The Formulation Of Compound Starter And Its Effects On The Quality Of Steamed Bread

Jiaozi,as a kind of a natural starter culture,is commonly used to produce Chinese northern steamed bread.To make the Jiaozi,koji or daqu is mainly used as fermenting strains,and cornmeal or wheat flour is used as raw material.Jiaozi has been repeatedly fermented for the production of steamed bread,which belongs to a mixed microbial fermentation system.Besides,koji or daqu is rich in a variety of enzymes,so that the steamed bread made under the action of microorganisms and enzymes has delicate texture and unique flavor,and is well accepted by extended consumers.The processing of the Jiaozi is complex,which is mainly based on workshops,where there are some security risks and the product stability is poor.Therefore,the paper focuses on a kind of compound starter,which can be easily used to produce stable high-quality steamed bread under the effect of the enzymes and micro-organisms of Jiaozis,which lay a theoretical foundation for its industrial application.1.In order to facilitate the quality evaluation of the northern steamed bread for further research,the quality evaluation system of northern steamed bread was firstly established.We used 17 kinds of commercially available Chinese northern steamed bread as raw materials,studied the relationship between physical properties and sensory evaluation items by multivariate statistical analysis,and established the quality evaluation system of Chinese northern steamed bread.The cluster analysis of physical properties of raw materials showed that when the similarity coefficient was 0.90,the hardness,chewiness and gumminess could be classified into one class,so the hardness was selected to replace the chewiness and gumminess in this study.The relationship between physical properties and sensory evaluation items of Chinese northern steamed bread was studied by partial least squares analysis and correlation analysis,and the results showed that the hardness,elasticity,specific volume,diameter ratio and color difference L value could be used as the key physical items in the quality evaluation system of Chinese northern steamed bread.Finally,the quality evaluation system was obtained by the principal component analysis of the five physical items,which was proved to be suitable for Chinese northern steamed bread.2.Three kinds of optimal Jiaozis were selected based on the effect of Jiaozi on the quality of northern bread,and their basic properties were analyzed.The results showed that for the three kinds of Jiaozis,the lactic acid bacteria contents were higher than 108 CFU / g,yeast contents were above 106 CFU/g,and the TTA values did not decrease with the decrease of pH,which may be related to their compositions.Besides,the glucoamylase activity ranged from 225 to 245 U/g,the ?-amylase activity ranged from 3.7 to 5.2 U/g,and the protease activity ranged from 0.2 to 0.5 U/g.Traditional separation method and PCR-DGGE method were used to analyze the diversity of microbial compositions of the optimal Jiaozis.The results showed that the lactic acid bacterias of the Jiaozis were predominantly Lactobacillus plantarum and Pediococcus pentosaceus,and a small amount of Lactobacillus bacillus?Lactobacillus brevis and Weissella confusa were also included;in the terms of yeasts,Wickerhamomyces anomalus and Saccharomyces cerevisiae were existed in all the three Jiaozis.3.In order to further verify the effect of mixed fermentation by microbes and enzymes on steamed bread quality,the qualities of steamed bread respectively made by the Jiaozi A,compound bacteria preparation,compound fermentation agent and blank were compared in the study.The results showed that the qualities of steamed bread respectively made by the Jiaozi A and compound fermentation agent were the closest.Wickerhamomyces anomalus?Saccharomyces cerevisiae?Lactobacillus plantarum and Pediococcus pentosaceus isolated from Jiaozis were used as the main fermentation strains,and the optimal combination of enzyme preparations was determined by single factor test and orthogonal test.As a result,the composition of the compound starter was 1.04% for Saccharomyces cerevisiae freeze-dried bacteria powder,1.00% for Wickerhamomyces anomalus freeze-dried bacteria powder,0.44% for Lactobacillus plantarum freeze-dried bacteria powder,0.27% for Pediococcus pentosaceus freeze-dried bacteria powder,amylase 30 U/g,glucoamylase 30 U/g and protease 0.1 U/g(based on the weight of batter).4.In order to clarify the effect of fermentation by enzyme and microbial on the quality of steamed bread,the basic characteristics of batters prepared by different fermentation agents were compared.The results showed that the mixed fermentation of microorganism and enzyme could speed up the acidification of batters,improve the microbial growth rate obviously,and enhance the content of organic acids and free amino acids significantly,which indicated that the combination of microorganism and enzyme had a synergistic effect on microbial metabolism,and contributed to the improvement of product quality.