Extraction of phenolic compounds from potato peel (Ramus variety) with solvent and ultrasound-assisted methods and evaluation of its antioxidant activity in soybean oil

In the present study the effects of extract from the peels of Ramus potato variety as a natural antioxidant in refined soybean oil were investigated using the Schaal oven and Rancimat methods. Phenolic antioxidants of potato peels were extracted by two different solvent extraction methods (Solvent with methanol and ultrasound-assisted method with different solvents including methanol، ethanol، hexane، acetone and water). The total phenolic compounds were determined according to the Folin–Ciocalteu method. Maximum amount of extract was obtained with water، followed by methanol and ethanol but maximum amount of phenolics was obtained with methanol، followed by water and ethanol by ultrasound method. Sonication improved the total phenolic compounds of the potato peel extract and shortened the extraction times. After 16 days storage at 63°C،soy bean oil containing 200، 800، 1600، and 2400 ppm of methanolic extract of potato peels، attained lower peroxide values (PV، 42. 67، 37. 35، 24. 65 and 19. 09 meq/kg، respectively) than the control sample (PV، 64. 08 meq/kg) indicating strong antioxidant activity. Oils treated with 200 ppm of BHA، BHT and TBHQ attaind PVs of 33. 20، 28. 88 and 9. 96 meq/kg، respectively، after 16 days storage at 63°C. Also، results Rancimat (at 90،120،150°C) showed that potato peel extract، at concentrations of 1600 and 2400 ppm exhibited strong antioxidant activity which was almost equal to synthetic antioxidants (BHA & BHT).