An immunoenzymatic assay to measure insulin-like growth factor 1 (IGF-1) in buffalo milk with an IGF binding protein blocking pre-treatment of the sample

In this study we developed a sandwich enzyme-linked immunosorbent assays (ELISA) with good performance, low cost and simplicity of execution, to facilitate the measurement of insulin-like growth factor 1 (IGF-1) in buffalo milk. This assay requires a pre-treatment method that consists of an acidification step to separate IGF-1 from its binding proteins (IGFBPs) and a subsequent pH re-equilibration, with a buffer containing excess insulin-like growth factor 2 (IGF-2), which blocks the IGFBPs and enables the IGF-1 molecules to remain free in solution. The limit of quantification was about 0.32 ng mL−1 of milk. The within- and between-assay coefficients of variation were 6.3% and 13%, respectively. Linearity and accuracy were acceptable. The comparison with the classic acid–ethanol extraction method applied to colostrum samples showed a high correlation of results, indicating a similar level of efficiency. The assay developed in this study can thus be applied for measuring IGF-1 in milk.