Abstract
This study examined the thermo-oxidative degradation of stigmasterol fatty acids esters. Stigmasterol stearate, oleate, linoleate and linolenate were synthesized by chemical esterification and their purity evaluated by 1H-NMR and GC–MS. The degradation of stigmasterol esters was examined after heating them at 60 and 180 °C for 1, 2, 4, 8 and 12 h. It was established that stigmasterol esters were prone to thermo-oxidative degradation, with time and temperature affecting the degree of degradation. The unsaturation of fatty acids affected the rate of stigmasteryl ester degradation. The kinetics of StS and StO degradation were similar and the additional double bonds in StL and StLn resulted in their faster decomposition. The esters degraded faster at 180 than at 60 °C. The sterol and fatty acid molecules degraded at different rates, such that the fatty acid moiety deteriorated faster than the sterol at both temperatures, independent of the time of heating and the level of unsaturation.
Highlights
Phytosterols (PS) are derived exclusively from plant sources and perform similar cellular functions in plants to Phytosterols, in their free and esterified forms, are added as functional compounds to food products, due to their blood cholesterol-lowering efficacy [2]
Thermo-oxidative degradation of phytosteryl esters is substantially affected by the unsaturation level of fatty acids and by the typical parameters that accelerate chemical reactions, such as temperature and time
The steryl moiety degrades at a slower rate than does the fatty acid moiety during heating at 60 °C; at 180 °C, the opposite was observed. This indicates that stigmasterol at elevated temperatures is more prone to oxidative degradation, and with it the stimulation of further degradation of ester molecules, demonstrating the free radical mechanism of degradation
Summary
Phytosterols (PS) are derived exclusively from plant sources and perform similar cellular functions in plants to Phytosterols, in their free and esterified forms, are added as functional compounds to food products, due to their blood cholesterol-lowering efficacy [2]. The benefits of cholesterol lowering were observed at a similar rate in individuals with hypercholesterolemia, mildly and moderately elevated blood cholesterol, and coronary heart disease [4]. Due to their solubility, plant steryl esters are well tolerated and can usually be added in higher amounts to high-fat food products such as margarines and spreads. Steryl esters incorporated into a low-fat low-cholesterol diet showed better efficacy in lowering blood cholesterol lipids than the diet alone [5]
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