In the first stage of the lipid oxidation reaction, hydroperoxides are
formed. They are unstable compounds and easily undergo further
multi-directional changes, leading to the formation of secondary oxidation
products resulting in an increase in LA and TBARS values. On the
other hand, lipid hydroperoxides could undergo decomposition to free
radicals in the presence of transition metal ions, such as Cu+1 and
Fe+2. Traces of these metals form alcoxyl and hydroxyl radicals which
probably additionally contributed to cholesterol oxidation and formation
of selected COPs. Correlation analysis between oxidation stability
indexes of lipids confirmed the above hypotheses. Negative correlations
between the level of cholesterol and all analyzed lipid indexes were
−0.43 on the LOO index, −0.72 on the LA index and −0.62 on the
TBARS index. Thus, the higher the value of the analyzed index was,
the less unchanged cholesterol it contained. Analogously the positive
correlations between the level of oxysterols and the lipid oxidation
indexes were: 0.60 on the LOO index, 0.84 on the LA index and 0.65
on the TBARS index. Thus, each of the lipid oxidation indexes could
be a marker of cholesterol oxidation, leading to the formation of
COPs.