There are several strains of Lactobacillus sourdough (LAB) available. L. sanfranciscensis is obligately heterofermentative, followed by L. hammers ii, L. pentosus, and L. kimchii. Other strains are facultatively heterofermentative, including L. curvatus and L. sakei.
Yijkl lactobacillus is a highly-regarded sourdough starter. It has the distinctive characteristics of a true sourdough culture. This sourdough starter uses the natural symbiotic relationship between yeast and lactic bacteria, Lactobacillus sanfranciscensis, and Candida milleri. Both sourdough bacteria consume the starch, releasing glucose and fructose sugars into the mix.
The process of sourdough fermentation is as old as bread. Humans have been mixing flour and water for 5,000 years, waiting for the dough to ferment. Humans have propagated this leavening process by storing leftover dough, and sowing seeds of the foment in the next batch. This practice is also known as traditional sourdough bread. The combination of wild yeast and sourdough bacteria results in a unique flavor in the bread.
While Lactobacillus sanfranciscensis has been known for a long time, it was once thought to be a San Francisco-specific strain. Its complex sourdoughs were gaining popularity in the city. Several groups studied San Francisco starters and discovered that they were, in fact, the defining microbe. In 1971, Kline and Sugihara isolated this strain.
The bacteria responsible for adding tang to bread are known as Lactobacillus sanfranciscensis. These bacteria outnumber yeasts 100-to-one in the sourdough culture. The resulting sourdough is an excellent example of bread with the sourdough microbiota. The sourdough starter culture is a living organism, and it is necessary for the proper functioning of the bacteria.
The sourdough microbiome is widely variable and depends on various parameters. Many factors, including geography, influence the diversity of sourdough starters. It can be exchanged, gifted, or passed on through generations, resulting in different sourdough communities. As a result, a global profile of sourdough starters will be produced.
The sourdough bacteria responsible for the famous San Francisco sourdough has been identified. This bacterium is found in nearly 90 percent of sourdough recipes. According to Ben Wolfe, a microbiologist at Tufts University in Boston, lactic acid bacteria are what gives sourdough its signature sour taste. The lactic acid bacteria are also found in other fermented foods.
Yeast cells and the number of bacteria in sourdough bread are important determining factors for the quality of the baked goods. The higher the lactic acid concentration in the final product, the better. Yeast cells are responsible for the bread’s flavor, but the sourdough lactobacilli are more effective at transforming carbohydrates and amino acids into flavor compounds.
The sourdough bacteria produce lactic acid in the same way as muscles do after a vigorous workout. These bacteria utilize glucose and fructose as energy sources. They produce lactic acid and ethanol. This lactic acid is also used to create energy. In addition to producing energy, sourdough lactobacilli also produce carbon dioxide.
To compare the leavening ability of sourdough yeasts, the percentage of CO2 production in the dough was measured. It was shown that sourdough yeast produced more gas than control that contained baker’s yeast alone. However, the levels of CO2 production were significantly lower than the other sourdough bacteria. The percentage of lactobacilli in sourdough yeast is 100:1.
The bacterial culture of sourdough is similar to that of other fermented foods and the soil they live on. The amount of microbes in bread depends on the types of cereals used, the type of flour, and the fermentation time. The bacterial activity in the digestive system is boosted by using probiotics and prebiotics. Therefore, these bacteria improve the viability of sourdough.
The sourdough bacterial strain Lactobacillus reuteri is a stable member of the sourdough microbiota. Five sourdough isolates were assigned to human and rodent lineages based on multilocus sequence analysis and host-specific physiological traits. Comparative genome hybridization revealed that model sourdough isolate LTH2584 had similar genome content to model rodent isolate 100-23. These results indicate that the sourdough isolates are of intestinal origin.
Sourdough begins with flour and water and forms a chick starter filled with bacteria and wild yeasts. The starter is then discarded and replaced with more flour to make a dough. The microorganisms consume sugars and produce carbon dioxide and acids. Acetic acid is the most common sourdough flavor and is found at a pH level similar to mayonnaise.
