and Summary Hydrogenation has been carried out in a“dead‐end” type reactor with various types of nickel catalyst and with automatic recording of hydrogen absorption. Oils with varying concentrations of sulfur and phosporus compounds, fatty acids and their salts, as well as partly oxidized oil have been hydrogenated. The resulting kinetic curves are characteristic for each catalyst type and for each inhibitor. An increase in the poison concentration in the reaction system results in lengthening of the induction period apart from the decrease of catalyst activity.

The increase in consumption of food fried in the so‐called ‘deep‐frying‐oil’entails the necessity of knowledge of both thermooxidative transformation occuring in the frying medium and chemical composition of oil absorbed by the fried product. The aim of this study was to correlate the quality of frying medium and oil extracted from potato fritters fried under rigorously controlled laboratory conditions in liquid and partially hydrogenated rapeseed oils. Oxidation and polymerization reactions predominated during deep frying of potato fritters in both frying media, but hydrolysis occured only to a small degree. The peroxide value was not a suitable quality control indicator for monitoring the thermooxidative transformation during deep frying. The most suitable method for examining such transformations was to study the content and composition of the polar fraction. A correlation existed between the amount of polymers and oxidized triacylglycerols (TAGs) and the amount of polar fraction. Small differences existed in the content of thermooxidative transformation products in the frying medium and the oil extracted from potato fritters. By monitoring anisidine value (AnV), E1%1cm and the content and composition of the polar fraction in the frying medium, it was possible to evaluate the quality of the fat in the fritters. Thus, the use of partially hydrogenated compared to liquid rapeseed oil in deep frying process may be preferred because at the same content of polar fraction and its components partially hydrogenated rapeseed oil contained a lesser amount of secondary oxidation products.

A rapid instrumental method for evaluation of stability of fats has been proposed. Acceleration of oxidation is accomplished by vigorous mixing of a heated sample with oxygen at atmospheric pressure. The volume of absorbed oxygen determined directly by means of a special manostatic device constitutes the measure of the course of the reaction. Experimental results are recorded on a strip‐chart plot of the volume of oxygen absorbed as a function of time. The start of rapid absorption of oxygen at the end of the induction period is taken as the end point. Samples of commercial low‐erucic rapeseed oil, soybean oil and lightly hydrogenated soybean oil had end points in the range of 50 to 100 at a temperature of 120 C.

No abstract