Tag Archives: climate change

Climate Change-Induced Water Stress: How Leaf Position Affects Water Use Efficiency in the Grape Vine

Posted on February 25, 2013 by Becca| Leave a comment

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According to scientists, climate change will affect various parts of the world differently than one another. Specifically, in regards to the Mediterranean region (as well as many others), a decrease in annual precipitation is currently predicted, based on past data and future forecast models. As a result of this predicted change, there has been substantial interest in research related to water use efficiency in both viticulture and agriculture in general, as precipitation changes will likely bring changes to the sustainability and quality of crops, so determining how to adapt to these changes is absolutely necessary for the future of viticulture and agriculture as a whole.

This type of research is not exactly new, and has been going on for many years. Current strategies for combating decreased water availability due to climate change include (but are not limited to) controlled irrigation and partial root zone drying. The problem with using irrigation in a climate that has significantly

By Photo by Lynn Betts, USDA Natural Resources Conservation Service. (USDA NRCS Photo Gallery: NRCSCA00061.tif) [Public domain], via Wikimedia Commons

By Photo by Lynn Betts, USDA Natural Resources Conservation Service. (USDA NRCS Photo Gallery: NRCSCA00061.tif) [Public domain], via Wikimedia Commons

reduced precipitation is the issue of where the water used for irrigation would come from. To work around this issue, scientists are currently looking at plant water use efficiency, and how pruning or other viticulture strategies can optimize plant water use in such a way that the need for supplemental irrigation is reduced. Of course, there are some “issues” with looking only at water use efficiency, as higher water use efficiency has been linked to lower fruit yield in grapevines. Therefore, optimization, and not necessarily maximization of water use efficiency is key.

The goal of the study presented today was to examine variations in leaf water use efficiency in the grapevine (Tempranillo, to be specific) under water-stressed conditions as well as under different light conditions, as well as throughout different parts of the canopy.

Methods

This study took place at a commercial vineyard in Mallorca, Spain during 1997, 1998, and 2000. 20 year old Vitis vinifera grapevines of the Tempranillo variety were utilized for the study. The study consisted of two plots (located adjacent to one another) containing 350 plants each and underwent one of the two following treatments: 1) Irrigation: irrigation was applied via a drip system twice per week, and was set to drip enough to account for 30% of evapotranspiration; 2) No irrigation: soil progressively became more and more water stressed throughout the treatment period.

Climate conditions were determined by a local weather experimental station nearby. Pre-dawn and mid-day leaf water potential, as well as leaf gas exchange was measured in June, July, and early August. There were a total of 6 replicates per treatment.

Net photosynthesis, stomatal conductance, and transpiration were all measured 6 times a day for every 3 hours between the hours of 6am and 8pm.

All measurements were done on leafs located in 8 different locations within the plant canopy. For each measurement day, 6 replicates per leaf location were measured.

Daily-integrated intrinsic water use efficiency and instantaneous water use efficiency were both calculated.

After harvest, leaves from each canopy location were harvested from six plants per treatment. Fresh weight, leaf area, specific leaf weight, and total leaf area of each canopy location were measured or calculated.

Results

• Irrigation resulted in stable plant water status throughout the growing season.
• Pre-dawn water potential decreased throughout the growing season for those plants in the non-irrigation treatment.
• The ratio of photosynthesis to stomatal conductance was significantly higher in water-stressed plants compared with irrigated plants.
• Photosynthetic active radiation (PAR) interception varied depending upon where in the canopy the leaf was located, with a decrease in PAR noted from the upper part of the canopy to the lower part of the canopy.
o Those leaves in the innermost part of the canopy showed the lowest PAR values, which makes sense due to the fact that the leaves are in the shade do not experience as much radiation from the sun as leaves in full sunlight.
• Water stress did not affect PAR values for any leaf position.
• Midday leaf temperature and leaf-to-air vapor pressure deficit did not differ between any of the leaf positions.
• Water stress resulted in an increase in midday leaf temperatures.
• Water use efficiency was extremely variable between the different leaf positions in the canopy.
o The lowest water use efficiency was in shaded leaves, whereas the highest water use efficiency was in the leaves at the top of the canopy.
o Leaves in sunnier positions had 3x greater water use efficiency than leaves in the shade.
• Water use efficiency was increased in water-stressed plants.
o Those leaves near the top (but not all the way on the top) of the canopy (i.e. those leaves with 67.5% light interception compared with the top leaves) were found to have the highest water used efficiency.
• There was a significant relationship between water use efficiency and the daily intercepted PAR of the leaf.
• South-facing leaves at the top of the canopy had the highest water consumption levels per leaf area than all other leaves.
• Shaded leaves showed the lowest rates of transpiration, however, since there were so many of them (making up 37% of the total number of leaves on the plant), the water use efficiency actually decreased compared to leaves at the top of the canopy.
• Total water consumption decreased in water-stressed plants.
o Moderately-stressed plants showed a 47% decrease in water consumption compared to irrigated plants.
o Severely-stressed plants showed a 70% decrease in water consumption compared to irrigated plants.

