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Rabrenovic B., Dimic E., Maksimovic M., Sobajic S.,Gajic-Krstajic L. (2011): Determination of fatty acid and tocopherol compositions and the oxidative stability of walnut (Juglans regia L.) cultivars grown in Serbia. Czech J. Food Sci., 29: 74-78.Five cultivars (Sampion, Jupiter, Sejnovo, Elit, and Geisenheim 139) of walnuts (Juglans regia L.) were collected during the 2008 harvest, from Cacak, Central Serbia. Two techniques of oil extraction were implemented -cold pressing and organic solvent extraction. The influence of the implemented methods on the fatty acid composition, tocopherol content as well as oxidative stability was examined. Predominant fatty acids were palmitic, oleic, linoleic, and linolenic acids. The oleic acid content of the oils ranged from 15.9-23.7% of the total fatty acids, while the linoleic acid content ranged from 57.2-65.1% and that of linolenic acid from 9.1-13.6%. The process of oil extraction had no significant effect on the content and composition of fatty acids in the oil. The total content of tocopherols ranged from 28.40 mg/100 g to 42.40 mg/100 g of the extracted oil. The most common tocopherol in all samples was γ-tocopherol. The oil extracted using the Soxhlet method contained higher amounts of total tocopherols while the stability of the oil samples, expresed as induction period, ranged from 5.0 h to 7.1 hours. Reduced stability of the oil samples as measured by the Rancimat method was negatively correlated with the level of linolenic acid and total content of tocopherols.

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Antioxidant (AO) activity of cold pressed pumpkin (Cucurbita pepo L.) seed oil, produced from three naked and one hulled variety, was assessed using a DC polarographic assay based on a hydrogen peroxide scavenge (HPS). Results are expressed as the decrease of the anodic oxidation current of hydrogen peroxide obtained upon addition of methanolic extract of the investigated oils. Strict correlations of HPS and (1) radical scavenging capacity against the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) (0.99), (2) the induction period estimated by a Rancimat test (0.99) and (3) total phenolic content estimated by Folin-Ciocalteu (FC) assay (0.99) were obtained. In addition, a significant correlation of HPS and the content of d-tocopherol (0.87), squalene (0.67) and color CIE a* (-0.89) was found. Based on the results reported, the polarographic assay was found to be suitable for determination of AO activity as an indicator of the quality and oxidative stability of oil.