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HYDROLYTIC FLAVOUR RELEASE FROM GLYCOSIDICALLY BOUND PRECURSORS IN FRUITS AND SOME OTHER PLANT-DERIVED FOODS

Objective

In many fruits and other plant tissues, the chemical compounds which contribute to flavours and fragrances occur in a bound form, linked to sugars. These conjugates, known as glycosides, are non-volatile and generally water soluble. The glycosylated aroma chemicals accumulate in the plant tissue but are not perceived by the consumer. However, if they are hydrolysed to remove the sugar during processing then the volatile aroma part of the molecule (often an aromatic or terpene-based chemical) is released. The glycosides are therefore precursors of recoverable flavour. This project aims to establish the potential of under-exploited, glycosidically bound flavour compounds in fruits and other plant derived foods. The work is focused on the basic information required in order to develop strategies for industrial applications. This includes elucidation of the structure of glycosidically bound precursors and aglycones including differentiation of enantiomers . Other studies relate to the impact of enzymatic hydrolysis of these precursors on flavour production and enhancement, as well as selection, purification, characterisation and production of exogenous enzymes liberating flavour compounds.

In a number of fruits and other plant tissues many secondary metabolites, including important aroma chemicals, are glycosylated and accumulate as non-volatile glycosides. These abundant glycosidically bound compounds can be hydrolyzed during processing to generate volatile aroma compounds. They are therefore precursors of recoverable flavour. For this reason, the following studies are envisaged to recognize the unexploited, high potential of glycosidically bound flavour compounds in fruits and other plant-derived foods fundamental to develop strategies for its industrial application, i.e. :

- Structural elucidation of glycosidically bound precursors and aglycones including enantiodifferentiations;

- Enzymatic precursor hydrolysis studies of flavour production and enhancement ;

- Selection, purification, characterisation, and production of exogenous enzymes liberating flavour compounds

With a as central analytical pool, parts a-c are strictly cross-linked enabling effective developments of selective enzymatic applications for flavour production and enhancement, i.e. leading to quality improvement of plant-derived foods
Work and achievements

Instrumental and analytical: 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, e.g. 2 ria grape leaves.

Enzymatic studies: The specificity of several enzymatic preparations against apple glycoconjugates has been established together with screening of enzyme preparations for ß glucosidase resistant to glucose inhibition. An improvement of the pH stab a-arabinofuranosidase B and ß xylosidase. The ability to express a yeast ß glucosidase in the fungus A. niger has been facilitated by the production of the necessary contructs

Progress

The significance of the above work is that it establishes the capabilities to carry on towards the primary objectives. The development of rapid LC MS/MS techniques for sensitive and selective subprofiling studies of polar flavour precursors opens the way The development of methods for easy access to malonylated glycosides enables future enzyme selectivity studies to be carried out. In addition, the fundamental knowledge gained concerning the composition of aglycones from grape leaves, establishes the basi The progress made in the enzymatic studies opens the way to future cooperation with various partners in applied work. The significance of the screening strategies and gene transfer to Aspergillus reflects the need to use approved food grade enzym
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. The purpose of this activity is to develop analytical tools to look at typical precursors and to develop enzymes of the types which could be applied for this purpose.

Call for proposal

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Coordinator

UNIVERSITÄT WÜRZBURG
EU contribution
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Address
SANDERRING 2
97074 WÜRZBURG
Germany

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Participants (4)