Formation of four cholesterol oxidation products and loss of free lipids, cholesterol and water in beef hamburgers as a function of thermal processing

This study aimed to evaluate the formation of four major cholesterol oxidation products or COPs (7-ketocholesterol, 25-hydroxycholesterol, 7α-hydroxycholesterol and 7β-hydroxycholesterol) as well as to quantify the loss of free lipids, cholesterol and water as a function of the length and type of beef hamburger thermal processing. We concluded that raw hamburgers, free or virtually free of COPs, maintained this characteristic after all selected thermal processing, since the formation of additional detectable quantities of COPs was not observed. Raw samples containing small amounts of COPs due to aging showed an 18.0–26.6% reduction in the level of these substances after thermal processing. Processed samples initially free of COPs showed a minor increase in the level of these oxidized derivatives after storage in a refrigerator at −4 °C for 4 weeks. In addition, a 15.4–24.0% reduction in the level of free cholesterol was observed in heat-processed samples when compared to raw hamburgers. The decrease of free lipids and water showed to be dependent of the type and length of the thermal processing and closely related to each other.