CHANGES IN PHYTOSTEROLS AND THEIR OXIDATION PRODUCTS DURING FRYING OF FRENCH FRIES IN RAPESEED OIL
 
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Pol. J. Food Nutr. Sci. 2005;55(4):381–387
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ABSTRACT
The goal of this study was to monitor changes in the composition of phytosterols and oxyphytosterols in rapeseed oil and French fries during multiple (14 times) deep-frying. Phytosterols (brassicasterol, campesterol, stigmasterol, b-sitosterol and avenasterol), after saponification, were separated by capillary GC. The oxidation products of campesterol, stigmasterol and sitosterol, such as: epimers of 7-hydroxy, 5,6-epoxy, 7-keto and triols, after transesterification and SPE fractionation, were identified by GC/MS and quantified by capillary GC. Results of this research indicate that the content of phytosterols significantly decreased during deep frying of French fries in rapeseed oil (ca. 60%). In addition, the content of oxyphytosterols, particularly triol derivatives, significantly increased. The content of total phytosterols in fresh, good quality rapeseed oil was 5.4 mg/g and decreased after the 14th frying to 2.0 mg/g. French fries prepared in the first frying oil contained 2.9 mg of phytosterols in 1 g of extracted lipids, but after the 14th frying they had only 1.1 mg of phytosterols in 1 g of extracted lipids. The level of total oxyphytosterols in fresh good quality rapeseed oil used for frying was 25.1 μg/g. After the 14th frying it increased to 197.1 μg/g. The content of oxyphytosterols in French fries during frying ranged from 16.8 to 147.6 μg/g of lipids extracted from the products. The dominating oxyphytosterols were epoxy- and 7-hydroxyphytosterols.