Monthly Archives: October 2011

Enhancing the Sweet Nectar: The Effect of Pollen Addition on Fermentation and Sensory Characteristics of Mead

Posted on October 28, 2011 by Becca| 7 Comments

For today’s post, I am going to stray away from our usual discussion of all things V. vinifera, and discuss current research related to another type of wine.  Part of the foray into something new is that well, for one, one can make wine out of more than just vinifera grapes, and two, I really don’t know too much about other types of wine and wanted to learn a little more myself!

That being said, today I’m going to present and discuss a current peer-reviewed article related to mead.

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Mead, also known as honey wine, has been consumed for centuries.  It is believed to be the oldest alcoholic beverage, and often conjures up images of ancient castles and heroic knights.  Honey has been used to create not only meads, but also “sherry-esque” wines, sparkling wines, and wines with some combination of fruit and honey.  Like grape wine, honey also displays several properties that are beneficial to one’s health, including antimicrobial and antioxidant properties.

The fermentation and maturation process for honey meads can be extremely variable in length, from a few months to many years.  There can often be many problems during this time which ultimately prolong the fermentation process, or stop it all together.  In grape wine, often these problems are related to the yeast strain involved in the fermentation process.  In fact, the same yeast strain that is often used in wine production has been used to start fermentation in honey meads as well (Saccharomyces cerevisiae).  When subject to similar stress conditions, S. cerevisiae behaves similarly in honey mead fermentation than in grape fermentation processes and runs the risk of failure.

As in grape fermentation, nutrients (particularly yeast-assimilable nitrogen; YAN) are critical in the growth and development of yeasts.  In honey mead, the level of nitrogen actually changes the sensory characteristics of the finished wine, specifically as a result of the amino acid composition. 

Another problem in honey mead fermentation comes as a result of the low pH and low mineral content of light honey (compared to dark honey), which results in poor yeast growth.  Often, supplements are added to help aid in the growth of yeast and ultimately the success of the fermentation process, including fruit juices, salts, acids, ammonium phosphate, potassium sodium tartrate, magnesium sulfate, calcium sulfate, citric acid, tartaric acid, and vitamins.  Other supplements that have been studied in improving the success of honey mead fermentation include thiamine chlorhydrate, yeast extract, pollen, and royal jelly (produced by bees).  Many of the previous studies have shown that pollen may be a important supplement in improving the fermentation process of mead, which is the primary focus of the study presented today.

Pollen, which is actually the primary focus of my Masters thesis from the University of Virginia (permission to dork out for a minute:  woohoo!), is the primary protein source for bees, and is also the male gamete of plants.  It is often used as a dietary supplement for protein, and more specifically, amino acids.  Pollen can contain up to 60% protein, which translate to a huge resource for the bees and other insects that feed upon it, as well as allowing it to be a great protein and amino acid supplement for other animals.  I can go on and on about pollen, but alas, I digress…

Based on the studies performed on honey mead fermentation thus far, the goal of the study presented today was to examine the influence of pollen addition on the fermentation process of honey mead, specially examining the fermentation kinetics, physiochemical characteristics, aroma profiles, and sensory characteristics of the finished wine.

Methods

Since I’m not sure how many of my readers are familiar with the winemaking process for honey meads, I will go into a little more detail about the process than I would for more familiar V. vinifera wines.

Commercial honey (at 75o Brix) was diluted with water until a honey of 20-22o Brix was obtained.  Acidity was corrected to 3.6.  Potassium metabisulfite was added to prevent lactic acid bacterial growth.  The diluted honey was divided into 5 L fermentation tanks and commercially produced pollen was added in concentrations of 10, 20, 30, 40 and 50g/L, for each treatment.  A control with no pollen added was also included.  After addition of pollen, turbidity and yeast-assimilable nitrogen (YAN) of the honey must was measured.

The honey musts were inoculated with a wine yeast strain of S. cerevisiae (ENSIS-LE5) at a dose of 15g/hL and incubated at 25oC.  Density and biomass were measured throughout fermentation.  At the completion of fermentation, the meads were cold stabilized at 6oC for one week, and then treated with gelatin (4g/hL) and bentonite (40g/hL).  Lastly, meads were filtered and bottled.  All treatments were performed in triplicate.

The following were measured for all mead treatments: nitrogen, amino acids, Beaumé degree, pH, total acidity, sulphurous anhydride, YAN, alcohol content, volatile acidity, residual sugars, and finally, major and minor aromatic compounds.  To simplify the aromatic profile of meads, the authors calculated an odor activity value (OAV) for each mead, calculated as the ratio between the concentration of each compound and its perception threshold.  An OAV greater than 1 were considered contributors to the aromatic profile of the mead.

