Abstract
The escalating global prevalence of neurobehavioral disorders necessitates innovative, efficacious interventions capable of modulating the Microbiota-Gut-Brain Axis (MGBA). This PhD thesis systematically engineered and validated a portfolio of novel, multi-functional synbiotic formulations, challenging the limitations of conventional systems by prioritizing targeted psychobiotic efficacy through metabolic tailoring and advanced matrix design. The research was delineated into three cohesive investigative thrusts. Initially, the underexplored psychobiotic potential of non-conventional yeasts was functionally profiled. Out of ten strains screened, strains including Wickerhamomyces anomalus GY4, Saccharomyces cerevisiae KFAY3 and Lachancea fermentati 9Y demonstrated superior gastrointestinal transit (GIT) resilience and critical adhesion properties (auto-aggregation and hydrophobicity). Phenomic analyses confirmed the metabolic superiority of W. anomalus GY4 in the in vitro generation of neuroactive compounds, notably exhibiting the highest yields of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and Short-Chain Fatty Acids (SCFAs). Secondly, an in vitro fermentation model was designed to elucidate the interaction between Fructophilic Lactic Acid Bacteria (FLAB) and a pre-digested soybean matrix. The soybean substrate, rich in proteins and bioactive precursors, was pre-digested under simulated gastrointestinal conditions to improve nutrient accessibility and reduce anti-nutritional factors (ANFs). Fermentation with high GIT resistant FLAB strains, specifically Apilactobacillus kunkeei PL34, not only significantly reduced inherent ANFs but also augmented the concentration of low-molecular-weight peptides, antioxidant activities and bioactive phenolic derivatives (e.g., isoflavones). Crucially, subsequent in silico analyses provided robust mechanistic evidence by predicting favorable Blood-Brain Barrier (BBB) permeability and potential affinity for neurotransmitter receptors and cytokine targets for the resulting compounds. Finally, the third study addressed commercial demands for metabolically healthy beverages by engineering a low sugar, phenolic-rich functional formulation from elderberry juice (Sambucus nigra L.). This involved leveraging the synergistic co-metabolism of optimized binary yeast cultures (Hanseniaspora uvarum and Metschnikowia pulcherrima with Hanseniaspora opuntiae). This strategy achieved a dual functional goal: significant saccharide catabolism resulting in up to 88.0% sugar reduction, coupled with the enhanced release of neuroprotective phenolics and a further substantial enrichment in the anxiolytic metabolite GABA. Collectively, this PhD research elucidated multifaceted microbial strategies for modulating the MGBA. Through systematic functional profiling and metabolic characterization, it established the psychobiotic potential of non-conventional yeasts, revealed gut-level mechanistic interactions between FLAB and pre-digested soybean substrates, and engineered a metabolically enhanced, low-sugar phenolic beverage with elevated neuroactive metabolites. The findings underscore that targeted microbial selection, coupled with rational substrate conditioning, constitutes an effective framework for designing next-generation functional foods capable of predictable and potent psychobiotic modulation.