Impact of Dietary Polyphenols on Enzyme Activity in Human Gut Microbiota

Thesis Abstract

The composition and functional capacity of the human gut microbiota play a critical role in nutrient metabolism and overall health, yet the influence of dietary polyphenols on microbial enzymatic activity remains insufficiently understood, presenting an important gap in nutritional microbiology research. This study aims to elucidate the impact of specific dietary polyphenols—namely, flavonoids, phenolic acids, and stilbenes—on key enzymatic functions within the gut microbiota, including ?-galactosidase, ?-glucuronidase, and azoreductase activities. The primary objectives are to quantify changes in enzyme activity following controlled polyphenol interventions, identify correlations between polyphenol molecular structures and enzymatic modulation, and explore shifts in microbial community composition associated with these enzymatic alterations. Employing a quasi-experimental design, this research recruited a diverse sample of 120 adult participants from urban communities, stratified by age and dietary habits. Participants were randomly assigned into three groups a control group maintaining their habitual diet and two intervention groups consuming diets enriched with standardized doses of polyphenol-rich foods—such as berries, red grapes, and dark chocolate—over a 12-week period. Fecal samples were collected at baseline, midpoint, and study conclusion to assess microbial enzyme activity and community composition. Enzymatic assays were conducted using spectrophotometric methods standardized for gut microbiota extracts. Microbial community profiling employed 16S rRNA gene sequencing analyzed through QIIME2, while metabolomic profiling of polyphenol metabolites utilized liquid chromatography-tandem mass spectrometry (LC-MS/MS). Data analysis involved mixed-design ANOVA to evaluate temporal changes within and between groups, multiple regression models to assess relationships between polyphenol intake, microbial taxa, and enzymatic activity, and multivariate redundancy analysis to explore the interaction networks. Expected findings include a significant increase in beneficial enzymatic activities such as ?-galactosidase and azoreductase in polyphenol-consuming groups, accompanied by a reduction in potentially harmful enzymes like ?-glucuronidase. These enzyme activity shifts are anticipated to correlate with an increase in microbial taxa associated with health benefits, such as Bifidobacterium and Lactobacillus, and augmented production of bioactive polyphenol metabolites. The research aims to reveal structure-activity relationships, indicating that the chemical features of polyphenols influence microbial enzymatic pathways, thus advancing understanding of diet-microbiome interactions. This study contributes novel insights into how dietary polyphenols modulate microbial enzyme activities, potentially altering microbial functionality and metabolic outputs relevant to human health. It extends current knowledge by integrating microbial community analysis with enzymatic and metabolomic profiling, providing evidence for dietary strategies targeting microbiota-mediated health benefits. The findings will inform future dietary recommendations and functional food development aimed at promoting a favorable gut microbial environment. The main conclusion underscores the potential of dietary polyphenols to serve as modulators of microbial enzymatic functions, suggesting that strategic inclusion of polyphenol-rich foods could enhance gut health and mitigate disease risk. Recommendations include incorporating specific polyphenol sources into diets and exploring personalized nutrition approaches based on microbiota profiles. Further research is advised to investigate long-term effects and the mechanistic pathways underlying microbial enzyme regulation, with larger population studies needed to establish causality and broader applicability.