical scavenging activity were applied to evaluate the effect of fermentation temperature and fermentation time on the antioxidant activity of RDP sauce.The results suggested that fermentation temperature affected antioxidant activity of RDP sauce obviously,the peak values of antioxidant activity were at 35 ?and 50 ?fermentation respectively.With the extension of fermentation time,antioxidant activity of the sauce increased,particularly within 10 days of the initial fermentation,and then tended to be stable.The antioxidant activity in vitro of RDP sauce was better than that of soy sauce,and all results showed that RDP sauce fermented by A.oryzae and Z.rouxii had the strongest antioxidant activities,followed by that of three-strain.Sauce melanin,volatile oils and other compounds of small molecule weight had good reducing power and DPPH radical scavenging capacity.Effect of the ways and size of adding Z.rouxii on antioxidant activity of RDP sauce were researched.The results showed that HEMF,4-VG and antioxidant activity of RDP sauce were affected obviously by Z.rouxii inoculum way.When Z.rouxii was added at pH5.0 in mash,compared with that adding Z.rouxii at the initial fermentation,HEMF,4-VG and reducing power increased by 38.15%,33.98% and 14.49%(P<0.05)respectively.The addition size of Z.rouxii could increase the antioxidant activity,HEMF and 4-VG content,and varied with the extension of fermentation.RDP sauce(?)fermented by adding 0.025% Z.rouxii was the best,the total amino acid content was 40.46 g/L,and compared with the sample(?)without adding Z.rouxii,the contents of essential amino acids and total antioxidant amino acids increased by 19.32% and 40.73%,reducing power and DPPH radical scavenging capacity were 5830.43 ?g AAE/m L and 5.02 ?L/mL(EC50) respectively.