Determination of bovine immunoglobulin G in bovine colostrum powders, bovine milk powders, and dietary supplements containing bovine colostrum products by an automated direct immunoassay with optical biosensor: collaborative study.

Nine laboratories participated in an AOAC collaborative study to determine bovine immunoglobulin G (IgG) levels in selected dairy powders and dietary supplements by surface plasmon resonance (SPR) methodology. Each sample matrix was dissolved in buffer and suitably diluted to fit within the standard curve. The sample extract was injected over a surface functionalized with affinity-purified, polyclonal goat anti-bovine IgG (H+L) antibody; IgG was then detected. SPR detection was used for the direct immunoassay and quantification was made against a calibration curve prepared from bovine serum IgG. Between each standard and sample, the surface was regenerated using 10 mM glycine at pH 1.5. The samples analyzed included the likely matrixes for which the assay would find commercial use, namely, high- and low-protein-content colostrum powders, tablets containing colostrum powder, infant formula containing colostrum powder, and some IgG-containing dairy powders, i.e., milk protein isolate, whey protein concentrate, and skim milk powder. Each laboratory provided data for the study and assayed blind duplicates of seven materials. Due to gross outliers in the majority of results from one laboratory, the data from eight laboratories were used for the statistical analysis. The repeatability RSD (RSDr) values ranged from 3.2 to 7.3%, and the reproducibility RSDR values from 13.0 to 22.6%.