Progress 10/01/12 to 01/18/17
Outputs
Target Audience:The main target audience for this project is wine makers with responsibility for red wine fermentations who are interested in optimizing and controlling extraction of pigments and tannins and influencing the level of these solutes in grape berries. The secondary audience is vineyard managers with an interest in the relationship between amino acid metabolism and phenolic accumulation in grapes during ripening Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The work provided the graduate student assistants with the opportunity to develop their analytical skills related to tannin, pigment and phenolic analysis. In addition some students learned skills related to amino acid extraction and analysis. How have the results been disseminated to communities of interest?The work has been presented at several industry technical meetings and resulted in a publication in a trade journal (CAPCA Adviser) What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The work has been aimed at two closely related objectives. The first objective was to identify components of the insoluble matrix of grape skins that influence phenolic extraction during winemaking. Our work showed that the cell walls of grape skins and mesocarp have an ability to bind tannins and that this binding capacity is probably an important factor in determining tannin extractability during winemaking. We determined that this binding capacity resides in the carbohydrate components of the cell wall and that intrinsic cell wall proteins probably also play a role in tannin extraction. This work provided information about the role that the insoluble matrix of the grape berry plays in tannin extraction, a component of fruit composition that has been overlooked as a factor in winemaking. Our work also addressed the fraction of tannin that binds irreversibly to the cell wall matrix during fermentation and is thus unavailable to extraction during winemaking. We also studied solutes that play an ancillary role in phenolic metabolism but that are important for continued operation of those pathways under normal conditions. The reason for undertaking this work was to gain a better understanding of how phenolic biosynthesis is integrated into the metabolism of the tissues in which it occurs. We focused on the amino acids directly related to phenolic biosynthesis. We have obtained accurate measurements of phenylalanine, methionine, glutamate, glutamine and ammonia in skin and mesocarp tissue in parallel with phenolic determinations during ripening. We studied the storage and mobilization of amino acids in the grapevine in relation to the early production of tannins in the hypodermal cells of berry skin and the parenchyma tissue outside of the seed coat. This work provided pool size and abundance data about individual amino acids in a variety of grapevine tissues and defined the experimental strategy to estimate pool sizes and turnover rates in berry tissues that produce large quantities of phenolic metabolites as part of the developmental process. The output from this work has been a better understanding of the role that the insoluble cell wall matrix plays in tannin partitioning during fermentation and a greater appreciation of how overall phenolic production is integrated into the global metabolism of the grapevine from flowering through harvest.
Publications
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Progress 10/01/14 to 09/30/15
Outputs
Target Audience:The target audience for this project is wine makers with responsibility for red wine fermentations who are interested in optimizing and controlling extraction of pigments and tannins and influencing the level of these solutes in grape berries. Changes/Problems:The scope of this project has been greatly reduced and research is no longer being carried out. The reason for this change is the anticipated retirement of PI at the end of June, 2016. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?The work has been presented at several industry technical meetings and resulted in a publication in a trade journal (CAPCA Adviser) What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The work on this project resulted in continued discussions with farm advisers related to nitrogen metabolism in Pinot family grape varieties. Some varieties are particularly prone to a disorder known as leaf curl and this seems to be caused by an abnormal accumulation of putrescine (1,4, diaminobutane). The discussions have suggested a number of ways to minimize putrescine accumulation during the early leaf growth.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Rhonda J. Smith, Larry J. Bettiga and Douglas O. Adams. Pinot Leaf Curl. CAPCA Adviser V18 No.4 48-54 (2015)
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Progress 10/01/13 to 09/30/14
Outputs
Target Audience: The target audience for this research is wine makers with responsibility for red wine fermentations who are interested in optimizing and controlling extraction of pigments and tannins, and influencing the level of these compounds in grapes. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest? A poster presentation of this work was presented at the annual meeting of the American Society for Enology and Viticulture. The work has also been presented at the annual Sonoma County Grape Day and at a talk on nitrogen influence on phenolic composition presented on the U.C. Davis campus. What do you plan to do during the next reporting period to accomplish the goals? The focus during the next reporting period is to identify specific vineyard sites for a comprehensive study of putrescine levels in leaves during the first 75 days of shoot growth. This is the time when Pinot leaf symptoms develop and the single time point snapshot of putrescine levels in symptom and non-symptom leaves that we currently have must be expanded so as to obtain a description of how the level of this toxic metabolite changes during shoot growth. This work could also include a study of fruit composition at harvest and an evaluation of how altered nitrogen content of fruit influences the level of tannin and pigments in berries.
