Thiols in red wine (Part 3): Thiols interaction in a Pinotage base wine

by | Aug 1, 2020 | Oenology research, Winetech Technical

PHOTO: Shutterstock.

When does 1 + 1 = 3? The work presented in this article forms part of series of experiments on the interaction between thiols and red wine matrices as described in Part 1.

 

Background

In sensory science there are terms that describe the relationship between aroma compounds in a food product. They are often used and are indeed very important, but might need to be clearly defined before we get to the core of the article. The concepts are ‘interaction’, ‘synergy’ and ‘masking’ effects. Let us consider them one by one.

When two or more compounds have an effect on each other, but neither dominates the other, this is known as an interaction. For example, it has been proven that adding ethanol to a regular wine will reduce the amount of volatile compounds in the head space of a glass; on the contrary, by adding water, the amount of aroma volatiles increases. The components of the wine matrix interact with the ethanol (or water) added and this creates a specific outcome/result.

In the case of a synergy (or synergistic effect), the effect of combining two or more substances is greater than the sum of the separate end results. A relatively easy example, reported in sensory science text books, is the intrinsic property of salt (NaCl). Once added in small amounts to sugar, it enhances sweetness. Sodium chloride in low levels has a sweet taste, which is masked once the level is higher. Sugar, as we all know, is sweet; but the combination of the two creates a greater sensation than the individual ones.

And this brings us to the last term, ‘masking effect’, most probably the easiest of the three to explain. Various food properties can be suppressed by others and, as consequence, not be picked up. At times, this masking effect is sought after; for example the addition of sugar to tonic water to hide the bitterness of quinine or, in some white wines, the sourness is masked by a relative high residual sugar concentration.

 

Problem statement

Given the complexity of wine and the numerous chemical compounds at play, it can be understandable why so many questions still need answers in the field of aroma and taste interactions. From an experimental point of view, it is logistically impossible to evaluate at once all probable combinations of the three chosen thiols 3MH, 3MHA and 4MMP. Therefore, Experiment 2 explores the interaction of two thiols at the time in Pinotage red wine, and specifically examines the synergistic and masking effects caused by them.

 

Approach

De-aromatised Pinotage wine was used as base for this part of the project which assessed the sensory impact of interaction between two thiols at a time as illustrated in Figure 1. The spiking of the compounds was done 24 hours before evaluation to allow for integration of the samples. A panel of trained judges executed the task and a total of 12 wines (x2 repeats) were tasted in a single session. Projective mapping was chosen as sensory method which allowed to evaluate the wines according to similarities and dissimilarities, as well as profiling each individual sample. The results were illustrated using 3D scatter plots also known as surface plots.

 

FIGURE 1. Experimental layout of Experiment 2.

 

Results

The information extracted from the results can be presented from different angles.

First, the data generated are twofold: descriptive and spatial. The frequency of attributes cited by the panel constitute the descriptive data and the positioning of the samples on the 2D space is the spatial. Each of them are analysed using specific statistical tools. From the results, we can see the relationship between the samples, the attributes, and the samples and attributes combined. For example, 4MMP x 3MH interaction leads to separations of the samples driven by increasing 3MH concentrations. The associated descriptors from low levels of 3MH to high, changed from ‘fruit jam’ and ‘oaky’ to ‘herbaceous’ and ‘coffee’. In the case of the interaction between 4MMP and 3MHA, the separation of the samples is driven by 4MMP increasing concentrations. Associated descriptors from low to high 4MMP ranged from ‘blackberry’ and ‘green’ at the lowest level, to ‘raspberry’, ‘oaky’, ‘yeasty’ and ‘nutty’ at the highest.

Secondly, the results from the 3D surface plots look at the interaction between two thiols at a time, but from a single attribute perspective. It is very interesting to notice how increasing concentrations of a specific compound do not necessarily result in a linear increase in their associated aroma intensity. Consider the descriptor ‘red berries’ for instance. When comparing the surface plots of 3MH x 4MMP and 3MHA x 4MMP (Figure 2a and 2b) we can clearly see an opposite behaviour. At level zero for 4MMP, a linear increase in the intensity of the attribute is observed for 3MH as the concentration is progressing. The same cannot be said for 3MHA; once more and more 3MHA is added to the matrix, the perception of ‘red berries’ follows a bell-shaped pattern in which a maximum intensity is reached, but decreases once the concentration keeps on increasing.

Interactions are often explained in terms of synergisms and masking effects as can easily be illustrated looking at Figure 2c and 2d. The attribute represented in those two plots is ‘blackcurrant’, very often associated with 4MMP. The pattern followed by the interaction of 3MH x 4MMP (Figure 2c) highlights a maximum synergistic effect once the first compound is added at medium concentration and the second one at high concentrations. In this case 1 + 1 = 3, since the intensity of this particular fruit note is surely higher than the simple sum of the two. In the case of 3MHA x 4MMP, the interaction is much more complicated. A synergism happens at the highest concentrations of both compounds and the intensity of ‘blackcurrant’ is amplified. On the contrary, once the additions are at medium levels, a masking effect comes into play and the intensity is hampered, resulting in the visual depression in the middle of the surface plot (Figure 2d).

 

FIGURE 2. Results from the 3D surface plots look at the interaction between two thiols at the time.

 

Take home message

This experiment demonstrated that, in the case of one thiol, the perception is often non-linear. Once a second thiol is added to the mixture, the effect is even more complex and cannot be predicted from the behaviour of single compounds. Even with a relative simple mixture of two compounds, we can see major synergistic and masking interaction effects and very seldom additive.

 

Abstract

We discussed the results of Experiment 2 in which we evaluated the interaction 3MH x 4MMP and 3MHA x 4MMP in a single wine base. From the results, we saw the attributes generated through interaction, the relationship between the samples and how interaction affected the perception of particular attributes.

 

– For more information, contact Valeria Panzeri at valeria.panzeri@icloud.com or Astrid Buica at abuica@sun.ac.za.

 

Valeria Panzeri Gonzalo Garrido Banuelos and Astrid Buica

Valeria Panzeri Gonzalo Garrido Banuelos and Astrid Buica

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