Biosynthesis of γ-aminobutyric acid in bread matrices

Wheat bread is one of the most discarded food at the global level. To fulfill the goals of waste reduction and increase the circular economy activities, the re-utilization of bread still fit for food in the food chain is a priority. However, the utilization of wheat bread waste in the food chain is challenging. Lactic acid bacteria (LAB) fermentation has been recently studied as a potential processing method for bread waste slurry and applied as a dough ingredient in bread production. In LAB fermentation, functional and bioactive compounds can be produced. Some LAB strains can produce γ-aminobutyric acid (GABA), a neurotransmitter in animals’ central nervous system with multiple physiological functions. GABA has received much attention due to its numerous beneficial bioactivities. Currently, information on GABA biosynthesis by LAB fermentation in bread substrate is not available. In this thesis, the effects of LAB strain selection and fermentation substrates in waste bread fermentation were studied. Four different fermentation trials using wheat bread as substrate were performed to select the best LAB strain, optimize bread matrix composition, and fermentation parameters for GABA production. Microbial growth, pH, total titratable acidity, organic acids (High Performance Liquid Chromatography ), sugar composition (High-Performance AnionExchange Chromatography and Pulsed Amperiometric Detection), and GABA content were assessed. Among the conditions tested, the addition of wheat bran as a nutrient source improved the GABA production most significantly. Thus, this condition was upscaled for bakery uptake and used in a baking trial to produce value-added bread containing GABA. LAB fermentation of waste bread to produce functional bioactive compounds was proven to be a potential processing method applicable to bakery products. The combination of two food sidestreams, waste wheat bread and wheat bran, can be implemented as a strategy to re-utilize food by-products in the food chain