A COMPARISON OF PROTEIN ASSAYS FOR THE DETERMINATION OF THE PROTEIN CONCENTRATION OF BEER

Seven protein assays have been compared for determination of the protein content of beer. Dialysis and ultrafiltration have been used to investigate possible interference and the protein content of the samples has been simultaneously monitored by sodium dodecyl sulphate-polyacrylamide gel electro-phoresis. The Fisons NA2000 Nitrogen/Protein Analyzer gave identical results to the standard Kjeldahl method but both measure nitrogen-containing compounds rather than protein. Colorimetric methods based upon the biuret reaction (including the Lowry and bicinchoninic acid protein assays) are particularly prone to interference from reducing substances and gave protein concentration values dependent upon the sample volume. The protein dye-binding assays (Coomassie Brilliant Blue and pyrogallol red-molybdate methods) were optimal for beer protein analysis displaying minimal inter ference and giving reproducible protein concentration values consistent with the protein content of the beers as indicated by electrophoresis.