As part of its continuing research efforts in the field of oxygen management, Nomacorc has been working with a number of research partners around the world. The complementary expertise of these partners has helped Nomacorc gain a better understanding of many topics, including wine phenolics, oxidation chemistry, wine aroma chemistry, wine metabolomics, applied enology, and sensory science. Here’s a conversation with Dr. Fulvio Mattivi, a researcher at the Edmund Mach Foundation in Trento, Italy, who has been using a highly innovative approach called metabolomics to provide better, more far-reaching analyses of the effects of oxygen on wine.
Can you tell me about the project you are working on with Nomacorc?
It’s a rather challenging project, because we want to investigate the effects of very minute amounts of oxygen at the bottling stage. We want to see if it’s true—and we believe it is, from empirical experience—that just a few milligrams of oxygen added at or after bottling can affect aromas, in particular those of white wines.
You’re using a technique called metabolomics. Can you tell us about the approach?
The keyword of metabolomics is “untargeted.” It means, in practice, that it can analyze in the same way compounds that we already know and compounds that are unknown. This is because the instrument, by itself, can measure everything that can be highlighted by the method you are using. Normally, the analysts prefer to select and set the instruments to see only what they know, in the optimal way. With metabolomics, we are trying to enlarge the coverage a lot. We’re significantly increasing the number of compounds that can be followed and measured, and we can then trace the compounds that are specifically reacting—in this case, to oxygen.
In other words, you can get a global portrait, but can also focus on factors that are not yet identified?
Right. We are not doing a new experiment, but the way we are doing it is totally new. The coverage we are looking for is a little ambitious as well, because we are using two separate techniques. One is bi-dimensional chromatography with time-of-flight mass spectrometry to detect the volatile compounds. It’s a technique that has recently emerged and that allows you to see, depending on the wine, between 600 and 800 compounds in a single analysis. It’s three times more than the best method of analysis we had before for volatile compounds. We are doing the same for non-volatiles with a method using ultra-high pressure liquid chromatography coupled to a hybrid spectrometer quadruple time-of-flight, operating at high resolution and mass accuracy. With this method we can profile, again, about 700 to 800 compounds in a single measurement. The total compounds are rather independent, so that means we’ll probably see in excess of 2,000 compounds in this experiment.
That’s quite a forest.
It is a like a forest, especially considering each of these compounds will generate around 10 to 20 signals. However, the majority of compounds in wine—at least 70 or 80 percent—do not change even if you are putting the wine through a strong oxidation. Most of them don’t move within this experiment. So, first we are collecting all the data, then we are filtering it in an experiment designed to sort out what is not changing, so we can forget about it, and then concentrate on a few dozen compounds that are moving. Then, we will see which of these compounds are consistent, meaning that they are reacting—maybe to a different extent, but reacting in all the wines we are looking at. We don’t want to find the solution only for the interaction of, say, Chardonnay with oxygen, but to find data that is generally valuable for all white wines. We completed this first experiment several months ago, and now we are working to progressively reduce the data set to gradually focus on a lower number of compounds that show growing evidence of their actual relevance to the underlying chemistry.
Are there any specific culprits you are identifying at this point?
When you are working with a high throughput technique, you have to start with some hypothesis. The main hypothesis here was that SO2 and ascorbic acid, which are the known exogenous antioxidants generally added before bottling to protect the wine, should be the first to react. By showing that these markers are reacting, we can prove that the experiment is able to see how small amounts of oxygen are divided between various compounds. You have to remember that we are talking about 3 mg/L of oxygen, which is entering dozens of reactions. What we want to do is to find the first, second, third reaction, and so on. The first two are clearly linked to the exogenous antioxidants, and now we are tracking several compounds also influenced by oxygen, both volatile and non-volatile.
How could that be applied to winery practices?
The technique of metabolomics is interesting because it allows us to investigate real problems for which we do not have a complete chemical explanation. Using it, we can see if, beyond known factors, there are others that can provide the explanation we are still missing. For instance, at this point it is not possible to predict which wine could be destroyed by just a few extra milligrams of oxygen—or stay the same, or be improved. One consequence is that since the winemakers don’t want to take risks, they need to use higher levels of SO2 to protect the wines. It should be possible to reduce the amount of SO2 being used if we can know exactly what compounds in wine are reacting specifically with oxygen. This is why we are looking for new markers beyond SO2 and ascorbic acid. The final aim is not just to improve our understanding of the wine chemistry, the hope is to discover useful markers that could be routinely measured in the near future to predict the interaction of a wine with the oxygen before bottling. At the moment, these other compounds can be measured using very expensive and complex techniques, but after knowing we can focus on a few of them, we can imagine a more routine way to analyze them and provide a new method to predict how a wine will interact with oxygen.
Photo credit: Edmund Mach Foundation.