Oxidation treatments affecting Sauvignon blanc wine sensory and chemical composition

[摘要] ENGLISH ABSTRACT: This study focussed on the effect of oxygen on the chemical and sensory evolution of Sauvignon blancwine under controlled oxidation conditions. The sensorial interactive effects between Sauvignon blancvarietal aroma compounds and compounds that typically arise during oxidation of white wines were alsoinvestigated.In the first research chapter the sensorial interactive effects of Sauvignon blanc impact compounds withaldehydes typically originating from oxidation of white wines were investigated. Four compounds, 3‐mercaptohexan‐1‐ol (3MH), 3‐isobutyl‐2‐methoxypyrazine (IBMP), 3‐(methylthio)‐propionaldehyde(methional) and phenylacetaldehyde were added together in a model wine medium at varyingconcentrations. The concentrations chosen were according to those reported in literature to occur inSauvignon blanc wines. The sensory effects of these compounds were profiled using a trained sensorypanel. Compounds were first profiled individually and results showed that the change in comcpoundconcentration not only led to a change in intensity ratings but also in some cases a change in thedescriptor.All four compounds in the same sample showed complicated interactive effects. Data were statisticallyanalysed using relatively novel techniques such as statistical networks that allowed deeper insights intothe interactions involved. Various observations were made such as the contribution of 3MH to the'green' character of the wine, the potent suppressing abilities of methional on 3MH and IBMP and theadditive effect of methional and IBMP contributing to the 'cooked' character of the sample.In the second research chapter the effect of repetitive oxidation on a fresh and fruity style Sauvignonblanc wine was investigated. Results showed the progress and evolution of aromatic and non‐aromaticcompounds during an oxidative aging period. A large range of chemical analyses were conductedtogether with extensive sensory profiling. Results showed a decrease in volatile thiols responsible forthe fruity nuances and an increase in oxidation‐related compounds, such as acetaldehyde, during thecourse of the oxidation. Sensory profiling showed the evolution of the wine aroma during oxidation. Thewine evolved from a fresh and fruity wine to slight oxidation and then developed extreme oxidativecharacteristics. The Control samples (no oxygen added) developed a 'cooked' character which couldindicate the formation of reductive compounds in these wines. Conversely, the wines that received asingle dose of oxygen did not develop this flavour and were perceived to be more fresh and fruity thanthe Control samples. The evolution of the wine colour was also monitored using a spectrophotometer aswell as a sensory panel and results suggest that the colour of the wine evolved before the disappearanceof the pleasant aroma. The advantages and disadvantages of oxygen exposure to this type of wine styleare discussed as well as the complexity of the wine matrix and sensory interactions occurring in the specific wine.The aim of the third research chapter was again to investigate further sensory interactions betweenSauvignon blanc varietal aroma compounds and an oxidation‐related compound. After the observationsreported in the second research chapter, the inclusion of acetaldehyde in an interaction study seemedto be of critical importance. Acetaldehyde can reach significant concentrations during oxidation and canhave a detrimental effect on wine aroma. This interaction study included three compounds, 3MH, IBMPand acetaldehyde. Acetaldehyde was able to effectively mask the 'green' character of the sample, whileit also enhanced certain fruity nuances when present at specific concentrations. 3MH was able tosuppress the oxidising character of acetaldehyde when present at sufficient concentrations.The results from this study clearly showed the complexity of the wine medium and the interactionsinvolved. It also highlighted the importance of performing these types of sensory studies in a simplemedium opposed to a complex matrix such as wine. The effect of oxygen on various aspects of the winewas investigated and the combination of chemical and sensory data delivered some interestingconclusions also involving interactions that occurred. This study paved the way for future investigationson the sensory relationships of Sauvignon blanc aroma compounds and the role of proper oxygenmanagement in the production of quality wines.

[发布机构] Stellenbosch University