Evaluation of fatty acid profile, physicochemical properties and antioxidant activity of grape seed and sesame oil combinations

Grape seed oil includs high contents of linoleic acid (68-76 %) which is essential fatty acid for human and necessary for body textures. despite being rich in essential fatty acids, grape seed oil has low oxidative stability which can be increased by using different methods such as mixing with the other oils that have high oxidative stability. Between vegetable oils, sesame oil is one of the most stable one against oxidation. This can be because of high percent of antioxidant phenolic compounds. The aim of this study is mixing grape seed oil with sesame oil for incresing the oxidative stability. In this study, samples of different proportions of sesame oil (0, 25, 50, 75 and 100 %) were mixed with grape seed oil (100, 75, 50, 25 and 0 %). The samples were evaluated for fatty acid profile, physicochemical properties and antioxidant activity. The iodine number was measured by Hanson method in edible oils and fats. The calculation of peroxide number was carried out according to AOCS No. 53-8 Cd method. The oxidative stability was evaluated applying the Rancimat method. In order to determine the composition of fatty acids, the methyl ester of fatty acids was prepared according to National Iranian Standard No. 4090. Then, analysis of fatty acids was carried out with a Gas Chromatography (China Techcomp Model) equipped with flame ionization detector according to AOAC No. 22/963. Total phenol and total antioxidant activity were measured according to Jannat et al. (2010) method. The total antioxidant activity was evaluated according to the iron oxidation antioxidant capacity assessment method described by Benzie and Strain (1996) and the absorbance of the samples at 593 nm was measured by Japan's Shimadzu Spectrophotometer. Measurement of phenolic compounds of all samples was performed on the basis of the FolinCyclotomy colorimetric method described by Velioglu et al. (1998). All tests were performed in three replications and analyzed in a completely randomized design using SAS software (version 9.29). To compare the mean of different characteristics, Duncan's multiple range test was used at 95% probability level. The results show that the highest percentage of fatty acid in various samples (sesame oil, grape seed oil and mixed ratios of these oils) is related to linoleic acid, followed by oleic acid, palmitic acid and stearic acid. In general, linoleic acid was the dominant component of sesame oil (42.52 %) and grape seed oil (62.50 %). By increasing the proportion of sesame oil from 25 to 75 %, the linoleic acid content of the samples decreased. While oleic, palmitic and stearic fatty acids increased in combined samples. The highest and lowest index of peroxide was related to grape seed oil (7. 21 mg /kg) and sesame oil (2.34 mg /kg), and with increasing the proportion of sesame oil in the oil mixture, the peroxide index significantly decreased (p≤0.05). The amount of iodine number of pure sesame oil samples (102.41 g /100 g) was less than grape seed oil (128.53 g /100 g) and increasing the proportion of sesame oil in the oil mixture reduced the iodine number of the samples. The content of phenolic compounds and the antioxidant power of sesame oil (204.43mg/l) was higher than grape seed oil (231.01 mg/l). The results of sensitivity measurement of pure oils and their mixture to oxidation one week after extraction, by Rancimat test showed that the 210 خاکباز حشمتی، باستانی و… نشریه پژوهشهای صنایع غذایی/ جلد 29 شماره 1 /سال 1398 highest and lowest stability was related to sesame oil and grape seed oil. With increasing the proportion of sesame oil in the oil mixture, the stability level increased significantly (p≤0.05). According to the National Iranian Standard No. 5950, the minimum stability value (in 110°C) is 12 hours. Thus, the stability of sesame oil (21.21 h) and the mixture of grape seed oil and sesame oil (12.79-18.42 hours) was acceptable within the national standard of Iran, while the stability of grape seed oil (7.33 h) was far less than the level approved by standard. The addition of sesame oil to grape seed oil increased the number of phenolic compounds, antioxidant strength and oxidative stability of the mixed oil samples. Considering the price of the product and the importance of the nutritional quality and stability of the oil, combining 75 % sesame oil and 25 % grape seed oil has the best nutritional quality and lower cost than pure sesame oil formula.