Metabolite profiles, antioxidant and antibacterial activities of coffee skin waste extract ( Coffea robusta I .)

Abstract This study aims to determine the metabolite profiles, antioxidant, and antibacterial activities of extracts from cascara and silverskin, coffee-skin by-products of Coffea robusta L . Cascara is the exocarp and mesocarp as a protective layer of coffee cherries, while coffee silverskin is an epidermis layer that serves as the main protector of coffee beans. The extraction of coffee silverskin and cascara was performed using the maceration method with water and 70% (w/v) ethanol as a solvent. The extract obtained was dried by air drying at room temperature and rotary evaporation followed by freeze-drying. The antioxidant activity assay employing the ABTS method indicated that the ethanolic extract of coffee silverskin exhibited moderate antioxidant activity with an IC 50 value of 113.75 µg/mL, while the ethanolic extract of coffee cascaras had an IC 50 value of 2471.73 µg/mL and was categorized as inactive antioxidant activity. LC-HRMS analysis revealed that the main metabolites in the silverskin, both ethanolic and water extracts were phenolic derivates, amino acids, fatty acids, fatty amides and caffeine. The antibacterial activity assay employing the disc diffusion method demonstrated that the ethanolic extract of silverskin at 2500 mg/L reduced the proliferation of Escherichia coli FNCC 0091 and Salmonella typhimurium FNCC 0050, with inhibition zones measuring 11.66 mm and 10.68 mm, respectively. The ethanolic extract of coffee silverskin shows potential as a functional food ingredient and active compound with antioxidant and antibacterial properties.