Determination of Soy in Meat

A number of methods may be used for determining soy flour in meat products. Highly purified soy products are more difficult to determine because the nonprotein components used to quantify the flour are reduced. Immunoassays have been used to directly measure protein content of soy products. Immunological methods for determination of soy proteins in meat are complicated by changes in the structure of the soy proteins during processing. These changes alter the available epitopes, changing the immunoreactivity of soy proteins. The epitopes available are dictated by the details of the processing. Other workers circumvented this problem by denaturing the soy protein with urea and mercaptoethanol, and then removing these agents by dialysis; whatever the initial protein conformation, all soy samples came to the same final conformation after the denaturing agents were removed. The assay used antibody made against the "renatured protein." These steps made the assay long and laborious. Attempts to develop a rapid assay were complicated by the same protein denaturation problems. Sodium dodecylsulfate gel electrophoresis coupled with immunoblotting may be the best quantitative approach.