Sensory evaluations of the different treatment meads were also performed.  The panel consisted of 10 panelists, between the ages of 30 and 50 (4 women and 6 men), who all had wine tasting experience and were trained in the evaluation of honey meads.  Each panelist evaluated visual characteristics (turbidity and color), aroma characteristics (quality and intensity), and taste characteristics (quality and intensity).  General acceptability was also determined.

Results

Honey Must

  •       The addition of pollen corresponded to a probable increase in alcohol content of the mead.
  •       Total acidity and tartaric acid were increased by pollen addition.
  •       pH remained constant.

o   The increase of acidity was due to weak acids.

  •       The addition of pollen increased the total polyphenol index by 0.130 absorbance units per gram of pollen.
  •       Honey must color was altered by the addition of pollen.

o   Brown and yellow colors were enhanced.

  •       The addition of pollen increased the turbidity and YAN levels.

o   According to the authors, pollen is a major source of YAN and could be used to enrich nitrogen-poor media.

  •       Pollen provided a good source of YAN, and the percentage of each individual amino acid remained constant as more pollen was added.
  •       Each 10g/L of pollen added provided an average of 70% of the amino acids that were already present in 1L of honey must.
  •       YAN levels in the 40g/L and 50g/L (pollen) meads were above 140mg/L, which is the minimum amount necessary for completing fermentation in grape musts.
  •       These results indicate that pollen provides a good supply of amino acids for completing honey must fermentation.

Fermentation Kinetics

·         In all treatments, when fermentation was complete, residuals sugars were less than 0.6g/L.

·         In the control mead (no pollen added), fermentation lasted 6 weeks, indicating that honey alone is deficient in nutrients required for yeast fermentation.

·         Fermentation rate increased with pollen supplementation.

·         Compared to the control mead, fermentations supplemented with pollen showed a significantly increased fermentation rate, and a reduction in time to reach a maximum rate.

·         Honeys with more than 30g/L of pollen added showed the highest fermentation rates and the shortest maximum time.

·         Increases in the fermentation rate was correlated with an increase in YAN levels and turbidity values, which resulted in the overall improvement of fermentation kinetics.

o   It is possible that the high polyunsaturated fats found in the pollen may have also contributed to the increased fermentation rate, since these compounds are metabolized by yeast cells during the fermentation process.

·         The fermentation efficiency of the control mead was approximately 81%.

o   The addition of pollen improved the fermentation yield and efficiency by more than 7% and 10%, respectively.

Physiochemical Characteristics

  •       The total acidity of the mead decreased with pollen addition.
  •       The final pH increased to more than 4.0 with pollen addition.

o   The authors suggest this higher pH value might reduce the microbial stability of the meads, thereby justifying the need to adjust the final pH accordingly.

  •       Volatile acidity increased with pollen addition.
  •       The yellow hue of the mead increased with pollen addition.
  •        Total phenolic index increased with pollen addition.
  •       From these results, it seems that pollen not only increases fermentation kinetics, but also improves the overall physiochemical characteristics of the final mead.

Aromatic Characteristics

  •       Isoamyl alcohols, acetaldehyde, and methanol increased with pollen addition.
  •       There was no correlation between the amount of pollen added and the total minor volatiles present.

o   The main contributors to the minor volatile component of the meads were alcohols and acids.

  •       All other aromatic families of compounds increased with pollen addition.
  •       Pollen addition significantly increased the proportion of acids in the meads’ aroma, specifically octanoic and hexanoic acids.
  •       The addition of pollen increased the proportion of esters, particularly ethyl succinate and phenylethyl acetate, resulting in an increased fruity odor.
  •       The addition of pollen increased the proportion of aldehydes in the mead.
  •       To summarize, the addition of pollen was associated with increased values for all aromatic groups (particularly the fruity and oxidative groups), regardless of the amount of pollen added to the must.
  •       Meads with 20 and 30g/L pollen added showed the highest contribution to the fruity aroma, and lowest contribution to the oxidative aromas.

Sensory Characteristics

  •       The most acceptable meads were the 30 and 40g/L meads, which showed the highest flavor and aroma ratings.
  •       The most significant difference between all the meads was the color.  With increasing pollen added, the more the mead changed from a pale yellow to an amber color.
  •        Aroma notes:

o   The control wine had floral notes, as well as vinegar-like characteristics, which decreased acceptability.

o   The 10g/L pollen mead had notes of “medicinal” and “floral”.

o   The 20 and 30g/L pollen meads had notes of almond, dried fruit, apple, caramel and sweets, with a bit of pineapple on the nose.

o   The 40g/L pollen mead had the strongest notes of honey.

o   The 50g/L pollen mead had notes of toast, bitter almond, and honey.

