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Kinetics of 25‐hydroperoxycholesterol formation during photo‐oxidation of crystalline cholesterol
Author(s) -
MedinaMeza Ilce Gabriela,
RodriguezEstrada Maria Teresa,
Lercker Giovanni,
Barnaba Carlo,
García Hugo Sergio
Publication year - 2014
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.6455
Subject(s) - oxysterol , chemistry , cholesterol , kinetics , limiting , peroxide , lipid oxidation , reaction mechanism , organic chemistry , catalysis , biochemistry , antioxidant , mechanical engineering , physics , quantum mechanics , engineering
BACKGROUND 25‐Hydroxycholesterol (25‐OH), a side‐chain product of cholesterol oxidation, has emerged as one of the important issues in food chemistry and biochemistry, because of its involvement in several human pathologies. This oxysterol is derived from both enzymatic and non‐enzymatic pathways. However, the latter mechanism has been scarcely studied in either food or model systems. In this work, a kinetic model was developed to evaluate the formation of 25‐OH and its precursor 25‐hydroperoxycholesterol (25‐OOH) during photo‐oxidation of cholesterol for 28 days under fluorescent light. 25‐OOH was estimated by an indirect method, using thin‐layer chromatography coupled with gas chromatography–mass spectrometry.RESULTS Peroxide value (POV) and cholesterol oxidation products (COPs) were determined. POV showed a hyperbolic behavior, typical of a crystalline system in which the availability of cholesterol is the limiting factor. Further reactions of hydroperoxides were followed; in particular, after photo‐oxidation, 25‐OOH (0.55 mg g −1 ) and 25‐OH (0.08 mg g −1 ) were found in cholesterol, as well as seven other oxysterols, including 7‐hydroxy and 5,6‐epoxy derivatives. The application of kinetic models to the data showed good correlation with theoretical values, allowing derivation of the kinetic parameters for each oxidation route.CONCLUSIONS The results of this work confirm that cholesterol in the crystalline state involves different oxidation patterns as compared to cholesterol in solution. Moreover, the numerical fit proved that hydroperoxidation is the rate‐limiting step in 25‐OH formation. © 2013 Society of Chemical Industry