Enhancement of γ-aminobutyric acid (GABA) content in fermented milk by using Enterococcus faecium and Weissella confusa isolated from sourdough

In recent years, the development of GABA-enriched foods through exploiting lactic acid bacteria (LAB) has gained much attention. In this study, Enterococcus faecium MDM21 and Weissella confusa MDM8 with high GABA-producing activity were isolated from sourdough and used as single or co-cultures (with Lactococcus lactis subsp. lactis BRM3) in manufacturing fermented milk rich in GABA. The studied strains were non-hemolytic and did not show irregular antibiotic resistance patterns. E. faecium MDM21 exhibited higher acidifying and proteolytic activity and produced higher amounts of GABA in milk than W. confusa MDM8 and Lc. lactis subsp. lactis BRM3, all as single starter cultures. However, higher GABA concentration and lower fermentation time were obtained when they were used as co-cultures with Lc. lactis subsp. lactis BRM3. Overall, the results showed that co-culture of E. faecium MDM21 and Lc. lactis subsp. lactis BRM3 can be introduced as a good candidate to develop novel functional dairy products. Novelty impact statement: To the best of our knowledge, this is the first report to identify Weissella confusa as a GABA-producing strain. New fermented milk with high GABA content was produced, whereas no precursor had been used in the formulation. Co-cultures with a potent proteolytic strain enhanced the GABA content significantly in the final product.