Stabilization of phytosterols in rapeseed oil by natural antioxidants during heating

Abstract

Antioxidants are substances that can reduce negative changes in fat. Many antioxidants are very effective during storage, but during heating they lose their properties. It is very important to find antioxidants that will be stable at high temperatures and protect fat throughout the entire frying process. The aim of this study was to estimate the effect of natural and synthetic antioxidants on changes in phytosterols of rapeseed oil during heating. Oil with antioxidants was heated at 180 7C for 4 h in a Rancimat ® and in an Oxidograph ® . Ethanol extract of rosemary, ethanol extract of green tea, and BHT were used in the study. The contents of phytosterols (sitosterol, campesterol, avenasterol, brassicasterol, stigmasterol) and oxyphytosterols (7a-and 7b-hydroxysterol, 5a,6a-and 5b,6b-epoxysterol, 7-ketosterol and triols) were estimated by gas chromatography. In all samples with antioxidants, a lower decrease of phytosterols and a lower increase of total oxyphytosterols were observed in comparison with the control sample (without antioxidant). The antioxidant effect depends on the type of the antioxidant and the heating conditions. The best results were observed in samples with natural antioxidants. BHT was a substance that protected phytosterols as well, but not as effectively as the other antioxidants.

Oxysterols: A world to explore

“…In a comparative study, fewer oxysterols were formed in green tea extract-enriched rapeseed oil than in rosemary and BHT-enriched ones. However, the POP content in rapeseed oil without antioxidants was higher than in the oil enriched with each of the three antioxidants (Kmiecik et al, 2009). …”

Effects of ferric chloride on thermal degradation of γ‐oryzanol and oxidation of rice bran oil

“…Statistical comparisons of the k value for each component are also shown in Table 1. The loss of g-oryzanol from the oil at high temperature would be caused by both the thermal oxidation of g-oryzanol itself as found in others phytosterols [13] and by antioxidant action against free radicals due to lipid autoxidation [22].…”

“…The degradation of both antioxidants and nutritive components, for example, phenolic compounds, tocopherol, and b-carotene, in oil at high temperature has been studied [10][11][12][13]. However, the degradation of g-oryzanol has been reported in only a few papers.…”

Content of phytosterols in raw and roasted buckwheat groats and by-products

“…An oxysterol level increases in meat during thermal processing (Derewiaka & Obiedziński 2009. These compounds have been found in nuts, rapeseed, rapeseed oil, also in fried potato chips and crisps (Rudzińska et al 2005;Kmiecik et al 2009). The resistance of phytosterols and stanols to oxidisation depends to a large extent on the temperature and duration of the applied processing.…”

“…Typically, mechanical processing is used in order to remove inedible or inassimilable parts or fractions, and thermal processing is applied to enhance digestibility or improve sensory attributes of food. Many technological processes used in the food industry as well as thermal processing applied in home cooking contribute towards degradation of phytosterols in ready to eat products (Kmiecik et al 2009). Blanching and deodorisation of rice bran oil during the refining process lead to a decrease in phytosterol content by 38% (Van Hoed et al 2006).…”