Fermentation of raffinose family oligosaccharides by different yeast and bacteria in sour beer cofermentations

Abstract

Legumes are a widespread and nutritious food source, ingested worldwide and used to produce a variety of products. They are however also known for producing gas and bloating when ingested. This is due in part to raffinose family oligosaccharides (RFOs), which cannot be fermented by humans. They are instead fermented by gut bacteria, which causes the symptoms. To improve legume products, RFOs can be removed and utilised in other products. The utilisation of RFOs as adjunct in sour beer was assessed in this study, as well as the impact on the product.

An important factor of this was the fermentation of RFOs by different yeast or bacteria. A range of Lactococcus cremoris strains and a Lactiplantibacillus rhamnosus strain were selected, alongside Brettanomyces claussenii and Saccharomyces cerevisiae yeast. These strains were tested for growth in media with RFOs, beer media and media with known concentrations of growth inhibitors.

Several strains showed growth in these conditions and were selected for small and large batch sour beer cofermentations. The produced beers were assessed for chemical and physical properties, using commercial sours beers for comparison. Cofermentations with Lc. cremoris TF121 and both yeast strains produced organic acids, which were present in substantially higher amounts when RFOs were added. Sugar utilisation combined with the organic acid profile in small and large batch sour beers showed signs of RFO fermentation. The large batch beers were also tested for sensory difference, using a Tetrad test which showed that a significant number of participants could differentiate between samples. The study shows promising results for the utilisation of legume by-products from food production.