  •       Mouthfeel increased as pollen addition increased.
  •       Flavor notes:

o   The 40 and 50g/L meads were noted for sweetness, with honey and floral flavors.

o   The 30g/L meads were noted for sourness.

o   The 20g/L meads had hints of bitterness.

In Conclusion…

According to the authors of this study, these results show that pollen could be a good activator of alcoholic fermentation in honey meads, which results in an increase in fermentation kinetics and improved physiochemical and sensory characteristics of the finished wine.  Based on their analysis, they came to the conclusion that the optimal dose of pollen to the honey must is 30g/L.  This allows optimization of the fermentation process, while not using an overly excessive amount of the resource.

Knowing very little about the fermentation process of honey meads, I found this study fascinating.  Since I also worked very closely with pollen during my Masters research, this study hit a little closer to home for me that it may for some others.  Since my expertise and experience with honey meads is very limited, I cannot critique the methods of the results of this study too much, other than the fact that based on the results, the authors’ evaluations and interpretations sound legitimate to me.

I’d be curious to see them break down the polyphenol content of the mead.  The results show that the total polyphenol index increased with pollen addition.  Does this make the mead healthier for those that consume it?  Is it better at protecting against oxidative or other stresses than a mead without pollen added?  I’d be very interested in reading a study focused on the health implications of this type of pollen-supplemented mead.

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

Source: Roldán, A., van Muiswinkel, G.C.J., Lasanta, C., Palacios, V., and Caro, I. 2011. Influence of pollen addition on mead elaboration: Physiochemical and sensory characteristics. Food Chemistry 126: 574-582.

Doi: 10.1016/j.foodchem.2010.11.045

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!

Posted in Enology

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Alternatives to Copper in Combating Downy Mildew in Organic Viticulture

Posted on October 25, 2011 by Becca| Leave a comment

Plasmopara viticola (a.k.a. Downy Mildew) is one of the most common diseases and more serious threats for Vitis vinifera varieties all over the world.  Early symptoms occur on the leaves of grape vines, exhibiting light green to yellow spots called “oil spots” (because they look greasy), which can be found on the lower surface of the leaf.  These spots are actually spores, which are spread through passing winds.  These spots eventually become necrotic and the tissue dies, which can severely weaken the plant and reduce its’ winter hardiness.  Berries that are infected will turn a dull-green or reddish purple, and will fall from the cluster.  This effectively reduces crop yield.

http://www.flickr.com/photos/jingleslenobel/4324953031/sizes/m/in/photostream/

Since cultivars that are resistant to P. viticola are extremely rare, it is essential to apply fungicides (particularly in rainy climates).  For organic vineyards, which are becoming increasingly popular all over the globe, downy mildew is controlled by regular sprays of copper compounds.  The use of this compound has been widespread, and for a very long period of time (~150 years).  Early excessive use of copper has resulted in the accumulation of copper in the topsoil of vineyards, which has had negative effects on the surrounding environments.  In Europe, there are now restrictions on the use of copper, allowing for no more than 3 to 6 kg/ha per year, depending upon which country in which the vineyard is located.  There is currently an interest in restricting these limits even more, which will require reevaluation of the use of copper to control downy mildew, and introduces a need to find other alternatives for the use of copper in controlling downy mildew that still fall under organic farming principles.

The current study presented today is the first (to the authors’ knowledge) that provides a comprehensive evaluation of alternatives to the use of copper in controlling downy mildew, and examines a wide array of ingredients that are nontoxic and acceptable under organic farming rules.

Methods

Both indoor trials (artificial infections) and field trials (natural infections) were performed in this study.

Materials Used

112 substances were tested for effectiveness against downy mildew: 9 were from animal origins; 7 were biocontrol agents; 1 was a homeopathic preparation; 4 were microbial extracts; 8 were natural derivatives; 48 were plant extracts; 2 were physical methods; 6 were synthetic materials; and 6 were mixtures of the previous groups.

Indoor Trials

Indoor trials were conducted in greenhouses or growth chambers in Italy and Switzerland.  Experimental sets contained an untreated control (water), a standard treatment (copper hydroxide) and 8 to 12 of the test treatments.  The dosages used were given via the manufacturer’s recommendations.  All experiments in Italy had four replicate plants per treatment, and all experiments in Switzerland had six replicate plants per treatment.

Plants

Grafted cuttings of Pinot Gris (on Kober 5BB) and seedlings of Chasselas were grown in individual pots on peat-rich pre-fertilized soil.  Plants were kept under natural light at temperatures between 18o and 28oC.  Plants were used for experiments when they had 10-15 fully developed leaves on 1-3 shoots.

