Independent Role of Beer Proteins, Melanoidins and Polysaccharides in Foam Formation

Abstract

Beer foam proteins, melanoidins, and carbohydrates were individually added to bottles of a solution consisting of a carbonated, ethanolic mixture containing iso-α-acids and the inorganic ion composition typically found in a Pilsner-style beer. Foam properties of the bottled solutions were tested using a pouring-style foam test. By this foam test, a beer protein with excellent foam and physical stability was identified. The protein was identical to barley lipid transfer protein by amino acid sequence homology. The protein's complete amino acid sequence was determined, and the molecular weights of the protein and sequenced peptides were analyzed by mass spectroscopy. A 40-kDa protein, identified in the literature as derived from barley protein Z, had adequate foam stability but poor solubility when isolated from the other proteins and from melanoidins. A 12-kDa protein of unknown origin had no independent foam stability. Melanoidins isolated from beer also formed stable foams. The melanoidins have foam-stabilizing properties that are independent of any role in aiding the foam properties of beer proteins. Beer polysaccharides foamed, but the foam stability was less than that of the proteins and melanoidins.