Browsing Masters Degrees (Institute for Wine Biotechnology) by Subject "Advanced chemometric techniques"
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- ItemVolatile metabolic profiling of SA Chenin blanc fresh and fruity and rich and ripe wine styles : development of analytical methods for flavour compounds (aroma and flavour) and application of chemometrics for resolution of complex analytical measurements(Stellenbosch : Stellenbosch University, 2012-03) Lawrence, Nina; Nieuwoudt, Helene; Tredoux, A. G. J.; Skov, T. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.ENGLISH ABSTRACT: The aroma and flavour of wine are important aspects that form the basis for consumers’ organoleptic experience of wine. Therefore, an understanding of the chemical composition of wine aroma is of major importance, to establish possible links between wine chemistry, sensory attributes and consumer preference for a product. For this purpose analytical chemistry and multivariate techniques are indispensable tools for the metabolic profiling of wine. Chenin blanc is one of the most important South African export white wine varieties. However, despite its importance, very limited profiling of Chenin blanc aroma compounds has been done and information is restricted to isolated and dated reports on a few chemical compounds only. Therefore, the overall aim of this study was to obtain an in-depth view of the volatile chemical profile of this cultivar. The first task was to perform targeted volatile metabolic profiling of the three dry and offdry Chenin blanc styles, fresh and fruity, rich and ripe unwooded and rich and ripe wooded. To this end, a new, simple and robust liquid-liquid extraction technique using dichloromethane was developed and validated for extraction of analytes prior to gas chromatography flame ionization detection (GC-FID) analysis, to quantify 57 analytes in one rapid analytical procedure. This method was applied to profile 48 Chenin blanc wines. Very successful discrimination between the three styles, using the quantified volatile compounds, was obtained with two multivariate methods. These were partial least squares regression-discriminant analysis, (PLS-DA), as well linear-DA, using best subset selection for identifying the most important variables. According to the classification models, a higher content of maturation derived, malolactic fermentation derived and wood derived compounds were predominantly characteristic of the wooded wines. Higher content of some terpenes and ethyl esters were predominantly associated with the rich and ripe unwooded style Chenin blanc wines, while the fresh and fruity style were generally characterized by high levels of acetate esters. Secondly, untargeted analysis of 21 wines was done with gas chromatography mass spectrometry (GC-MS). Mathematical chromatography, using PARAllel FACtor analysis (PARAFAC and PARAFAC2), was applied to the GC-MS data for resolution of the complex chromatographic results by multi-way modeling, and to derive unbiased multivariate classification models of the three styles. This approach provided excellent style differentiation, without the arduous task of analysis of numerous standards and setting up of calibration curves, required by the targeted approach described above. Additionally, the data generated during this study will form part of the current South African wine aroma database, which does not contain any data regarding Chenin blanc at present.