Sprays and Inoculations

All treatments were sprayed on the tops and bottoms of all leaves until near run-off.  The plants were then left to dry before being inoculated with downy mildew.  Downy mildew treatments were sprayed on the abaxial surface of the leaves, between 6 and 12 hours after the treatments were applied.  After inoculations, plants were incubated at 20-21oC and 80-99% relative humidity in the dark for 24 hours.  Then, plans were maintained at a temperature of 18-25oC and 60-80% relative humidity, and undergoing a 16 hour day and 8 hour night schedule.  Once “oil spots” were noted on the leaves (usually 6-10 days after downy mildew inoculation), plants were once again incubated overnight in the dark at 20oC and 80-99% relative humidity (to promote sporulation).  

Disease incidence (percentage of leaves with oil spots or visible sporulation) and disease severity (percentage of the leaf area occupied by sporulating lesions) were calculated.

Field Trials

The best treatment(s) that displayed efficiencies comparable to copper applications under greenhouse conditions were used for the field trials.

Two experimental vineyards were used, one in Rovereto, Italy, and the other in Frick, Switzerland.  The Italian vineyard featured Cabernet Sauvignon vines on Kober 5BB rootstock (pergola trentina trellis system) and the Swiss vineyard featured Riesling-Sylvaner and Chasselas vines on Kober 5BB rootstock (guyot trellis system).  All soil and weed management practices were performed in ways approved for organic viticulture.

Treatments

Each vineyard contained four replicates per treatment arranged in a randomized complete block design (great set-up, for you non-statisticians out there).  Each replicates’ surface area was 18m2 and included 6 to 8 plants.  Each trial had an untreated control, and a standard treatment of copper hydroxide (in addition to the other compound treatments of interest).  In Italy treatments were sprayed at 7 day intervals, and in Switzerland, treatments were sprayed at 5-10 day intervals (dependent upon weather, plant growth, and downy mildew risk).

Disease incidence and disease severity were measured as they were in the indoor trials.  Leaves were assessed for disease every week in Italy, and 5 to 7 times per season in Switzerland.  To measure disease, 50 leaves and 50 bunches were randomly selected and analyzed.

Results

Indoor Trials

  •       There were 103 different experimental treatments, with a total of 218 various combinations and dosages.
  •       24% (n=38) of these treatments were found worthy of field tests.
  •       Disease severity in the untreated control ranged from 17.8 to 71.6%.
  •       Disease severity in the copper hydroxide treatment ranged from 1.4 to 12.5%.
  •       Disease incidence in the untreated control ranged from 64.9-100%.
  •       Disease incidence in the copper hydroxide treatment ranged from 23.3-96.6%.
  •       63.4% of the different treatments significantly inhibited disease development compared to the control.
  •       36.5% of the different treatments were as effective as the copper hydroxide treatment.
  •       Animal Origins:

o   Chito plant, Enzicur, propolis, whey and grana significantly reduced downy mildew symptoms compared to the control.

  •       Biocontrol Agents:

o   Serenade and Trichodex were as effective as the copper hydroxide treatment.

  •       Inorganic Materials:

o   Armicarb, SaluKarb, Gro-stim, Kendal, and Ulmasud were as effective as the copper hydroxide treatment.

  •       Microbial extracts and Natural Derivatives:

o   Agat 25 K and Diamant were as effective treatments, except when applied at concentrations below 5-10%.

o   GBA plant wash soap, Siva 50, and Tecnobiol significantly reduced downy mildew expression.

o   Penergetic-p liquid and Phyto-Vital were the only natural derivative treatments that showed the same effectiveness as the copper hydroxide treatment.

  •       Plant Extracts:

o   Addit, BioZell 2000B, BM-608, Elot-Vis, Inulex, Jobeck Special Herb, licorice extract, Norporin BS liquid, Novosil, OA-21-0-N, Oak-ES, Plex-W, Quillaja liquid extract, Quiponin BS, R1, S1, S2, Saponin and Timorex all showed reduce downy mildew expression compared with the untreated control.

o   Disease levels for all of these substances were equivalent to those in the copper hydroxide treatments.

  •       Synthetic Materials:

o   Beta-amino-butyric-acid, benzothiadiazole, and high levels of Tween 80 were as effective as the copper hydroxide treatments.

  •       Other Copper Formulations:

o   New copper formulas showed effectiveness similar to copper hydroxide, however, not in lower concentrations. 

§  The level of downy mildew control decreased logarithmically to copper levels.

§  The minimum level of copper necessary for effectiveness against downy mildew was 0.26g/L.

§  Higher rates of copper did not increase the efficiency of the treatment.

