Bioactive compounds from coffee husk (Coffea arabica) obtained by green extraction methods: Characterisation, antioxidant capacity and inhibition of lipid peroxidation.

Abstract

Coffee husk, the principal by-product of wet coffee processing, is an underutilized agro-industrial residue with significant potential as a source of bioactive antioxidant compounds. In the present study, four green extraction methods were evaluated: aqueous extraction (AQU), ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and enzyme-assisted extraction (EAE), for the recovery of bioactive compounds from the husk of two Coffea arabica varieties (var. caturra chiroso from Tolima and var. castillo from Antioquia, Colombia). Antioxidant capacity was determined by ABTS, DPPH, FRAP and ORAC assays. Principal component analysis (PCA) was applied to evaluate varietal differentiation. Selected extracts were assessed in an accelerated oxidation model using linseed oil. AQU yielded the highest total polyphenol content (831.63 mg GAE/100 g) and antioxidant capacity (14,036.27 μmol Trolox/100 g by ABTS). MAE generated the most enriched profiles in hydroxycinnamic acids and condensed tannins. UAE showed greater extractive efficiency with hydroalcoholic solvents. EAE was the least efficient method, attributed to the lignocellulosic recalcitrance of the matrix. PCA explained 88.1% of the total variance, separating varieties by bioactive profile; the caturra chiroso variety exhibited higher antioxidant capacity. AQU extracts at 250 mg/L delayed hydroperoxide formation in linseed oil by up to 37.3%, whilst MAE extracts showed pro-oxidant behavior towards peroxide formation but retarded the appearance of polar compounds at 250 mg/L (29.0%). These results demonstrate that coffee husk is a valuable source of natural antioxidants recoverable through green chemistry principles, with potential application in functional foods and cosmetic products.