| This dissertation systematically studied the microbial diversity in Chinese traditional sour congee collected from four different areas.Research was carried on by using lactic acid bacteria strains and yeasts being of characteristics of potential probiotic which were isolated,purified and identified from naturally fermented sour congee.A new type of fermented beverage was developed by using millet as the raw material and inoculating fermentation.And then the volatile flavor components in beverage were determined by head space solid phase micro-extraction and gas chromatography-mass spectrometry(SPME-GC-MS).It provides a theoretical basis for improving the flavor of traditional products for public taste and the industrialized production of traditional food.In four different regions of the traditional sour congee samples,the structure and diversity of bacterial and fungi were studied by 16S rDNA amplicon sequencing and ITS sequencing respectively.The results show that at the level of the phylum,the dominated bacterium is Firmicutes,nevertheless,H2 also contains 49%of Proteobacteria,and the main advantage of fungal is Ascomycota in the four samples.At the level of the genus,the predominant bacterium is Lactobacillus,of which Pseudomonas in H2 is 48%,and the predominant fungal is Pichiaceae and Meyerozyma in the four samples.There were significant differences in the community structure of sour congee samples in four different areas.40 strains of lactic acid bacteria and 12 strains of yeasts were obtained from 4 kinds of sour congee samples by isolation and purification.Based on 16S rDNA sequencing analysis,16 strains of lactobacillus were identified,including,3 strains of L.plantarum,5 strains of L.fermentum,3 strains of L.reuteri,I strain of L.pentosus,1 strain of L.pontis,1 strain of L.brevis,I strain of L.sp..Through extraction of genomic DNA from yeast and ITS sequencing analysis,5 strains of yeasts were identified,including,Pichia kudriavzevii,Pichia kudriavzevii culture-collection CBS,Pichia kluyveri,Meyerozyma guilliermondii and Rhodotorula mucilaginosa.The lactic acid bacteria and yeast were screened from traditional four sour congee samples.The lactic acid bacteria were inoculated into the millet juice for acid production test and sensory evaluation,and the excellent lactic acid bacteria Ml,M5 and M12 were selected.Y1,the yeast with best properties,was selected by some index analysis.The lactic acid bacteria and yeast were re-screened at inoculation proportion of 1:1,so that M1 and Y1 were choosen as the best strains in this study eventually.Through the single-factor experiments and orthogonal experiments of fermentation temperature,fermentation time and inoculation rates of lactic acid bacteria and yeasts to determine the optimized fermentation conditions.The result was showed as follows:when millet as the raw material,inoculation rates of lactic acid bacteria and yeasts was 3:1,and fermented temperature was 34℃ for 24 h,and the unique flavor of millet beverage could be produced.The volatile compounds in the millet beverage were determined by SPME-GC-MS.19,31,30,52 kinds of volatile compounds were detected in millet fermented systems with inoculating no strain,the lactic acid bacteria M1,the yeasts Y1 and mixture of M1 and Y1,separately.Acetic acid,2-methyl-1-propanol,3-methyl-l-butanol,ethyl acetate were detected in the beverage produced by fermentation of millet with lactic acid bacteria and yeasts. |
