ON THE ESTIMATION OF THE PROTEIN-CONTENT OF MILK, CHEESE AND MEAT BY MEANS OF THE BIURET REACTION

A review is given of the different composition of biuret test solutions and experiments with the estimation of protein content of milk, cheese and meat by means of the biuret method are reported. The pure protein and the casein content of skimmed milk and the protein content of whole milk could be determined with biuret test solutions containing potassium hydroxide and a detergent. The use of the biuret method is advantageous in the case of cheese and meat, which are dissolved in potash lye or alkaline detergent solutions. Disturbances of the biuret method caused by lactose, fat or turbidity were eliminated after addition of hydrogen peroxide, by means of extraction or of additional measurements with a copper-free, zinc-containing biuret reagent. Deviations of the color intensity of biuret complexes were compensated by inclusion of standards in the measurement series.