Optimisation of extraction conditions from eggplant peel by using response surface methodology

Antioxidants by eliminating and neutralizing the harmful free radicals play very important role in preventing oxidative deterioration of food. Eggplant is one of the vegetable has oxygen radical scavenging capacity and its activity has been correlated to content of phenolic and flavonoid compounds in eggplant’s peel. In this study the effects of solvent type (ethanol: water 100:0, ethanol: water 0:100, ethanol: water 50:50), time of ultrasound-assisted extraction (10, 15 and 20 min) and temperature (40, 45 and 50 ºC) on efficiency, total phenol content, total flavonoid content of extract was investigated and optimisation of extraction conditions were done with response surface methodology by using central composite design. The results of variance analysis showed that type of solvent and extraction temperature had the most effect on extraction efficiency and amount of total phenolic content and flavonoids. The optimised condition of extraction was obtained as ethanol: water ratio (25.19:74.81), 49.94 °C and 11.23 min for temperature and time of extraction respectively. Then the extract obtained under optimised condition and antioxidant activities of extract was compared to synthetic antioxidant (TBHQ) by useing of DPPH radical scavenging and beta-carotene-linoleic acid tests. Antioxidant activity of extract was related to phenolic and flavonoid content in both methods and by increasing in these compounds antioxidant activity of the extract increased. Eggplant peel extract due to have phenolic and flavonoid compounds has antioxidant activity and it can be suitable alternative for synthetic antioxidant.