Beer Fluorescence and the Isolation, Characterisation and Silica Adsorption of Haze-Active Beer Proteins

Abstract

The fluorescence spectra and lifetimes of diluted beer have been explored and found not to report on protein removal either by silica or tannic acid, nor polyphenol uptake by PVPP. Comparing the fluorescence spectra of beer with that of tea and hops, it seems that proteins, complex polyphenols and iso-a-acids can contribute to the intrinsic fluorescence of beer, although the contribution from polyphenols must be minimal since treatment with PVPP does not dramatically change the background fluorescence. To eliminate the problem of background fluorescence haze-active protein was isolated. Steady-state and time-resolved fluorescence techniques were used to characterise these and to monitor their uptake by different silica gels as a function of pH. Heat treated large pore volume, small surface area silicas were the more effective adsorbers for the proteins under study, with pH 4 being optimum. Using both intrinsic amino acid fluorescence and the extrinsic fluorophore fluorescamine, the timeresolved fluorescence anisotropy has been measured and the radius of the isolated haze protein found to be ~ 35 Å. Comparisons have been made with proteins of known size and structure such as human and bovine serum albumins (HSA and BSA). Key words:Beer, fluorescence, haze-active protein, polyphenols, silica adsorption. -2863(9'8-32The intrinsic fluorescence characteristics of beer are expected to be complex due to the overlap of emissions from numerous species. Nevertheless once the different origins of the fluorescence have been identified, by comparison with the isolated species, new insights may be found into the brewing and stabilisation processes. With this goal in mind, various constituents in beer have been studied and compared using steady-state and time-resolved fluorescence techniques.The interaction of protein with amorphous silicas, eg., silica hydrogels, silica xerogels, is of interest to the beverage industry. Of importance is its role in the prevention of chill haze, and subsequent risk to permanent haze formation in fruit-based beverages or cereal based beverages, such as beer. Chill haze forms as a result of the interaction of haze-active proteins with polyphenols. In order to maintain the clarity of beer and to extend colloidal shelf life, the brewing industry selectively removes these proteins from beer by adsorption onto and into amorphous silicas. Information regarding the detailed structure and amino acid sequence of these haze-active proteins is limited. In general terms, there are two types of protein present in beer: hydrophilic and hydrophobic. The hydrophilic proteins are responsible for haze formation and need to be removed whereas the hydrophobic proteins provide foam stability and must remain 16 . Bentonite removes both hazeactive and foam-active protein whereas silica gel offers specificity for haze-active proteins 20 . This specificity is a result of the proline residues in the haze-active proteins. These proline rich proteins are known to originate from malt and have an isoelectric point in the re...

Rapid Determination of Bitterness in Beer Using Fluorescence Spectroscopy and Chemometrics

“…In all three samples two distinct peaks are seen with excitation /emission maxima around 290 /350 nm and 340 /430 nm, respectively. The first peak probably arises from protein fluorescence, mainly attributed to tryptophan, while the second peak can be related to fluorescence from complex polyphenols or iso-␣-acids, as suggested by Apperson et al 4 Sample B has a significant higher IBU value than sample A, and thus was expected to contain a higher amount of iso-␣-acids. However the intensity of the peak around 340 /430 nm is not very different for the two samples, indicating that the bitter acids are not the main contributors to the fluorescence signal obtained in this area.…”

“…Fluorescence spectroscopy applied directly on food samples evaluated with chemometrics, has among others been suggested for analysis of sugar 7,19 and the oxidative stability of various dairy products 5,10,27 . The intrinsic fluorescence or autofluorescence of undiluted as well as diluted beer was investigated in 2002 by Apperson et al 4 . Inner-filter effects were shown to appear in the fluorescence signal from the undiluted beer samples, expressed by the fact that protein fluorescence was only obtained upon dilution with distilled water.…”

“…In the patent no dilutions were suggested; in this way, a rapid bitterness determination was possible, with no need for sample preparation. However, in Apperson et al 4 , no multivariate analysis was performed to calibrate the signals to the reference values and in the patent 24 no results are given regarding the performance of the method.…”

Fluorescence Spectroscopy for Characterization and Differentiation of Beers

“…The emission at 295 /315 nm has been attributed to tyrosine and not ␤-catechin or epicatechin -the proanthocyanidin monomers. The fluorescence maxima for both catechin and epicatechin occur at 315 nm, when excited at 265 and 280 nm, respectively, hence, they may overlap tyrosine and tryptophan fluorescence 8 .…”

“…Both techniques have been successfully used in the analysis of crude oils, pharmaceuticals, polycyclic aromatic hydrocarbons, motor oils, and humic matter in water [4][5][6][7] . Fluorescence spectral data and lifetimes in diluted beers have been explored recently 8 . We have reported on the application of total fluorescence spectroscopy to characterize beers 9 .…”