Haze- And Foam-Forming Substances in Beer

Abstract

A study of recent literature on haze-and foam-forming substances in beer suggests the following picture:Traces of true protein, apparently above 150,000 in molecular weight (MW), exist in beer. Apart from these, the main complex nitrogenous substances are present in compounds in the 5,000-70,000 MW region. Nevertheless, these are not proteins, but amino-acid complexes (proteoses) coupled with non-nitrogenous substances.As is well known, haze and haze precursors are proteoses coupled with polyphenols. These two species can be joined by hydrogen bonds to give compounds which are readily dissociated. However, a much firmer, covalent, linkage can be formed. This type of linkage arises from oxidation of polyphenols to quinones, which in turn can oxidize and couple with several groupings on proteoses. One of the most probable points of attack is the sulphydryl group of cystine, and the relatively high percentage of cystine in haze indicates that this occurs. It seems likely that this reaction, to form acidic complexes, occurs mainly in the initial stages of mashing and boiling. In beer, further coupling between pairs or triplets of polyphenolic or quinolic groupings can take the products into the very high molecular weight region of hazes.Correspondingly, the foam-enhancing proteoses tend to be lower in cystine content and to show less combination with polyphenols. However, they too are largely in the form of complexes and the evidence suggests that here the proteoses are mainly combined with glucose polymers, a reaction which takes place during kilning and possibly during boiling. These complexes are less acidic than the poly phenolic ones and tend to be rather lower in molecular weight.

Antigenic Beer Macromolecules an Experimental Survey of Purification Methods

“…4 We separated the molecules of Traction X on a column of Scphacryl S-200, a bisacrylamidc cross-linked dextran gel which has not been used before in beer studies (Fig. 2).…”

“…For example, the same beer antigens were present in several of the protein peaks obtained after anion exchange with this elution mode. 20 We made anion exchange experiments at pH 8-6 in two different buffer systems and cation exchange at pH [3][4][5]. Elution was based on linear ion gradients.…”

“…Separation of beer macromolecules accord ing to physico-chemical parameters and subsequent locali zation of proteins, carbohydrates, and phenols as well as foam-and haze-forming fractions has been the topic of numerous papers. 4 Although contributing significantly to our knowledge a synthesis of this extensive evidence is far from easy, and beer macromolecules have not yet been iso lated in homogeneous form. A main problem has been the lack of sufficiently specific methods for the identification and quantitative determination of structurally and/or functionally distinct components.…”

Interactions of Proteoses and Polyphenols in Worts, Beers and Model Systems

“…3 Complexation of protcoses with polyphenols results in products with proper ties markedly different from the reactanls.7" Added to this, the polyphcnols themselves are subject to oxidation and other processes which progressively alter their properties as beer ages.5 Fortunately, knowledge of the chemistry of fiavanoid polyphenols advanced significantly in the past decade, facilitating thereby the identification of specific chemical entities in the haze-forming process. Following from the demonstration that certain oligomeric flavanoid polyphenols44 are involved in haze formation1020 our interest has been mainly in the measurement of individual flava nols.…”

Fractionation of protein components from beer by density gradient centrifugation

“…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).…”