Investigation on the Antioxidant Activity of Gallic Acid, Methyl Gallate and Syringic Acid in Soybean Oil

In the present study, oxidative stability of gallic acid, methyl gallate, and syringic acid at four concentration (200, 400, 800, and 1600 ppm) and three temprature (110, 120, and 130 °C) levels in soybean oil was studied using rancimat. The results showed that the fatty acid profile of this oil, mainly consist of linoleic acid (51.01 %), oleic acid (24.50 %), palmitic acid (12.20 %), and linolenic acid (7.10 %). Among various tempretures, the induction period of gallic acid, methyl gallate, and syringic acid (200-1600 ppm) was at the range of 2.90 to 17.49, 2.38 to 16.94, 1.27 to 5.41 h, respectively. With increasing the conceration of gallic acid, methyl gallate, and syringic acid or decreasing temperature, the oxidative stability was increased, thus oxidation rate was decreaed. Antioxidant activity of gallic acid and methyl gallate in soybean oil were not difference at different temperatures, but syringic acid showed lower power in oxidative stability of soybean oil, as compered with control sample. Generally, gallic acid and especially methyl gallate have high potential in increasing oxidative stability of edible oils, specially soybean oil.