University of Helsinki’s Prabin Koirala unveils breakthrough turning brewery waste into gut-healthy foods

Researchers at the University of Helsinki have found a novel way to give brewery leftovers a second life, transforming them into nutritious food ingredients that could improve gut health and help cut waste.

Prabin Koirala, from the university’s Faculty of Agriculture and Forestry, has shown in his doctoral research that brewers’ spent grain, the main by-product left over after brewing beer, can be turned into valuable components for healthier foods through fermentation with lactic acid bacteria.

Brewers’ spent grain typically consists of husks, residual grains, and other plant material. It is produced in large quantities worldwide as the brewing industry grows, often posing a disposal challenge. Koirala’s study suggests that this waste stream could instead become a sustainable resource for the food industry.

In his research, Koirala explored how lactic acid bacteria starters adapt to the complex structure of spent grain. His experiments demonstrated that adding fermented spent grain to wheat bread improved its texture, moisture retention, and fiber content. Beyond these technological benefits, tests simulating human digestion in the laboratory indicated that fermented spent grain increases the production of substances beneficial for gut health, hinting at potential health advantages for consumers.

“The dual impact of dextran produced by lactic acid bacteria enhances both the texture and quality of food while supporting gut health,” said Koirala. “Also, the study aligns with the circular economy principles by reducing food industry by-products and waste, and promoting the development of healthy, fiber-rich food products.”

One of the key innovations in Koirala’s work involves adding sucrose to the spent grain during fermentation. This process encourages the lactic acid bacteria to produce dextran and oligosaccharides, two valuable compounds for both food manufacturers and consumers.

Dextran, a long-chain carbohydrate composed of glucose molecules, is already known in the food industry for its ability to improve texture and extend shelf life. In bread, for instance, dextran helps make the crumb softer and moister. Beyond its role in food, dextran has medical applications, including as a substitute for blood plasma.

Oligosaccharides, on the other hand, are shorter carbohydrate chains that act as prebiotics. They stimulate the growth of beneficial gut bacteria, potentially improving digestive health and supporting the immune system. Oligosaccharides naturally occur in foods such as onions, garlic, and asparagus, but Koirala’s research shows that they can also be produced during the fermentation of spent grain.

By turning what is often considered waste into functional ingredients, Koirala’s work addresses two significant challenges facing the food sector: sustainability and health. The growing consumer interest in gut health and sustainable food systems makes his findings particularly timely.

“In practice, food industry by-products can be transformed into valuable food ingredients through lactic acid bacteria fermentation,” Koirala explained. “This provides food manufacturers with a sustainable ingredient that improves product quality and offers health benefits to consumers.”

Koirala’s research adds to a broader trend of exploring upcycling in food production, where materials previously viewed as waste are reimagined as valuable resources. As sustainability becomes a central focus across industries, such innovations could help reduce environmental impact while meeting the rising demand for health-focused food products.

Koirala will defend his doctoral dissertation titled Upcycling of brewers' spent grain via in situ synthesis of dextran and oligosaccharides by lactic acid bacteria - Regulatory mechanisms and effects on gut microbiota metabolites at the Faculty of Agriculture and Forestry, University of Helsinki, on 1 July 2025. The public examination will be held at Biokeskus 2, Auditorium 2041, Viikinkaari 5, starting at noon. Associate Professor Felis Giovanna from the University of Verona will serve as the opponent, and Kati Katina as the custos.

The dissertation is also available electronically via Helda, the University of Helsinki’s digital repository.