WINETECH Technical Yearbook 2021

compounds), can be present at perceivable concentrations in the same wine at one time. Seeing that these two aroma groups contribute such contrasting flavours, it is important to understand the sensory interactive effects between them and the Two fruity volatile thiols, 3-mercaptohexan- 1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) were used in this study. Each of the volatile thiols was added to a model wine at two levels based on the thiol content found in commercial South African Sauvignon blanc wines: ● 3MH Level 1 (considered as “low”) = 500 ng/L. Level 2 (considered as “high”) = 2 500 ng/L. ● 3MHA Level 1 (considered as “low”) = 100 ng/L. Level 2 (considered as “high”) = 400 ng/L. One reductive compound, ethanethiol (EtSH) was added at concentrations just below and above the sensory perception threshold of 1.1 μg/L. EtSH imparts flavours, such as onion, rubber and effect it can have on the wine. MATERIALS AND METHODS

sulfidic-like aromas, when present at sufficient concentrations (Goniak & Noble, 1987). During the initial sensory assessment of the wines, the judges reported that the perception of the samples changes, complicating the sensory evaluation procedure. To overcome this, a new sensory method was developed to allow for the evaluation of samples that are similar and change over time. In this method, judges evaluated the wines continuously over a 120-second period generating unlimited attribute intensity data over time. RESULTS Figure 1 shows the sensory profile of a single sample over time generated using the data obtained from the new sensory method. The intensity of four attributes, namely guava, passion fruit, cooked veg and H 2 S, showed specific trends during the study. ● An increase in 3MH increased the perceived intensity of guava, passion fruit and tomato leaf in the samples. However, the intensity of the attributes changed over time. The strongest signal was captured at the beginning of the sensory evaluation and the intensity decreased over the 120-second period.

FIGURE 1. Sensory profile of a single sample over time (x-axis). Data shows the average intensity scoring (y-axis) of all judges for each attribute (Du Toit, 2020).

● When 3MH was added at the higher concentration (level 2), the perception of guava and passion fruit decreased faster over the 120-second period compared to the sample to which 3MH was added at the lower concentration (level 1). ● Interactive effects between 3MH and 3MHA indicated a synergistic effect as

the intensity of guava was significantly higher when the samples contained both compounds compared to when the compounds were added individually. This synergism was, however, not seen for passion fruit. ● Interestingly, the synergistic effect of 3MH and 3MHA on the guava attribute

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