Quantification of bovine IgG in milk using enzyme‐linked immunosorbent assay

Abstract

A double sandwich enzyme‐linked immunosorbent assay (ELISA) procedure for the quantification of IgG in bovine milk was developed for detecting the concentration of IgG in various homogenized HTST, UHT, evaporated and raw milk samples as well as skim milk powder. ELISA results were consistently lower than radial immunodiffusion (RID) values for the same sample, suggesting interference by an unknown constituent in the milk matrix. This difficulty was overcome by using a reference milk, quantified previously for IgG by RID. A significant linear relationship (y=2.03x‐0.034, r=0.891, n= 150, p<0.001) was obtained for IgG content in unknown raw milk samples determined by ELISA using serial dilutions of the reference milk (y) or commercial IgG (x) to construct standard curves. The slope of the regression line could be used as a correction factor. Alternatively, IgG in unknown samples could be directly quantified from absorbance values of reference milk serial dilutions assayed on the same ELISA plate. Using this procedure, homogenized, HTST pasteurized milk contained from 65 to 79% of the IgG found in raw milk. Skim milk powder also retained a major portion of IgG, while evaporated and UHT pasteurized milk were virtually devoid of IgG.

Keywords:

• bovine milk
• ELISA
• IgG