Coffee By-Products: An Overview of Their Antimicrobial Properties

Coffee is among the most widely consumed beverages globally being cultivated in nearly 80 countries. Its processing generates large quantities of by-products, including mucilage, pulp/husks, silverskin, parchment, and spent coffee grounds. Although traditionally treated as waste, these residues are increasingly recognized as valuable resources rich in bioactive compounds exhibiting antioxidant, antimicrobial, and health-promoting properties. This review explores the antimicrobial potential of coffee by-products, with particular emphasis on their chemical composition and mechanisms of action. Compounds such as caffeine, chlorogenic acids, polyphenols, and melanoidins have demonstrated inhibitory effects against a broad spectrum of bacteria, including both Gram-positive and Gram-negative bacteria. Many of these compounds, which originate from plant’s defensive system or result from Maillard reactions, are known to disrupt microbial membranes, inhibit DNA repair, and interfere with pathogen metabolism. However, the available literature on their antimicrobial effectiveness remains limited. In the context of the rising worldwide concern over antimicrobial resistance, coffee by-products represent a sustainable and promising source of novel antimicrobial agents. Their valorization may support advances in food preservation, pharmaceutical innovation, and waste management practices, contributing to the implementation of a circular economy framework in the coffee industry while promoting environmental, economic, and social sustainability.