Steradienes are steroidal hydrocarbons
formed by a sterol dehydration reaction. Steradienes are generally formed
during heat treatment or during refining steps especially during the bleaching process
at the surface of the acid-activated bleaching earth or during the deodorization
at elevated temperatures (109-112) . During the bleaching process
steradienes are formed due to a dehydration catalyzed by the acid-activated
bleaching earth. By increasing the bleaching temperature, increasing bleaching earth
concentration and increasing degree of acid activation, the steradiene content
linearly increases. During deodorization, steradiene formation promotes by the temperature
and steradienes are distilled and condensed in the deodorizer distillate. Depending
on the refining conditions, commercially refined vegetable oils have steradiene
levels ranging between 1–100 mg/kg (112).
Hydrogenation is typically used to
partially hardened fats, and improves the oxidative stability, melting point
and the texture of the finished product. The major consequence of hydrogenation
is the changes in the fatty acid profile and production of trans fatty
acid isomers. However, all compounds, including minor components, are affected.
The formation of saturated sterols during hydrogenation has been reported, for
instance, sitostanol was found in hydrogenated soybean and coconut oil (78).
Chemical interesterification has been
used as an alternative to partial hydrogenation to obtain zero trans oil
products. It has been reported that the content of total sterols were reduced
to 3.2 and 5.5% during interesterification of olive oil and palm stearin at 90
and 120?C, respectively. However, the distribution of sterols remained
unchanged in the esterified product. Interesterification caused an increase in
esterified sterol. Distribution of fatty acids in the esterified sterols
followed the fatty acid composition of the oil blend (113).