Study On Microbial Screening?Identification And Special Fermentation Agent Of Chuantou Steamed Bread In Pucheng

Chuantou steamed bread in Pucheng is intangible cultural heritage of Shaanxi,favored by the vast number of consumers at home and abroad.The fermentation process of traditional sourdough is long and inefficiency,affected by seasonal conditions,which is difficult to achieve standardization,industrial production.A number of local sourdough by separation,purification and identification are randomly selected,and the research of fermentation conditions,production process and preservation is to develop of special fermentation agent for chuantou steamed bread.The main results are as follows:(1)The sourdough of Chuantou steamed bread were sampled from Chuantou steamed bread heritage,Chuantou steamed bread production workshop in xiguan,Chuantou steamed bread factory,Gaoyang village,Nine hall,Shilong village,Xing Pu halal food factory and 2self-employed and investigated the diversity of yeast and lactic acid bacteria by plate separation,purification and identification.The contents of yeast in the sourdoughs were from 4.03×10~2 to1.8×10~6 CFU/g(dry base),while the lactic acid bacteria were from1.08×10~3 to 1.94×10~6 CFU/g(dry base).Based on the results of 26S rDNA D1/D2 region and Internal Transcribed Spacer(ITS)sequence amplification and sequencing,54 yeast isolates were identified as Saccharomyces cerevisiae,Wickerhamomyces anomalus,Pichia kudriavzevii and Sporidiobolus pararoseus,respectively.S.cerevisiae in the 8 samples except Gaoyang village were detected,which was the advantage of yeast.Seven lactic acid bacteria(LAB)isolates were identified as Pediococcus pentosaceus(n=2)and Lactobacillus helveticus(n=5)in Chuantou steamed bread production workshop in xiguan and 2self-employed according to their 16S rDNA sequence.The results indicated that Saccharomyces cerevisiae and Lactobacillus helveticus were the dominant species in the sourdough of Chuantou steamed bread.(2)Five groups of Chuantou steamed bread samples were made according to the ratio of 10:1,1.5:1,1:1,1:1.5,1:10,respectively,which determined by pH meter,texture and aroma.The results showed that the pH increased firstly and then decreased in Chuantou steamed bread,when the ratio of the two microbes was 1:1,the pH reached the lowest value.When the ratios of the Saccharomyces cerevisiae:Pediococcus pentosaceus were in 1:1and 1:10,the texture characteristics of the Chuantou steamed bread were relative good.The aroma substances of the five groups of Chuantou steamed bread were diverse,among which the most abundant and diversity ones were detected from 1:1(Saccharomyces cerevisiae:Pediococcus pentosaceus)in Chuantou steamed bread samples.Compared to the samples which are from the intangible cultural heritage,the ratio of 1:1 in Chuantu Steamed bread was considered as the best in term of sensory evaluation,the main characteristics of pH,texture and flavor.(3)By vacuum freeze-drying,it is the single factor test,the factor of which are pre-freezing temperature,pre-freezing time,skimmed milk powder,L-monosodium glutamate,trehalose,and sucrose,and the prerequisite of which is the ratio of the two microbes(Saccharomyces cerevisiae:Pediococcus pentosaceus=1:1).The orthogonal experimental design based on single factor on protective agents comes to conclusion that four factors have an effect on the survival rate of strains,which is skimmed milk powder>trehalose>L-monosodium glutamate>sucrose,and the best protectant formula is 16%of skimmed milk powder,2%of trehalose,3.5%of L-monosodium glutamate and 13%of sucrose.Therefore,the best freezing conditions of Saccharomyces cerevisiae and Pediococcus pentosaceus is 16%of skimmed milk powder,2%of trehalose,3.5%of L-monosodium glutamate,13%of sucrose and that pre-freezing temperature is-40?,pre-freezing time is 2h.(4)On the basis of the optimum ratio and culture conditions,the freeze-drying conditions of mixed bacteria and the application effect of the starter were verified.The significant effect by the single factor experiment of sensory score that is amount of mixed bacteria powder,fermentation time,secondary-water addition and proofing temperature is picked out.The orthogonal experimental design of four factors and three levels is carried out in order to find out the primary and secondary order of the influence factors of sensory evaluation of chuantou steamed bread:mixed bacteria powder>proofing temperature>secondary-water addition>fermentation time,and optimum conditions that mixed bacteria powder is 0.35%,fermentation time is 12h,secondary-water addition is 43%and proofing temperature is 30?.The index of nine group of chuantou steamed bread by orthogonal experiment that texture,moisture content,the ratio of height to diameter and specific volume are measured.The optimal result of each index and orthogonal experiment are uniform.Therefore,the optimum condition of chuantou steamed bread using compound freeze-dried bacteria can be used for actual production.The special starter making chuantou steamed bread will future promote the production of standardization and industrialization,which is of great significance.