The Next Step Toward a “Super Wine”: Fortification with Resveratrol May Not Affect Sensory Characteristics of Some Wines

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“Functional foods” or “superfoods” are growing increasingly popular among consumers looking for a healthier alternative to their current diet.  Functional foods, which are often enhanced or fortified with compounds designed to better ones’ health (i.e., antioxidants), intend to provide increased physiological benefits to those that consume them, thus potentially providing more of a health benefit than “normal” food would provide.  In general, it has been shown that people are more willing to purchase functional foods than the comparable food items that have not be enriched in any way.  The use of wine as a functional food, though a relatively young idea (within the past three years or so), is no different in regards to consumer willingness to pay preferences.  In fact, The Academic Wino discusses a paper previously regarding this exact topic, finding that participants in that particular study would be willing to pay $8.39 USD ($5.89 Euros) more for resveratrol-enriched red wines than red wines not enriched with the compound (read that review here).

Resveratrol, which is a plant-derived phenol that has been linked to a wide variety of health benefits, is found in many species, including peanuts, blueberries, bilberries, and grapes.  It has been shown to protect against a wide variety of ailments, including diabetes, colon and breast cancers, cardiovascular disease, and neurological disorders.  The health benefits of resveratrol have been most studied in grapes, and also the wine produced from those grapes.  Found in the skins of grapes, it functions in the plant to act as an antioxidant and antibiotic, particularly when in a stressful environment (i.e. when under attack by Botrytis cinerea).  Recently, the idea of creating a “functional wine” that is fortified/enriched with resveratrol, has become increasing enticing for those more health-conscious individuals.

After vinification of the grapes, the average red wine contains about 7mg/L of resveratrol, with rosé wines coming in second at 2mg/L, and finally white wine following with 0.5mg/L.  Rosés and white wines contain significantly less resveratrol on average than red wines, due to the lack of skin contact with the juice, however, vinification techniques which increase the maceration type of white and rosé wines have shown to result in an increase in total resveratrol, which mirrors that of red wines (to see The Academic Winos’ most recent review of this topic, click here).

Increased maceration time is not the only way to increase resveratrol levels in wine.  Techniques such as pomace pressing, malolactic fermentation, thermovinification, postharvest controlled UV-radiation, and short, anoxic treatments with dry nitrogen all work to increase resveratrol levels in the finished wine.  Some techniques may have the opposite effect, and work to decrease the levels of resveratrol in the finished wine.  These techniques include fining, filtering, and natural variations in different grape varieties.  By increasing resveratrol, it has been shown that the levels of other phenolic compounds increase as well, such as (+)-catechin and (-)-epicatechin, which result in the potential of higher bitterness in the wines, and thus lower consumer acceptance of the finished wine.

As a result of this change in other phenolic compounds after the increased resveratrol concentrations due to vinification techniques, scientists have been looking toward other methods that may not have this negative effect on wine aroma and flavor.  Two methods of particular interest are first genetic restructuring, such that the plants naturally produce higher levels of resveratrol in the skins of grapes, and second direct enrichment of resveratrol into the finished wine.  Scientists have already created wines that use the enrichment method, however, very little is known about the resveratrol concentration and stability over time and aging.  Therefore, the overall goal of the study reviewed today, which was recently published in the Australian Journal of Grape and Wine Research, was to measure changes in resveratrol levels in wine over time, while simultaneously measuring sensory characteristic (aroma/flavor) and changes therein.  This is reported to be the first study of its’ kind to follow the chemistry and sensory characteristics of resveratrol-enriched wines over time.

