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.

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.

Vrbiková L., Schmidt Š., Kreps F., Tmáková L., Čertík M., Sekretár S. (2014): Degradation of selected nutrients in sunflower oils during long-term storage. Czech J. Food Sci., 32: 595-600.We investigated the influence of long-term storage (10 months) at an average ambient temperature of 25°C on oxidative stability of sunflower oils (made in Slovakia, Czech Republic, Austria, and Hungary) and their nutrients. Chemical properties were determined and changes in oxidative stability monitored. Oil samples were collected and analysed for the content of tocopherols and β-carotene. Degradation of nutrients depends on chemical composition of oils and storage conditions. It was found that the concentration of both antioxidants decreased in all the samples with the increase in storage time. According to the results, losses of total tocopherols and β-carotene in refined sunflower oils stored in transparent 5-l PET bottles and exposed to daylight at ambient temperature were found to be 52-64% and 63-65%, respectively. The country of origin had no statistically significant impact on the oxidative stability of stored sunflower oils.

The experiment focused on the possibility to utilise the antioxidant potential of rapeseed meal to stabilize fats. The lard, which was used for this purpose, was characterized by gas chromatography. At first the non-sieved meal was added in lard. It is the least technologically difficult method of utilizing meal. Then, the meal was sieved to obtain five fractions, which were added to lard. The aim was to find a fraction of meal that would best stabilize the lard. The results of lard stability with added fractions were compared with the stability of lard enriched with non-sieved meal. Finally, we obtained ethanol and ethyl acetate extracts from non-sieved meal and from the fraction which was the best stabiliser of lard. The aim was to study the effect of these extracts on the stability of lard. Rapeseed meal has stabilized the lard already at 0.5 wt. % content. The non-sieved meal addition of 1, 2 or 4 wt. % has improved the stability of lard by 1.2-2 times. Adding 8-15 wt. % of meal into lard has increased its stability by 3-8 times. The best lard stability has been determined in the fraction retained on the sieve with mesh size 0.15 mm. The lard with added sieved meal has gained a comparable stability the same as after addition of non-sieved meal. The lard with the same additions of extracts (ethanol and ethyl acetate) from non-sieved meal and from meal with sizes 0.15-0.315 mm was more stable than the lard with addition of meal alone. The lard containing ethanol extracts (0.5 wt. %) has a better stability than the lard containing butylated hydroxytoluene (0.02 wt. %).

Microorganisms produce wide range of surfactants, generally called biosurfactants. These compounds are mainly divided according to their molecular weight, physico - chemical properties and mode of action. Saponins, plant surfactants, have properties of  soap and they are high foaming and therefore are used in cosmetic (shampoos, liquid soaps et cetera) and food industry (sweeteners, food additives into the effervescents et cetera). Most of them are spread in plants of agriculture importance and some of them are basic segments in human food. They often occur in plants (in more then 100 species). Saponins can be find in vegetables as a soya, a bean, a lentil, a spinach, a tomato, a potato, a garlic, a onion. Today biosurfactants are mainly used in bioremediation but they can be utilized in many sectors of food industry. We have paid attention to some microbial and plant surfactants and their prospects of exploitation in this industry.

doi:10.5219/170