Determination of immunoglobulin Y concentration in yolk extract prepared by water dilution method: Comparisons among three strains of chickens

In avian species, immunoglobulin Y (IgY) is found abundantly in egg yolk as well as in blood. Although the concentration of IgY in yolk has been previously reported by many investigators, the reported IgY concentrations have varied from 1 to 25 mg/g yolk. In the present study, we determined yolk IgY concentration in three strains of chickens, taking into consideration the IgY recovery rate in yolk extract; in addition, we estimated the concentration factor of yolk IgY against plasma IgY. Egg yolk and plasma samples were collected from two commercial layers, Dekalb and Nagoya, and one inbred strain, PNP/DO. Extraction of yolk IgY was followed by the water dilution method reported by Akita and Nakai (Journal of Food Science 57, 629-634, 1992) with minor modification, and IgY concentration was measured by ELISA. The recovery of IgY from the yolk was in the 50 to 60% range, and no significant difference was observed among the strains. PNP/DO showed the highest concentration of IgY expressed as mg/g yolk (12.2), and Dekalb and Nagoya had almost the similar concentration of IgY (Dekalb, 6.2; Nagoya, 5.7). In all strains, the concentration of plasma IgY was proportional to that of yolk IgY, and the concentration factor of yolk IgY against plasma IgY was approximately 0.8. On the other hand, when the yolk IgY concentration was expressed as mg/mL water in yolk, the concentration factor of yolk IgY against plasma IgY represented approximately 1.7 regardless of the strains. Taken together, our findings suggest that the concentration of IgY in the yolk should be determined by considering the recovery rate during the process of IgY extraction; in addition, it raised the possibility that blood IgY might be concentrated in egg yolks of chickens.