Methods

Wines were produced from commercial kits of juice concentrates.  The red Cabernet Sauvignon and the white Riesling were created.  Juice was chaptalised using super fine sucrose to achieve an alcohol level of 14%.  Juices were rehydrated and inoculated with the yeast strain EC1118, following the manufacturers’ instructions.  Fermentation occurred in stainless steel tanks, with Cabernet Sauvignon wines undergoing an oak chip treatment (Hungarian oak, medium plus) from days 2 through 8 to yield aroma and flavor results similar to commercially available Cabernet Sauvignon wines.  Free SO₂ levels were adjusted to 25-30mg/L, and then cold stabilized.  After cold stabilization, wines were filtered and the resveratrol treatments applied.  Three treatments of 0mg/L resveratrol (control), 20mg/L resveratrol, and 200mg/L resveratrol were added to the wines.  SO₂ levels were once again adjusted accordingly, and the wines were subsequently bottled.

Basic wine chemical analysis were performed, including measurements of pH, titratable acidity (TA), free and total SO₂, ethanol, antioxidant capacity, and resveratrol levels.  Chemical analyses were performed on two bottles per treatment in duplicate, at bottling, 6, 18, 31, 44, and 58 weeks post bottling.

Sensory analysis (aroma, flavor, and visual) was performed by faculty, staff, and students of Brock University’s Cool Climate Oenology and Viticulture Institute in Ontario, Canada.  Triangle tests were performed using these untrained panelists at 6 and 32 weeks after bottling.  Cabernet Sauvignon and Riesling wines were analyzed in separate sessions, with two sessions for each wine style.  For more detailed description on the exact methodology of these sensory analysis sessions, please feel free to ask.  In lieu of space in this post, I will omit this information for now until prompted.  I do have relatively detailed information at the ready, should you require it for your interpretation of the results.

Descriptive analysis of wines was performed at 16 and 40 weeks after bottling.

Results

Basic Wine Chemistry

•       Titratable acidity (TA)

o   TA was significantly higher for the 20mg/L and 200mg/L treatments in Riesling wines compared to 0mg/L control wines at 18, 31, and 44 weeks after bottling.

o   TA was only slightly different for Cabernet Sauvignon wines across all treatment levels and all times.

•       Free SO₂

o   Free SO₂ concentrations decreased over time for all treatments.

o   Free SO₂ concentrations were not significantly affected by resveratrol concentrations, though small differences were noted for Riesling wines at 58 weeks and Cabernet Sauvignon wines at 31 and 58 weeks after bottling.

•       pH

o   There was no effect of resveratrol treatment on pH in all wines.

•       Antioxidant Capacity (AC)

o   For most time points, AC was higher for 20mg/L and 200mg/L resveratrol treatments in Cabernet Sauvignon compared to the 0mg/L control.

o   At all time points, AC was significantly higher for 200mg/L resveratrol wines in Riesling compared to the 0mg/L control.

•       Wine Color and Phenolics

o   Wine color hue and color density was significantly different in 20mg/L and 200mg/L resveratrol treated Cabernet Sauvignon wines than the control, with color density increasing and wine color hue decreasing with increasing levels of resveratrol enrichment.

§  This suggests resveratrol treatment is associated with a higher ratio of red to yellow/brown colored pigments.

o   Total red pigments in Cabernet Sauvignon decreased significantly for each treatment over time, with the color shift from red/blue to yellow/brown.

o   Total hydroxycinnamate and phenolic concentrations were significantly higher in resveratrol enriched Riesling wines (200mg/L displaying the highest levels).

o   Browning and pinking of Riesling wines increased over time for all treatments, with more hue change occurring with the highest level of resveratrol enrichment.

•       Resveratrol

o   After an initial drop at 6 weeks after bottling, trans-resveratrol was stable over the remaining 58 week aging period.

§  This initial drop may have been due to resveratrol and other phenolic compounds binding to themselves or other phenolic compounds.

o   Cis-resveratrol was detected in both Cabernet Sauvignon and Riesling wines, with the highest concentration occurring at week 6 after bottling.  After 6 weeks, cis-resveratrol levels dropped below the level of detection for this analysis.

