Rapid determination of total cholesterol in egg yolk using commercial diagnostic cholesterol reagent

A rapid and accurate method for cholesterol determination using a commercial diagnostic cholesterol reagent (‘enzyme method’) was developed and evaluated with four different yolk preparations. The cholesterol content of The National Institute of Standards and Technology (NIST) Standard Reference Material in whole egg powder, fresh, frozen, and dried egg yolk was determined using gas chromatography and the enzyme method. All samples were subjected to direct saponification and solubilization prior to analysis. No treatment was applied to control samples, which were analyzed by the enzyme method. Solubilization of samples was performed at 0.85, 2 and 5% (w/v) NaCl concentrations. Solubilization measured in terms of cholesterol value was best at 2 and 5% NaCl levels. For egg powder standard and fresh or frozen egg, the cholesterol values obtained by the enzyme method from saponified or solubilized samples were not significantly different from values obtained by gas chromatography. For solubilized dried egg yolk the enzyme method gave results indistinguishable from chromatography for saponified yolk. However, the results obtained by the enzyme method and gas chromatography from saponified dried egg yolk were significantly different. The simple and rapid procedure developed for sample preparation (solubilization) eliminates the need for saponification prior to cholesterol determination using the enzyme method, and provides an alternative to an expensive and time-consuming gas chromatographic method.