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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.

Various grape seed samples collected in wineries, as a by‐product before and after the fermentation process of pomace and after fermentation and distillation process of pomace, are used for oil extraction by cold pressing. Fatty acid profile, content and composition of tocopherols, content and composition of phenols, as well as the oxidative stability of oils are investigated. Obtained results show that cold pressed grape seed oils are characterized by different nutritional quality and oxidative stability, due to peculiar effects of the fermentation and distillation processes. Cold pressed oil obtained from cleaned and dried seeds of grapes after fermentation and/or distillation process is richer in bioactive compounds compared to the oil obtained from grape seeds without fermentation. On the other hand, the high temperature in distillation process of pomace has a negative effect on the content of some bioactive compounds and oxidative stability of oil from this waste material. Practical Applications: In this paper, different cold pressed grape seed oils are analyzed for nutritionally important compounds and oxidative stability. The results show that, depending on the source of grape seeds as waste material, the nutritional quality of the obtained oils differs. In the production of high quality cold pressed grape seed oil, seeds from different sources of waste should not be mixed. It is not recommended to use the seeds from the waste material after distillation process in the production of high quality cold pressed grape seed oil. Some chemical characteristics of cold pressed grape seed oils obtained from different winery waste are analyzed. The different waste materials have a pronounced effect on the quali‐quantitative profiles of bioactive compounds and induction period of oils. Obtained results show that cold pressed grape seed oils are characterized by different nutritional quality and oxidative stability, due to peculiar effect of fermentation and distillation processes. For production of high quality cold pressed oil, seeds from different winery waste material should not be mixed.

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Plum kernels of the “Čačanska rodna” variety, by-products from plum brandy production, were collected before and after fermentation and distillation, and used for cold-pressed oil production. Fatty acid and tocopherol contents were determined by capillary GC and HPLC, while the oxidation stability of the resulting cold-pressed oils was tested by the Rancimat method. The results showed that oleic fatty acid was dominant in the oil samples with a content of 56.6 to 61.8%, regardless of the plum kernels’ origin. The fermentation and distillation processes had a pronounced effect on the tocopherol content and oxidative stability of the resulting kernel oils. Tocopherol contents were 61.8 mg·100g-1, 87.4 mg·100g-1, 79.6 mg·100g-1 of oil, while the induction periods were 38.7, 44.4 and 33.6 hours for samples before fermentation, after fermentation and distillation, respectively. Based on the results, it could be concluded that the fermentation process increased the content of tocopherols in kernel oil whereas the high temperature during the distillation process adversely affected the tocopherol content and oxidative stability of the obtained kernel oil.

The refined sunflower and palm oils are used in the food industry for the production of fried potatoes. Literary data have shown that palm oil had less tendency to degradation than sunflower oil due to its fatty acid composition. However, palm olein is a palm oil fraction and therefore has a different composition of fatty acids. The aim of this study was to investigate the quality of the refined palm olein in relation to the refined linoleic type sunflower oil during the production of fried potatoes. The oil samples were used for multiple frying during the seven days (40 minutes per day at a temperature of 165 o C). The peroxide value and free fatty acid content (acid value) were determined by standard analytical methods. The results showed that the peroxide value in sunflower oil and palm olein increased by 75.0% and 77.8%, while the acid value increased by 50.0% and 26.8%, respectively, in relation to their initial values in the fresh oil samples. Based on these results, it can be concluded that the palm olein was more suitable for frying. However, this finding cannot be reported with certainty because the quality of the oil depends on many more parameters, not only on those analysed in this paper.