Bisulfite bleaching, polymeric

Calculate the polymeric color of the bisulfite bleached sample as follows ... 

Polymeric color was determined using the bisulfite-bleached sample using the following formula ... 

Fractionation of Red Wine Polymeric Pigments by Protein Precipitation and Bisulfite Bleaching... 

The Hagerman and Butler method for tannin analysis was combined with bisulfite bleaching of monomeric anthocyanins to give estimates of polymeric... 

Figure 4. Correlation between the amount of polymeric pigment as determined in the Somers assay at wine pH and the sum of LPP and SPP as determined by combined protein precipitation and bisulfite bleaching. 2003 American Society for Enology and Viticulture. AJEV 54 301-306...

The routine analysis of polymeric pigments in wine is based on the work of Somers who showed that monomeric anthocyanins are bleached with bisulfite whereas polymeric pigments are not (i,5). Thus, the difference in absorbance readings at 520nm before and after bleaching with bisulfite is widely used as a measure of the amount of polymeric pigment present in red wine. 

As red wines age, the monomeric forms of anthocyanins undergo condensation reactions with other anthocyanin or tannin molecules to form polymeric pigments. The polymeric pigments are less sensitive to bisulfite bleaching and changes in pH (10). The color analysis method of Somers and Evans (10) as described above takes advantage of these differences to follow color changes as wines age. 

The acetate buffer is set at pH 4.9 because 4.9 is the pi of BSA and thus affords maximum precipitation of the tannin/protein complexes formed during the precipitation reaction. Coincidentally pH 4.9 is particularly good for measuring absorbance due to polymeric pigments because the anthocyanins have their minimum absorbance at that pH (d). Since any remaining monomeric anthocyanins are bleached with bisulfite, this procedure assures that all of the remaining 520 nm absorbance is due to polymeric pigments (LPP + SPP). 

The procedure in the polygon in Figure 1 is the Hagerman Butler assay for tannin. The only modification is that we retain the supernatant after centrifugation of the precipitation reaction mixture and bleach the monomeric anthocyanins with bisulfite. The residual absorbance represents pigments that do not precipitate with protein and do not bleach in the presence of bisulfite. We have designated this material small polymeric pigment solely to denote these two characteristics. The LPP removed from the sample by protein precipitation... 

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