Reference Number: 87
Year: 2008
Link: Link to original paper
Summary
Introduction
Exopolysaccharides (EPS) are exogenous microbial metabolites which are secreted mainly by bacteria and microalgae during growth. In addition to natural polysaccharides present in cereal grains flour and dough, microbial flora is usually involved in production of polysaccharide on sourdough fermentation.
Methods
Total polysaccharides (microbial and flour) were extracted from sourdough and dough samples dehydrated and were added at the rate of 0%, 0.25%, 0.5%, 1%, 1.5%, 2% and 2.5% (w/w flour based) on the dough to investigate its effects on the rheological properties of the dough.
Results
Addition of polysaccharides to the dough increased the water absorption and decreased the dough softening after 20 min. Resistance to extension after 45, 90 and 135 min resting time was decreased by increasing the percentage of the added polysaccharides. Longer fermentation time for each level of polysaccharides led to greater stability. No significant differences were observed in the extensibility of dough. The overall effects of different levels of added polysaccharides resulted in a decrease in resistance to extension ratio of the samples. Energy input decreased in all cases. It seems therefore that addition of polysaccharides may be useful when bread is to be made with stronger flour and longer fermentation time is needed.
SIGNIFICANCE OF THIS STUDY
Bacteria in sourdough starters produce complex polysaccharides called exopolysaccharides that play an important role in contributing to the optimum structure of sourdough breads. They are called ‘exo’ polysaccharides because they are released by bacteria into the surrounding during the fermentation process. The study found that longer fermentation times resulted in increased levels of exopolysaccharides which resulted in more texturally stable breads. Both microbial expolysaccharides and plant polysaccharides contribute to the structural layout that is important in creating sourdough bread that is texturally superior to modern fast fermented breads.