Thermal oxidation of cholesterol: Preliminary evaluation of 2-methyl-6-heptanone and 3-methylbutanal as volatile oxidation markers

Cholesterol oxidation in food and model systems is usually monitored by evaluating Cholesterol oxidation products, but the analysis is time-consuming and expensive. Therefore, the determination of volatile compounds deriving from Cholesterol thermoxidation could be valuable to identify Other possible oxidation markers. Cholesterol alone and in the presence of a triacylglycerol mixture (tripalmitin, tristearin, and triolein) were thermoxidized at 170°C for 15min. In both model systems, the total volatile compounds increased three times when oxidation time rose from 5 to 15min. The main classes of volatile compounds were aldehydes, ketones, alcohols and hydrocarbons, displaying a similar behavior in both systems. After 5min of oxidation, 2-methyl-6-heptanone was the main volatile compound, followed by 3-methylpentane, 2,3-dimethyl-1-pentene and 3-methylbutanal. To verify if 2-methyl-6-heptanone could be used as volatile marker of Cholesterol oxidation, data were compared with the total Cholesterol oxidation products content of each system. A significant correlation between total Cholesterol oxidation products content and 2-methyl-6-heptanone amount was found when Cholesterol was oxidized alone (r(2)=0.994) and in presence of triacylglycerols (r(2)=0.998). When egg yolk was thermoxidized at 80°C for 6h, 3-methylbutanal was the volatile compound that better explained the oxidative trend in this food system, showing a significant correlation with Cholesterol oxidation rate (r=0.91). In conclusion, 2-methyl-6-heptanone and 3-methylbutanal could represent an easy and cheaper strategy for monitoring Cholesterol oxidation in model systems and food samples, respectively; however, a deeper investigation on the amount and type of volatile compounds generated from Cholesterol oxidation according to the food matrix, should be carried out.