Proteins and amino acids in beers, their contents and relationships with other analytical data

Fluorometry, ion-exchange chromatography, electrophoretic separations and Fourier transform-infrared (FT-IR) spectra were used to determine and characterize amino acids and proteins in 15 different beer samples. Proteins precipitated by ammonium sulfate yielded complex electrophoretic patterns. The major bands corresponded to 45-40 kDa as determined by a two-dimensional gel electrophoresis (2-DE). Proteins and some amino acids are partially responsible for nutritional value and stability of beer. Therefore, electrophoretic analysis revealed that protein characterization of beer during all technological stages might be useful in its quality. FT-IR protein spectra showed the presence of I, II and III amide bands. Protein distribution and amino acid composition of beer differ significantly, depending on the raw materials and enzymatic reactions used in beer technology. Concentrations of histamine (3.02-3.23 mg/l), proline (1.60-3.13 mg/l) and tyramine (3.61-7.4 mg/l) increased during beer fermentation. Statistically significant change was registered in the protein content of the final product, which was less than that in wort (p < 0.005). Levels of tyramine and proline, which were higher than in wort (p < 0.025) showed significant changes. This investigation shows that, in Israeli, Mexican and Brazilian beers, the contents of protein and amino acids are in accordance with the international standards. (C) 1999 Elsevier Science Ltd. All rights reserved.