Impacts
What was accomplished under these goals?
We studied the major reduced-nitrogen metabolites in leaves of Pinot noir exhibiting symptoms of Pinot leaf curl. We measured ammonia and amino acids in leaves exhibiting symptoms of leaf curl and ones from an adjacent portion of the vineyard not exhibiting symptoms. We also studied levels of the diamine putrescine (1,4,-diaminobutane) in symptom and non-symptom leaves. We found no correlation of symptoms with the level of glutamine or ammonia in any of the 14 sites we studied, but in 12 of the 14 sites the level of putrescine in the leaves was significantly elevated in leaves showing symptoms. We also studied total amino acids in leaves from symptom and non-symptom vines. In seven of the 14 sites the total amino acids in symptom leaves was higher than in non-symptom and when this was observed the elevation was always contributed by amino acids in the glutamate family of amino acids. Interestingly, the level of the putrescine precursors arginine and ornithine was always much lower than the putrescine itself, indicating that considerable turnover of these amino acids must occur to produce the level of putrescine observed.
Publications
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Progress 01/01/13 to 09/30/13
Outputs
Target Audience: The target audience for this project is winemakers that focus on extraction of tannins and pigments from red grapes during winemaking. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? The work provide the graduate student assistant the opportunity to develop her analytical skills related to tannin, pigment and phenolic analysis. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals? During the next reporting period we hope to carry out experimental fermentations with several grape varieties to determine if different varieties loose more or less fruit tannin to the insoluble matrix. Some varieties are notoriously difficult to extract tannin from and we would like to see if these varieties also incorporate more of the fruit tannin into the insoluble matrix. In the next reporting period we would like to begin to address the mechanism (covalent attachment vs strong hydrogen bonding) of tannin loss to the insoluble matrix during winemaking.
Impacts
What was accomplished under these goals?
One of the objectives of this project has been to determine how tannins are partitioned among the various components that result when red grapes are transformed into wine. These components include wine, skin and seed pomace after fermentation, and gross lees. In the past we have not been able to account for all of the tannin present in the grape in these fractions, some of the tannin in the grape was always missing when the amount found in the post-fermentation components were summed and compared to the amount of tannin found in the fruit at harvest. Two years ago we determined that a significant fraction of the tannin we measured in the fruit became irreversibly bound to the insoluble matrix during winemaking. We devised a method using acid cleavage of tannins in butanol that can give a sound estimate of the amount of tannin bound to the insoluble matrix. Using this method in conjunction with a standard protein precipitation protocol for tannin measurement, a photometric determination of anthocyanins based on absorbance change with changing pH, and reaction of non-tannin phenolics with ferric chloride under basic conditions, we have been able to account for nearly all of the tannin present in fruit and show how it is partitioned during red winemaking. To assess the importance of desorption of tannin from the insoluble matrix we conducted a Port style wine experiment where we measured the amount of tannin in the wine before and after addition of alcohol to arrest the fermentation. The most significant finding from this work was that the amount of tannin in the fruit that becomes irreversibly bound to the insoluble matrix steadily increases during winemaking. While addition of ethanol did indeed desorb some tannin from the pomace, the amount desorbed was small compared to the total amount extracted from the fruit during winemaking
Publications
