A study of the beer chill-proofing behaviour of a water-insoluble papain conjugate of hydrous titanium(IV) oxide-use of hydrous titanium(IV) oxide as a novel chill-proofing agent

Abstract

An active papain (EC 3.4.22.2) conjugate of hydrous titanium(IV) oxide has been found to exhibit substantial ability to chill-proof beer. However, this ability has been shown to be nearly identical to the chill-proofing abilities found to be exhibited by an inactive S-carboxymethyl derivative of the papain conjugate, which was prepared by treating the papain conjugate with bromoacetic acid, and by free hydrous titanium(IV) oxide. Further, the chill-proofing achieved by each material was observed to correlate with reductions in the absorbance of beer in both the ultraviolet and visible regions of the spectrum. On this basis, it is concluded that chill-proofing by these materials occurs solely by the adsorption of beer constituents and that this adsorption is probably non-specific. The rider to this conclusion is that the coupling of papain to hydrous titanium(IV) oxide, in order to give an active immobilized enzyme that acts as a reusable chill-proofing agent, is without efficacy. The broader significance of these observations in the development of enzymic chill-proofing agents is discussed. The potential of free hydrous titanium(IV) oxide as an adsorbent chill-proofing agent has been examined. It has been shown that the treatment of beer for 12 h at 4°C with fresh hydrous titanium(IV) oxide (200 g/hl) produces nearly complete chill-proofing. Chill-proofing is enhanced both by prolongation of treatment and by increased number of treatments. Further, beer that had been chill-proofed by hydrous titanium(IV) oxide was found to contain titanium(IV) at a concentration below the detection limit (2 p.p.m.) of the adopted colorimetric method of analysis. These results auger well for the safe commercial use of hydrous titanium(IV) oxide as a novel and effective chill-proofing agent, particularly as hydrous titanium(IV) oxide may be prepared conveniently on site from a readily available and inexpensive material, titanium(IV) chloride.