Field Trials

  •       The treatment selection criteria for determining which treatment to use in the field trials were: 1) efficacy at low doses; 2) absence of phytotoxic effects in the indoor trials; 3) the price/economic efficiency of the material; and 4) the availability of the material in large enough quantities to use in vineyard management.  This resulted in the usage of 32 treatments from the indoor trials.
  •       Natural downy mildew infections were observed at both vineyards during all years of the study.
  •       In Switzerland, downy mildew killed 60-95% of the leaf canopy in untreated plants.
  •       In Italy, downy mildew killed around 60% of the leaf canopy in untreated plants.
  •       Chito Plant, Serenade, Trichodex, Armicarb, Myco-Sin, Quiponin BS, S1, S2, salix extract, Saponin, Timorex, Agat 25 k, Zonix, Tecnobiol, Elot-vis, Inulex, and Enzicur all showed downy mildew control on bunches at greater than 60% control.
  •       Myco-sin was the best performer of the bunch, providing 70-99% disease control.
  •       The copper hydroxide treatment significantly protected the plants with control rates between 68 and 100% on leaves, and 61-99% on bunches.
  •       Inulex, Chito Plant, and Naturam 5 showed toxic effects, and BM-608 + Trapper promoted disease development.

Summary

Basically, what the current study found was that without taking anything else into account, there are many compounds available that provide protection against downy mildew that is just as effective as the copper hydroxide sprays.  However, this study also found that many of these compound would not actually be useful as alternatives for copper in organic viticulture, as a result of other disadvantages that outweigh the advantages of disease control.

For example, some compounds are simply not produced in quantities large enough to be able to apply to a vineyard (let alone multiple vineyards) while other are simply much too expensive.  Other compounds (such as Myco-sin) showed phytotoxic effects down the grapes or other parts of the environment, which would result in a no-better alternative to an already environmentally-damaging copper spray.  Also, many compounds studied would have to undergo lengthy registration and bureaucratic hoops that would prove costly in the long run.  Many other compounds, while seemingly effective in the indoor trials, proved to be ineffective in the field trials, due to their poor “rainfastness” (in other words, they are ineffective in wet weather).  The paper described in detail many of the problems with a large number of the compounds reported in the results above, which I’ll skip for now in lieu of space.

After all is said and done, this study found that the most promising candidates for replacing copper as an organic agent for protecting against downy mildew are the biocontrol agent, T. harzianum (Trichodex), and the plant extract, Y. schidigera (Norponin BS liquid), and S. officinalis (S2).  These compounds displayed effectiveness comparable to the copper hydroxide treatments, and they did not display any negative side-effects that many other compounds displayed (i.e. phytotoxicity or poor performance in rainy weather).  The authors contend that these alternatives warrant further study.  They also suggest that in the meantime, since they found that different formulations of copper were also effective, that organic viticulturists attempt to use these different formulas that contain lower levels of copper, until a suitable alternative can be found.

Please feel free to leave your comments/questions below, and I’ll try to answer them to the best of my ability!

Source: Dagostin, S., Schärer, H-J., Pertot, I., and Tamm, L. 2011. Are there alternatives to copper for controlling grapevine downy mildew in organic viticulture? Crop Protection 30: 776-788.

DOI: 10.1016/j.cropro.2011.02.031
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!

Posted in Viticulture

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Phenolic Composition of Organically Grown Grapes Do Not Change with Different Winemaking Techniques

Posted on October 20, 2011 by Becca| Leave a comment
flickr.com/photos/quinnanya/2922863195/

It has been well documented that the phenolic composition of wine differs depending upon a variety of factors: including, but not limited to; the type of grape, environmental conditions, disease pressures, soil type, geographical location, and grape maturity status.  Studies have shown that different vinification techniques may also be a source of variation in regards to total phenolic composition of wine. 

For example, some studies have shown that by using extended maceration techniques, the extraction of phenolic compounds is improved.  Other studies have shown that the use of pectolytic enzymes, which function to improve juice yield and clarify the wine, shows mixed results, depending upon which study one looks at.  Some studies have shown that using pectolytic enzymes promote color and improve the quality of the wine, while other studies found that these enzymes result in a decrease in total anthocyanins and wine color.

In the short study reviewed today, published earlier this year in the Journal of Food Science, the authors examined organically grown Monastrell grapes, and whether there were any differences in phenolic composition of the resulting wine after using three different winemaking techniques.

Methods

The grapes used in this study were of the Monastrell variety that were grown under organic conditions in D.O. Jumilla. 

Three different vinification treatments were used in this study: 1)10 day maceration of the pomace (control); 2) 21 day extended maceration; and 3) 10 day maceration with the addition of 3g/100kg of enological enzymes.  All other vinification techniques were identical between treatments.

The first analysis of the wines was at bottling, then later every month for the next 3 months.

