Improving the Thermoxidative Stability of Soybean Oil Using Some Herbal Extracts

Abstract

: Soybean oil is considered one of the world’s major oil seed crop. Refined and deodorized soybean oil is used extensively in frying oils, salad oils and many other foods. In spite of the technological treatments of the oil still it contains 84.53% of unsaturated fatty acids which make it prone to autoxidation and the development of rancidity. Thus, the present study aims at reducing oxidation by using natural antioxidants extracted from herbs rather than using the synthetic antioxidant TBHQ which may cause health hazards and toxicological concerns. General quality tests and fatty acid composition of the refined soybean oil used in the present study was assessed. Rosemary, thyme and sage were extracted using Clevenger apparatus. Yield, total phenolic and flavonoids were measured in the herbal extracts. The antioxidant activity of the extracts was measured by two methods (DPPH and FRAP). The herbal extracts were introduced at 400 ppm to soy oil in the presence of a control and a synthetic antioxidant TBHQ at 150 ppm. Oven test was used for accelerating oxidation (180 o C ±5 C for 18hrs at 3hrs interval) and results were tested by measuring acid value, peroxide value, iodine value, CD and CT, para Ansidine value and total oxidation (TOTOX value). Shelf life estimation was also measured using Anton’s bar rancidity device. Results of the oven test showed promising results for essential oils added to soybean oil as compared to control and TBHQ where rosemary showed a clear inhibition of oxidation in secondary oxidation tests (acid value and para Ansidine) whereas, thyme and sage showed more oxidation inhibition in the primary oxidation tests (peroxide value, CD, CT and iodine value). Calculation of shelf life of samples showed best results at 20 o C up to 30 o C but all decreased at 40 o C under the conditions used in the apparatus. Sensory evaluation tests after18hrs of heating were acceptable especially for rosemary and thyme. As for the fresh state all samples were acceptable with no significant differences between them.