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The main purpose of this article was to investigate the influence of individual processes in physical refining on tocopherol content in sunflower and rapeseed oils. During refining some chemical parameters, the oxidative stability of oils and some minor compounds such as chlorophyll and betacarotene, were determined. Those analytical data with explained chemical backgrounds gave more qualitative overview of what happened to the same lot of oils being processed in a continuous operation. Some processes were compared with a laboratory oil refining. Crude rapeseed oil contained 656 mg/kg of total tocopherols, followed by high oleic sunflower with 373 mg/kg of tocopherols and classic sunflower oil with 332 mg/kg of tocopherols. The most serious refining processes were bleaching and physical deodorization process, the tocopherol losses being 14.9-17.4% and 20.2-27.1%, respectively. In the refined oils, chlorophylls and FFAs were almost completely removed and the oxidative stability increased 2-3 times. Vegetable oil refining process caused relatively great losses of minor compounds but this, in turn, prolonged the shelf life of edible oils.Practical applications: It was proved that refining of sunflower and rapeseed oils in the oil refinery improves their basic chemical parameters. The loss of tocopherols can be minimized by shortening the time and lowering the temperature during the final step of physical refining, but it has to remain within requirements on quality of refined edible oils.

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The aim of this study was to investigate the influence of microwave heating on sunflower and corn oil in two types of microwave oven. The microwave ovens had the same output power and varied mainly in time of dissipation. The oil samples were heated for 90% and 70% of the total heating time by the two types of ovens, named as the first and the second oven, respectively, and the remaining time was dissipation pause. It was observed that greater dissipation pause in second microwave caused degradation of oil almost two times lower than did heating in the first microwave oil. In microwave heated oils the focus was on analysis of primary and secondary oxidation products, the fatty acids content, the tocopherol content and tocopherol degradation kinetics. The rate of tocopherol degradation in oils heated in the first oven was on average 2-times higher than in the second oven. Oils heated for 10 min in the second oven were found to contain twice the tocopherol content, three times lower peroxide value, three times lower conjugated dienes and aldehydes compared with oils heated in the first type of oven. This is the first report about gentle microwave heating of oils and its dependence on time of heating and dissipation time.Practical applications: In order to dissipate heat during heating, microwave ovens are designed with different default magnetron pause. It was proved that in oils heated by microwave oven with longer dissipation pause there was less degradation of oils and their antioxidants. For the manufacturer it is important to conveniently select the lengths of heating a heat dissipation periods. By judicious selection of these two time characteristics healthier microwave heated food with lower degradation of lipids and their antioxidants can be obtained, since overheating is largely avoided.