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Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: The experiments reported were done to confirm previous results concerning the partitioning of tannin among various solid and liquid fractions during fermentation of red winegrapes. Previous results indicated that a significant fraction of the tannin found free (acetone extractable) in the skins and seeds of grapes becomes associated with the insoluble matrix of the grape berry during fermentation. In low tannin wines this represents tannin that winemakers would like to release so as to have more tannin in the resulting wine. Experiments were also conducted to determine the effect of incubation time, pH, sugar, ionic strength and particle size on tannin binding to the cell wall material of grapes. Tannin in skins and seeds of Cabernet Sauvignon fruit from the U.C. Davis vineyard was measured prior to fermentation. After fermentation tannin was measured in the resulting wine, lees and pomace. Free tannin in these fractions was measured by extracting with 70% acetone and then measuring the tannin in the aqueous fraction after removing the acetone. An aliquot of the pomace and lees were retained and the bound tannin in pomace skins and lees was determined by heating the insoluble material at 96C for 1 hour in n-butanol/HCl with ferrous sulfate and then reading the absorbance at 520nm. Recovery of tannin after fermentation was assessed by comparing the tannin recovered in the various fractions after fermentation with the amount found in the fruit prior to fermentation. The fermentation was carried out in triplicate and the recovery of tannin was 99.7%, 93.5%, and 100.8%. The second objective was to determine the effect of incubation time, ethanol, sugar, ionic strength and particle size on tannin association and irreversible binding of tannin to the cell wall material. This was done by preparing a uniform lot of grape cell wall material that could be used for in-vitro measurements of tannin binding. Total tannin bound to the cell wall material was determined by measuring the amount of tannin removed from a tannin solution that approximated a wine but without ethanol. After incubation the "free" tannin on the insoluble matrix was removed by washing the cell wall material with 70% acetone and the irreversibly bound material was assessed by the butanol/HCl procedure described above. A time course showed that most of the binding of tannin to the insoluble matrix occurs within the first four hours followed by a slow accumulation up to 100 hours. Because of this result, experiments to assess the effect of temperature, pH, ethanol, sugar, ionic strength and particle size were all set for four-hour incubations. Decreasing particle size and increasing ionic strength with NaCl led to higher tannin binding. Increasing ethanol and sugar (sucrose ) concentrations and temperature decreased the amount of free and irreversibly bound tannin associated with the cell walls. Interestingly, pH and bisulfite addition had no effect on the amount of free or irreversibly bound tannin. This work has been presented at departmental seminars and a portion of the results shown at a day long workshop (Flavor 101c) put on by the Department of Viticulture & Enology. PARTICIPANTS: The graduate student working on this project was Mr. Steve Nelson. Some of the work was completed as part of his Masters degree research and provided him with training in experimental winemaking, experimental design and analytical methods to assess tannins and phenolics in grape berries and partitioning of tannins and pigments during winemaking. TARGET AUDIENCES: The target audience for this work is practicing winemakers. When the work has been presented we have made an effort to emphasize the importance of tannin binding to the cell wall matrix as an important factor in determining the amount of tannin extracted from fruit into wine. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The findings related to tannin partitioning during fermentation constitute an outcome in that they show that tannin present in grape berries at harvest can be accounted for in the components of the fermentation after winemaking. It is known that only a small fraction of the tannin present in fruit is extracted and remains in the wine after fermentation. This work establishes that while the concentration of tannin in lees is high, this is not quantitatively important because of the small volume of lees compared to other components. The seeds and the skins from the pomace account for most of the tannin in the fruit that is not extracted during winemaking. The skin material contains two fractions of "bound" tannin; that which is loosely bound and can be recovered with 70% acetone and that which is irreversibly bound. The amount of irreversibly bound tannin more than tripled in our experiment. The outcome of the experiments to evaluate parameters that influence tannin binding to cell wall material is one that should have practical implications. The finding that pH and bisulfite addition have no influence means that lowering pH and adding bisulfite to prevent unwanted microbial growth can be carried out with confidence that these procedures are not altering the tannin extraction in the fermentation. The finding that increasing ionic strength actually increases tannin binding to cell walls is consistent with the idea that binding to the cell walls is partly a hydrophobic interaction. This result should allow winemakers to design extraction protocols to optimize the amount of tannin extracted during fermentation of red grapes.