Sensory Analysis

•       6 weeks after bottling:

o   Significant differences in aroma/flavor were found for Riesling wines treated with 200mg/L resveratrol compared to the controls.

o   No differences in aroma/flavor were found for Riesling wines treated with 20mg/L resveratrol compared to the control, nor were any difference in aroma/flavor found in any of the Cabernet Sauvignon treatments compared to the controls.

•       32 weeks after bottling:

o   Significant differences were found for bitterness in Riesling between the 200mg/L treatment compared to the control and the 20mg/L treatment compared to the 200mg/L treatment.

o   No significant differences were found in aroma/flavor in Riesling between the 20mg/L treatment and the control treatment.

o   No significant differences were found in aroma/flavor in any Cabernet Sauvignon treatments.

o   Significant differences in color were found for 20 and 200mg/L Cabernet Sauvignon treatments versus the control, and 200mg/L Riesling versus the control.

Descriptive Sensory Analysis

Figure 3 from Gaudette and Pickering, 2011

doi: 10.1111/j.1755-0238.2011.00144.x

 

•       16 weeks after bottling:

o   The 200mg/L resveratrol treatment in Riesling wines rated higher in bitterness than the control wines.

o   Floral and vegetal aromas were higher in 20mg/L resveratrol Riesling wines than the controls.

•       40 weeks after bottling:

o   The 200mg/L resveratrol treatment in Riesling wines rated higher in bitterness than both the 20mg/L and control treatment wines.

•       As a reminder, there were no significant differences in aroma/flavor descriptors in any of the Cabernet Sauvignon wines at any time point after bottling.

Conclusions

This study is the first of its’ kind (to our knowledge) that follows the basic wine chemistry and stability of resveratrol in wines over time, with the inclusion of a sensory analysis.  The results of the study show that resveratrol appears to be stable for at least 58 weeks, after which the stability is unknown to the end of the allotted experimentation time.  The results also provide evidence to support the hypothesis that enrichment of wine with resveratrol may provide increased antioxidant protection for wines over some period of aging time.  Resveratrol-enriched wines stored up to approximately one year may provide greater health benefits to consumers than wines not enriched in the powerful antioxidant. Of course, in order to truly determine if health benefits are further increased due to resveratrol enrichments, the proper medical study would need to be completed.

Enrichment of Cabernet Sauvignon wines did not appear to alter the aroma/flavor of the wines.  This could be a varietal effect, or it could be due to the oak chip treatment during fermentation.  It is possible that the oak treatment may have masked any potential sources of bitterness, and the fact that this particular varietal is already associated with a higher level of bitterness compared to a white wine may have made any differences more subtle and difficult to distinguish.  More varietals of varying levels of initial bitterness should be analyzed to see if this lack of an effect is consistent across many varieties, or if it is Cabernet Sauvignon-dependent.  Higher bitterness was detected in Riesling wines treated with resveratrol, which may have been more noticeable due to the fact that Riesling wines have a naturally low level of bitterness to begin with and any changes would be much more noticeable than they were in Cabernet Sauvignon.

The results of this study provide important information on resveratrol-enriched wines, and provide a launching point for those wishing to create this type of “functional food”.  For some wine varietals, such as Cabernet Sauvignon, it appears that resveratrol enrichment does not have a negative influence on the aroma/flavor of the wine.  For other wine varietals, such as Riesling, the influence on the aroma/flavor may be less desirable for consumers.  Some varietals may require some flavor tweaking (such as Riesling), while other may be good to go to the consumer without any further modifications.  While there may not be a simple recipe for creating a resveratrol-enriched “super food”, the results of this study show promise that a wine enriched in resveratrol may not only be good for you, but may also have no negative impacts on the aroma/flavor of the resulting wine (varietal and vinification technique-dependent).

Do you have any experience functional foods or functional wines in any way?  Do you have any comments/questions?  I’d love to hear from you!  Please feel free to comment below!

Source: doi: 10.1111/j.1755-0238.2011.00144.x

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!