Diversity Of Yeast Analysis Of Traditional Starter Cultrue And Its Influence On The Quality Of Chinese Steamed Bread

The special flavor and good taste of traditional steamed bread depend on the diversity of microbial species in traditional starters. This study investigated the diversity of yeast and bacteria in traditional starters firstly. Then the dough fermentation characteristics of yeasts were mensurated. The qualities of steamed bread made by different mixed starter cultrues were also compared. This study would provide some theoretical basis for the development of Chinese traditional starters.Yeast and bacteria communities in Chinese starter culture were analyzed by culture-dependent and cultrue-independent(PCR-DGGE) methods. 5 yeast species, Saccharomyces cerevisae, Wickerhamomyces anomalus, Saccharomycpsis fibuligera, Torulaspora delbrueckii and Saccharomyces boulardii were isolated. PCR-DGGE method detected 3 yeasts, including S. cerevisae, W. anomalus and Sp. fibuligera. The results of culture method showed that S. cerevisae and W. anomalus were the predominant yeasts and they totally accounted for more than 70% of the strains isolated from each sample. 8 Lactobacillus species and 2 Acetobacter species were detected by culture-dependent and PCR-DGGE method. Acetobacter tropicalis, Pediococcus pentosaceus, Lactobacillus plantarum and Enterococcus durans totally occupied more than 48% of strains isolated from each sample, which could be the dominant bacteria.The fermentation characteristics of yeasts isolated from traditional starters were studied. S. cerevisae and S. boulardii were of excellent ability in CO2 producting, while T. delbrueckii had the best ability of gas retention. Nuclear Magnetic Resonance(NMR) results showed that T. delbrueckii had the most obvious effects on water distribution and migration of the fermented dough among 5 yeast species. Compared to other yeast species, T. delbrueckii could increase the content of total and reducing sugar in dough. X-ray diffraction(XRD) results displayed that the fermentation of different yeast species had no significant influence on the type of starch crystal in dough. All of the 5 yeast species had no distinct impact on the acidity of fermented dough.The aroma volaties of steamed breads were determined by headspace solid phase micro-extraction combined with gas chromatography mass spectrometry(HS-SPME-GC-MS). The results indicated that the flavor of steamed bread made by mixed S. cerevisae, W. anomalus and T. delbrueckii(4:10:1) was most close to that of traditional steamed bread. In addition, mixed 3 strains can improve the physical and chemical quality of steamed bread as well as taste of bread.