Application of modern analytical techniques and chemometric methods to the chemical characterisation of South African wines : determination of non-volatiles

De Villiers, A. J. (Andre Joubert) (2004-12)

Thesis (PhD)--Stellenbosch University, 2004.

Thesis

ENGLISH ABSTRACT: The present study deals in the first instance with the improvement of current analytical techniques for the analysis of the non-volatile content of wines. An improved sample preparation method, using solid phase extraction (SPE), was initially developed for the analysis of organic acids, sugars and phenolic compounds. Consequently, modem analytical methodologies were assessed to obtain optimal techniques for the separation of various non-volatile compounds. A capillary electrophoresis (CE) method, demonstrably more reliable than currently used high performance liquid chromatography (HPLC) and CE methods, is proposed for the analysis of organic acids. HPLC with refractive index (RI) or evaporative light scattering detection (ELSD) proved more suitable than CE for the analysis of sugars in dry wines. Liquid-chromatography-mass spectroscopy (LC-MS) offered superior sensitivity and resolution compared to the relatively new technique of CE-MS for the analysis of wine phenolics. LC-MS was further applied for the efficient and sensitive analysis of non-coloured phenolics and anthocyanins in wine. Negative- and positive electrospray ionisation, respectively, were used in conjunction with an ion-trap mass analyzer, for the identification of 34 phenolics and 31 anthocyanins in red wine samples. Complementary CE and LC methods were developed to allow the identification of artificial dyes in red wines, added illegally to improve their colour. Also, the application of stir bar sorptive extraction (SBSE) with liquid desorption and micellar electrokinetic chromatography (MEKC) for the analysis of bitter acids in beer is reported. In the second part of the thesis, the analytical results obtained for South African red and white wines were evaluated. Following comparison of the results with literature reports, several pattern recognition techniques were employed. A classification function obtained by linear discriminant analysis (LDA) was used to classify both red and white wines according to variety, based on their chemical composition. This classification is achieved independent of the factors of wine age or geographical origin, making it useful for authenticity evaluation.

AFRIKAANSE OPSOMMING: Hierdie studie het as primêre doel die verbetering van bestaande analitiese metodes vir die analise van nie-vlugtige komponente in wyn. In die lig hiervan, is eerstens 'n toepaslike monster-voorbereidingstegniek, gebasseer op soliede fase ekstraksie (SPE), ontwikkel vir die gelyktydige analise van organise sure, suikers en fenoliese komponente vanuit die wyn matriks. Vervolgens is moderne analitiese rtietodes ondersoek en gepastde skeidingstegnieke is ontwikkel vir die verskillende chemiese wyn-komponente. Kappillêre elektroforese (CE) en hoë-druk vloeistof-chromatografie (HPLC) in kombinasie met verskeie deteksie-metodes is vergelyk. Hieruit is 'n verbeterde CE metode vir die analise van organise sure is ontwikkel, terwyl HPLC in kombinasie met refraksie-indeks- en verdampings lig verstrooiings deteksie (ELSD) die beste resultate lewer vir die analise van suikers in droë wyne. Die toepasbaarheid van vloeistof-chromatografie met massa spektrometriese deteksie (LC-MS) vir die analise van fenoliese komponente is gedemonstreer, terwyl CE-MS onvoldoende resolusie en sensitiwiteit toon vir die analises. LC-MS is vervolgens ook gebruik vir die identifikasie van 34 fenoliese verbindings en 31 antosianiede in rooi wyn. Komplementêre HPLC en CE metodes is ontwikkel vir die identifikasie van onwettige sintetiese kleurstowwe in' rooi wyn. 'n Addisionele monstervoorbereidingsstap, roerstaaf sorptiewe ekstraksie (SBSE), is saam met vloeistof-desorpsie en misellêre elektrokinetiese chromatografie (MEKC) gebruik vir die analise van hops bitter sure in bier. In die tweede deel van die tesis word die resultate verkry m.b.v. bg. tegnieke vir die analise van Suid-Afrikaanse rooi- en wit wyne, bespreek. Die resultate is vergelyk met waardes uit die literatuur, en verskeie statistiese metodes is gebruik om die data te ondersoek. Met behulp van chemometriese metodes is 'n klassifikasie funksie verkry wat die klassifikasie van Suid-Afrikaanse wyne volgens druifsoort, gebasseer op die chemiese samestelling van die wyne, toelaat. Die klassifikasie is moontlik, onafhanklik van die ouderdom of geografiese oorsprong van die wyne.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/49850
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