Circular economy approach to coffee processing residue valorization: Bioactive by-product extracts for managing pre- and post-harvest fungal pathogens

Abstract

The coffee industry generates a large amount of waste that is usually discarded, creating an environmental and economic problem. However, these by-products can be a valuable source of bioactive compounds with antimicrobial properties and present an opportunity for use in crop protection, either pre- or post-harvest. Following the principles of the circular economy, this study proposes the extraction and characterization of bioactive products from coffee by-products, as well as the evaluation of their antifungal activity against pathogens that affect coffee plants and/or stored coffee beans, such as Fusarium xylarioides, Aspergillus flavus, A. niger, and Penicillium verrucosum. In vitro activity assays demonstrate high antimicrobial activity of the husk, parchment, defective green beans with silverskin, and silverskin extracts, with minimum inhibitory concentrations ranging from 15.6 to 375 μg mL⁻¹ against F. xylarioides, 31.2–1000 μg mL⁻¹ against A. flavus, 62.5–1000 μg mL⁻¹ against A. niger, and 62.5–1500 μg mL⁻¹ against P. verrucosum, depending on the by-product extract used. The most effective extract, derived from silverskin, was evaluated for pre-harvest protection of coffee plants and demonstrated complete inhibition of F. xylarioides-induced tracheomycosis at 15.6 μg mL⁻¹. In turn, a concentration of 62.5 μg mL⁻¹ of the silverskin extract was sufficient to prevent fungal growth of A. flavus, A. niger, and P. verrucosum on coffee beans. This concentration also prevented mycotoxin production by A. flavus, while a higher concentration of 125 μg mL⁻¹ was required to prevent aflatoxin production by A. niger. The reported findings support coffee by-products extracts as promising alternatives to synthetic fungicides, with the potential to improve the sustainability of the coffee industry.