Carbohydrate degradation and consumption dynamics during bread dough fermentation and yeast- and enzyme-based strategies to modulate it

Promovendus/a: Nore Struyf

Promotor(en): Prof. dr. ir. Christophe Courtin, Prof. dr. ir. Kevin Verstrepen

The intensity of dough fermentation depends on the availability of fermentable substrates in dough. As the content of fermentable sugars in wheat is low, the majority of sugars consumed during fermentation have their origin in the degradation of larger carbohydrates by wheat- or yeast-based enzymes. While the dogma stands that maltose release from starch is important for fermentation, the impact of wheat fructan degradation by yeast invertase on total CO2 production has never been studied. More insight in the share of every carbohydrate in the total production of CO2 during fermentation can lead to strategies to modulate dough fermentation dynamics. Such strategies can result in both technological and nutritional benefits.

In a first part, the substrates that are determinative for the production of CO2 during dough fermentation were identified. After two hours of fermentation, 70% of the sugars consumed by yeast in whole meal dough were derived from invertase-mediated fructan and sucrose degradation. Invertase-mediated sugar release was crucial during the first hour of fermentation, while amylase-mediated sugar release was predominant in the later stages.

After analysis of the substrates important for fermentation, enzyme- and yeast-based strategies were developed to modulate the dynamics of substrate degradation and consumption during fermentation. The enzyme-based strategies were based on the degradation of damaged starch by different starch-degrading enzymes. More specifically, the impact of maltose- versus glucose-producing enzymes on dough fermentation kinetics was studied. It was shown that glucose-producing enzymes increased the CO2 production rate during the initial stages of fermentation, while maltose-producing enzymes prolonged the productive fermentation time.

Next, yeast-based strategies were explored. By using substrate-limited yeast strains that are unable to consume maltose, the fermentation process occurs independently of amylase-mediated release of maltose. The release of maltose during fermentation is highly variable and unpredictable, which means that fermentation processes that are independent of maltose consumption are more controlled and less subjected to overproofing and dough collapse.

Next to controlling fermentation time, yeast-based strategies can be applied to lower the fructan content of dough. Fructan serves not only as an energy source for yeast, but is also a member of the FODMAP – Fermentable Oligo-, Di-, Monosaccharides and Polyols – family. In people suffering from irritable bowel syndrome (IBS), FODMAPs induce negative health effects. In this work, it was shown that the use of alternative yeasts (Kluyveromyces marxianus) for dough fermentation can enhance fructan degradation, leading to breads that are low in FODMAPs.

The research performed has led to strategies to steer the fermentation process and hence improve the technological and/or nutritional value of (whole) wheat bread. Technological improvements are flexible fermentation times leading to optimal loaf volumes. Nutritional benefits are the development of breads that are low in FODMAPs, relevant for IBS patients.