A Comparison of Various Procedures for Determining Total Yolk Lipid Content

Abstract

Studies were conducted to compare several lipid extraction and quantification procedures. The methods evaluated were: 1) the Association of Official Analytical Chemists (AOAC) yolk lipid procedure (acid hydrolysis/ether extract); 2) a modified Folch procedure (chloroform-methanol extraction); 3) a hexane-isopropanol extraction (HIP); and 4) a yolk fat-by-difference calculation [(yolk fat = total yolk – (yolk protein + yolk water + yolk ash)]. The HIP method was investigated due to its relative safety and simplicity, because chloroform's relative safety in the laboratory has been questioned. In addition, several modifications of the modified Folch and the HIP procedure were evaluated. A total of eight replicate groups of eggs from three flocks were used. Each replicate consisted to 20 to 30 eggs from a flock within 24 hr of oviposition. The eggs were broken out and the yolk separated by hand and removed of adhering albumen or chalazae. The yolk contents were collected, homogenized, and 5 subsamples were removed for each of the analyses previously described. Results indicate that there are differences between the methods tested in the absolute level of fat but that the variation within the different methods was very close. The modified Folch and HIP procedure resulted in the highest total fat values (35.03 and 34.25%, respectively) while the AOAC and fat-by-difference methods yielded the lowest total fat values (33.38 and 33.05%, respectively). The variation within each method was comparable as determined by their coefficients of variation of 2.03% for the fat-by-difference, 3.70% for the modified Folch, 4.11% for the AOAC, and 5.21% for the HIP procedure. The results would indicate that any of the procedures evaluated would be satisfactory for determining total yolk lipid both on the basis of accuracy and precision. The most suitable method may better be selected on relative safety of the procedure and individual laboratory constraints.