POLYPEPTIDES WITH ENHANCED FOAM POTENTIAL

The ability of beer to produce a good foam is strongly influenced by the level of foam active polypeptides. It has previously been proposed that a means of ensuring an adequate level of such species is to add an exogenous preparation of foam active protein 3. One such preparation, hydrolysed liquid egg white (HLEW), has been shown to impart a good foam to beer with substandard foam performance, without detriment to product quality. The foam active properties of this material are the subject of the work described here. HLEW was characterised by a combination of reverse phase chromatography and polyacrylamide gel electrophoresis to reveal a heterogeneous mixture of low molecular weight (2100-6000 daltons) relatively hydrophilic polypeptides. When this material was subjected to foaming and the foam positive and foam negative fractions similarly characterised, it was apparent that the foam positive fraction consisted almost exclusively of hydrophobic polypeptides. Accordingly, preparative reverse phase chromatography was used to isolate foam active fractions from the hydrophobic species present. These fractions were subsequently subjected to both functional and physical characterisation. It was apparent from a small-scale Rudin test that the foam activity per unit dry weight of protein was enhanced in the foam active factions; in one case an enhancement of 2 fold greater than the HLEW itself was observed. Moreover, upon addition to beer a positive effect on HRV was achieved with as little as 0.0025 mg protein/ml beer. Physical characterisation of the foam active material revealed the presence of tightly bound polypeptide aggregates which could only be separated by the use of protein denaturing agents.