Publications
- No publications reported this period
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Previous work indicated several parameters that influenced tannin extraction during normal fermentation of red grapes. In vitro the level of ethanol present influenced the amount of tannin that binds to the insoluble matrix and the amount that becomes immobilized by covalent bonds. In vitro experiments also showed temperature could influence tannin binding to cell wall material. In the 2011 season the objective was to conduct an experiment on a small experimental wine lot with the goal of evaluating the influence of ethanol and temperature on tannin extraction. We conducted an experiment with Merlot fruit harvested from the Davis experimental vineyard which consisted of 12 separate fermentations of approximately 30Kg each. There were four treatments, each one done in triplicate. The control triplicate was a typical fermentation without any additions or temperature adjustments. One treatment consisted of adding ethanol at a final concentration of 18% at approximately 10 degrees Brix to simulate a Port style wine fermentation. A third triplicate was heated just prior to pressing and a fourth was cooled prior to pressing. During fermentation samples were obtained each day for soluble tannin and bound tannin determinations. Samples of pomace were collected from each lot and retained for analysis. Fruit samples were used to measure tannin in the fruit at harvest. The berries were assayed for tannin by protein precipitation after acetone extraction and removal of the solvent. This served as a measure of the tannin in the fruit at harvest, including acetone extractable tannin in the skin and bound tannin in the skin. A measured amount of the lees material was extracted with aqueous acetone. The acetone solution and the insoluble material from the lees were assayed for tannin by protein precipitation. A weighed aliquot of the insoluble lees material was retained and subjected to the acid butanol procedure for proanthocyanidin analysis. This provided a measure of the amount of tannin bound to the solid lees material. The combined procedure provided a measure of bound and extractable tannin in the lees. We previously used this protocol to determine the time course of tannin binding to cell wall material. Results showed that ethanol addition in the middle of fermentation had little influence on the tannin extracted. Although winemakers frequently report additional tannin extraction when musts are heated just prior to pressing, our results showed little effect. Likewise cooling the must just prior to pressing had little influence on the amount of tannin in the resulting wine. This work shows the importance of testing results obtained in vitro to see how factors that influence tannin binding to cell walls, such as ethanol concentration and press temperature influence tannin extraction in actual fermentations. The primary mechanism for disseminating the information from this project was two invited talks to industry groups and an abstract of a paper to be presented at the American Society for Enology and Viticulture annual meeting in Portland, Oregon in late June 2012. PARTICIPANTS: The graduate student working on this project was Ms. Meredith Bell. This was the second year of her Masters degree research and provided her with training in experimental winemaking, experimental design and analytical methods to assess tannins and phenolics in grape berries and partitioning of tannins and pigments during winemaking. TARGET AUDIENCES: The target audiences for this work are winemakers that are concerned with red wine fermentations. Making the results known to this target audience will highlight the importance of bound tannins to the overall process of tannin extraction from fruit during winemaking. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The major outcome from this research was that we were able to test the effects of ethanol concentration and press temperature on tannin extraction during winemaking. In vitro results indicated that these parameters can influence tannin binding and immobilization on cell wall material. However, in the experiment we conducted, the variables found to be important in vitro had little effect in the actual fermentations. We were able to show that the bound tannin increases in a linear fashion during fermentation, which confirmed our previous observations. The increase in non-extractable tannin represents tannin from the skin and seeds that becomes attached to the insoluble matrix of the berry such that after fermentation it is no longer extractable with acetone. While the mechanism for this phenomenon is unknown, it represents a significant portion of the extractable tannin in fruit at harvest. The major impact of this work will be in helping us understand how tannin is partitioned during winemaking. Identifying the winemaking parameters that influence tannin binding to the insoluble matrix should enable winemakers to more carefully control tannin extraction during red wine fermentations. It is likely this work will impact winemaker's fermentation design and strategy to control tannin extraction.