Standard physiochemical measurements of the wine were taken at analysis (pH, density, volatile acidity, total acidity, and alcohol degrees).  Total phenolic compounds were broken down into levels of anthocyanins, flavonols, hydroxycinnamic acids, and stilbenes.  All analyses were performed in triplicate.  Antioxidant activity was also measured.

Results

  •       Physiochemical

o   All physiochemical measurements were found to be in the normal range for red wine.

  •       Antioxidant Activity

o   No significant differences in antioxidant activity were found between any of the vinification treatments.

o   During the 3 month storing process, there were no significant changes in antioxidant activity between any of the vinification treatments.

§  These results agreed with some studies, yet disagreed with others.

  •       Phenolics

o   Average levels of phenolic compounds in the enzyme treatment equaled the average levels of phenolic compounds in the control treatment.

§  These results did not agree with some studies.

o   Average levels of phenolic compounds in the extended maceration treatment were similar to the average levels of phenolic compounds in the control treatment.

§  These results were opposite of some studies.

o   After 3 months of storage, there was a significant decrease in phenolic compound levels.  The control wines lost 43%; the enzyme treatment lost 35.1%; and the extended maceration treatment lost 31.9%.

§  These results agreed with some studies.

  •       Anthocyanins

o   Average concentrations of anthocyanins in the enzyme treatment were similar to the average concentrations of anthocyanins in the control treatment and the extended maceration treatment.

§  These results agreed with some studies, yet disagreed with others.

o   There was no correlation between anthocyanin content and antioxidant activity in any treatment.

§  These results agreed with some studies.

o   After 3 months of storage, there was a decrease of 40-50% in regards to anthocyanin concentrations, with no significant differences observed between any of the vinification techniques.

§  These results agreed with some studies.

  •       Hydroxycinnamic Acids

o   There was no difference in the concentration of hydroxycinnamic acids between the enzyme treatment wines and the control wines.

§  These results were opposite of some studies.

o   There was no difference in the concentration of hydroxycinnamic acid derivatives between the extended maceration treatment wines and the control wines.

§  The concentrations of hydroxycinnamic acids and their derivatives in this study were higher than some studies, yet lower than in other studies.

o   There was no correlation between hydroxycinnamic acid derivative content and antioxidant activity.

§  This result agreed with some studies.

o   After 3 months of storage, there were no significant changes in hydroxycinnamic acid concentrations for any of the treatments.

§  This result agreed with some studies.

  •       Stilbenes

o   The average concentration of trans-resveratrol-3-o-β-glucoside was similar in the enzyme treatment and in the control treatment, and the concentration in the extended maceration treatment was lower.

§  These values were higher than those found in some studies, yet lower than those found in other studies.

o   There was no correlation between stilbene concentrations and antioxidant activity in any of the treatments.

§  This result is opposite from some studies.

o   After 3 months of storage, there were no changes in the concentration of trans-piceid.

§  These results agree with some studies.

  •       Flavonols

o   There were no significant differences in flavonol concentrations between any of the treatments.

o   There was no correlation between flavonol content and antioxidant activity.

§  This result is opposite from some studies.

o   After 3 months of storage, there were no significant differences in flavonol concentrations in any of the treatments.

§  This result is in agreement with some studies.

What does this all mean?

The results of this study can easily be summed up in just a couple of sentences.  First, vinification technique had no effect on the antioxidant activity and the phenolic composition of organic wine.  Second, changes in phenolic composition over 3 months of aging were not related to vinification technique.

One thing I wanted to point out, if you haven’t noticed already, is that after nearly all of the results presented, I indicated whether other studies have found the same result.  One may have noticed that the results of this study were extremely variable in regards to how they compared with the results of this study.  Therefore, one must take the results of this study with a grain of salt. 

I have some confidence that the results of this particular study are accurate.  Though, how can it be that their results at times are so different than the results from other studies?  I think what it boils down to what was briefly mentioned in the introduction of this post.  Phenolic composition of wine differs depending upon a variety of factors: including, but not limited to; the type of grape, environmental conditions, disease pressures, soil type, geographical location, and grape maturity status.  If any of these conditions (or other conditions not described) are different between studies in any way, it is likely that the results may be different.  There can be no blanket statement regarding how phenolic composition will change using certain vinification techniques, since almost any difference in production will cause huge variation in results.

Therefore, I conclude to say that vinification technique had no effect on the antioxidant activity and the phenolic composition of organic wine made with Monastrell grapes.  This may not be the case for other grape varieties undergoing different vinification techniques than those studied here, but alas, I suppose that is not the point of this short and sweet study!

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

Source: Mulero, J., Zafrilla, P., Cayuela, J., Martínez-Cachá, A., and Pardo, F. 2011. Antioxidant Activity and Phenolic Compounds in Organic Red Wine Using Different Winemaking Techniques. Journal of Food Science 76(3): C436-C440

DOI: 10.1111/j.1750-3841.2011.02104.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!

