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Hydrolytic flavour release from glycosidically bound precursors in fruits

The perceived flavour of many foods and beverages of plant origin, including wine and other fermented drinks, reflects the release of volatile aroma compounds. Many of these are secondary metabolites based on aromatic compounds which are complexed in the plant tissue, with sugar molecules in the form of glycones. These are often soluble in water and will be extracted on pressing juice, for example. However, for the same reason they are not volatile and hence their presence may not be perceived by the consumer. If the sugar molecule is separated the resulting compound (termed an aglycone) becomes volatile and contributes to the appreciation of flavour. In theory, the flavour can be enhanced if the sugar is removed using enzymes. In many cases, this could be achieved by one class of enzymes known as glucosidases. To do this requires suitable food grade enzymes, as well as an understanding of the chemistry of the precursors involved. Analytical tools were developed to look at typical precursors and to develop enzymes of the types which could be applied for this purpose.
%In order to separate and analyse compounds of interest, new column packings were prepared. This included synthesis of new cyclodextrin (CD) derivatives with improved discrimination capacity and more general use. The specificity of several enzymic preparations against apple glycoconjugates has been established together with screening of enzyme preparations for beta glucosidase resistant to glucose inhibition. The development of techniques for sensitive and selective subprofiling studies of polar flavour precursors and methods for easy access to malonylated glycosides enables future enzyme selectivity studies to be carried out. In addition, fundamental knowledge was gained concerning the composition of aglycones from grape leaves.

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