A comprehensive review of coffee melanoidins: from structural characterization to biological activity

Coffee is a globally consumed beverage and a primary dietary source of melanoidins, which are by definition high-molecular-weight (HMW) nitrogenous macromolecules formed via Maillard reactions during roasting. Recent research has shifted the definition of melanoidins from simple end-stage polymers to a dynamic structural process involving both low-molecular-weight (LMW) and HMW fractions. These compounds comprise approximately 23% of the brewed coffee content and significantly influence its organoleptic properties, including color, aroma, and foam stability, as well as biological activities. This review provides a comprehensive analysis of the chemical architecture of coffee melanoidins, characterized by a unique polysaccharide-dominated skeleton (primarily arabinogalactans) integrated with proteins and phenolic compounds like chlorogenic acids. Furthermore, we examine the factors influencing their formation-such as bean species, geographical origin, and roasting degree-and evaluate their metabolic fate within the gastrointestinal system. Emerging evidence highlights the diverse biological activities of coffee melanoidins, including potent antioxidant, anti-inflammatory, antimicrobial, and prebiotic effects, within others. This review underscores the role of coffee melanoidins as significant dietary bioactive components with the potential to modulate human physiology and prevent chronic metabolic and oxidative stress-related diseases.