Effect of processing conditions on the oxidation of cholesterol in ghee

Abstract

Abstract:The cholesterol oxidation products (COP) in fat-rich dairy products were identified and quantified. Fresh cream contained no COP whereas fresh butter contained trace levels of 78-hydroxy-and 5,6a-epoxycholestero1. Low levels of various major COP were present in ghee (clarified butter fat). Intermittent heating and frying of ghee induced severe oxidation of cholesterol and a number of COP were detected by GC and TLC. Most atherogenic COP, viz 25-hydroxycholesterol and cholestantriol, were formed more in intermittently heated ghee (8.1-9,2% of the total COP) than in fried ghee samples (7.1 %).

Formation of cholesterol oxidation products (COPs) in animal products

“…Furthermore, milk has a low level of polyunsaturated fatty acids and of pro-oxidant trace elements such as iron and copper. In other studies, traces or low levels of 7b-hydroxycholesterol and 5,6a-epoxycholesterol (Kumar & Singhal, 1992) and 7-ketocholesterol (Pie et al, 1990) were detected. Nielsen, Olsen, Jensen, and Skibsted (1996) reported the total COPs content of butter and dairy spread were 1.4 and 2.7 mg/kg lipid, respectively.…”

“…The most predominant oxidized cholesterol detected was 7-ketocholesterol, 20-hydroxycholesterol, 25-hydroxycholesterol, 7a-hydroxycholesterol, 7b-hydroxycholesterol, 5,6a-epoxide, 5,6b-epoxide and triol. Many studies demonstrated that the amount of COPs in foods can frequently reach 1% of total cholesterol and occasionally 10% or more (Kumar & Singhal, 1992). Cholesterol oxidation is initiated by the abstraction of the allylic C-7 hydrogen, with the subsequent formation of C-7 COPs such as 7a-and 7b-hydroxycholesterols and 7-ketocholesterol (Smith, 1987).…”

“…Many studies demonstrated that the amount of COPs in foods could frequently reach 1% of total cholesterol and occasionally 10% or more (Addis, 1986). The lipid oxidation has been associated with quality deterioration caused by the development of off-flavors and off-odors during storage (Kumar & Singhal, 1992). More recently, interest in the possible toxicological effects of lipid oxidation products, particularly cholesterol oxidation products (COPs), has increased.…”

Oxidised cholesterol in milk and dairy products

“…However, in other studies, traces (at the detection limit of 0.1 mg kg À1 in the lipids) or low levels of 7 bhydroxy-and 5,6a-epoxycholesterol (Kumar & Singhal, 1992;Sander et al, 1988;Sander et al, 1989a) and7-ketocholesterol (Nourooz-Zadeh &Appleqvist, 1988b;Pie et al, 1990) were detected. According to Nielsen et al (1996a), the total COPs content of butter and dairy spread were 1.4 (without 7-ketocholesterol) and 2.7 mg kg À1 lipid, respectively.…”

“…Ghee (clarified butter) is produced from butter by removing water at a clarification temperature between 105 and 118 1C (Sserunjogi, Abrahamsen, & Narvhus, 1998). At this temperature, the formation of various COPs can be observed (Jacobson, 1987;Kumar, Sambaiah, & Lokesh, 1999;Kumar & Singhal, 1992;Prasad & Subramanian, 1992;Sen, Banerjee, Murherjee, & Sen, 1994). Very high amounts of COPs were detected in Indian ghee: 12.3% of the initial cholesterol (2100 mg kg À1 ) was oxidised to COPs (Jacobson, 1987;Sen et al, 1994).…”