Bread has been a staple food for thousands of years, and sourdough is experiencing a resurgence in popularity. Many people appreciate its natural ingredients, nutritional benefits, and unique flavor. However, the biological process behind sourdough fermentation remains surprisingly complex. What exactly happens during this fermentation, and how does wheat fiber affect the final quality of the bread? These questions guided Victor González Alonso’s doctoral research at the Vrije Universiteit Bruxelles (VUB) to study how a particular wheat fiber called arabinoxylan acts during sourdough fermentation.
“Wheat accounts for the majority of calories and fiber consumed in Europe, and arabinoxylan plays an important role in this. Arabinoxylan helps determine the structure and quality of bread,” explains González Alonso.
Wheat fiber and sourdough fermentation
Arabinoxylan (AX) exists in two major forms. Water-extractables (WE-AX) usually have a beneficial or neutral effect on the dough, while non-water-extractables (WU-AX) can have a negative impact on bread quality. Until recently, scientists had limited understanding of how microorganisms in sourdough interact with these fibers.
To explore this question, González Alonso investigated the fermentation of several types of flour, including one enriched with additional AX. He used advanced DNA analysis and metabolite profiling to track changes in microbial populations to better understand how fermentation progresses.
“We observed that sourdough forms a stable microbial ecosystem with a complex balance of lactic acid bacteria and yeast,” he says. “Although higher fiber content did not change much this process, we clearly demonstrated that sourdough fermentation converts some WE-AX to WU-AX.”
Enzymes and microorganisms create the flavor of bread
One unexpected discovery concerned the cause of this fiber change. This change was not caused by the bacteria themselves, but by enzymes already present in the wheat. These enzymes become active as the dough becomes more acidic during fermentation.
When this happens, large fiber molecules break down into smaller pieces, which can affect both the digestibility and texture of the bread. The researchers also identified bacteria that contribute to flavor development. Lactococcus lactis It reminded me of a buttery scent, Limosylactobacillus yeast It produces sugar alcohols and adds a mellow sweetness.
Testing results on real bread
The team expanded their research beyond laboratory experiments. In pilot-scale baking trials, bread was produced using flour enriched with high levels of AX. The resulting sourdough bread was not only more nutritious, but also exhibited a wider range of flavors.
“Sourdough remains a fascinating interplay of biology and craftsmanship,” concludes González Alonso. “And our research shows that sourdough fermentation has a greater impact on wheat fiber than previously thought.”
