Investigation of the effects of age, vintage and style on phenolic composition of Pinot Noir wines of a major New Zealand producer : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Pinot Noir has become the most important red grape variety and built a solid reputation for the New Zealand wine industry. In terms of quality attributes, phenolic compounds are thought to be important for the colour, basic tastes, and mouthfeel of red wine. This thesis investigates the phenolic composition of Pinot Noir wines and the potential effects of age, vintage, and style on phenolic compounds as well as wine colour. The first stage included a general exploration of phenolic compounds of Pinot Noir wine where colour properties, total phenolics, and tannin concentrations of 22 Pinot Noir wines produced by Pernod Ricard Winemakers (New Zealand) Ltd. were determined using spectrophotometric measurements including the modified Somers assay and the methylcellulose precipitable (MCP) tannin assay. Generally, strong age-related trends were observed concerning colour properties and total phenolics, whilst tannin concentration fluctuated between vintages and styles. The second aim was to focus on separating polymeric phenolics from monomeric phenolics using three different methods including isoamyl alcohol extraction (F-iso), solid phase extraction (SPE), and size exclusive chromatography (SEC). Five polymeric fractions were examined using spectrophotometric measurements. The red colour of polymeric phenolic material in old wines tended to be more resistant to changes in pH as indicated by a reduction in the factor A520 pH1/pH3.4 from 2.6 to 1.1 during ageing, with the degree of ionisation of these bleachable polymeric components increasing during ageing. This result for Pinot Noir wines is the first report of this age-related trend in polymeric material. In addition, colour and phenolic properties and tannin concentrations in extracted polymeric fractions were significantly influenced by wine age and style (P < 0.05). Tannin fractionation to some extent contributed to the discrimination of style, for example, MCP tannin in SEC fraction and total phenolics in SEC fractions contributed to the discrimination of super premium wines. The final aim was to characterise the composition of monomeric and polymeric materials using three chromatographic techniques. The monomeric material was analysed using RP-HPLC, while the phloroglucinol adducts of the total isolated polymeric material were determined by both HPLC and Orbitrap-UPLC-MS/MS to explore tannin composition as well as quantification markers of polymeric pigments. Six monomeric phenolics, total monomeric red pigments and one type of polymeric pigment were significantly affected by vintage, age, and style (P < 0.05): i.e. protocatechuic acid, caftaric acid, trans-coutaric acid, grape reaction product (GRP), quercetin-3-glucoside, malvidin-3-glucoside, total red pigments, as well as the M3G-C/EC (A type)-F trimers and the corresponding T-A-F (A type)-F adducts (A, malvidin-3-glucoside; F, catechin/epicatechin; T, condensed tannin). General decreasing patterns with age were seen in p-hydroxybenzoic acid, caftaric acid, coutaric acid, flavan-3-ols, resveratrol, malvidin-3-glucoside, total red pigments, as well as yield of tannin, mDP (mean degree of polymerisation), average molecular weight, and catechin and epicatechin extension units, and coloured T-A and A-methlymethine-T adducts, whilst general increasing patterns were seen in p-coumaric acid, proportions of catechin and epicatechin terminal units, seed-derived epicatechin gallate subunits, and skin-derived epigallocatechin subunits, as well as proportions of A-type polymeric pigments. Considering wine colour, the decreased proportion of malvidin-3-glucoside, T-A and A-methlymethine-T adducts, as well as the increased proportion of other red pigments measured by RP-HPLC contributed to the change of colour density and hue with age (3-19 years). In contrast, increased proportions of T-A-F (A type), A-F (A type)-T, T-F-A-F (A type) and T-A-F (A type)-F adducts resulted in colour reduction and compositional stability in old wines. The discrimination of one group of regionally distinct wines was driven by monomeric phenolics, whilst the discrimination of super premium wines was driven by the significantly higher colour density, SO2-resistant pigments, total phenolics, and tannin concentrations, as well as higher proportions of malvidin-3-glucoside-(epi) catechin dimers and the corresponding T-A-F adducts. With respect to wine age, vintage and style, this study has established three main associations with wine attributes: the first between wine age and colour properties, the second between style and colour and phenolic parameters, and the third between wine age and style, and monomeric and polymeric phenolics. High-quality wines have been found to be positively correlated with higher colour and phenolic parameters, and tannin concentrations, as well as higher proportions of malvidin-3-glucoside-(epi) catechin dimers. Thus, any modifications in winemaking techniques that could improve wine colour, total phenolics and tannin concentration, and malvidin-3-glucoside-(epi) catechin dimers are important to improve the perceived quality of the wine.