Conclusions

The results of this study indicate that there were significant differences between the locations of the leaves in the canopy in regards to water use efficiency. The authors speculated that these differences could be due to the differences found in PAR and light exposure. In regards to the entire plant, it was found that water use efficiency increased when the plants were under water stress. This makes sense, as when the plant has less water to work with it needs to make sure it’s spending the appropriate amount of resources on water consumption while at the same time reducing the resources needed for evapotranspiration. In other words, it is in the plants’ best interest to become more efficient at using water when water is scarce, so it doesn’t prematurely shrivel and die due to poorly managed resources (though at some point, this will happen anyway if no water is ever seen again).

The results also indicated that the shadiest of areas on the plant had cumulatively the lowest water use efficiency (or highest daily water loss)

By Agne27 at en.wikipedia [Public domain], from Wikimedia Commons

By Agne27 at en.wikipedia [Public domain], from Wikimedia Commons

compared to all other locations. The authors suggested that by using selective thinning or pruning in this area could decrease the total water loss and increase the water use efficiency of the grape vine. Of course, one must be careful when undertaking a new pruning management plan, as water use efficiency will not be the only thing changed after the pruning occurs.

It is important to note that pruning has influence on many other factors, including the maturation of the grape and the overall quality of the fruit, so it is important to find some sort of middle ground if selective pruning is of interest to you. Selective pruning may be a good approach to adjusting to climate change-induced water stress, however, it is important to take all factors into consideration before just tearing apart your entire vineyard canopy. It is advised to experiment with a small number of vine first prior to partaking in a vineyard-wide pruning management regime.

One other side note to mention is that this study examined just one grape variety (Tempranillo). It’s possible other grape varieties may behave slightly differently in regards to their water use efficiency and their ability to adapt to changes in water availability, so certainly further studies using more grape varieties is warranted.

What do you all think of these results? What other vineyard management programs do you think could be applied after seeing the results of this study? Those of you with experience in vineyards under high water stress, or those that may be experiencing change in water availability at your vineyard: what sorts of vineyard management practices are you doing to adapt to the conditions? Please feel free to comment!

Source: Medrano, H., Pou, A., Tomás, M., Martorell, S., Gulias, J., Flexas, J., and Escalona, J.M. 2012. Average daily light interception determines leaf water use efficiency among different canopy locations in grapevine. Agricultural Water Management 114: 4-10.

Posted in Viticulture

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Getting to Know Your Friendly Neighborhood Yeast: The Many Benefits of Schizosaccharomyces in Winemaking in a Changing World

Posted on February 6, 2013 by Becca| 2 Comments

 

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Welcome to The Academic Wino!  If you are new here, please read the “About Me” page to find out more about myself and the blog. If you would like to receive free updates on articles like this by email, then sign up here or you can subscribe to the RSS feed. Also, check us out on Twitter, Facebook, Google+, and or Pinterest. Thanks for visiting!

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Traditionally, the yeast strain most commonly used in winemaking is Saccharomyces cerevisiae. However, with more and more desire to create a truly unique wine and to also keep up with the changing market (and changing climate), winemakers are looking for more alternatives to the traditional approaches in order to create something different than all the rest. One way to achieve this uniqueness is to utilize new strains of yeast in order to keep ahead of the game and remain competitive in today’s market.

Image source: http://commons.wikimedia.org/wiki/File:Dry_yeast.jpg (PUBLIC DOMAIN)

Image source: http://commons.wikimedia.org/wiki/File:Dry_yeast.jpg (PUBLIC DOMAIN)

Specifically in the review paper summarized today (see full citation of the source below), some are now looking into using non-Saccharomyces yeast strains to produce wines with more unique characteristics. Particularly, species of the genus Schizosaccharomyces are known to reduce the malic acid content in wines and have started to generate research interest.

