Phytosterols are one class of food constituent with serum cholesterol-lowering properties by inhibiting cholesterol absorption. These reasons led to an increasing availability of phytosterol-enriched foods. The content of phytosterols in rapeseeds ranged from 4.7 mg/g to 6.3 mg/g of seeds depends on variety. After pressed in industrial conditions their content in the oil was 8.7 mg/g. In extracted oil the level of phytosterols was 25% higher then in pressed oil. During refined process, especially neutralization, the decrease of phytosterols content was 20%. Using the rapeseed oil to multiple deep frying of French fries generated next 64% losses. The most important reasons for phytosterols content decrease are their autoxidation processes. Autoxidation of sterols is theorized to be a free radical process. Some processes, such as refining plant oils and deep frying or storage, intentionally induce oxidation to produce phytosterol oxidation products (oxyphytosterols). They were determined in rapeseeds on the level 10-15 μg/g of seeds. During industrial production of rapeseed oil the content of oxyphytosterols systematically increased and after refining it was 100-110 μg/g. During multiple deep-frying of French fries in rapeseed oil oxyphytosterols content increased and after 14^th frying their content was 200 μg/g in used oil and 150 μg/g in French fries. Oxyphytosterols are absorbed by humans and their subsequent metabolic conversions may be of toxicological significance.

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