The Effect of Solvent Type, Time and Extraction Method on the Chemical Compositions and Antioxidant Activity of Eggplant Peel Extract

Antioxidants are compounds that protect the body against free radical damages. Eggplants are one of the most common vegetables consumed all around the world, containing large amounts of bioactive compounds with medicinal properties. The aim of this study was to investigate the effect of solvent type (80% ethanol and 80% methanol and water), extraction method (ultrasonic bath and soaking) and extraction time (20, 60 and 80 minutes) on the amount of phenolic, flavonoids and anthocyanin compounds and DPPH  radical scavenging activity, Fe reducing power and total antioxidant capacity of eggplant peel extracts. The results showed that 80% ethanol was the best solvent for extraction of phenolic compounds (86.87 mg gallic acid/g), whereas the maximum flavonoids content (18.23 mg rutin/g) was extracted using 80% methanol. The anthocyanin content of the extracts varied in the range of 0.8-4.33 (mg cyanidine/g), and the use of ultrasound significantly increased the anthocyanin extraction. The DPPH radical scavenging activity and Fe reducing power of the ultrasound extracts were more than the extracts obtained from soaking method. The maximum DPPH radical scavenging activity (51.96%) and Fe reducing power (2.46, absorption at 700 nm) were related to aqueous and methanol extracts, respectively and derived from ultrasonic bath method and extraction time of 80 minutes. The maximum total antioxidant capacity (2.23 and 2.27, absorption at 695 nm) was related to methanolic extracts obtained from ultrasonic bath and extraction time of 60 and 80 minutes. As a result, utilization of ultrasound is a useful method for extraction of bioactive compounds present in eggplant peel. In addition, the obtained natural antioxidant compounds can be used in food formulations as alternatives to synthetic antioxidants and functional foods.