Application Of Mixed Bacteria In Mixed Rice-flour Dough Fermentation

In this study,two typical lactate acid bacteria strains obtained from China Microbial Preservation Center:Lactobacillus bulgaricus(Lb 1.2717)and Streptococcus thermophilus(St1.2718),as well as activated Angel yeast,were selected to inoculate in rice-flour mixed dough at logarithmic anaphase.The physicochemical and texture characteristics,fermentation activity,sensory evaluation and colony of rice-flour mixed acid dough were studied by the ratio of bacteria and fermentation time.The optimum ratio of mixed strains and fermentation time were selected to produce rice-flour mixed acidic dough.Finally,the optimal rice-flour mixed sour dough was selected.On the basis of single factor experiment,response surface methodology and principal component analysis were combined to select the optimal formula for rice bread processing.The main results are as follows:1.Eighteen hours and ten hours were selected as the logarithmic growth anaphase of lactic acid bacteria and yeasts.At this time,lactic acid bacteria and yeasts grew well in the medium and had strong reproductive ability.Activated Lactobacillus bulgaricus,Streptococcus thermophilus and Angel yeast were inoculated into rice-flour dough in different proportions.2.Through the determination and analysis of physicochemical and texture characteristics,fermentation activity and sensory evaluation of rice-flour mixed sourdough,the optimum mixture ratio of fermented rice-flour mixed acidic dough was determined to be yeast:lactic acid bacterias(Lb1.2717+St 1.2718)2:1,and the fermentation time was about 10-15h.The results showed that the pH value of rice-flour mixed sourdough was stable at about 3.4,and the titratable acidity(TTA)remained stable after increasing.At this time,the texture characteristics of rice-flour mixed acid dough were obviously improved,the hardness and adhesiveness decreased,and the elasticity and resilience increased.At this time,the rice-flour mixed sourdough produced by fermentation has better fermentation activity,more mellow ester flavor and slightly acidic taste.The structure of melon pulp are suitable for compact and uniform size,thin stomatal wall,less toughness and good elongation.The maximum number of yeast colonies were 6.0 log10cfu/g after 12-16 h fermentation.The maximum colony number of lactic acid bacterias were 9.5-9.9 log10cfu/g after 12-18 h fermentation.According to the total number of lactic acid bacteria and yeast colonies,the fermentation time was determined to be 12-14 hours.The G'and of G" rice-flour mixed sourdough fermented by mixed bacteria were higher than those fermented by yeast.3.According to the optimized rice-flour mixed acidic dough,rice bread was made.On the basis of single factor,the acidic dough addition,fermentation time,water addition and white sugar addition were selected to carry out four-factor and three-level response surface methodology.Combined with principal component analysis,the optimal formula of rice-flour mixed bread was obtained:sourdough addition 25%,fermentation time 2 h,water addition 51%,white sugar addition.Volume 15%.The physicochemical and texture characteristics,specific volume and color difference of rice-flour mixed bread fermented with sourdough and ordinary bread were measured.Compared with the blank group,the rice-flour mixed bread fermented with sour-dough had lower hardness and chewiness,better elasticity,38%increase in specific volume and yellowish-red color.Through sensory evaluation and electronic nose analysis,it was found that rice-flour mixed bread dough with sourdough had stronger ester flavor and higher organic acid and terpenoids contents.