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Item Microbial polyphenol oxidases in tea catechin oxidation: A novel approach to tea biotransformation(Elsevier Ltd on behalf of the Institution of Chemical Engineers, 2025-12-01) Muthulingam P; Rashidinejad A; Popovich D; Punyasiri PAN; Nanayakkara CM; Mesarich CHBlack tea processing is a complex biochemical process influenced by both plant-derived and microbial enzymes, during which catechins undergo enzymatic oxidation to form compounds such as theaflavins and thearubigins - key contributors to tea's colour, flavour, and health benefits. While endogenous polyphenol oxidases have traditionally been regarded as the primary agents of catechin oxidation, emerging evidence highlights the significant role of bacterial species in modulating tea quality through enzymatic transformations. In this study, bacterial communities were isolated from various stages of black tea processing and screened for extracellular polyphenol oxidase (PPO) activity. Among 43 isolates, Alcaligenes faecalis exhibited the highest PPO activity. Enzyme profiling of A. faecalis revealed peak laccase and catechol oxidase activities at 36 h (12.6 U/mL and 3.6 U/mL, respectively), while peroxidase activity peaked earlier at 24 h (4.2 U/mL) in nutrient broth. High-performance liquid chromatography (HPLC) analysis showed a concentration-dependent decline in epigallocatechin gallate (EGCG) from 816.24 mg/L to 333.33 mg/L, accompanied by the formation of gallic acid (up to 29.81 mg/L), epigallocatechin, gallocatechin, gallocatechin gallate, and tea pigments. These results confirm the enzymatic degradation and transformation of EGCG into key tea polyphenols, closely mimicking traditional black tea oxidation. A proposed bioconversion pathway outlines the microbial transformation of EGCG into tea pigments. These findings demonstrate the functional contribution of tea-processing-associated bacteria and propose microbial enzymes as a novel biocatalytic tool to enhance black tea fermentation and improve product quality. Future research should focus on enzyme purification and industrial scalability to integrate microbial biotransformation into tea production.Item A Study of the Interaction, Morphology, and Structure in Trypsin-Epigallocatechin-3-Gallate Complexes(MDPI (Basel, Switzerland), 2021-07-28) Liu J; Ghanizadeh H; Li X; Han Z; Qiu Y; Zhang Y; Chen X; Wang A; Tresserra-Rimbau A; Bresciani LUnderstanding the interaction between proteins and polyphenols is of significance to food industries. The aim of this research was to investigate the mode of aggregation for trypsin-EGCG (Epigallocatechin-3-gallate) complexes. For this, the complex was characterized by fluorescence spectroscopy, circular dichroism (CD) spectra, small-angel X-ray scattering (SAXS), and atomic force microscope (AFM) techniques. The results showed that the fluorescence intensity of trypsin-EGCG complexes decreased with increasing the concentration of EGCG, indicating that the interaction between trypsin and EGCG resulted in changes in the microenvironment around fluorescent amino acid residues. The results of CD analysis showed conformational changes in trypsin after binding with EGCG. The results from SAXS analysis showed that the addition of EGCG results in the formation of aggregates of trypsin-EGCG complexes, and increasing the concentration of EGCG resulted in larger aggregates. AFM images showed that the trypsin-EGCG complex formed aggregates of irregular ellipsoidal shapes with the size of about 200 × 400 × 200 nm, with EGCG interconnecting the trypsin particles. Overall, according to these results, it was concluded that the large aggregates of trypsin-EGCG complexes are formed from several small aggregates that are interconnected. The results of this study shed some light on the interaction between digestive enzymes and EGCG.