Mutually stimulating interactions between lactic acid bacteria and Saccharomyces cerevisiae in sourdough fermentation
“Interactions between microorganisms are key to their performance in food habitats. Improved understanding of these interactions supports rational improvement of food fermentations. This study aimed at identifying inter- actions between lactic acid bacteria and yeast during sourdough fermentation. Therefore, the lactic acid bacteria Lactobacillus plantarum and Lactobacillus sanfranciscensis were co-cultured with the yeast Saccharomyces cerevisiae in a newly developed medium, as well as in situ in a sourdough-like environment. L. sanfranciscensis was found to be stimulated by a secreted factor of S. cerevisiae in any tested in vitro situation, whereas L. plantarum and S. cerevisiae stimulated each other only in the presence of glucose, fructose and lactose as carbon source, but not with galactose, maltose, sucrose and starch. Moreover, it was demonstrated that L. sanfranciscensis is stimulated by CO2 and another yet to be identified factor produced by yeast in a sourdough-like environment. In conclusion, S. cerevisiae produces growth factors stimulatory to lactic bacteria. The nature and the efficacy of these growth factors depend on the target species and on the supplied carbon source. “Abstract della ricerca riportata negli Approfondimenti.
Mutually stimulating interactions between lactic acid bacteria and Saccharomyces cerevisiae in sourdough fermentation. Sander Sieuwerts, Peter A. Bron, Eddy J. Smid, Kluyver The Netherlands Wageningen University, Laboratory of Food Microbiology, P.O. Box 17, 6700 AA Wageningen, The Netherlands . LWT – Food Science and Technology 90 (2018) 201–206
Grain Starch is composed of two substances:
- amylopectin: is a branched-chain polysaccharide, can be composed of about 1 to 6000 molecules of glucose. It tends to be placed in the central part of starch granules and is not soluble in water. Generally it represents 80% of the total.
- Amylose is instead a linear chain polysaccharide. It can contain up to 600 glucose molecules. Tend to be around 20% of the total. It melts at high temperatures and in water. These two constituents determine the differences between the starches, depending on their ramifications and degree of polymerization.
Starch represents 67-68% of whole wheat and between 78-82% of the flour produced by grinding. The semicrystalline structure of the starch granules is damaged by mechanical operations, in particular by the grinding process that shatters it. The level of damaged starch directly influences the water absorption and the mixing properties of the dough and therefore has a great technological importance. The damaged starch absorbs 2 to 4 times more water than normal starch granules. The crushed starch granules are subject to the action of alpha and beta amylase (1); the former transform starch into maltose and dextrins (2) and the latter transform it into maltose.
An excessive value of damaged starch involves a high water absorption, sticky dough, longer leavening times and dark color of the crust. A better knowledge of the levels of damaged starch in flour is essential for their best use. The optimal value of damaged starch varies with the use of flour and is highly dependent on the protein content of the flour, alpha-amylase activity and the type of bread desired. Starch is a polymer of glucose and comes in two different forms: amylose and amylopectin.