Application of modern chromatographic technologies for the analysis of volatile compounds in South African wines

[摘要] ENGLISH ABSTRACT:The present study was initiated by the wine industry of South Africa to overcome thelack of available information on the flavor and aroma of South African wines. Theaim was to develop new analytical methods and improve existing ones for the analysisof volatile compounds in the South African wines. Initially a new analytical methodbased on stir bar sorptive extraction (SBSE) in the headspace mode for the analysis of37 pre-selected volatile compounds was developed and validated. Consequently, themethod was improved by making important modifications and increasing the numberof compounds analyzed to 39. This method was successfully applied to a largenumber of Pinotage wines of vintages 2005 and 2006. The quantitative data of thesewines were subjected to chemometric analysis in order to investigate possible co-/variances. A clear distinction was observed between the two vintages, where the2005 wines were more characterized by wood-related compounds and the 2006 winesby the fermentation compounds. The developed method was further applied to othercultivars of vintage 2005, including two white (Sauvignon Blanc and Chardonnay)and three red (Shiraz, Cabernet Sauvignon and Merlot) cultivars. In a similar fashion,the quantitative data of the six cultivars of vintage of 2005 were analysed bychemometric methods. Significant differences were observed between the two whitecultivars and among the four red cultivars. It was shown that among these cultivars,the major role-players were the wood and fermentation related volatiles. A strikingobservation was the confirmation of the unique character of the Pinotage winescompared to the other red cultivars, mainly influenced by the high level of isoamylacetate and low level of isoamyl alcohol, the former being categorized as a varietalcompound for Pinotage expressed by a fruity (banana) odor.In addition, advanced chromatographic technology in the form of comprehensive twodimensionalgas chromatography (GC × GC) coupled to time-of-flight massspectrometry (TOFMS) was investigated for the detailed analysis of volatilecompounds in young South African wines. This work focused primarily on Pinotagewines. In the first instance, solid phase micro extraction (SPME) in the headspacemode in combination with GC × GC-TOFMS was used. Due to the high resolutionand large peak capacity of GC × GC, more than 200 compounds previously reportedas wine components were identified. These compounds were dominated by the highly volatile and less polar compounds, mainly due to the characteristics of SPME. In anattempt to further extend these results, another selective extraction method, solidphase extraction (SPE) was used in combination with GC × GC-TOFMS analysis.Using this technique, more than 275 compounds, most of them unidentified using theprevious method, were detected. These groups of compounds include volatile phenols,lactones as well as mostly aromatic esters and norisoprenoids, which can potentiallyinfluence the aroma and flavor of wine. The techniques developed as part of this studyhave extended our knowledge of the volatile composition of South African wines.

[发布机构] Stellenbosch University