Aims The aim of this study was to investigate the effectiveness of bread as substrate for gamma-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.

The aim of this thesis was to create an optimized bioprocessing to solubilize the maximal amount of proteins from the wheat bran without losing their nutritional and technological quality. The hypothesis of this thesis was that a maximal degradation of the aleurone cell wall components would lead to a maximal amount of soluble proteins originally located inside the aleurone layer. The literature review further looked into possible extraction methods for wheat bran proteins. Fine wheat bran was chosen to be bioprocessed by using experimental design to find optimal conditions for protein solubilization. Bioprocessing was done either by using starter culture alone or a combination of selected enzymes and starter culture. Independent studied factors were time (8 h, 16 h, 24 h), temperature (20 °C, 27.5 °C, 35 °C) and enzyme dosage (5 nkat/g, 50 nkat/g, 500 nkat/g). Optimization was carried out by applying response surface methodology to analyze the relationship between the response and the independent variables. Optimized bioprocessing of wheat bran led to maximal protein solubilization of >50% for wheat bran both bioprocessed with starter culture and with starter culture and enzymes after fermentation time of 24 h. Thus, the amount of soluble protein increased 23%. This indicated that the use of enzymes did not improve the breaking down of the aleurone cell walls for protein liberation. Furthermore, the use of enzymes affected heavily the protein degradation for fermentations longer than 8 h. Since the amount of solubilized protein was higher for wheat bran bioprocessed for 8 h with starter only (>46%) than for wheat bran bioprocessed for 8 h with starter and enzymes (>40%), the use of enzymes for a larger scale production does not seem feasible.