Posted in Enology

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Grape Pomace: The Diabetes Wonderdrug

Posted on October 18, 2011 by Becca| 3 Comments

Before I launch into today’s post, I just want to give a big hello to those visiting from the blog Swirl, Sip, Snark, who recently wrote a great mini-review of this blog!  Of course, hello to both my new and returning visitors!

I’ve been neglecting the medicinal side of academics as of late, so this post features current research related to just that.

Type 2 diabetes has been on the rise throughout the United States and the rest of the world, in large part as a result of the increase incidence of obesity.  With the increasing frequency of Type 2 diabetes, there has also been an increase in discovering ways in which to treat the disease.  One approach recently has been to increase phytochemicals in the diets of those diagnosed with Type 2 diabetes, which would improve glycemic control, and also reduce postprandial hyperglycemia, an early symptom of the disease.  Basically, postprandial hyperglycemia occurs when pancreatic β cells no longer secrete the required level of insulin for normal function, which if not treated, can sometimes lead to an irreversible state of diabetes.

This postprandial hyperglycemia is a function of the amount of starch (the body’s primary source of glucose) digested by the body, and the rate in which this digestion occurs.  To reduce this postprandial hyperglycemia, current research has examined ways in which to reduce or slow the digestion and absorption of carbohydrates, specifically by inhibiting starch hydrolyzing enzymes in the digestive tract.  Hydrolysis occurs in mammals by the enzymatic actions of α-amylase, which creates by-products that are further hydrolyzed by α-glucosidase, which ultimately creates and releases glucose into the blood stream.  By slowing this process, theoretically one would reduce or eliminate postprandial hyperglycemia, which would ultimately result in the reduction or elimination of Type 2 diabetes.

Some phytochemicals that are gaining interest in helping to decrease the rate of postprandial hyperglycemia and Type 2 diabetes are polyphenols and other antioxidants that have been shown to have a multitude of health benefits.  It has been well documented that red wine, and particularly the grapes that red wine is created from, contains high levels of polyphenols and antioxidants that have been shown to have numerous health benefits.  Grape pomace, a by-product of the winemaking process, which contains the skins and seeds of grapes, is extremely rich in these polyphenols and antioxidants, and should therefore be considered for use as potential health aide.  Currently, grape pomace (a.k.a. grape marc or grape residues) is used for many purposes; including, but not limited to use as fertilizers, animal feed, and even potential meat preservers.

http://www.flickr.com/photos/marianneperdomo/260169941/

These polyphenols and antioxidants in the skins and seeds of grapes may play a role in the reduction of postprandial hyperglycemia and Type 2 diabetes when ingested, however, very little research has been done to investigate this possibility.  The study reviewed today, which was published in 2010 in the journal Nutrition and Metabolism, sought to examine the potential benefits of grape pomace on Type 2 diabetes, by comparing pomace made from red grapes, white grapes, and apples as a type of control that is also rich in antioxidants, but may have different bioactivities.  Extracts created from these different sources of pomace were examined for their total phenolic contents, flavonoids, free-radical scavenger activities, and their inhibitory effects on α-glucosidase.

Methods

Red grape pomace extracts were created from Cabernet Franc grapes, and white grape pomace extracts were created from Chardonnay grapes.  Grapes were sources from a vineyard near Blackstone, Virginia, USA.  Apple pomace extracts were created from the National fruit product company, INC, in Winchester, Virginia, USA.  The following were measured for each extract:  total phenolic content, total flavonoid content, oxygen radical absorbance capacity, DPPH radical scavenging activity, and α-glucosidase inhibition (in vitro and in vivo).

In vitro α-glucosidase inhibition assays involved using rat intestinal acetone powder, which was used to create mammalian α-glucosidase.  This solution was mixed with the different extracts and maintained for 75 minutes, in order to determine in vitro inhibition of α-glucosidase.  Acarbose was used as a positive control (a chemical known to inhibit α-glucosidase).

For the in vivo animal experiments, wild-type B6 mice were initially fed a rodent feed containing 60% carbohydrates, 23% protein, and 17% fat.  Animals were housed and experiments performed at Virginia Tech, Blacksburg, VA, USA.  For those mice in the diabetes treatment group, diabetes was induced with STZ dissolved in a 10mM sodium citrate buffer.  After 5 to 7 days, those mice with a fasting blood glucose level of 126mg/dL were considered to have diabetes, and were then randomly assigned to two different treatment groups.  The two treatment groups for the in vivo study were the control group, which received only water by oral gavage, and the red grape pomace extract group, which received the red grape pomace extract solution via oral gavage. 