Schizosaccharomyces yeasts are used frequently in the production of rum and cocoa liquors in Madagascar, and have been previously thought of as spoilage yeasts in wine. In the past, these yeasts have been isolated from fermentation vessels where the fermentation process was stuck or stopped, or from wines with significant “off” aromas, however, up until now it hadn’t actually been determined if these yeasts were the source of these issues, or if they just happened to be in the “wrong place at the wrong time”.

Recent studies have shown that mixtures or use in sequential fermentations could actually improve the complexity of wines and improve the aromatic profile of the wine. Though not the yeast Schizosaccharomyces, currently, there is a commercial kit available that utilizing as sequential inoculation of the yeast strains Torulaspora delbrueckii and Saccharomyces cerevisiae.

It is thought that by using Schizosaccharomyces strains of yeasts during malolactic fermentation, the “green apple” aroma could be significantly reduced (“green apple” is often caused by malic acid, which is effectively reduced by Schizosaccharomyces). Schizosaccharomyces has also been shown to reduce gluconic acid and ethyl carbamate levels, which would increase the overall quality of the finished wine. Gluconic acid is known to be produced after grapes are attacked by various fungi, including Botrytis or Aspergillus, therefore employing Schizosaccharomyces could help “save” wines made from grapes attacked by these organisms.

Taxonomic research from the 1960s classified four species belonging to the Schizosaccharomyces genus, though more recently this number has been

Schizosaccharomyces pombe: By David O Morgan (The Cell Cycle. Principles of Control.) [Attribution], via Wikimedia Commons

Schizosaccharomyces pombe: By David O Morgan (The Cell Cycle. Principles of Control.) [Attribution], via Wikimedia Commons

reduced to three. The three species currently known to be part of the Schizosaccharomyces genus are: 1) S. japonicus; 2) S. octosporus; and 3) S. pombre. These yeasts are native to climates ranging from temperate to very hot.

In terms of fermentation, Schizosaccharomyces yeasts can produce wines with alcohol degrees ranging from 10o to 12.6o when in anaerobic conditions, and 13o to 15o when in slightly aerobic conditions. During malolactic fermentation, Schizosaccharomyces yeasts can metabolize malic acid and produce ethanol and carbon dioxide. Malic acid, along with tartaric acid, constitute between 70% and 90% of the wine’s total acidity which can have a significant effect on the aromatic profile of the wine. Winemakers often aim to remove as much of the malic acid as possible, particularly from red wines in colder climates where malic acid levels are much higher than they are in warmer climates. Research has shown that Schizosaccharomyces yeast strains are probably the best yeasts for reducing malic acid content, and found that they can reduce malic acid levels by between 75% and 100% (most other strains can only reduce malic acid levels by 20-25%).

Warning: things are about to get hard core organic chemistry here, so you may want to look away if that isn’t your cup of tea (or should I say glass of wine?)….

One of the things that makes Schizosaccharomyces yeasts so potentially desirable is the mechanism by which it reduces malic acid and then transitions to alcoholic fermentation almost in concert with this process. In very basic terms, for every one molecule of malic acid, one molecule of alcohol and two molecules of carbon dioxide are produced. Getting more specific, this is basically what is occurring in the wine when Schizosaccharomyces is employed:

1. Malic acid is broken down into pyruvic acid when in the presence of Manganese2+ and Manganese3+ ions.
2. The pyruvic acid then goes into the alcoholic fermentation process.
a. Pyruvic acid gets decarboxylated resulting in acetaldehyde while then gets further reduced to ethanol.

When in anaerobic conditions, breaking down 2.33g/L of malic acid by the above process yields 0.1% v/v alcohol. Currently, S. pombre is available commercially for this purpose.

Traditionally, the organisms used during malolactic fermentation (or anytime where malic acid is reduced) have been Oenococcus oeni and Lactobacillus plantarum. Both of these organisms are lactic acid bacteria, and are known to produce undesirable by-products during malolactic fermentation, including the production of biogenic amines. Employing Schizosaccharomyces yeasts gets around this issue, as they do not result in the production of the undesired biogenic amines.

Another question that comes up in terms of the use of new yeasts strains in winemaking is how will they behave when in an “aging on the lees” situation? In simple terms, lees are basically the dead yeasts and other molecules that have deposited or precipitated into the wine during the after fermentation. Many winemakers choose to age their wine on the lees, as even though the cells are

By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

By Agne27 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

technically dead, the cellular components interact with the wine to create more complexity in the aromatic profile of the wine and often times increase the quality of the finished wine. Recent research has shown that the cell wall composition of Schizosaccharomyces is complex and show great potential for improving the quality of the finished wine, including the stability of the wine’s color.

