Effects Of Fatty Acids And Micro Components Of Walnut Oil On Oxidative Stability

Walnut(Juglans regia L.) has a vast distribution and a long history of cultivation with its great edible value and medical value. Walnut oil rich in both unsaturated fatty acids as linoleic acid, linolenic acid and minor components as tocopherols, flavone, β-carotene which was prepared by modern technology with walnut as raw materials, for the reason that walnut oil has a extensive physiological functions and biological effects in the body. However, due to the abundant unsaturated fatty acids, especially polyunsaturated fatty acids, walnut oil is easy to oxidative which reduces its organoleptic qualities and nutritional value. The object and results of this paper were as follows:Firstly, the physico-chemical properties, fatty acid, micro component content and oxidative stability of walnut oil were determined following extraction either using solvent or aqueous enzymatic methods. The result showed that the preparation methods have significant effects on the physico-chemical properties,micro component content and oxidative stability and have no different influence on the fatty acid composition. On the whole, according to the changes of their peroxide value and oxidative stability index(OSI), walnut oil extracted by the solvent method contained more content of antioxidant component and a higher oxidative stability compared with the aqueous enzymatic.Secondly, the oxidation stability of walnut oil was evaluated by the Rancimat method and oven method and the correlation between the two methods was analyzed. Single factor experiment and Box-Behnken experiment were investigated at the same time to determine the effects of temperature, airflow and sample weight on the OSI of walnut oil. Results showed that OSI which measured by the Rancimat method had highly significant correlation with theperoxide value, conjugated value and carbonyl value(p< 0.01). The rate constant and the activation energy changed with the temperature during the oxidation of walnut oil, which due to the shelf-life of walnut oil predicted by the Rancimat method and oven method was some difference with the real shelf-life. Although oven method can be instead by the Rancimat method to determine the oxidative stability of walnut oil, it is not accurate to extrapolate the shelf-life of walnut oil by the Rancimat method.Thirdly, six kinds of walnut oil grown in different area of China had been analyzed for physicochemical properties, fatty acid composition, micro component contents and oxidative stability by variance analysis. The correlation between lipid composition, micro component contents and OSI has been analyzed by regression analysis at the same time. Result showed that, six kinds of walnut oil with varying degrees of difference on their physicochemical properties, lipid composition, micro component contents and oxidative stability.It was a good correlation obtained between lipid composition, micro component contents and OSI by regression analysis(p< 0.01). The relative contribution of each fatty acid composition: linoleic> stearic acid> palmitic acid> oleic>linolenic; the relative contribution of four antioxidants compositional to the production of hydroperoxides were tocopherols> phenolics> flavonoids>β-carotene, and to the production of carbonyls were phenolics> tocopherols>flavonoids> β-carotene.At last, walnut oil has been blended with almond oil and sweet apricot kernels oil, and physicochemical properties, antioxidant activity in vitro,oxidative stability and storage stability of walnut oil and its blends had been determined and be analyzed by analysis of variance and regression analysis. The result showed that, add almond oil and sweet apricot kernels oil in walnut oil had a significant impact on its physicochemical properties, antioxidant activity in vitro, oxidative stability and storage stability. Blended with almond oil and sweet apricot kernels oil will significantly increase the oxidative stability and antioxidant activity in vitro of walnut oil and the higher ratio of almond oil and sweet apricot kernels oil, the better oxidative stability and antioxidant activity in vitro of walnut oil. So that, blend with almond oil and sweet apricot kernels oil could significantly prolong the shelf-life of walnut oil.