Study Of Effects Of Bacterial Community Structure Of The SFD On Volatile Flavour Compounds In CSB

Spontaneous fermented dough(SFD)is a traditional starter culture to make Chinese steamed bread(CSB)with a long history in China.The flavour of CSB leavened by SFD is rich and abundant,which makes it favoured by consumers.The SFD is a mix culture with diverse strains which are responsible for the flavor compounds of the CSB.However,the bacterial community structure of SFD and the correlation between bacterial community structure and volatile flavour compounds of CSB is still unclear.The present study aimed to focus on those two aspects and is of great importance for understanding the mechanism underlying the formation of flavor of CSB.It also provided theoretical basis for developing commertial starter cultures containing LAB.This paper investigated the bacterial community structure of traditional SFD with the help of metagenomic high-throughput sequencing technologies,combining with PCR-DGGE and traditional cultured methods.GC-MS and multivariate analysis methods are adopted to investigate the relationship between LAB structure of SFD and volatile flavour compounds of CSB.The results of this study have been listed as follows:1.The main volatile flavour compounds of traditional CSB were determined.The results show that CSB mainly contains 57 kinds of volatile flavour compounds,including ethanol,hexanol andethyl acetate et al.Significant differences of volatile flavour profile were found between CSBs fermented by LAB starter cultures and dry yeasts.15 volatile flavour compounds were regarded as contributor to this difference,including 2-pentyl furan,benzaldehyde,heptanal,etc.In addition,differences within groups of CSB made by SFD were more significant compared to that made by yeasts.This may due to the microbial diversity of SFD.2.Metagenomic and PCR-DGGE were combined to analyze the bacteria structure of SFD.Results indicated that Lactobacillus were the dominant genus in the 8 spontaneous fermented dough samples,along with less abundant Pediococcus,Weissella and Leuconostoc.Furthermore,in the level of species,Lactobacillus plantarum,Lactobacillus brevis,Pediococcus pentosaceus and Lactobacillus sanfrancises are the dominant species.97 strains of LAB were isolated and identified.They were 24 Lactobacillus brevis,23 Pediococcus pentosaceus,17 Lactobacillus plantarum,15 Lactobacillus sanfranscensis,13 Lactobacillus fermetum and 5 Lactobacillus crosrum.3.Effects of LAB on volatile flavour compounds of CSB were preliminarily analyzed.The volatile flavour compounds of wheat four hydrolysate(WFH)after fermented by 6 species of LAB were detected and analyzed.Results showed the existence of differences between species.Effects of interactions between 4 LAB on the growth of LAB and the production of volatile flavour compounds were also studied.It turned out that Lactobacillus plantarum F inhibited other 3 species when cocultured while Lactobacillus sanfranscensis S promoted the others.What’s more,the mutual interactions still existed when species were mixed cultured.The interactions were the most obvious when 3 LAB species were mixed cultured,and the kinds of volatile flavour compounds detected are the most at the same time.It suggested that interactions between different species of LAB may influence the production of volatile flavour compounds during the fermentation process.4.The flavour profiles of CSBs that fermented by different LAB were preliminarily analyzed by PCA(principal component analysis)and HCA(hierarchical clustering analysis).Similar results were obtained: 15 samples were divided into 4 classes.It indicated that the structure of LAB in spontaneous fermented dough has a strong effect on the flavour profile of CSB.38 volatile flavour compounds were considered to account for the differences.Among them,18 were considered to be related to bacterial metabolism,including 1,3-Butadiene,11-Methyldodecanol,3-Methyl-1-butanol acetate and etc.Moreover,both Lactobacillus plantarum F and Lactobacillus sanfranscensis S were principal flavour producers.Pediococcus pentosaceus J was supposed to be the coordinator.Both flavor producers and coordinator were important for the flavour formation of CSB.