Green extraction of soluble dietary fibre from coffee silverskin: impact of ultrasound/microwave-assisted extraction

Coffee silverskin (CSS), a potential source of soluble dietary fibre (8%-11%), is a major coffee by-product obtained during the coffee roasting process. Ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) have been considered as efficient and economic novel extraction techniques. In this study, UAE, MAE and simultaneous ultrasound-microwave-assisted extraction (UMAE) techniques were investigated for soluble dietary fibre (SDF) extraction from CSS and compared with conventional solvent extraction (CSE). The highest recovery rate of SDF was accomplished by UMAE (42.7 +/- 0.4%), which was 1.5-fold, 1.9-fold and 1.2-fold of the recovery rates achieved by CSE, UAE and MAE, respectively. The extraction time of UMAE was 20 min, which was the same as UAE and MAE, and 4.5-fold less than CSE. It implied that the combination of UAE and MAE could enhance the extraction process by increasing the recovery rate as well as by reducing extraction time as compared with CSE or other individual novel extraction methods applied. Nutritional composition and physicochemical characteristics of the SDF extracts from CSS were also investigated in the study.