The two strains of sourdough differ in their sensitivity to acidity. Yeasts, including Candida milleri, can tolerate acid levels up to 10 times higher than those of other types of bacteria. However, the two strains cannot live together without maltose. They need maltose to survive and help create tangy sourdough bread.
Traditional sourdoughs contain both yeasts and lactobacilli for leavening. Yeasts produce CO2 and contribute equally to the production of bread volume and crumb hardness. When sourdough yeast is added to bread dough, the specific volume of the bread increases the highest and the lowest volume. Yeasts containing S. cerevisiae and L. sanfranciscensis have the highest volume and lowest bread hardness.
Sourdough starters are microbial communities that are naturally occurring and are found in the flour used to make bread. The diversity of microbes in these cultures varies greatly, and it is unlikely that geographical location affects its diversity. Rather, the composition of the sourdough starter culture and its maintenance are likely to influence the diversity of the microbial community.
A recent study shows pneumococci strains isolated from sourdough are proteolytically active on gluten and are a potential starter culture for type III sourdough fermentation. These isolates were previously described as L. rhamnosus and L. fermentum, but their identities have recently been questioned. Researchers are now wondering if these isolates should be included in the starter cultures for type III sourdough.
We performed our experiment using two strains of L. Plantarum DC400 and F. sanfranciscensis SD8 as controls. The samples were centrifuged at 5,000 g for 20 min and stored at -20degC for further analysis. We determined the pH value of the two doughs using a pH meter equipped with a food penetration probe. The yeast and lactobacillus concentrations were measured on a standardized sample of 10 g of dough homogenized in 90 ml of sterile peptone water.
To test for these LAB strains in sourdough, we performed 16S rRNA-PCR-DGGE. We collected one sample from each refreshment step and backstopped it ten times. Then, we identified the dominant LAB strains and a single nonflour bacterium. We also postulated the absence of L. sanfranciscensis in semi sterile conditions.
After identifying the dominant LAB strain, we used DGGE of the 16S rRNA gene amplicons from the samples to determine the final composition of the microbiota. The results of these experiments were compared with a standard sourdough recipe. Consequently, we can conclude that LABs are the major cause of residual error in sourdough production.
Fixed strain effect
The fixed strain effect in sourdough was examined using qPCR to determine the relative fitness of L. reuteri strains. This study found that the presence of L. reuteri LTH2584 or 100-23 reduced the lactic acid production of a sourdough starter by more than 50 %. This finding has broad implications for the sourdough industry and its users.
The results indicated that the differences largely influenced the fixed strain effect in the raw materials used for the fermentation process. The different strains exhibited distinct differences in the fermentation process, affecting the microbial composition and food flavors. Furthermore, abiotic conditions were more favorable for the growth of Lactobacillus reuteri than other strains. The findings also support the notion that the two types of bacteria can coexist and thrive in the same food environment.
YPD-based fermenting media containing S. cerevisiae strain yB10-F9 depleted maltose by 36% after six h of fermentation. Yeast in anaerobiosis prefers glucose and represses genes involved in catabolism. However, this effect was not observed when the glucose concentration in the dough was lower than 0.2 mm.
The Fixed strain effect in sourdough fermentation was also observed in other fermentations. The most common obligately heterofermentative LAB strains are L. sanfranciscensis, L. hammers ii, and L. pentosus. In addition, L. kimchii and L. hammers ii are facultatively heterofermentative strains.
The fixed strain effect in sourdough fermentation was observed with L. reuteri LTH5448. This strain can persist for ten years in the yeast culture, a unique opportunity to study host-specific gut symbiont selection. Furthermore, SER sourdough isolates cluster separately from the intestinal strains and show horizontal gene transfer and loss of genes. Competitiveness in sourdough is mediated through energy and carbohydrate metabolism. In contrast to the rodent isolates, SER strains showed higher relative fitness than the LAB.