Revista Mexicana de Ingeniería Química Revista Mexicana de Ingenier´ ıa Qu´ ımica Vol. 10, No. 1 (2011) 47-57 UNUSUAL OXIDATIVE PATTERN IN THERMO-OXIDATION OF DRY FILMS OF CHOLESTEROL PATR ´ ON OXIDATIVO INUSUAL EN LA TERMO-OXIDACI ´ ON DE PEL ´ ICULAS SECAS DE COLESTEROL I.G. Medina-Meza 1 , M.T. Rodr´ ıguez-Estrada 2 , G. Lercker 2 , I. Soto-Rodr´ ıguez 3 and H.S. Garc´ ıa 1∗ 1 UNIDA, Instituto Tecnol´ ogico de Veracruz, M.A. de Quevedo 2779, Veracruz, Ver. 91897, M´ exico. 2 Dipartimento di Scienze degli Alimenti, Universit`a di Bologna, viale Fanin 40, I-40127, Bologna, Italy 3 Facultad de Bioan´alisis, Universidad Veracruzana, and Facultad de Medicina, Universidad Crist´obal Col´ on, Veracruz, M´ exico. Received 22 of November 2010; Accepted 10 of February 2011 Abstract Formation of cholesterol oxidation products (COPs) during dry heating of cholesterol films at 150 ◦ C for 48 h was studied. A method based on aminopropyl solid-phase extraction (SPE), followed by GC-MS analysis was employed for the identification and quantification of COPs. Two kinetic runs were performed: 60 min and 48 h of treatment. In the short run (60 min), 7-ketocholesterol and 25-hydroxycholesterol were detected in similar amounts after 30 and 15 min, respectively. Oxysterols present in higher amounts in the long run (48 h) were 7β-hydroxycholesterol (12.6 mg/g) and 5,6α-epoxycholesterol (13.4 mg/g). However, compounds whose formation is related to enzymatic oxidation and/or irradiation were detected, as 6-ketocholestanol (3.38 mg/g) and 4β- hydroxycholesterol (2.04 mg/g). 25-hydroxycholesterol (0.12 mg/g) was found after only 1 h, reaching 0.99 mg/g after 48 h of treatment. The results suggest that due to the physical state of cholesterol, the oxidative pattern was changed, favoring unusual routes, such as formation of 4β-OH and 6-keto from breakage of the epoxide ring. Regarding 25-hydroxycholesterol, it is assumed that the solid state favored exposure of the side chain, rendering it more susceptible to oxidation. Keywords: 6-ketocholestanol, 4β-hydroxycholesterol, 25-hydroxycholesterol, cholesterol oxidation, thermo- oxidation. Resumen Se estudi´ o la formaci´ on de productos de oxidaci´ on del colesterol (POCs) durante calentamiento de una pel´ ıcula seca de colesterol a 150 ◦ C. La metodolog´ ıa empleada fue extracci´on en fase s´olida (SPE), seguida por an´ alisis en GC-MS para la identificaci´on y cuantificaci´on de los POCs. Se realizaron dos cin´ eticas, de 60 min y 48 h de tratamiento. En la cin´ etica corta (60 min), se detectaron 7-cetocolesterol y 25-hidroxicolesterol en cantidades similares despu´ es de 30 y 15 min, respectivamente. Los oxiesteroles presentes en mayores cantidades en la cin´ etica larga (48 h) fueron el 7β-hidroxicolesterol (12.6 mg/g) y el 5,6α-epoxicolesterol (13.4 mg/g). Sin embargo, se detectaron compuestos cuya formaci´ on est´ a relacionada a la oxidaci´ on enzim´ atica y/o por irradiaci´ on, como el 6-cetocolestanol (3.38 mg/g) y el 4β-hidroxicolesterol (2.04 mg/g). El 25-hidroxicolesterol (0.12 mg/g) fue encontrado despu´ es de solo 1 h, llegando a 0.99 mg/g despu´ es de 48 h de tratamiento. Los resultados sugieren que, debido al estado f´ ısico del colesterol, el patr´on oxidativo se modifica, favoreciendo rutas inusuales, como la formaci´ on del 4β-hidroxicolesterol y 6-cetocolestanol por ruptura del anillo ep´oxido. Por lo que se refiere al 25-hidroxicolesterol se asume que el estado s´ olido favorece la exposici´ on de la cadena lateral, siendo ´ esta entonces m´as susceptible a la oxidaci´on. Palabras clave: 6-cetocolestanol, 4β-hidroxicolesterol, 25-hidroxicolesterol, oxidaci´ondelcolesterol, termo- oxidaci´ on. ∗ Corresponding author. E-mail: hsgarcia@itver.edu.mx Tel.: +52-229-9341469, ext. 116; Fax: +52-229-934-5701, ext. 201 Publicado por la Academia Mexicana de Investigaci´ on y Docencia en Ingenier´ ıa Qu´ ımica A.C. 47