| The sour liquid method is a traditonal method to produce mung bean and sweet potato starch with nearly one thousand years of history in China. In order to take better advantage of sour liquid method,improve the traditional starch extraction technics,expand the range of application of sour liquid method,as well as solve the pollution problem in starch industry,we studied the sour liquid method and its application to rice starch extaction in this paper.The main contents and results described as follows:(1) 44 cultures were isolated from mung bean sour liquid,long rice sour liquid and waxy rice sour liquid,and 12 of which were provisionally identified as yeast,3 2 as Lactobacillus casei strain and Lactococcus lactis subsp.lactis strain respectively by phenotypic and molecular identification.At the meantime,16S rDNA of 6 culture s with different physiological and biochemical characteristics were amplified by two pairs of universal primers of 16S rDNA and specific primers of LAB respectively. And 12 accession numbers for 16S rDNA in GeneBank were obtained as follows:H M188409～HM188420;(2) Screening LAB strains isolated from sour liquids by using the bacterial suspension prepared from LAB strains to deposit the mung bean starch.The results showed that:the Lactococcus lactis subsp.lactis strains had stronger strach deposition capacity than the Lactobacillus casei strains,and yeast strains can be effectively cooperative with LAB strains to starch deposition.There were differences among different strains,so we selected MBSL3 and LRSL9 which were with the strongest starch deposition capacity as well as the yeast strain WY for the further study.The optimal compound proportion of MBSL3,LRSL9 and WY was 3:1:1;(3) Using the strains MBSL3,LRSL9 and WY to make the sour liquid,this paper studied the effects of bacterium quantity,starch milk initial pH,starch milk concentration, temperature, and keep-standing time on the sour liquid making technique.And the optimal technique of sour liquid making was determined by L9(33) orthogonal test on the 3 factors including bacterium quantity,starch milk initial pH and starch milk concentration.The result showed the optimal conditions were bacterium quantity 8%,starch milk initial pH 5.5,starch milk concentration 35%,temperature 25℃and keep-standing time 8h.Through the optimal technique,we got the high quality sour liquid with pH 3.73, viable amount of about 1.03×109cfu/mL,acidity 15.72%;(4) The sour liquid made by the optimal technique was applied to rice starch extraction.This paper studied the waxy rice and long rice starch extraction technique.The optimal rice extraction technique was determined by L9(33) orthogonal test on the 3 factors including liquid to material ratio,extraction time and temperature.The result showed the optimal conditions were liquid to material ratio 1:4,extraction time 22～24h and temperature 30℃.By this rice extraction technique,we got the long rice starch with residual protein 3.34% odds,starch amount 87.09%;and the waxy rice starch with residual protein 3.18% odds,starch amount 87.48% in average;(5) Add the sour liquid made by the optimal technique to the rice starch extracted by the alkali and enzymatic method,then measure the pH change in the rice starch extraction.The result was that,aftter adding sour liquid,the pH decreased and it could neutralize the alkali liquid from alkali method effectively;(6) Comparing the components and properties of rice starch extracted by differ ent methods,the components indicators including residual protein,starch purity,water,as h,crude fat,acidity;and the properties indicators including starch granules by scanning electron microscopy(SEM),RVA viscosity curve,transparency(OD),whiteness degree,fr eeze-thaw stability,retrogradation stability and SDS-PAGE of residual protein of rice starch were determined.The results were as follows:the sour liquid method can be used for rice starch extraction;and the alkali cooperated with sour liquid method wa s better for rice starch extraction.
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