Significant abilities of titanium(IV)-activated glass fibre paper and its papain conjugates to chill-proof beer

Abstract

It has been demonstrated that titanium(IV)-activated glass fibre paper, unlike untreated glass fibre paper, acts as a potent agent for chill-proofing beer: three treatments of beer with titanium(IV)-activated glass fibre paper (0.2m 2/l) for 12 h were found to produce complete chill-proofing. Chill-proofed beer was found not to be contaminated with titanium(IV) species at a concentration above a detection limit of 2 p.p.m., so augering well for the safety of titanium(IV)-activated glass fibre paper as a chill-proofing agent. The physical form of titanium(IV)-activated glass fibre paper provides a major advantage over particulate chill-proofing agents in that it may be easily and rapidly separated from beer. The chill-proofing ability of titanium(IV)-activated glass fibre paper was found to decline with repeated use of the material. Moreover, all the observed chill-proofing effects were paralleled by reductions in the absorbance of beer across the ultraviolet and visible regions of the spectrum. These results demonstrate that titanium(IV)-activated glass fibre paper imitates hydrous titanium(IV) oxide in its effects upon the properties of beer and accord with other evidence that the surface of titanium(IV)-activated glass fibre paper is chemically similar to that of hydrous titanium(IV) oxide. The mechanism of the chill-proofing action of titanium(IV)-activated glass fibre paper is concluded to be analogous to that of hydrous titanium(IV) oxide and probably to involve the non-specific adsorption or ligand bonding of beer proteins and polyphenols to titanium(IV). Two papain (papain, EC 3.4.22.2) conjugates of titanium(IV)-activated glass fibre paper, of different catalytic activities, have been examined for chill-proofing ability. The chill-proofing behaviour observed for each papain conjugate was found not to differ from that observed for the corresponding catalytically-inactive S-carboxy-methyl derivative, prepared by treatment of the papain conjugate with bromoacetic acid, nor to differ greatly from that of titanium(IV)-activated glass fibre paper. On this basis the chill-proofing abilities of the papain conjugates are attributed solely to their abilities to adsorb beer constituents and not to their catalytic activities.