After 30 minutes of either the water or red grape pomace extract solution treatment, mice were challenged with 0.2mL of a potato starch suspension, which was administered by oral gavage.  Ultimately, this in vivo experiment would determine if red grape pomace extract had any effect on the glycemic response of diabetic mice, following a potato starch challenge.  Blood samples were collected from the mice at 0, 30, 60, and 120 minutes following the starch challenge, and blood glucose levels were measured.

Results

In vitro study of grape and apple extracts

  •       Total phenols and total flavonoids:

o   The red grape pomace extract had the highest levels of both (followed by white grape pomace extract and then the apple extract, which had the lowest levels).

o   The red grape pomace extract had significantly higher levels of phenols and flavonoids than the apple extract.

o   Flavonoids made up 72% and 66% of the total phenols in the red grape and white grape pomace extracts, respectively, while they only accounted for 50% of the total phenols in the apple extracts (suggestive of marked differences in phenolic profiles between grapes and apples).

  •       Oxygen Radical Absorbance Capacity (ORAC) and DPPH radical scavenging activity

o   The red grape pomace extract had the highest ORAC, compared to the white grape and the apple extracts.

o   The grape pomace extracts tended to have higher DPPH radical scavenging activity than the apple extract, but this was not statistically significant.

  •       In vitro α-glucosidase inhibition experiment

o   Both the red and white grape pomace extracts significantly inhibited α-glucosidase, whereas the apple extract showed no effect (suggests that grape pomace may contain specific α-glucosidase inhibitory compounds that other extracts do not).

o   Both the red and white grape pomace extracts showed strong inhibition of α-glucosidase than even the commercial extract (acarbose).

o   At a dose of 1.5mg/mL, the red grape pomace extract inhibited α-glucosidase activity by 47%, which was significantly higher than the white grape pomace extract, which inhibited α-glucosidase activity by 39%.  The apple extract did not inhibit α-glucosidase.

o   There appeared to be a dose-dependent inhibition of α-glucosidase by the red grape pomace extract, between the concentrations of 0-2.5mg/mL.  The inhibition of α-glucosidase by the red grape pomace extract at the highest concentration of 2.5mg/mL was 64%.

  •       In vivo postprandial hyperglycemia inhibition study in mice

o   The administration of red grape pomace extract (dose of 400mg/kg body weight) successfully suppressed postprandial hyperglycemia in STZ-induced diabetic mice.

o   The red grape pomace extract treatment group had postprandial hyperglycemia significantly reduced by 35% compared to the control group that did not receive any pomace extract.

What does this all mean?

The results of this study show great promise for those suffering from postprandial hyperglycemia and Type 2 diabetes.  The in vitro studies showed that the grape pomace extract were highly successful in inhibiting α-glucosidase, whereas apple extract did not have such an effect.  This indicates that grape pomace extracts may contain certain compounds that are specific for reducing or inhibiting α-glucosidase, where other extracts may not.

Currently Acarbose is used for treatment of the symptoms of diabetes.  However, this treatment is known for creating adverse gastrointestinal side effects, which are caused by the inhibition of α-amylase (in addition to the desired inhibition of α-glucosidase).  By inhibiting α-amylase, the body is less able to digest carbohydrates, thus leaving a very uncomfortable accumulation of undigested carbohydrates in the large intestine.  However, this study determined (results not shown) that grape pomace extracts do not inhibit α-amylase, and only target α-glucosidase, thereby grape pomace extracts would be a more ideal treatment for Type 2 diabetes as a result of the decreased side effects.

In the in vivo study, the results clearly indicate that administration of red grape pomace extract had a significant inhibitory effect on α-glucosidase.  Specifically, according to the authors, the results suggest that red grape pomace extracts can potentially act in an anti-diabetic manner, resulting from the suppression of postprandial hyperglycemia through the inhibition of α-glucosidase.

Of course, these studies were performed on mice, and not, humans, thereby one must use caution in extrapolating these results to human patients.  However, these results do show great promise that grape pomace may be a significant therapy for treating postprandial hyperglycemia and Type 2 diabetes, and justify further research on the subject (eventually using human study subjects).  This article was the first of its kind to look at using grape pomace extracts for this type of medicinal purpose, and based on the very positive results of this study, hopefully it will not be the last! 

Grape pomace isn’t just for compost or fertilizer anymore!

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

Source: Hogan, S., Zhang, L., Li, J., Sun, S., Canning, C., and Zhou, K. 2010. Antioxidant rich grape pomace extract suppresses postprandial hyperglycemia in diabetic mice by specifically inhibiting alpha-glucosidase. Nutrition and Metabolism 7: 71

DOI: 10.1186/1743-7075-7-71
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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