Beer contains approximately 500 mg/L protein depending on the brewing procedures employed. This protein is in the form of polypeptides, the majority of which lie within the 10-40 kD size range. Some of these polypeptides are responsible for causing colloidal haze, some enhance foam stability and the remainder appear to have no function in beer except to contribute to mouthfeel. Those polypeptides involved in haze formation were described in a previous paper. To continue these studies, data is presented to show that foam polypeptides are highly glycosylated and that purified foam glycoprotein contains low levels of the amino acid proline. As silica preferentially adsorbs polypeptides rich in proline, it is unlikely to adsorb this material and damage foam stability. The molecular sizes and composition of glycoproteins recovered from untreated beer, purified foam and beer from which the foam component has been removed are presented. These fractions include the polypeptides responsible for foam stability and those that appear to have no role in physical stability.
Beer contains approximately 500 mg/L protein depending on the brewing procedures employed. This protein is in the form of polypeptides, the majority of which lie within the 10-40 kD size range. Some of these polypeptides are responsible for causing colloidal haze, others enhance foam stability and the remainder appear to have no function in beer except to contribute to mouthfeel. The polypeptides responsible for haze formation are those that can combine with polyphenols to produce a visible cloudy haze. This is undesirable as it can have a negative effect on the beer's shelf life. One way to reduce this effect is to remove these polypeptides using silica gels. It is important that this removal is selective, and the desirable foam enhancing polypeptides are not removed.Data will be presented to show that beer polypeptides are glycosylated and that silica preferentially adsorbs glycoproteins, particularly those with protein components rich in the amino acid proline. The molecular size and composition of glycoproteins recovered from untreated beer, cooked adjunct, silica exposed to beer and beer aged for one year are presented. Glycoproteins involved in foam, and the apparently functionless polypeptides, will be discussed in a subsequent paper.Key words: Amino acids, beer stability, carbohydrates, mashing, polypeptides, silica gel. -2863(9'8-32It has been known for many years that silica gel is an effective beer stabilizer as it selectively removes those polypeptides that are responsible for causing haze formation. However, it is not clear what size of polypeptides are involved and what proportion of total beer protein they constitute. Also, it is not clear to what extent silica structure effects the ability to adsorb haze-causing polypeptides.Beer contains approximately 500 mg/L protein. Most of this is in the form of polypeptides that are in the 5-100 kD size range. Due to the combined hydrolytic and destructive effects of malting, mashing, boiling and fermentation, there is a very small range of polypeptides present in beer. Three major components have been identified, a polypeptide of 40 kD known as Protein Z 9 , a polypeptide of 9.7 kD known as LTP1 19 which is involved in foam stability, and a group of polypeptides that range between approximately 10 kD to 30 kD. These originate from barley hordein, are rich in the amino acids proline and glutamic acid and are involved in haze formation 3 .The formation of permanent haze occurs when the proline-rich polypeptides combine with specific polyphenols, particularly the flavanol dimers procyanidin B3 and prodelphinidin B3 17 . This haze forming reaction can be prevented by removing either the protein component with silica gel, or the polyphenol component with PVPP (polyvinylpolypyrrolidone).Silica gel (SiO 2 ) is a highly porous structure with a large surface area. Its surface is covered with silanol (SiOH) groups that bind to proline residues in polypeptides. Silica is highly selective for haze protein due to the high levels of proline present in these polypeptides...
The fluorescence spectra and lifetimes of diluted beer have been explored and found not to report on protein removal either by silica or tannic acid, nor polyphenol uptake by PVPP. Comparing the fluorescence spectra of beer with that of tea and hops, it seems that proteins, complex polyphenols and iso-a-acids can contribute to the intrinsic fluorescence of beer, although the contribution from polyphenols must be minimal since treatment with PVPP does not dramatically change the background fluorescence. To eliminate the problem of background fluorescence haze-active protein was isolated. Steady-state and time-resolved fluorescence techniques were used to characterise these and to monitor their uptake by different silica gels as a function of pH. Heat treated large pore volume, small surface area silicas were the more effective adsorbers for the proteins under study, with pH 4 being optimum. Using both intrinsic amino acid fluorescence and the extrinsic fluorophore fluorescamine, the timeresolved fluorescence anisotropy has been measured and the radius of the isolated haze protein found to be ~ 35 Å. Comparisons have been made with proteins of known size and structure such as human and bovine serum albumins (HSA and BSA). Key words:Beer, fluorescence, haze-active protein, polyphenols, silica adsorption. -2863(9'8-32The intrinsic fluorescence characteristics of beer are expected to be complex due to the overlap of emissions from numerous species. Nevertheless once the different origins of the fluorescence have been identified, by comparison with the isolated species, new insights may be found into the brewing and stabilisation processes. With this goal in mind, various constituents in beer have been studied and compared using steady-state and time-resolved fluorescence techniques.The interaction of protein with amorphous silicas, eg., silica hydrogels, silica xerogels, is of interest to the beverage industry. Of importance is its role in the prevention of chill haze, and subsequent risk to permanent haze formation in fruit-based beverages or cereal based beverages, such as beer. Chill haze forms as a result of the interaction of haze-active proteins with polyphenols. In order to maintain the clarity of beer and to extend colloidal shelf life, the brewing industry selectively removes these proteins from beer by adsorption onto and into amorphous silicas. Information regarding the detailed structure and amino acid sequence of these haze-active proteins is limited. In general terms, there are two types of protein present in beer: hydrophilic and hydrophobic. The hydrophilic proteins are responsible for haze formation and need to be removed whereas the hydrophobic proteins provide foam stability and must remain 16 . Bentonite removes both hazeactive and foam-active protein whereas silica gel offers specificity for haze-active proteins 20 . This specificity is a result of the proline residues in the haze-active proteins. These proline rich proteins are known to originate from malt and have an isoelectric point in the re...
Colloidal stabilisation of all malt and adjunct lager beers through selective removal of haze sensitive glycoproteins using silica gel and tannoid polyphenols using polyvinylpolypyrrolidone (PVPP) or a polyvinylpyrrolidone (PVP)-modified silica gel has been demonstrated during full brewery production. At this scale PVPP and the PVP-modified silica gel exhibited equivalent binding capability for tannoid polyphenols although PVPP removed additional polyphenolic species. Characterisation of proanthocyanidins following treatment at 4°C with PVPP and the PVP-modified silica gel silica co-product confirmed that PVPP removes a wider range of polyphenolics. Both products exhibited poorer polyphenolic binding capability at 4°C as would be expected for a physical adsorption process.
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