Isolation of beer foam polypeptides by hydrophobic interaction chromatography and their partial characterisation

Barley and malt proteins, of infusion (IoB) and decoction (EBC) mashing worts as well as commercial wort and beer, obtained from the Castlemaine Perkins brewery, Brisbane, were gel filtered, with or without further treatments. A general, similar pattern of protein and peptide profiles emerged from barley malt and beer. This confirmed the widely assumed fact that beer proteins descend from barley, some transformed and others perhaps mostly unchanged by processing. In the gel-filtrate profiles, a maximum of 8 or 9 fractions were discerned. These fractions were collected and quantified for protein contents and amino acid compositions. The first four fractions contained the proteins and polypeptides of molecular weight higher than 14,000. Consequently, the remaining fractions contain the smaller peptides (<14,000), that were completely removed by dialysis. The effects of processing on proteins and peptides varied contingent upon the type of processing step considered and the pre-chromatographic treatment. Malting was the most effective process remarkably increasing the soluble protein contents, especially the smaller peptide fractions and the colour development. This is the first report, as far as we are aware of, on the gel filtration profiles of wort and beer low molecular weight peptides including those of barley wort. The importance of the smaller peptides in foam formation and retention cannot be overemphasised. The amino acid composition of the fractions revealed much more diversity than was observed in the comparison of the profiles. Proline content of fraction 1 resembled that of barley soluble proteins while fractions F2, F3 and F4 that of glutelin and only fraction 8 that of hordein. The latter, suggests that hordeins or, at least the peptide products rich in proline, are likely to be completely digested to amino acids, during malting.

Section: )79087 %2( (-7'977-32supporting

confidence: 90%

Section: )79087 %2( (-7'977-32mentioning

confidence: 99%

The Gel Filtration Chromatographic-Profiles of Proteins and Peptides of Wort and Beer: Effects of Processing - Malting, Mashing, Kettle Boiling, Fermentation and Filtering

Osman¹,

Coverdale²,

Onley-Watson³

et al. 2003

“…The major proteins associated with beer foam formation and stability are protein Z, a barley protein with a molecular weight of 40 kD 13 , a 17 kDa protein 27 and Lipid Transfer Protein 1 (LTP1) 5,12,25 . It has been widely accepted that it is the property of the polypeptide hydrophobicity rather than size of the polypeptide that is important in giving a stable foam 21,24 . LTP1 has been found to constitute up to 40% of the protein content of the foam fraction.…”

Section: -2863(9'8-32mentioning

confidence: 99%

The Effect of Proteinase A on Foam-Active Polypeptides During High and Low Gravity Fermentation

Brey

Costa

Rogers³

et al. 2003

The ability of beer to produce good foam is influenced by the level of foam-active polypeptides. Specific polypeptides with hydrophobic domains, such as Lipid Transfer Protein (LTP1), are important components of beer foam. Although, high gravity brewing is a commercially viable technique, it has the disadvantage of producing beer with less foam stability compared to lower gravity brewed counterparts. It is thought that proteinase A plays a key role in the degradation of these hydrophobic polypeptides responsible the beer foam stability. The object of this study was to compare and quantify the loss of hydrophobic polypeptides and specifically foam-LTP1 during high gravity (20°Plato) and low gravity (12°Plato) wort fermentations and to evaluate the effect of proteinase A on these polypeptides. The losses of hydrophobic polypeptides and foam-LTP1 were generally greater in high gravity brews. Furthermore, the results obtained suggest that proteinase A alters the hydrophobicity of these polypeptides rather than their molecular size. Approximately 20% of hydrophobic polypeptides and approximately 57% of foam-LTP1 appeared to be proteinase A resistant. These differential losses of hydrophobic polypeptide and foam-LTP1 could have implications for the foam stability of the finished product.

“…Slack and Bamforth 17 measured hydrophobicity and suggested that polypeptides can uncoil their structure to reveal more hydrophobic regions which results in a more stable foam. Onishi and Proudlove 16 isolated beer fractions of increased hydrophobicity that appeared to have identical polypeptide composition. Bamforth 4 showed there was a correlation between hydrophobic protein and foam stability.…”

mentioning

confidence: 99%

Beer Polypeptides and Silica Gel Part II. Polypeptides Involved in Foam Formation

Leiper

Stewart

McKeown

2003

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.