Effects of heat-treatment on insulin-like growth factor-1 in bovine milk

Heating milk at 90 °C gave an immunochemically active form of insulin-like growth factor-1 (IGF-1), measureable using a sandwich-type ELISA without acid–ethanol pre-treatment. In non-heat-treated milk, most of the IGF-1 was in the latent form with its binding protein. On separation of heat-treated milk into casein and whey, the immunoreactive IGF-1 was found in the casein fraction. At UHT temperatures the growth factor concentration was lower. Denatured β-lactoglobulin interfered with the immunochemical assay, and resulted in lower recoveries compared with acid–ethanol pre-treatment. The concentration of IGF-1 in colostrum samples analysed by acid–ethanol extraction or heat treatment showed a good correlation, but the recoveries from heated samples were lower, probably because of denaturation of β-lactoglobulin. Heating of milk to 90 °C for 1 min provided an easy way to analyse low IGF-1 concentrations, at least in milk and casein solutions.