Study On Isolation & Identification And Fermentation Properties Of Microorganisms From Sourdough

In this paper, the sourdough as flavor leaven in CSB production and the steamed process of steamed bread are studied. Moreover, the advantage bacterium of yeast and lactic acid bacteria in the sourdough are isolated and the effect of complex strains on quality of CSB is investigated in this study. The main research conclusions are as follows:1. G dough is selected by its strong fermentation ability as the leaven from 8 sourdoughs collected in surrounding areas and then the steamed bread with G dough technique is studied. The optimal technique of fermentation of dough is obtained by single factor test and orthogonal experiment. The results demonstrate that, the sequence of conditions affecting the secondary fermentation of dough is fermentation time, awakening time, the secondary water addition and fermentation temperature. Moreover, the optimal technique of the secondary fermentation of dough is 4 hours fermentation in 30℃,20 minutes awakening and 18% secondary addition water.2. Totally 8 yeast-like strains and 7 lactobacillus-like strains were isolated from G dough that has a strong fermentation capacity and 6 strains with good comprehensive characters were isolated by re-screening. Then the 6 strains are preliminarily identified by morphological observation and physiological and biochemical test. Finally, those strains are identified by the molecular biology technology, The results of molecular biological technology show that the strain Y1 is Pichia membranifaciens, Y4 and Y8 are saccharomyces cerevisiae, R3、R4 and R7 are all Lactobacillus planetarium.3. Mixed culture for sourdough fermentation were made of different yeasts Y1、Y8 and lactic acid bacteria R3, the culture were used in two combinations in dough fermentation experiment to study their effects on the dough characteristics, these characteristics were evaluated by measurement of the decrease in pH, the dough rising capacity and the populations of two microorganisms in the fermenting dough during the dough fermentation process. The results were as follows:strain Y8 and R3 combination for sourdough fermentation, after the dough fermentation. pH in dough decreased from 5.94 to 3.49, fermentation ability kept about 1.4 during the period of 6hto12h dough fermentation, the viable counts were 1.11×108CFU/g for Y8,and 2.1×108CFU/g for R3:Y1+R3 combined strains fermentation had a decreased pH from 5.97 to 3.57,during the 6h dough fermentation, fermentation ability was about 0.89,the number of viable cells was 1.12×108CFU/g tor Y1,and 1.71×108CFU/g for R3. The two combination strains were chosen to co-ferment steamed bread experiments, the results showed that different yeasts had different effect on quality of CSB, the CSB fermented by sourdough adding Y8 have the highest sensory score 7.73 points. In conclusion, combination of Y8 (saccharomyces cerevisiae) and R3 (Lactobacillus planetarium) can obtain a better fermented dough, so the mixed culture strains can be the optimal starter during steamed bread dough fermentation.