Evaluation of two extraction methods for the determination of egg yolk cholesterol

Controversy concerning egg cholesterol values exists in recent literature due to varying procedures used for cholesterol determination. The purpose of the present study was to investigate the efficacy of direct sample saponification (Method A) versus saponification of a lipid extract (Method B) for analysis of yolk cholesterol. Method A resulted in a value of 19.1 +/- .4 (SE) mg cholesterol/g of yolk for the National Institute of Standards and Technology (NIST) reference (cholesterol in whole egg powder) as compared with the NIST certified value of 19.0 +/- .2 mg/g. Method B resulted in a significantly lower value of 14.6 +/- .5 mg/g. Egg yolk cholesterol values were determined to be 196 +/- 4.2 mg per egg by Method A and 132 +/- 11 mg per egg by Method B. Various amounts (1, .5, .25 g) of yolk cholesterol assayed by either method proportionately decreased cholesterol values as yolk amount decreased; however, Method B consistently resulted in lower yolk cholesterol. These data suggest that both Methods A and B are valid for determining relative differences between treatments; however, the NIST standard data indicate that for quantification of absolute cholesterol values, direct saponification is more accurate. The NIST standard of cholesterol in whole egg powder should be used as a control for comparing cholesterol data regardless of extraction method used.