Fractionation and characterization of beer proteins

Abstract

A combination of large scale gel filtration with preparative isoelectric focusing and ion exchange chromatography has been used for fractionation of beer proteins. From gel filtration on Sephadex G-150, a high molecular weight fraction, eluting close to the void volume of the column, a fraction appearing corresponding to a molecular weight of 44,000 and a fraction containing rather low-molecular weight (about 10,000) components were obtained and used for preparative isoelectric focusing in the pH-range 3.5-10. The high-molecular weight fraction was rich in carbohydrate and cross-reacted with yeast antibodies. After preparative isoelectric focusing the amino acid composition of the isolated subfractions resembled that of yeast cell wall components. Preparative isoelectric focusing of the two fractions with molecular weight about 44,000 and 10,000 revealed the presence of two classes of components based on their amino acid composition. One class, which seemed to be present in low concentration in nearly all isolated subfractions, had an amino acid composition resembling that of barley glutelins. In the fraction with molecular weight about 44,000 another class of components -having an amino acid composition resembling barley albumins and globulins -Were observed in the region with isoelectric points of about pH 4-5. They cross-reacted immunologically with antibodies against soluble barley proteins. This class of components could also be separated from the glutelin-like constituents by ion exchange chromatography. However, they could not be completely separated from carbohydrate by the fractionation procedures employed. Carbamylation experiments demonstrated that approx, half of the e-amino groups of lysine residues of these proteins were blocked. Furthermore, partial amino acid sequence determination by the Edman procedure revealed a strong heterogeneity with respect to N-terminal amino acid residues. These observations are consistent with a suggestion that a large part of the beer proteins might be polypeptide chains crosslinked by carbohydrates.

Changes in protein molecular weight during cloudy wheat beer brewing

“…Proteins in beer are a heterogeneous group of substances with M w ranging from around 100 kDa down to the polypeptide class of materials (11)(12)(13). There are three major groups of protein in barleybrewed beer.…”

Fractionation of protein components from beer by density gradient centrifugation

“…ley protein (8,17). Its composition is also reminiscent of the "foaming protein" fraction of molecular weight about 40,000 g' mole -t isolated by ASANO and HASHIMOTO (1) and the barley protein Z recently isolated by HEJGAARD (7).…”

“…Beer proteins are a heterogeneous group of substances varying widely in isoelectric points and molecular weights, and also to some extent in firmly bound carbohydrates and polyphenols (1,3,6,11,13,17). Hence, it is understandable that even the combined use of several protein fractionation methods has failed to produce beer protein fractions which meet the criteria for homogeneity (1,13,17).…”

“…Hence, it is understandable that even the combined use of several protein fractionation methods has failed to produce beer protein fractions which meet the criteria for homogeneity (1,13,17).…”

A Method for the Preparative Separation of Beer Proteins and Glycocompounds

“…Furthermore, beer proteins have relevance for their effects on human health ranging from the confirmed role as allergens 8 , to the potential benefices on cardiovascular disease prevention 13,14 . Beer contains a variable amount (20-600 mg/L) of proteins 29 , with molecular masses from about 5 kDa up to more than 100 kDa 26 , arising mainly from malted barley or from other cereals (such as wheat, maize, rice…) employed in beer production. It has previously been reported that these proteins are partially glycated through the Maillard reactions that occur during the diverse technologies for malt and wort production and processessing 15,16 .…”