Thermo-Induced Endogenous Contaminants (TECs) in Tea—A Review of the Prevalence, Health Risks, Analytical Techniques, Pathways, and Processing Effects

Abstract

Tea, a globally consumed beverage, is valued for its unique flavor and health-promoting properties, while recent studies observed thermo-induced endogenous contaminants (TECs) with genotoxic and carcinogenic potential in tea products. However, research on this topic remains fragmented. This is the first systematic review to comprehensively analyze the multiple TECs within the tea matrix. Our work bridged the knowledge across the prevalence, health risks assessment, analytical challenges, formation pathways of TECs, and processing influences in tea to provide a unified view. Multiple TECs have been detected at concerning concentrations in tea products, while their co-occurrence may result in additional synergistic or cumulative toxic effects. However, the complex tea matrices and the diverse physicochemical properties of these compounds hinder the simultaneous analysis of multiple TECs. Drying is identified as the critical process in the formation of TECs, as most TECs originate from Maillard reactions. The effects of tea components and processing factors on the formation of each TEC in tea differed. The core novelty of this work is a visual conceptual framework that synthesizes these key findings, thereby identifying current research gaps. Future research should focus on developing robust analytical methods for simultaneous TEC determination, optimizing processing to balance tea quality and TEC reduction, elucidating tea matrix effects on TEC formation, and conducting health risk assessments of TEC mixtures in tea products. This work aimed to provide a foundational roadmap linking the tea industry and the scientific community to solve these growing concerns.