Free radical scavenging activity-based antioxidant analysis and infrared spectroscopy of peppermint-flavored coffee drink

Abstract

Peppermint essential oil canserve as a healthy flavoring additive to coffee drinks and provide health benefits by enhancing their antioxidant activity. Hence, this study aimed to examine the antioxidant activity of peppermint-flavored coffee drinks using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azinobis-(3-ethylenebenzothiazoline)-6-sulfonic acid (ABTS) free radical scavenging assays. Furthermore, Fourier transform infrared-attenuated total reflectance spectroscopy was performed to investigate the profile of compounds contributing to the antioxidant property. The experiments were conducted using a Complete Randomized Block Design with six replications. Two-factor treatments were as follows: soaking time (S), 0 (S0), 5 (S1), and 10 (S2) min; peppermint essential oil concentration (E), 0 (E0), 0.5 (E1), and 0.75% (E2) (v/v). N otably, both DPPH and ABTS assays revealed increased antioxidant activity of peppermint-flavored coffee drink where the coffee was soaked for 10 min in 0.75% peppermint solution. The coffee soaked for 10 min in 0.5% and 0.75% peppermint solutions showed a high scavenging effect against ABTS free radical, with 93.73 and 94.30% inhibition activity and half-maximal inhibitory concentrations of 0.272 and 0.267 ppm, respectively. Additionally, a new peak was observed at 1640 cm−1in peppermint solution-soaked coffee beans,which corresponded tothe C=C functional group in the limonene spectrum, an antioxidant compound in peppermint. Altogether, the findings show that peppermint essential oil enhanced the antioxidant activity of the coffee.