Role of beer lipid-binding proteins in preventing lipid destabilization of foam

The negative effect of fatty acids on the foam stability of beer has been assessed. Long-chain. fatty acids are far more damaging than short-chain fatty acids on the foam stability, of beer at the concentrations employed. Polypeptides have been isolated from an all malt beer by hydrophobic interaction chromatography. Using this technique five groups of polypeptides were isolated, group 1 being the least hydrophobic and group 5 the most hydrophobic, all of which exhibited similar polypeptide compositions by SDS-PAGE. All five hydrophobic polypeptide groups bound [C-14]linoleic acid; however, group 5, the most hydrophobic group, bound the most linoleic acid. Groups 1 and,5 were titrated with cis-parinaric acid (CPA) to produce binding curves, which were compared with a binding curve obtained for bovine serum albumin (BSA). Groups 1 and 5 both produced binding curves that saturated at approximately 5.5 muM and 4 muM CPA and had association constants (K-a) of 6.27 x 10(7) and 1.62 x 10(7) M-1, respectively. In comparison, BSA produced a binding curve that saturated at 6 muM CPA and had a K-a of 3.95 x 10(7) M-1. Further investigation has shown that group 1 is pH sensitive and group 5 pH insensitive with respect to lipid binding. The lipid-binding activity of group 5 was also shown to be unaffected by ethanol concentration. Linoleic acid (5 muM) when added to beer resulted in unstable foam. Group 5 was added to the lipid-damaged beer and was shown to restore the foam stability to values that were obtained for the control beer. It has therefore been demonstrated that proteins isolated from beer have a lipid-binding capacity and that they can convey a degree of protection against lipid-induced foam destabilization.