| Traditional starter culture has a long history for preparation of popular fermented stable foods in China, resulting in a unique flavor of traditional fermented foods due to its complex and diverse microflora. However, few research focused on bacterial flora between sourdough from different regions of China and lack systematic study on the correlation between strains and flavor.In this paper, the diversity of microbial community in traditional starter cultures from different areas of China was investigated systematically. Furthermore, the fermentation performance and biological function of lactic acid bacteria(LAB) isolated from sourdough as well as its metabolic substances were evaluated, and thus provided the theoretical reference for the basic study of Chinese traditional starter culture.High-throughout sequencing results showed that the sourdoughs collected from four regions i.e. Shandong, Shanxi, Gansu and Qinghai have a large differences in the bacterial communities. Thereof sourdough from Shandong province was identified to own most plentiful of species as high as 274 kinds of bacteria, including 128 unique species, which is much higher than those in sourdough from other area. In addition, two different matrix sourdoughs of barley and buckwheat from Qinghai province have high similarity in bacterial communities, indicating that the flora constitution in sourdough rely on region.Based on the culture-dependent and 16 S rDNA gene sequencing methods, 13 LAB strains were obtained from Shandong sourdough, which belonged to 8 species of bacteria i.e. L. paracasei, L. plantarum, Lactobacillus sp., Pediococcus pentosaceus, L. curvatus, L. fermentum, L. helveticus, L. acidophius.In order to explore the resources of LAB in sourdough, the fermentation performance(acidifying capacity, species and amount of free amino acid, and metabolites) of the 13 LAB strains were investigated. The results showed that the sourdough fermented by LAB reached the desired acidity and greatly increased the composition and content of free amino acid in sourdough, especially the essential amino acids. Moreover, L. helveticus D01 yields high amount of proline and glutamic acid, and L. acidophilus D02 yields high amount of arginine. HPLS-MS and GC-MS methods were used for analysis the metabolites in sourdough. The results showed a variety of new compounds were formed after dough fermentation by LAB. Based on the above results, five LAB strains(L. helveticus D01, L. acidophius D02, Lactobacillus sp. D03, L. fermentum D04 and L. curvatus D05) was screened out.To further evaluation of biological properties of LAB isolated from sourdough, five LAB strains were tested by oral administration of BABL/c mice with LAB for four weeks. The results of serum biochemical indexes showed that almost five bacteria had no effect on glutamic transaminase(ALT), total bilirubin(TBIL), creatinine(CREA), uric acid(UA), total cholesterol(TC) and other five biochemical indexes, which indicates that five LAB strains isolated from sourdough are safe for host. In addition, L. casei D02 and L. fermentum D04 could significantly(p<0.05) decrease the level of uric acid(UA) in mice after intragastric administration and uric acid is one of the indicators to evaluate the renal function. It is deduced that the two strains could affect nitrogen metabolism and hold a potential function for renal regulation.Changes in the intestinal microflora and its function is an important index for the probiotic evaluation and screening of strains from sourdough. The results of viable counting revealed that partial of Lactobacillus increased the number of lactic acid bacteria in the intestinal flora, reduced the amount of opportunistic pathogenes, thus promote the health of host. Acid and bile salt tolerance test of mice intestinal flora showed that gavaging L. fermentum D04, L. curvatus D05 and Lactobacillus D03 could enhance the tolerance of intestinal flora to acid and bile salt. In addition, the results of nutrition metabolism and related metabolic enzyme activity of intestinal flora showed that L. fermentum D04 enhanced the effect on metabolism of intestinal flora in mice, indicating that LAB might improve the metabolism of intestinal flora through strengthening the relevant enzyme activities.In conclusion, the flora structure and biological properties of strains in sourdough from four areas of China were evaluated by high-throughput sequencing and traditional separation methods, which provides a protocol and plentiful of data for screening the safety and good properties of probiotic microorganisms from sourdough. |
PDF Full Text Request