Biosynthesis of γ-aminobutyric acid by lactic acid bacteria in surplus bread and its use in bread making

Aims: The aim of this study was to investigate the effectiveness of bread as substrate for γ-aminobutyric acid (GABA) biosynthesis, establishing a valorization strategy for surplus bread, repurposing it within the food chain. Methods and results: Surplus bread was fermented by lactic acid bacteria (LAB) to produce GABA. Pediococcus pentosaceus F01, Levilactobacillus brevis MRS4, Lactiplantibacillus plantarum H64 and C48 were selected among 33 LAB strains for the ability to synthesize GABA. Four fermentation experiments were set up using surplus bread as such, added of amylolytic and proteolytic enzymes, modifying the pH or mixed with wheat bran. Enzyme-treated slurries led to the release of glucose (up to 20 mg g-1 ) and free amino acid, whereas the addition of wheat bran (30% of bread weight) yielded the highest GABA content (circa 800 mg kg-1 of dry weight) and was the most suitable substrate for LAB growth. The selected slurry was ultimately used as an ingredient in bread making causing an increase in free amino acids. Conclusions: Besides the high GABA concentration (148 mg kg-1 dough), the experimental bread developed in this study was characterized by good nutritional properties, highlighting the efficacy of tailored bioprocessing technologies as means to mitigate food wastage. Significance and impact of study: Our results represent a proof of concept of effective strategies to repurpose food industry side streams.