Research Of Dominant LAB In Sourdough And Its Fermentation On The Quality And Flavor Characteristics Of Steamed Bread

Steamed bread is a traditional staple food in China. Using traditional sourdough starter in making steamed bread would give its products a better taste, rich flavor and a relatively long shelf life. However, this traditional sourdough starter’s microbial composition is complex, the production equipment used is poor and often relies on the experience of producers, and also lacks a clear standard of production. The study of traditional sourdough is still too fragmented with the strains isolated from it not being applied scientifically, thereby resulting in a waste of resources. Two excellent traditional sourdoughs screened by a former study of our research group were used in this study. From these two sourdoughs, this study was able to isolate, identify and analyze the dominant lactic acid bacteria(LAB) strains which were used to ferment the wheat sourdough. The wheat sourdough would be applied in steamed bread fermentation process. Comparative studies were carried out on quality and volatile flavor characteristics between LAB fermented sourdough steamed bread and traditional fermented sourdough steamed bread. The main contents and conclusions were as follows:1. The p H and TTA values of the traditional sourdoughs were determined during the activation and fermentation processes. After the activation and fermentation processes: the p H value of Henan Zhumadian and Hebei Xingtai samples was stable around 3.70, the TTA value of Henan Zhumadian samples fluctuated when fresh materials were added, while the TTA value of Hebei Xingtai samples rose from 11.0 to 17.7. Considering the microbial count for samples of these two regions, the amount of LAB was stable at 109 cfu/g, whereas the ratio of LAB to yeast colonies was stable at 100: 1.2. Using a selective media, a total of 131 strains of LAB from Henan Zhumadian and Hebei Xingtai traditional sourdoughs were isolated and purified. Identification by 16 S r RNA gene sequencing analysis method revealed that 122 strains were LAB and 9 strains were acetic acid bacteria. The LAB included 9 species: 37 strains of L.sanfranciscensis, 31 strains of L. plantarum subsp plantrum, 22 strains of L. crustorum, 13 strains of W.cibania, 8 strains of W.paramesenteroides, 4 strains of L. pentosus, 2 strains of P. pentosaceus, 2 strains of L. fermentum, 3 strains of L. brevis. The acetic acid bacteria included 3 species: 7 strains of A. pasteurianus subsp pasteurianus, 1 strains of A. malorum, 1 strains of A. tropicalis.3. Dominant LAB in the two areas’ sourdoughs was studied by PCR-DGGE technique. 6 species were detected. L.plantarum, L.sanfranciscensis, A.tropicalis, and L.crustorum were detected as dominant LAB of these two areas’ samples, which was consistent with the conclusion 2.4. L. plantarum subsp. plantarum ZS3-11(LPP15)and L. sanfranciscensis XD1-4(LS28)which were isolated from traditional sourdoughs of Henan Zhumadian and Hebei Xingtai area respectively,were applied to wheat sourdough fermentation process. After 10 to 12 hours of sourdough fermentation, the results showed a decrease in the p H value of both sourdoughs to 3.70~4.00. LPP15 and LS28 were able to grow well in wheat dough. When fermented for about 10~12hr, both strains’ total colonies were up to theirs maximum, which eventually stabilized at 8.8 ~ 9.2 log cfu/g.5. Steamed bread properties such as specific volume, texture profiles, sensory evaluation and volatile flavor compounds of LPPS and LSS were studied. YS was used as blank control, and HZS, HXS as experimental control. The results of specific volume for all samples were in the order of LSS > LPPS> YS > HXS = HZS. The hardness, gumminess, cohesiveness and flexibility of LPPS and LSS were improved significantly compared to the other samples. After integrating the sensory evaluation scores, the sample scores from high to low were LSS > LPPS > HXS > HZS > YS. A total of 121 kinds of volatile flavor compounds were detected in all steamed breads. The amount of volatile flavor compounds in sourdough fermented steamed bread was 1.60 to 1.85 times that of YS, and their kinds were also significantly increased. Also, unique volatile flavor substances were detected in LPPS and LSS such as 2-ethylhexan-1-ol, 3-nonen-1-ol, 10-undecen-1-ol, 3,7,11-trimethyl-2,6,10-dodecatrien-1-ol, perhydrofarnesyl acetone, palmitic acid, 1-Acetoxypentane, hexyl acetate, isopropyl palmitate, 9,12-octadecadienoic acid ethyl ester, 3-decene,(E, E)-2, 4-heptadienal, 2-decenal,(E, E)-2, 4-nonadienal, 2-undecenal,(E, E)-2, 4-Decadienal, 4-heptenal, etc.