Assessing the Differences in Phenolics, Antioxidant and Anti-Tyrosinase Activities of Spent Coffee Ground Fractions

Abstract

Spent coffee ground (SCG) is among the high-volume by-products generated from coffee processing. The present study aimed to determine phenolic acids, antioxidant activity and tyrosinase inhibitory effect of fractions obtained from crude extracts of SCG. The fractionation was performed using different polarity-based solvents, resulting in n-hexane, ethyl acetate and aqueous extracts. Total phenolic content was evaluated by Folin – Ciocalteu method while individual phenolics were quantified using HPLC-DAD. Antioxidant activity was assessed by DPPH and ABTS assays. Inhibition of tyrosinase was determined using an in vitro bioassay. The ethyl acetate fraction was shown to have a higher amount of total phenolic content (227.17 mg GAE/g) compared to the other fractions and the methanol crude extract. It also exhibited  higher antioxidant activity than the other fractions and was identified as the most effective tyrosinase inhibitor (87.59  8.62 mg KAE/g). Gallic acid, chlorogenic acid, ferulic and salicylic acid had positive correlations with antioxidant activity, with Pearson’s correlation coefficients ranging between 0.808 and 0.990. Through the correlation analysis, most of the monitored phenolic acids were shown to contribute to the inhibition of tyrosinase. The study has provided a better understanding of phenolic-rich SCG with the hope that it can further the use of this valuable by-product in food and cosmeceutical industries.