Reference Number: 18
Enzymatic and microbial conversion of flour components during bread making determines bread quality. Metabolism of sourdough microbiota and the activity of cereal enzymes are interdependent. Acidification, oxygen consumption, and thiols accumulation by microbial metabolism modulate the activity of cereal enzymes. In turn, cereal enzymes provide substrates for bacterial growth. This review highlights the role of cereal enzymes and the metabolism of lactic acid bacteria in conversion of carbohydrates, proteins, phenolic compounds and lipids. Heterofermentative lactic acid bacteria prevailing in wheat and rye sourdoughs preferentially metabolise sucrose and maltose; the latter is released by cereal enzymes during fermentation. Sucrose supports formation of acetate by heterofermentative lactobacilli, and the formation of exopolysaccharides. The release of maltose and glucose by cereal enzymes during fermentation determines the exopolysaccharide yield in sourdough fermentations. Proteolysis is dependent on cereal proteases. Peptidase activities of sourdough lactic acid bacteria determine the accumulation of (bioactive) peptides, amino acids, and amino acid metabolites in dough and bread. Enzymatic conversion and microbial metabolism of phenolic compounds is relevant in sorghum and millet containing high levels of phenolic compounds.
Significance of the study
The current review focusses on the effect of sourdough fermentation on bread quality and nutrition. The paper states that both these parameters are dependent on the enzymatic and microbial conversions of specific components at the dough stage, and the activity of cereal enzymes is an important determinant of the microbial ecology of sourdough.
It is said that two main factors differentiate sourdough processes from fast fermentation processes. First, the presence of lactic acid bacteria and yeasts that trigger changes in the dough stage by modulating the pH of the dough which in turn activates various enzymes. Second, the fermentation time of sourdough processes ranges from 8 h to over 144 h. This long fermentation time compared to fast fermented processes allows for a substantial contribution of endogenous enzymes (enzymes present within the cereal flour) to biochemical conversions at the dough stage leading to increased bioavailability of minerals, fibre, vitamins and amino acids.