Fructans are sucrose derived oligo- and polymers of fructose. These are not digested in the upper parts of the gastrointestinal tract and thus are considered a dietary fibre. However, for a small part of the population, fructans can cause negative health effects since they belong to the FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) family. FODMAPs are small, osmotically active molecules that are poorly absorbed in the upper gastrointestinal tract and are rapidly fermented in the colon causing gastrointestinal symptoms in sensitive subjects, especially patients suffering from IBS.
During dough fermentation, fructans are partially hydrolyzed by yeast invertase. As preliminary research shows that the extent of this hydrolysis is yeast-dependent, the goal of this work is to generate more insight in the variation in invertase activity and substrate specificity between different industrial Saccharomyces cerevisiae (S. cerevisiae) strains. These insights can be used to control fructan levels during dough fermentation.
Analysis of a representative subset of industrial yeast strains showed a high variability in the capacity of the strains to hydrolyse sucrose and fructo-oligosaccharides. Using 4 strains, one bakery strain and 3 non-bakery strains with varying invertase activities, we showed that this variability serves as a simple yet effective handle on fructan hydrolysis during bread making. Indeed, using industrial yeast strains with a high activity towards fructo-oligosaccharides efficiently reduced wheat grain fructans during dough fermentation to a final fructan level of 0.3% dm, which is around the low-FODMAP cut-off value. In contrast, more fructan was retained in bread fermented by strains with a low invertase activity resulting in fructan levels around 0.6% dm. The non-bakery strain produced lower levels of CO2 in fermenting dough resulting in lower loaf volumes. Therefore, CO2 production and loaf volume could be increased by the addition of 3% glucose.
In conclusion, this study shows that variation in yeast invertase activity and specificity can be used to modulate the fructan content in bread, allowing the production of both low fodmap bread and bread with a higher soluble dietary fibre content.
Read more about this research in the publication 'Variability in yeast invertase activity determines the extent of fructan hydrolysis during wheat dough fermentation and final FODMAP levels in bread'. Please contact Jitka Laurent, if you would like more information.
Each year EFFoST and Cargill present the Student of the Year award to six students and also give them the opportunity to showcase their research. In this article, Jitka Laurent who won the 3rd prize for the EFFoST PhD Student of the Year discusses her research. Currently, Jitka is a PhD candidate at the Laboratory of Food Chemistry and Biochemistry at KU Leuven.