One consequence of the wine making process is a large amount of “winery waste” (skins, seeds, water, winemaking byproducts, etc). In the interest of recycling or reusing this waste, there have been many studies examining potential used for it, including turning it into fertilizers, incorporating them into meat preservers, using them as alternative fuels, and also as potential therapies for disorders such as diabetes.
It is well known that the skins and seeds of grapes are loaded with health beneficial polyphenols, which possess many important properties such as functioning as an antioxidant, anti-inflammatory, anti-carcinogen, and possessing antibacterial activities. These polyphenols in the skin vary widely, depending upon a host of factors, including grape variety, terroir, vintage, geographic origin, and winemaking process.
Some studies have shown that grape skin extracts (red grapes) can protect against many different diseases, particularly when combined with green tea. Other studies found that also including hibiscus in the mix greater increased the potential health benefits of the resulting beverage. The study presented today aimed to examine the antiviral activities (against influenza) of hot water grape skin extracts and also the use of grape skins as tea infusions by measuring the antioxidant activities, color, and sensory characteristics.
To prepare the tea infusion samples, first two batches of wine wastes (30kg each) were collected from a commercial winemaking facility in New Zealand. Pinot noir (after fermentation) and Pinot gris (no fermentation) were the grape variety sources of the wine waste. Wastes were freeze dried, and then the seeds manually removed. They were stored at -20oC until ready for use.
Commercial green tea leaves and dried hibiscus petals were purchased from local markets.
Grape skins, green tea, and hibiscus petals were ground to a smaller size for packaging. Five formulations of tea infusions were created for analysis: 1) 100% Pinot Noir skins (100PN); 2) 100% Pinot Gris skins (100PG); 3) 50% Pinot Noir skins + 25% green tea + 25% hibiscus (50PN25GT25H); 4) 50% Pinot Gris skins + 50% green tea (50PG50GT); and 5) 50% Pinot Noir + 50% Pinot Gris skins (50PN50PG).
The following were measured/performed/assayed for each formulation: antiviral activity, cytopathic effect inhibition assay, in vitro cytotoxicity of skin extracts in MDCK cells, antioxidant activity, total phenolic content, superoxide anion radical scavenging activity, free radical scavenging activity (DPPH), and objective color. A sensory evaluation was also performed.
For the sensory evaluation, the five formulations of skins/tea were packed into teabags (6.5cm x 5.0cm at about 2g each). Each teabag was sealed in individual plastic packaging and then used in the sensory evaluation.
The sensory evaluation consisted of two sessions with the same panelists. During each session, panelists were given an envelope containing the 5 tea infusions, 5 sets of questionnaires, and an instruction sheet on how to brew the tea infusions. They then brewed each tea infusion and were told to consume them using their normal tea consumption patterns. Panelists answered a questionnaire regarding demographics, as well as their attitudes toward health, life style, tea consumption habits, and environmental awareness.
Panelists were asked to evaluate the tea using a 9 point hedonic scale for overall acceptability, aroma, flavor, aftertaste, color, astringency, and bitterness. The panelists also were told to indicate if the tea infusions had a satisfactory complex flavor profile that did not require the addition of milk or sugar. In addition to the sensory characteristics, the panelists’ purchase intention was also evaluated.
One or two weeks after the first session, the second session occurred. The same procedures were followed during the second session as in the first session, except this time, panelists were given a brochure listing the ingredients and possible health benefits of the grape skins, along with copies of abstracts from published papers showing these results. This information was read before the sensory and purchase intention evaluations.
Reminder of tea infusion codes:
- 100% Pinot Noir skins = 100PN
- 100% Pinot Gris skins = 100PG
- 50% Pinot Noir skins + 25% green tea + 25% hibiscus = 50PN25GT25H
- 50% Pinot Gris skins + 50% green tea = 50PG50GT
- 50% Pinot Noir + 50% Pinot Gris skins = 50PN50PG.
- 100PN and 100PG extract demonstrated complete protection of MDCK cells from influenza virus, without any negative cytotoxic effects on the cells.
o These effects were dose-dependent, ranging from 0.1-100mg/mL.
o There were no varieties differences regarding antiviral activity.
- The order of lightness were found to increase in the following order: Hibiscus (darkest) < 50PN25GT25H < 100PN < 50PN50PG < Green Tea < 50PG50GT < 100PG (lightest)
- There was a negative correlation between lightness and redness.
- Grape variety contributed to the final color of the tea infusions.
o Infusions with Pinot Noir skins had higher red pigments than infusions with Pinor Gris.
