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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.

This work focuses on degradation of α‐tocopherol and formation of α‐tocopherol degradation products in sunflower oil heated at frying temperature. We determined the content and measured the kinetics of α‐tocopherol, α‐tocopheryl quinone, α‐tocopheryl fatty acid formation in heated sunflower oil without aeration (So) and in aerated oil (air flow 20 L/h) (SoAir). During 10 h of So oil heating, the α‐tocopherol was depleted and the content of α‐tocopheryl quinone in So grew from 3 to 84 mg/kg, as did the content of tocopherol free fatty acid esters from the initial 5 to 185 mg/kg. In SoAir oil, the rate constants of formation and decomposition of tocopherol degradation products were determined. Accelerated oxidation in SoAir caused depletion of the degradation products of tocopherol after 2 h of heating. The reason for this was significant oxidation and polymerization of fatty acids in SoAir oil. The unique features of this work are the syntheses and spectral analysis of tocopherol oxidation products and the development of a suitable method for quantitative analysis of α‐tocopheryl fatty acids. For the first time, we confirmed formation and degradation of tocopheryl fatty acids during oil heating at frying temperature. Practical applications: All the results presented here, consisting of organic syntheses, qualitative and quantitative analysis of α‐tocopheryl fatty acids as well as oxidation and degradation products of tocopherols and fatty acids, will aid future research focused on the degradation of tocopherols. So far the content of α‐tocopheryl fatty acids has not been determined by GC‐FID or HPLC‐UV. This is why there has been little interest in α‐tocopheryl fatty acids, although they are formed both in culinary treatment of food and in oil refining. Free fatty acids (FFAs), fatty acids (FAs), oxidation [o], products (i) and products (ii) are unspecified products of α‐tocopheryl FAs and α‐TQ degradation. Degradation products of α‐tocopherol were formed in heated sunflower oil and further heating of oil caused decomposition of α‐tocopherol degradation products.

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The paper describes laboratory deodorization of rapeseed oil (Ro), model sunflower (SoM), and model rapeseed (RoM) oils, its effect on the tocopherol content and the kinetics of tocopherol degradation. We now present a novel approach to analysis of alpha‐tocopherol degradation product as well as kinetic study esters of alpha‐tocopherol with fatty acids and alpha‐tocopheryl quinones. Alpha‐tocopherol esters were found to be the principal products of tocopherols degradation in high temperature experiment. A laboratory deodorization, lasting 2 h caused formation of 70–128 mg/kg of alpha‐tocopherol esters in model oils and 25 mg/kg of alpha‐tocopherol esters in rapeseed oil without modification. The commercially available sunflower and rapeseed oils contained 3–12 mg/kg of alpha‐tocopherol esters. The alpha‐tocopherol esters are formed at higher rate than alpha‐tocopheryl quinone, which was unstable at high deodorization temperature. Tocopherols took no part in non‐radical thermal reactions, taking place in second high‐temperature experiments with oxygen‐free atmosphere. We proved by DART TOF‐MS the formation of polymeric fatty acids via Diels–Alder reaction taking place in heated oils. Practical applications: Although an extensive research have been conducted in the area of high‐temperature degradation of tocopherols, this is the first report on formation of fatty acids esters of tocopherols during oil deodorization. The proof of their presence in deodorized oils, deodorization condensates, deep‐fried foods, and oils constitutes a breakthrough. We ingested them as yet unknowingly. Their degradation is not nearly as fast as that of tocopherol itself or its oxidation products. In the course of their hydrolysis in stomach tocopheryls of fatty acids could thus become the source of unoxidized tocopoherols. We found out that during laboratory deodorization of vegetable oils were formed esters of tocopherols with fatty acids. During heating of oils are free fatty acids the acid catalyst of esterification.