Steranes regular

Sterols Sterols are polycyclic alcohols derived from sterane. Sterols constitute most of the unsaponifiable fraction of an oil. The sterol profile is characteristic of each oil. The Codex Alimentarius (Codex-Stan 210-1999) indicates the total sterol content (ppm) and the percentages of each sterol type in regular sunflower oil, as shown in Table 6. 

Only the 20.R isomers of the regular steranes and 4-methylsteranes exist initially, but they undergo isomerization to form an equilibrium mixture containing approximately equal amounts of 20.R and 20 S isomers (Figs. 5.15 and 5.16). This process appears to require higher temperatures than the isomerization ofpristane. Similar temperatures to those at which the 20S/R isomerization occurs are required for another isomerization process of the regular steranes that affects the C-14 and C-17 cyclic positions in concert. The 14a,17a isomer is converted into an equilibrium mixture of 14a,17a and 14p,17(3 isomers (Fig. 5.15) that contains rather more of the latter. 

The steranes are a class of biomarkers containing 21 to 30 carbons that are derived from sterols, and they include regular steranes, rearranged diasteranes, and mono-aromatic and tri-aromatic steranes. Among them, the regular C27-C28-C29 homologous sterane series are the most common and useful steranes because they are highly specific for correlation. The concentrations of C29 steranes (24-ethylcholestanes) compared to the C27 and C2g-steranes may indicate a land plant source. 

Ster/Hop, sterane-hopane ratio, 5a,14a,17a(H)-cholestane (20R)/17a,21 P(H)-hopane. This ratio, measured directly from SIM fragmentograms, reflects the relative proportion of a ubiquitous and frequently prominent regular sterane to Cao-hopane. 

End member 1 Dominated mainly by n-alkanes (63.8%), regular isoprenoid hydrocarbons (pristane and phytane, 1.5%), tri- and tetracychc MM series (5.0%), the hopane series (7.4%) with a predominance of 17a(H),2ip(H)-hopane and both C-22 SIR configurations for the homologs > 31, and the diasterane/sterane series (0.6%). In addition, a minor contributions from different imsubstituted and substituted PAHs recorded 4.09% and 3.03%, respectively. 

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