Bioavailability, absorption, digestion and metabolism of natural hydroxycinnamic acids in gastrointestinal tract

Hydroxycinnamic acids (HCAs) including ferulic, caffeic, coumaric, rosmarinic and chlorogenic acids are widely present in plant-based foods and herbal extracts. They are renowned for their health-promoting properties such as antioxidant, anti-inflammatory, antidiabetic and anticancer activities. However, their bioavailability is low and their metabolic pathways within the gastrointestinal tract are highly complex. Hence, understanding how HCAs are transformed, absorbed, and metabolized during digestion is crucial to evaluate their physiological relevance. This review highlights the bioavailability, absorption, digestion and metabolism of natural HCAs. It comprehensively examines the bioavailability, absorption and digestion mechanism of natural HCAs across different digestive compartments, including the oral cavity, stomach and intestinal tract. Additionally, it critically discussed the key factors influencing the digestion and metabolism of HCAs such as pH, digestive enzymes and microbial composition. In the oral cavities, HCAs undergo limited enzymatic and oral bacterial degradation, with some exhibiting antimicrobial activity. Absorption in oral cavity and stomach is minimal, and HCAs are relatively stable under acidic gastric conditions. However, acidic environment in the stomach promotes partial degradation through reaction with salivary components to form thiocyanate and oxathiolone derivatives. The intestinal tract serves as the main site for HCAs absorption and degradation. The presence of various enzymes and alkali conditions causes the production of HCA metabolites such as glucuronides, sulfates and methylated derivatives. The metabolites possess the health benefits similar to those of the intact HCAs compounds. Further studies on the bioavailability, absorption and degradation metabolism of HCAs are strongly required for enhanced nutraceutical and therapeutic applications.