Finally, in addition to reducing malic acid levels, gluconic acid levels, and ethyl carbamate levels, and also improving the stability of wine color, Schizosaccharomyces yeasts strains have been shown to produce lower levels of alcohol than traditional Saccharomyces yeasts strains. With increasing temperatures to due climate change, many vineyards are seeing changes in grape ripening, with some reaching maturity earlier and earlier, resulting in wines with higher and higher alcohol content. Using Schizosaccharomyces yeast strains may help combat this “by-product” of climate change, as the alcohol levels produced by the yeast are lower than their Saccharomyces counterpart when presented with the same starting material.

The authors of the study highlight some issues, with one being that the methods for isolating other Schizosaccharomyces yeast strains have yet to be developed. Media and other methods should be developed in order to test these other strains to determine their usability in the winemaking process.

I think these yeasts show great promise for use in winemaking today, as winemaking of the future molded by a changing climate. Certainly more research would need to be done on these strains to get a better sense of how exactly the aromatic profiles are changed, however, so far the research to date has shown Schizosaccharomyces may be a positive addition to the winemaker’s “toolbox”.

I’d love to hear what you all this of this topic! Have you any experience with this yeast? Even if you haven’t, please feel free to comment!

Source: Suárez-Lepe, J.A., Palomero, F., Benito, S., Calderón, F., and Morata, A. 2012. Oenological versatility of Schizosaccharomyces spp. European Food Research and Technology 235: 375-383.

Posted in Enology

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Is Soil Dryness Responsible for Early Grape Ripening in Australia?

Posted on January 29, 2013 by Becca| 1 Comment

 

Climate change, be it brought on by anthropomorphic sources or the natural cycle of the earth (I’m not trying to start that debate), is continuing to be touted as having a significant influence on agriculture and also viticulture worldwide.  Scientists have been predicting that growing and ripening seasons are likely to change in some places, while some (if not all, eventually) will find that the variety of grapes traditionally grown in their region will no longer survive there and other varieties of grapes will have to be planted in order to keep up with the changing environment and climate.

In Australia, studies have found that many grapes varieties in 11 of 12 grape growing regions have been ripening earlier in time periods between 35 and 115 years.  It was noted that these early ripening years were correlated with increases in temperature.  One study in particular by Webb et al (2012) surmised that the earlier ripening in these regions was quite possibly due to temperature increases, soil drying, and/or changes in vineyard management techniques.

By Amanda Slater (originally posted to Flickr as Barossa Valley. SA) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

By Amanda Slater (originally posted to Flickr as Barossa Valley. SA) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

The author of the study presented today (White 2013) claims that there are several issues with the conclusions that Webb et al (2012) came up with.  First, he claimed that the data Webb et al (2012) used was for areas of land around 2500 hectares, whereas the vineyards they were analyzing were significantly smaller at 0.2 to 16 hectares.  The “behavior” of any given piece of land can be radically different even at relatively close distances.  Assuming the environmental information ascertained from a 2500 hectare plot is similar to a random tiny vineyard of no more than 16 hectares in size could be dangerously inaccurate, resulting in missed data or other important hydrological and geographical information unique to that particular vineyard or area.

White (2013) also noted that the soil data used by Webb et al (2012) was for the entire continent of Australia and not for any one particular vineyard site.  Again, similar to the concept described above, the soil in one particular area may be radically different from the soil in another, thus using the average for an entire continent may lead to inaccurate results.

Next, White (2013) noted that the water data used by Webb et al (2012) did not include data from regions by which some of the study vineyards were located.  This may have resulted in some loss of data and loss of result accuracy.

Finally, the last beef that White (2013) had with the study by Webb et al (2012) was that they only used growing season rainfall totals, whereas White argued that the more appropriate variable would be the annual rainfall total.  Just because the vines are dormant in the winter does not mean that the rainfall occurring at that time has no influence on the growth and development of the vine the following spring and summer.

Focusing on Soil Dryness

One of the claims Webb et al (2012) made is that earlier ripening could be due to increased soil dryness.  As a result of the aforementioned flaws in the study design, White (2013) sought to examine this claim further, to either confirm or refute the hypothesis based on more accurate data.

