Exploration of Using Cyclodextrins as Novel Additives and Fining Agents in Wine

Abstract

Volatile phenols are responsible for some off-odours in wine, for example, the objectionable smoky, ashy notes associated with smoke taint and the sweaty, horsey, barnyard character associated with Brettanomyces. Various strategies have been evaluated for use by the wine industry to ameliorate wines with excessive levels of volatile phenols. The current project aimed to explore cyclodextrins (CDs) as a novel approach to amelioration. CDs are a group of glucose-based oligosaccharides, which are characterised by their truncated cone structure, and hydrophilic outer surface and hydrophobic inner cavity. These properties offer CDs the ability to form inclusion complexes with hydrophobic guest molecules in aqueous environments, which has been exploited by various industries, including the food and beverage industries. Chapter 1 comprises a review of literature concerning smoke taint and CDs. The limited knowledge regarding interaction between CDs and wine constituents is discussed, and then the research aims are stated. Chapter 2 comprises a study into the formation of inclusion complexes between CDs and volatile phenols in model wine, confirmed by sensory and nuclear magnetic resonance (NMR) analysis techniques. A limitation associated with conventional headspace gas chromatography mass spectrometry (HS GC-MS), namely the interaction of CD with the normalising standard is identified. A new HS GC-MS method is therefore developed to address this issue by isolating the normalising standard from the sample mixture as an additional liquid phase that still shares the same headspace during sample extraction. The inclusion of volatile phenols by CDs is then characterised using the validated method, demonstrating the reduction in headspace residuals of volatile phenols, following the addition of CD. Chapter 3 explores the potential of CD polymers to remove volatile phenols from a model wine system. The preparation of hexamethylene diisocyanate (HDI) crosslinked CD polymers is described. Several parameters influencing the removal of volatile phenols by CD polymers are then characterised, for example, the time required to achieve adsorption equilibrium, isotherms (Langmuir and Freundlich models), adsorption capacity and reusability. A batch adsorption test described in this chapter achieved up to 77% removal of volatile phenols. Chapter 4 adopts the methods and materials developed in previous chapters, and describes the impact of CDs and CD polymers, when used as treatments for smoke taint, on wine parameters. The treatments were applied to smoke affected must at different stages of fermentation. Reductions in the headspace concentrations of volatile phenols was observed following treatment, but certain aroma compounds were also lost, based on HS GC-MS and sensory analysis. The potential for a CD polymer to remove volatile phenol glycoconjugates was also investigated. Chapter 5 summarises key findings from this thesis and discusses future directions for related research.