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

Fluorometry, ion-exchange chromatography, electrophoretic separations and F ourier transform-infrared (FT-IR) spectra were used to determine and charac terize amino acids and proteins in 15 different beer samples. Proteins prec ipitated by ammonium sulfate yielded complex electrophoretic patterns. The major bands corresponded to 45-40 kDa as determined by a two-dimensional ge l electrophoresis (2-DE). Proteins and some amino acids are partially respo nsible for nutritional value and stability of beer. Therefore, electrophore tic analysis revealed that protein characterization of beer during all tech nological stages might be useful in its quality. FT-IR protein spectra show ed the presence of I, II and III amide bands. Protein distribution and amin o acid composition of beer differ significantly, depending on the raw mater ials and enzymatic reactions used in beer technology. Concentrations of his tamine (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 wa s registered in the protein content of the final product, which was less th an that in wort (p < 0.005). Levels of tyramine and proline, which were hig her than in wort (p < 0.025) showed significant changes. This investigation shows that, in Israeli, Mexican and Brazilian beers, the contents of prote in and amino acids are in accordance with the international standards. (C) 1999 Elsevier Science Ltd. All rights reserved.