EFFECT OF POLYDIMETHYL SILOXANE ON RAPESEED OIL TRANSFORMATION DURING DEEP FRYING

During deep fat frying a series of undesirable transformations occur. These include oxidation, polymerization, and hydrolysis. Use of additives to reduce the access of air to the frying oil may be one of the preventive methods. Such additives reduce the amount of foam formed. In this work, polydimethyl siloxane (PDMS) at 3 ppm was added to the frying rapeseed oil for frying potato fritters. It was found that oxidation was significantly limited as it reduced peroxide, anisidine, E^1%_lcm values and oxidized triacylglycerol (TAG) contents. Polymerization was also limited as a reduction in the contents of TAG polymer and dimer occurred. Addition of PDMS also reduced degradation of polyenoic acids of the frying oil. Oil without PDMS was less resistant to these transformations.     

CORRELATION OF QUALITY OF FRYING OIL AND OIL EXTRACTED FROM POTATO FRITTERS FRIED IN LIQUID AND PARTIALLY HYDROGENATED RAPESEED OILS

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), E^1%_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.