In the spirit of all things holiday and winter (well, for those of us in the Northern hemisphere anyway), today’s post highlights some brand new research involving mulled wine (a.k.a. Glühwein).
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One of my favorite winter beverages is mulled wine: that warm, delicious, spicy blend of heaven! There are a large number of people who consume mulled wine/Glühwein on a regular basis, and even more who frequently use wine for cooking. Surprisingly, biological effects of mulled wine or other wine thermally treated for cooking purposes has never been studied until now. The biological effects of wine not thermally treated have been well documented, with red wine in particular harboring many positive health effects for humans including Champagne’s cardiovascular health benefits, red wine’s role in decreasing incidence of dementia, and the role of grape pomace in decreasing the symptoms of diabetes.
The heating process may change the physical and chemical properties of the wine, which could possibly change the biological effects of the wine. It is known that alcohol evaporates when exposed to warmer temperatures and that polyphenolic compounds are subject to degradation caused by thermal stress. It is possible that these physical and chemical alterations could change the healthy biological effects of the wine, though surprisingly, this has never been studied until now.
The goal of today’s short and sweet study was to examine the direct vasodilatory effects of thermally treated wine in guinea pigs and in rats, while comparing the results to non-thermally treated wine, and dealcoholized wine (without thermal stress).
Methods
Aortic rings from guinea pigs and rats were prepared and used for measuring the vasodilatory effects when exposed to different wine treatment types. Both species were used, since studies have shown that biological health effects are sometimes species-specific.
Wine samples were the red wine Vinagra, 2006 vintage, from the Bric winery in Slovenia. Thermally treated wines were created by heating for 45 minutes in two controlled baths at 75oC and 125oC. The 75oC treatment represents the heating conditions for mulled wine/Glühwein, and the 125oC treatment represents the heating conditions for wine used in food preparations. Dealcoholized wine was used as the thermal stress-free control.
The following chemical compounds were measured and analyzed: total phenolic content, flavonoid and nonflavonoid content, anthocyanin content, catechin content, antioxidant capacity, trans-resveratrol, and ethanol.
Results
- Wine heated at 125oC and the dealcoholized wine showed similar decreases in volume and ethanol content.
- Total phenolic concentrations increased with the decrease in sample volume.
- Wine heated at 125oC showed a 10% reduction in the individual phenolic fraction compared to the dealcoholized wine.
o This indicates heat-induced degradation of some phenolic compounds.
- Wine heated at 75oC showed no degradation of the phenolic fraction.
- Antioxidant capacity corresponded to the total phenolic composition of each sample.
- Resveratrol levels were highest in the dealcoholized wine and lowest in the wine heated at 125oC.
- Vasodilatory activity of the intact wine was dose-dependent and stronger in the guinea pig aorta than the rat aorta.
o This result indicates species-specific responses.
- Thermal treatment of wine did not affect its overall direct vasodilatory activity in both rats and guinea pigs.
- The order of vasodilatory potency in the rat aorta (though again, not significantly different) was: dealcoholized wine > wine heated at 125oC > intact wine = wine heated at 75oC.
- The order of vasodilatory potency in the guinea pig aorta (though again, not significantly different) was: dealcoholized wine = wine heated at 125oC > intact wine = wine heated at 75oC.
What does this all mean?
The authors of this study were able to determine that thermally treating wine did not have any negative impacts on the vasodilatory effect of wine, even though there were some physical and chemical changes. With heating came a reduced alcohol level and reduced volume, while at the same time an increase in total phenolic concentration and increase in antioxidant capacity (possibly due to the reduced volume concentrating those compounds already present).
The authors did note that while they found an increase in the total phenolic concentration, there were some structural changes that occurred in the individual phenolic fraction of the wine (including a reduction in resveratrol). However, since wine in a complex solution, positive health benefits cannot be attributed to one compound alone. Therefore, whatever changes heating caused for some specific individual phenolic compounds, it was not enough to damage or negatively affect the vasodilatory benefits of the wine.
The authors mentioned in their discussion that one should be wary of the types of heating of wine, and how results may be different depending upon if the treatment is acute or more long-term. For example, if a wine is exposed to high temperatures for several hours, it may spoil and become damaged beyond repair (long-term exposure). Alternatively, more acute heating (as was examined in this study), may be enough to kill any microorganisms or stabilize wine in the winemaking process, without causing any great harm to the health-beneficial components of the wine. Of course, a study would be necessary to examine the difference between these two exposure types, in order to determine what kind of damage is or isn’t done under varying thermal circumstances.
Overall, the authors of this study found that with acute thermal heating, such as with mulled wine/Glühwein or the heating of wine for cooking purposes, the beneficial vasodilatory activity is retained, regardless of any particular physical or chemical changes that may have occurred.
I’d love to hear your thoughts on this study/topic! Please feel free to comment below!
Happy Holidays and Merry Winter
Source: Mudnić, I., Budimir, D., Jajić, I., Boban, N., Sutlović, D., Jerončić, A., and Boban, M. 2011. Thermally treated wine retains vasodilatory activity in rat and guinea pig aorta. Journal of Cardiovascular Pharmacology 57(6): 707-711.
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!
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