RAPID-DETERMINATION OF TOTAL CHOLESTEROL IN EGG-YOLK USING COMMERCIALDIAGNOSTIC CHOLESTEROL REAGENT

A rapid and accurate method for cholesterol determination using a comm ercial diagnostic cholesterol reagent ('enzyme method') was developed and evaluated with four different yolk preparations. The cholesterol c ontent of The National Institute of Standards and Technology (NIST) St andard Reference Material in whole egg powder, fresh, frozen, and drie d egg yolk was determined using gas chromatography and the enzyme meth od. All samples were subjected to direct saponification and solubiliza tion prior to analysis. No treatment was applied to control samples, w hich 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 leve ls. For egg powder standard and fresh or frozen egg, the cholesterol v alues obtained by the enzyme method from saponified or solubilized sam ples were not significantly different from values obtained by gas chro matography. For solubilized dried egg yolk the enzyme method gave resu lts indistinguishable from chromatography for saponified yolk. However , the results obtained by the enzyme method and gas chromatography fro m saponified dried egg yolk were significantly different. The simple a nd rapid procedure developed for sample preparation (solubilization) e liminates the need for saponification prior to cholesterol determinati on using the enzyme method, and provides an alternative to an expensiv e and time-consuming gas chromatographic method. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.