Effects of phenolic compounds extraction from acorn fruit ́s (Quercus branti var persica Lindl.) with different solvents on antioxidant activity in oxidative stability of sunflower oil

The species of oak, the Quercus genus, is classified into Fagaceae family. Acorns (Quercus branti var persica Lindl.) have been traditionally used for treatment of many diseases such as diarrhea, collywobbles, hemorrhoid, rickets, anemia, eczema and varix. The objective of this research was extraction of phenolic compounds with various solvents and determination of antioxidant activity of the extracts in oxidative stability of sunflower oil. Phenolic compounds were extracted with methanol (80%), ethanol (70%) and water and total phenolic content was measured by Folin-Ciocalteu method. Extracts of acorns at three different concentrations (250, 500 and 1000 ppm), BHA and BHT at two concentrations of 100 and 200 ppm and TBHQ at 200 ppm were added to the sunflower oil and all samples were kept at 70°c for 12 days. Protective effects of the extracts in stabilizing sunflower oil were tested by measuring peroxide and thiobarbituric acid values at definite time intervals. Total phenolic content of water, ethanolic and methanolic extracts were 79.38, 138.49 and 183.96 (mg tannic acid equivalent/gr dry extract), respectively. During the experimental period, the peroxide and thiobarbitoric acid values of the control samples were raised from 26.23 to 328.88 (meq peroxide/ kg oil) and 0.073 to 0.58 (mg malon aldehyde/kg oil) respectively. TBHQ showed the highest oxidative stability at all days of the experiment. Methanolic extracts (at 500 and 1000ppm concentration) was the best among other extracts and stronger than BHT. Also, other extracts at various concentrations were comparable with BHA and BHT at different levels.