Glycon structure

To avoid the above mentioned problems which are due to side activities of commercial glycosidase preparations and the specificity of glycosidases for both, the glycon as well as the aglycon moiety, an isolation and structural determination of individual constituents in a precursor fraction should be attempted. This requires the availability of preparative separation techniques that enable a gentle isolation of reactive aroma precursors from the complex glycosidic fraction of wine. 

The involvement of metal ions in the color of anthocyanins and flavonoids was discovered almost a century ago, whereby the different colors of flowers originated from the same molecules under different conditions . The crystal structure of the pigment complex affords better understanding of the color and the role of metal ions , where Fe(III) and Mg(II) bind anthocyanins via the catechol moiety and Ca(II) binds flavone glycosides through a vicinal diol on the glycone. 

Glycon Specificity.— Like other glycosidases, /3-gaIactosidases exhibit strict specificity requirements for the structure of the glycon part of the substrate molecule. Only the changes in substituents on C-5 of the d-galactose residue seem to be compatible with hydrolyzability. 

Figure 4.2.2 Top Fischer projections of a few common glycitols and glyconic acids. Note the symmetrical structure of D-mannitol. Bottom Molecular structures of (a) linear D-mannitol, (b) bent D-glucitol, (c) D-glucaric acid, and (d) crystal structure of water-in-soluble D-galactaric acid. In the latter structure the intermolecular hydrogen band pattern is indicated.

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