- 100PG, 50PG50GT, and 50PN50PG showed the highest yield of extracts compared to the other infusions.
o This result may be due to the presence of residual soluble sugars in the Pinot Gris skins that did not undergo fermentation during the winemaking process.
Total Phenolic Content
- Total phenolic content of the tea infusions decreased as follows: 50PG50GT > 50PN25GT25H > 100PN > 50PN50PG > 100PG.
o 50PG50GT had a 9-fold higher total phenolic content level than 50PN25GT25H, and a 50-fold higher phenolic content level than the remaining three tea infusions.
o The higher phenolics of the 50PG50GT and 50PN25GT25H were likely due to the green tea present in the infusions.
o Total phenolic content of green tea alone was higher than all of the infusions tested.
o Total phenolic content of 50PG50GT was higher than some commercial herbal infusions of peppermint and chamomile.
- Superoxide anion scavenging activity decreased in the following order: 50PG50GT > 50PN25GT25H > 50PN50PG > 100PN > 100PG.
- The addition of green tea increased total phenolic content proportionally in the 50PN50GT infusion and at a lower level in the 50PN25GT25H infusion, though the superoxide anion scavenging activity did not reflect this increase (did not increase in the same levels as the polyphenols did).
o This may be due to an antagonist interaction between the grape skins and the green tea, instead of a synergistic one.
- Compared with standard controls, the superoxide anion scavenging activity of all of the tea infusions was relatively low, which may be due to low efficacy of the heating process used in the tea preparation.
- The DPPH radical scavenging activities of the tea infusions were similar to the superoxide anion scavenging activities, and decreased in the following order: 50PG50GT > 50PN25GT25H > 100PN > 50PN50PG > 100PG.
o Stronger DPPH activity was noted in 50PG50GT and 50PN25GT25H due to the presence of green tea, which is rich in antioxidant polyphenols.
- Compared with standard controls, the DPPH scavenging activity of all of the tea infusions was relatively low, which may be due to low efficacy of the heating process used in the tea preparation.
- Levels and composition of individual polyphenols were different for 100PN versus 100PG.
o Catechin and epicatechin were 4 times higher in 100PN than in 100PG.
o Rutin was found at high levels in 100PG only.
- The addition of green tea increased the content of epigallocatechin, epicatechin, epicatechin gallate, and gallocatechin.
- The addition of hibiscus increased the content of chlorogenic acid.
- Only bitterness and color were significantly different between the 5 tea infusions.
o 50PN25GT25H and 50PG50GT were indicated as higher in bitterness, likely due to the presence of green tea.
- Most of the panelist found infusions with Pinot Noir more refreshing than calming, whereas most of the panelist found infusions with Pinot Gris more calming than refreshing.
o This difference could be attributed to the winemaking process, with Pinot Noir undergoing a fermentation step that results in more diverse acids, compared to Pinot Gris which would have more sugars.
§ This could result in a more sharp taste for Pinot Noir versus a softer taste for Pinot Gris.
- Gender did not play any role in purchase intention of any of the tea infusion samples.
- Purchase intention was moderate and there were no preferences for one tea infusion over another.
- Information on the health benefits of the tea infusions before consumption increased their overall acceptability and purchase intention.
The overall results of this study showed that grape skins, regardless of the variety, are rich in antiviral activities. As a result of this, they may provide some protection against influenza, or other viral diseases. The results also showed that when green tea was added to the grape skins, polyphenol content markedly increased. Antiradical/scavenging activity also increased to some degree, though not in the proportion that was to be expected, which the authors attribute to possible antagonistic effects instead of synergistic effects. Also, due to the heating of the tea preparation process, some of the antiradical/scavenging activity may have been lost.
More work should be done to study other combinations of grape skins and green tea, and to further evaluate the influence of hibiscus addition, which was not discussed in as great detail in this study (or which the results were more inconclusive). I’d be curious to see how other grape varieties perform under these tests, and if their polyphenol content is an indication of their ability to protect against viral infections.
I’d also be curious to see a study where patients stricken with influenza are given one of the tea infusions, to see how effective they are in an actual person, instead of a petri dish full of cells.
Overall, I think this a great study that warrants further research to help develop the ideas and hypotheses set forth by the researchers.
I’d love to hear what you all think! Please feel free to comment below!
Source: Bekhit, A.E.A., Cheng, V.J., McConnell, M., Zhao, J.H., Sedcole, R., and Harrison, R. 2011. Antioxidant activities, sensory and anti-influenza activity of grape skin tea infusion. Food Chemistry 129: 837-845.
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!