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

Abstract

Four high-molecular weight proteose fractions from beer were precipitated to varying extents by four different tannin fractions, as shown turbidimetrically in a simple assay. According to this test the most acidic proteose fraction reacted least with all four tannins and the formation of insoluble proteose-tannin complexes was strongly dependent on pH. Moreover, tannins obtained from hops displayed greater tanning power with beer proteoses than did either a tannin isolated directly from barley or one prepared by aerial oxidation of barley prodelphinidin B3. The different reactivities of tannins to proteoses, however, did not correlate well with their reactivities to cinchonine sulphate (CS). Whereas the amounts of break precipitated on boiling a wort moderately were related to the amounts of hop tannins added, barley flavanols had little effect on break formation. In beer, about 50% of the proteoses were of low molecular weight (< 10,000 Daltons) and some were complexed with flavanols. In contrast, isolated fractions of high molecular weight beer proteoses (MW> 10,000 Daltons) were not associ ated with flavanols. The most acidic of these proteoses were the least stable in solution, being precipitated from beer by down-shifts in pH. The tanning power of unstabilised beer as measured by reaction with cinchonine sulphate was shown to arise from the cumulative effects of at least four different beer components, which should be considered when interpreting the effects of different haze-stabilisation treatments.

Effect of the Removal of Sensitive Proteins and Proanthocyanidins on the Colloidal Stability of Lager Beer

“…So it may seem contrary that the assay for oxidizable polyphenols fitted least well in the haze development model. We have, however, demonstrated already that the values obtained in the assay for oxidizable polyphenols depend not only on the content of simple flavanols, but also on the content of SHG-absorbable higher-molecular-weight substances (25). Our results, therefore, are in agreement with the proposal (40) that the key polyphenolic constituents in the determination of colloidal stability are the dimeric proanthocyanidins.…”

“…Monomeric flavanols, flavonol glycosides, phenolic acids, 4dimethylaminocinnamaldehyde, and HPLC-grade solvents were obtained from sources mentioned previously (23)(24)(25)(26)(27)(28)(29).…”

Characterization of Stabilized and Unstabilized Beers

“…These proteoses, with MW-10,000 daltons, were only precipitable by 15% (w/v) TCA in PAGIF and smaller ones were not detected in our experiments. According to the literature (McMurrough et al 1985;Dale and Young 1988), the acidic proteoses with PI values in the range 4-6 have been cited as a major factor in the formation of :hill haze. The ammonium sulfate precipitates obtained from beers following cold storage (1 "C during filtration and PVPP treatment) contained fewer acidic proteoses than did the original untreated samples.…”

“…Haze formation is regarded usually as a consequence of the tanning reaction between polyphenols and proteins (Belleau and Dadic 1981;Maza Selas 1987;McMurrough et al 1985;Yu 1987). Simple flavanols (anthocyanogens), owing…”

Enzymes in the production of beverages and fruit juices

“…This type of complex is frequently manifested as a 'chill-haze', which appears on cooling but which may re-dissolve at room temperature or above. This is generally attributed to hydrogen-bonding, as shown in Figure 7.2, or to hydrophobic interactions with proline residues (McMurrough et al, 1985;Haslam and Lilley, 1988). At a later stage, nucleophilic substitution of phenolic rings by protein sulphydryl groups may lead to a 'permanent' haze that does not re-dissolve when warmed.…”