| Abstract
| - The negative effect of fatty acids on the foam stability of beer has been assessed. Long-chain fattyacids are far more damaging than short-chain fatty acids on the foam stability of beer at theconcentrations employed. Polypeptides have been isolated from an all malt beer by hydrophobicinteraction chromatography. Using this technique five groups of polypeptides were isolated, group 1being the least hydrophobic and group 5 the most hydrophobic, all of which exhibited similarpolypeptide compositions by SDS-PAGE. All five hydrophobic polypeptide groups bound [14C]linoleicacid; however, group 5, the most hydrophobic group, bound the most linoleic acid. Groups 1 and 5were titrated with cis-parinaric acid (CPA) to produce binding curves, which were compared with abinding curve obtained for bovine serum albumin (BSA). Groups 1 and 5 both produced bindingcurves that saturated at approximately 5.5 μM and 4 μM CPA and had association constants (Ka) of6.27 × 107 and 1.62 × 107 M-1, respectively. In comparison, BSA produced a binding curve thatsaturated at 6 μM CPA and had a Ka of 3.95 × 107 M-1. Further investigation has shown that group1 is pH sensitive and group 5 pH insensitive with respect to lipid binding. The lipid-binding activity ofgroup 5 was also shown to be unaffected by ethanol concentration. Linoleic acid (5 μM) when addedto beer resulted in unstable foam. Group 5 was added to the lipid-damaged beer and was shown torestore the foam stability to values that were obtained for the control beer. It has therefore beendemonstrated that proteins isolated from beer have a lipid-binding capacity and that they can conveya degree of protection against lipid-induced foam destabilization. Keywords: Beer; foam; hydrophobic polypeptides; lipid; linoleic acid
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