Method of determining soy material in foods

A method of determining the amount of soy material in a food product by determining the fluorescence intensity at a wavelength of about 445 nanometers produced by excitation at a wavelength of 360 nanometers in the ultraviolet portion of the spectrum of a solution prepared by extracting a weighed sample of the food product with a preselected amount of a 6M. aqueous solution of guanidine hydrochloride, comparing the result with a standard curve for representative soy materials derived from soy beans containing high proportions (at least 50 percent) of protein wherein maximum fluorescence intensity at about 445 nanometers wavelength is plotted against amount of soy material, then calculating the percentage of soy material in the sample of food product from the amount of soy material found and the weight of the sample.