Lactobacillus brevis R2Δ as starter culture to improve biological and technological qualities of barley malt

The application of lactic acid bacteria (LAB) can be a challenging yet promising tool to control the endogenous microbiota during malting and to improve malt quality. In this study, a food-grade malt-based ingredient was fermented using an antifungal strain, Lactobacillus brevis R2Δ, and applied on barley grains during steeping and germination. Different variations of starter culture concentration and cell-free supernatant were compared to a control solution during pilot-scale malting trials. All treated barley samples showed a significant decrease in aerobic bacteria (up to 99.8% reduction) and a promotion of yeast growth when compared to the untreated control. The number of kernels contaminated with Fusarium spp. could be reduced by more than 90%, as confirmed by qPCR analysis. Shorter rootlets coincided with lower malting losses (−31.8%) and with increased extract yield (+3.1%). Differences in the enzymatic activity between the malts did not significantly alter the processability of the malts during brewhouse operations. Throughout yeast fermentation, no negative impact of LAB could be detected for the majority of attributes tested. Overall, the treatment containing living starter cultures and the highest amount of total titratable acidity (71 mmol L⁻¹) showed the most promising results when aimed at further enhancing the quality and safety of barley malt.