Antioxidative phenolics obtained from spent coffee grounds (Coffea arabica L.) by subcritical water extraction

Response surface methodology (RSM) was employed to optimize subcritical water extraction (SWE) of spent coffee grounds (SCG) with emphasis on the yield of total phenolics and radical scavenging capacities on 2,2-azinobis-(3-ethylbenzothiazolin-6-sulfonic acid) (ABTS(center dot+)) and 1,1-dipheny1-2-picrylhydrazyl (DPPI-1(center dot+)). The analysis involved three variables: temperature (160-180 degrees C), time (35-55 min) and solidto-liquid ratio (14.1-26.3 g/L). The optimal conditions for total phenolic compounds (86.23 mg GAE/g), antioxidant activity in terms of ABTS** (81.38 mmol TE/100g) and DPPH center dot+ (42.13 mmol TE/100 g) scavenging activities were predicted to be in ranges of 160-180 degrees C/37.9-55.0 min/14.1 g/L. The verified TPC (88.34mg GAE/g), antioxidant activity on ABTS(center dot+) (88.65 mmol TE/100g) and DPPF1* (38.28 mmol TE/100g) based on superimposing contour plots (179 degrees C, 36min, and 14.1 g/L) were in good agreement with the predicted data obtained under optimal conditions. 3-O-caffeoylquinic acid, 4-0-caffeoylquinic acid and 5-O-caffeoylquinic acid were found to be the major contributor to the antioxidant activities of SCG extract. (C) 2015 Elsevier B.V. All rights reserved.