Modified immunoassay for the detection of soy milk in pasteurized skimmed bovine milk

Utilization of soy milk and soy protein as a food supplement or as a replacement for milk and milk products is increasing. This form of food modification presents several different problems: quality assurance cannot always be given, people with soy allergy may be unknowingly exposed and regulatory bodies have difficulty in detecting the cases of deliberate adulteration. Therefore, a reliable means of detecting and quantifying soy protein in milk is needed. In the present study we have modified an ELISA technique to overcome the problem of quantitation of soy protein in milk. The results are reproducible, show low cross-reactivity with milk protein and sensitivity is good (assay range 3.5-70 mu g soy protein/cm(3)). The assay measures soy protein and the correlation with soy milk added to bovine milk is linear.