Influence of chemical composition of polysaccharides on aroma retention

The aim of this paper was to link physico-chemical characteristics of both xanthan and guar gums with the behaviour of aroma compounds in model systems. The chemical compositions of guar gums and xanthan gums were determined from several commercial samples. The guar samples differed mainly in their mannose/galactose (M/G) ratio, which varied from 1.23 to 1.83. The xanthan samples showed a large range of molecular weights, protein and acetate contents as well as pyruvate groups content. The impact of these variations on aroma retention was determined by measuring the partition coefficient of ethyl butanoate, ethyl hexanoate, ethyl octanoate and ethyl decanoate in polysaccharide solutions prepared at 0.1% (w/w). For guar samples, results clearly indicated that the M/G ratio could play a critical role in retention of ethyl hexanoate whatever the molecular weight of guar samples. Indeed, a low M/G ratio, i.e. a high density of galactose residues, induced a release of this non-polar compound. A competition between galactose residues and ethyl hexanoate to bind water molecules could explain this salting-out effect. On the contrary, the high retention of ethyl decanoate was clearly linked to the molecular weight of guar samples involving hydrophobic interactions with the macromolecules. In xanthan solutions, the intrinsic proteins could participate in the retention of ethyl hexanoate and ethyl decanoate while the different molecular weights of the polysaccharide samples seemed not to affect their retention. The different levels of acetate groups had apparently only an influence on ethyl hexanoate behaviour.