Abstract
Abstract (description) The objectives of this project included the development of methodology for the preparation of
tannins standards that can be used to investigate the function of tannin structure in wine quality.
Isolated tannin standards of different structures were used to investigate the relationship of tannin
polymer length and the effect of the wine matrix on tannin-protein interactions involved in
astringency. The structures of different tannins were determined to investigate tannin conformation,
tannin solubility and colloid formation in wine. The outcomes of this project include fundamental
knowledge that contributes to our understanding of tannin interactions such as astringency, colloid
formation and extractability.
Summary
The composition and content of tannin in wine is primarily determined by the interactions of grape tannin as it is extracted from the grape berry and with other compounds to form wine tannin, polymeric pigments and colloids. The interaction of tannin with proteins forms the basis of astringency, which plays a significant role in wine quality. The role of tannin structure in these interactions is generally not well understood. The main limitation to research that advances our knowledge in this area is the lack of tannin standards of defined structure that can be used to investigate how tannin structure influences wine quality.
The objectives of this project were to develop methodology for the preparation of tannin standards that can be utilised to investigate the function of tannin structure in wine quality. Specifically, methodology was developed for the preparation of tannin standards that could be utilised to investigate the molecular assembly of tannin polymers including order of subunit assembly, secondary and tertiary structure. These standards were then utilised to investigate the interaction of tannin polymer length with proteins involved in astringency.
This project also investigated the role of the wine matrix on determining tannin solubility and astringency.
Methodology developed for preparing tannin standards utilised a combination of preparative diol and C18 phase high performance liquid chromatography to isolate and separate individual tannins structures from cacao, grape seed and pre-veraison grape skin. A range of tannin structures were identified for isolation and purification including homopolymers of increasing polymer length, polymers with varying degrees of galloylation and polymer length, and polymers with varying degrees of tri-hydroxylation and polymer length.