It has been shown that more than 40% of
sterols are lost during oil refining processes. Therefore, the by-products of
refining industries can be excellent sources of PS. Solvent crystallization,
counter current chromatography, supercritical fluid extraction, and enzymatic
transesterification are some of the current techniques employed for phytosterol
It is possible to obtain considerably pure (95.88%) form of PS using solvent
crystallization method from soybean oil deodorizer distillate with a net yield
of 6.64% (226).
Some PS can have antioxidative effects. 4-Desmethyl
sterols and 4-methyl sterols with an ethylidene group in the side chain, as
well as their esters, have been found to be effective in stabilizing oils at
temperatures similar to those reached in deep-frying (227).
The antioxidant activity of the ethylidene group is based on the formation of
an allylic free radical at carbon atom 29 followed by isomerization to a
relatively stable tertiary free radical at carbon atom 24 (228). It has been indicated that incorporation of phenolic
acids, such as gallic acid, with PS through esterification can confer their
excellent antioxidant activities to PS (229, 230).
?5-avenasterol, fucosterol, vernosterol and citrostadienol were found to be
effective antioxidants in oils heated at 180?C (231-233). It has been indicated that
fortification of canola oil triacylglycerol with a mixture of canola oil sterol
fraction and rice bran oil sterol fraction provides a concentration dependent
protection during frying (234).
Virgin olive oil during repeated frying
operations was more stable in comparison to other vegetable oils. The content
of ?5-avenasterol in olive oil from certain areas in the
Mediterranean region was up to 36%. The presence of sesame seeds and rice bran
oil in frying oils provides additional stability, which is due to the high content
of anti-polymerization sterols (?5-avenasterol, ?7-avenasterol,
and citrostadienol). Another group of compounds naturally occurring in rice
bran oil is oryzanols, which are esters of ferulic acid with 4-desmethyl sterols
and 4,4-dimethyl sterols (227, 235). Oryzanols have been shown to
possess strong stabilization effects during frying applications (236).