Soil moisture can be simply defined as the balance “between rainfall and actual evapotranspiration, with a variable small surplus in winter going to drainage” (White, 2013).  In other words, the soil will be moist or dry depending upon how much rain it got, plus the amount of moisture that is lost through evapotranspiration (think moisture lost due to heat to the atmosphere) with a small amount draining into the water table far below the surface.  As air temperatures increase, potential evapotranspiration increases.  In other words, as air temperature increases, more water is lost from the plant to the atmosphere.

By Tomas Castelazo (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

By Tomas Castelazo (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

It is important to note that as temperatures and carbon dioxide increase, plants have a mechanism to conserve their water by closing their stomatal pours on the leaves.  By closing the stomata, the amount of water that is lost by the plant to the atmosphere decreases and remains within the plant and within the soil around the plant for survival.

So in reality, as White (2013) noted, for most vegetation in areas that are known to have low rainfall or suffer from near drought-like conditions, the decrease in water loss by the plant is directly affected by increased temperatures and increased carbon dioxide, thus counteracting the potential loss of water to the atmosphere had these stomatal closing mechanisms not been in place.  Hydrological research also found that catchment runoff (i.e. runoff from the higher elevations to the lower elevations)  increases with increasing carbon dioxide, thus supporting the idea that as temperatures and carbon dioxide increase, water is not lost into the atmosphere but is in fact retained in the plant and in the soil around the plant.

Due to the results of this research in plant physiology and catchment hydrology as mentioned just previously, White (2013) concluded that annual rainfall may be a good surrogate for soil moisture when the measurements of soil moisture are not readily available.  The overall goal of the study was to determine if trends in annual rainfall confirmed or refuted the theory that soil drying has an effect on earlier ripening in grapes based on the conclusions made by Webb et al (2012).

Briefly, the annual rainfall data and the grape ripening data from 5 different grape growing regions in Australia and over an 11 year moving average were analyzed using a linear mathematical model.

Conclusions

The results of the study found that 3 out of 5 grape growing regions showed positive annual rainfall trends (i.e. increased annual rainfall over time), while 2 out of 5 regions showed negative annual rainfall trends (i.e. decreased annual rainfall over time).  Only one of each was statistically significant.  According to White (2013) the model results are consistent with the data collected from those same regions in Australia during those same time periods.

Since there was a significant increase in annual rainfall during this 11 year period, White (2013) said it was not possible that soil drying would be contributing to the early ripening found at vineyards throughout the region.  In fact, if anything, the soil was getting wetter while the grapes were ripening earlier!

At the site that did see a significant decrease in annual rainfall, there was actually no change in grape ripening found in previous studies.  So, if Webb et al (2012) were correct in their assumption, this site should have seen either no change in annual rainfall plus no change in ripening date, or a decrease in rainfall plus an earlier ripening date.  Since neither of these scenarios played out, White (2013) ascertained that soil dryness was not contributing to earlier ripening in the grapes of Australia.

Based on these results, White (2013) expressed confidence that soil dryness did not influence the date of ripening for grape varieties in Australia.  In fact, it is likely that there are other factors involved that are significantly affecting this date, with the more likely culprits, according to White (2013), being vineyard management practices and increased air temperatures.  According to White (2013), vineyard management practices had changed around this time period, which is something that should be significantly considered as a major player in earlier grape ripening.

Personally, I don’t lay the blame on any one factor in particular.  I think many different factors act in concert to speed up the ripening process of these grapes, and thereby more complex mathematical models taking more of these factors into consideration should be tested.

I’d love to hear what you all think!  Please feel free to leave your comments!

Source: White, R.E. 2013. Has soil drying contributed to earlier grape ripening in wine regions of southern Australia? Australian Journal of Grape and Wine Research 19 (1): 123-127.

Posted in Environmental Science

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Grape Stem Extracts: An Example of Utilizing Winery Waste for a More Sustainable Industry

Posted on November 5, 2012 by Becca| Leave a comment

In this age of changing climate, there is an ever present push to find more ways to be more environmentally friendly and sustainable in all industries and settings.  If you’re at all familiar with the content here on The Academic Wino, you’re probably already well aware of the fact that the wine industry is no different in regards to this quest for sustainability.  To be specific, there have been quite a large number of studies now at this point examining the utilization

Photo by heydrienne: http://farm1.staticflickr.com/107/259825037_fa80e1dd28.jpg

of wine industry waste into other functional products, instead of simply discarding the waste to wreak havoc on the environment.

