Nourooz-Zadeh oil for one year at 4

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Nourooz-Zadeh and Appelqvist
(160) indicated that industrial processing (viz., chemical
refining and deodorization) of soybean oil causes no increase in the level of
the autoxidation products of the free sitosterol compared to the crude soybean
oil at the detection level of 0.2 ppm. Their results also indicated that storage
of a refined soybean oil for one year at 4 ?C caused no significant increase in
the level of free sitosterol oxides when compared to the freshly refined
soybean oil (160). In agreement with Nourooz-Zadeh and Appelqvist (160), Lambelet et al. (161) could not detect any epoxy compounds and triols in deodorized low
erucic acid rapeseed oil. However, they found 0.3-0.8 ppm of 7-hydroxy
derivatives of sitosterol and campesterol in semi-refined and fully refined low
erucic acid rapeseed oil. They also found three uncommon compounds, which were
tentatively identified as 6?-hydroxycampestanol, 6?-hydroxysitostanol, and 6?-hydroxybrassicastanol.
Their results indicated that quantities of oxyphytosterols present in
semirefined low erucic acid rapeseed oil were not highly modified during
deodorization, whatever the temperature of the stripping operation between 200
and 250 ?C  (161).

In another investigation,
bleaching experiments were carried out on a sample of sunflower oil at 80 ?C
for 1 h with 1 and 2% of both acidic and neutral earths. The bleaching caused a
reduction of the hydroxyphytosterol with partial formation of steratrienes,
steroidal hydrocarbons with three double bonds in the ring system at the 2-,
4-, and 6-positions. In the sample bleached with acidic earths levels of 1% and
2% there was a significant increase of the steratrienes derived by dehydration of
the hydroxysterols with an average dehydration of ~30% and ~42%, respectively. In
the case of the oil bleached with neutral earths, the formation of steratrienes
was lower, with average dehydrations of about 7 and 14% at earths levels of 1
and 2%, respectively. These results clearly show the effect of the acidity of
the earths on the dehydration of the hydroxysterols (135).

Recoveries of the
hydroxysterols after bleaching with acidic earths were very low and, in
particular, at the level of 2% of earths, only ~6% of the initial 7?-hydroxy-?-sitosterol
was left in the oil. In the case of the bleaching with neutral earths, recoveries
of the hydroxysterols were higher, with average values of 29 and 14% at earths
levels of 1 and 2%, respectively. 7-Keto-?-sitosterol was more stable with
respect to the hydroxysterols in this process, with similar recovery values for
different bleaching conditions (average value of 76%) (135).

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