Though there are certainly more studies than I have been able to present on this blog, here are some examples of what has been done so far in regards to utilizing wine industry waste:

As you can see from just the headlines of these posts, there have been many applications examined for wine industry waste in nearly every possible use imaginable.  Most research to date has focused primarily on the grape pomace (a.k.a grape marc), which is made up of the leftover skins and seeds of the grapes after pressing.  One major source of wine industry waste that has been examined very little is the grape stems.  Prior to pressing, during the sorting process, stems are separated from the grapes and discarded.  To date, very few studies have examined what, if any, nutritional value these stems have, and can they be utilized for other purposes instead of being discarded and adding to the significant environmental issues associated with industry waste.

The study present to you all today aimed to add to the small list of literature

Photo by quinn.anya: http://farm2.staticflickr.com/1201/1486163719_2113050d91.jpg

related to the utilization of grape stems by examining their antioxidant activity and the possible applications for their use as natural antioxidants for the betterment of human (or animal) health.

 

 

 

Methods

Grape stems were supplied by the Spanish winery, Antonio Nadal S.L., Mallorca.  Stems were collected from the Vitis vinifera grapes, Manto Negro (red) and Prensal Blanc (white).  Stems were collected during the destemming process and prior to grape pressing.

Stems were dried, ground, and stored at -20oC until ready for use.  Ground stems were prepared into extract using acetone and also ethanol (two separate extracts).  There were a total of 4 extracts tested: 1) red grape stems with acetone; 2) red grape stems with ethanol; 3) white grape stems with acetone; and 4) white grape stems with ethanol.

The following were measured and analyzed in stem extracts:  total polyphenols, flavanols, and antioxidant capacity.

Results

  • The author reports high polyphenolic concentrations in all grape stem extracts.
  • Total polyphenol concentrations were higher in red grape stem extracts than white grape stem extracts.
  • Grape stem extracts prepared with acetone had higher concentrations of total polyphenols than grape stem extracts prepared with ethanol.
  • Concentrations of flavanol were higher in red grape stem extracts than white grape stem extracts (same pattern as with total polyphenols).
  • Grape stem extracts prepared with acetone had higher concentrations of flavanols than grape stem extracts prepared with ethanol (same pattern as with total polyphenols).
  • Flavanols made up 70% of the total polyphenol content of the grape stem extracts.
  • The author reports high antioxidant capacities in all grape stem extracts, with the red grape stems extracts having higher antioxidant capacities than the white grape stem extracts.
  • Antioxidant activity was significantly correlated with total polyphenols and flavanols.

What does this all mean?

Overall, this study found that red grape stem extracts prepared in acetone have the higher levels of total polyphenols, flavanols, and antioxidant capacities than all other extracts.  The authors stated that all four extracts had high levels of these three things, though if one were to create a hierarchy of what is contains the highest to lowest levels (keeping in mind the low levels are still relatively high), it would be the following:  red grape stem extracts with acetone > red grape stem extracts with ethanol > white grape stem extracts with acetone > white grape stem extracts with ethanol.

This was a very simple study that showed straightforward results (i.e. none of their results contracted one another and were similar to those of other studies).  However, I would have liked to see them compare the grape stem extracts with

Photo by thisisbossi: http://farm4.staticflickr.com/3086/3203423692_30356dc38e.jpg

grape seed extracts, grape pomace extracts, grapes themselves, and finished wine.  The authors claim that the total polyphenol and flavanol levels as well as antioxidant capacities of all the grape stem extracts were high; however, they didn’t have any type of control to prove it.

I am guessing that they were comparing the levels they found in their grape stem extracts with the levels found in the literature, however, I know from experience that comparing your numbers directly with the numbers of another study may be problematic, as there are almost always differences in regards to methods or individual researcher techniques that may alter the results from study to study.  I would be more confident in the results had there been a control to which they were comparing.

Assuming the analysis is correct, it seems as though grape stems may be potentially useful as supplements benefitting human health, or potentially other applications that utilize products high in total polyphenols or antioxidant capacities.  By recycling the entire grape and not just the skins and seeds, the wine industry may come one step closer to being more sustainable and friendlier to the environment than ever before.

Source: Llobera, A. 2012. Study on the Antioxidant Activity of Grape Stems (Vitis vinifera). A Preliminary Assessment of Crude Extracts. Food and Nutrition Sciences 3: 500-504.

Posted in Environmental Science

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