Publications
- No publications reported this period
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: This project had one primary objective during the 2010 season; to conduct an experiment on a small experimental wine lot with the goal of determining when during fermentation tannin becomes irreversibly bound to the insoluble matrix. We conducted an experiment with approximately 100Kg of Merlot harvested from the Davis experimental vineyard. Following crushing and destemming the crushed fruit was partitioned into three separate lots of approximately 30Kg each. During primary fermentation samples were obtained each day for soluble tannin and bound tannin determinations. Samples of pomace were collected from each lot and retained for analysis. Fruit samples were used to measure tannin in the fruit at harvest. The berries were counted, weighed, peeled, seeds were separated from pulp, and tannin in the skins measured by protein precipitation after acetone extraction and removal of the solvent. This procedure served as a measure of the tannin in the fruit at harvest, including acetone extractable tannin in the skin and bound tannin in the skin. After racking, the volume of the lees was measured and a sample of the solid lees material was collected. A measured amount of the lees material was extracted with aqueous acetone. The acetone solution and the insoluble material from the lees were assayed for tannin by protein precipitation. After the acetone treatment to remove the extractable tannins, a weighed aliquot of the insoluble lees material was retained and subjected to the acid butanol procedure for proanthocyanidin analysis. This provided a measure of the amount of tannin bound to the solid lees material. The combined procedure provided a measure of bound and extractable tannin in the lees. The experiment enabled us to determine the time course of tannin binding to cell wall material. The outcome of this experiment was that we obtained estimates for the amount of tannin in the fruit at harvest, and how that tannin was partitioned during winemaking. Thus far the primary mechanism for disseminating the information from this project was an invited talk to the Napa Valley Wine Technical Group. PARTICIPANTS: Ms. Meredith Bell was the individual that worked on this project. This opportunity provided training in experimental winemaking, experimental design and analytical methods to assess tannins and phenolics in grape berries and all of the components that result from winemaking. TARGET AUDIENCES: The target audiences for this work are winemakers that are concerned with red wine fermentations. Making the results known to this target audience will highlight the importance in bound tannins to the overall process of tannin extraction from fruit during winemaking. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The major outcome from this research is that we were able to determine when tannin that is not extractable with acetone becomes bound to the cell wall. Prior to this work we knew there was a large increase in immobilized tannin but we did not know when it became bound. It was important to include measurements for the bound or non-extractable in order to account for all of the tannin that entered the fermentation. Another outcome was that we were able to show that the bound tannin increases in a linear fashion during fermentation. It is thought that this increase in non-extractable tannin represents tannin from the skin and seeds that becomes attached to the insoluble matrix of the berry such that after fermentation it is no longer extractable with acetone. While the mechanism for this phenomenon is unknown, it represents a significant portion of the extractable tannin in fruit at harvest. The major impact of this work will be in helping us understand how tannin is partitioned during winemaking. Understanding the winemaking parameters that influence this phenomenon should enable winemakers to more carefully control tannin extraction during red wine fermentations. It is likely this work will impact winemaker's ability to control tannin extraction.
Publications
- No publications reported this period
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: During the past year this project had one primary objective; to conduct an experiment on a small experimental wine lot with the goal of accounting for all of the tannin in fruit at harvest, showing how it is partitioned during fermentation and taking into account tannin that might be tightly bound to cell wall material in the pomace and gross lees. We conducted an experiment with approximately 100Kg of Merlot harvested from the Oakville Station. Following crushing and destemming the crushed fruit was partitioned into three separate lots of approximately 30Kg each. After fermentation each lot was pressed and the pomace was carefully weighed. Samples of pomace were collected from each lot of pomace and retained for analysis. Fruit samples were used to assess tannin in the fruit at harvest. The berries were counted, weighed, peeled, seeds were separated from pulp, and tannin in the skins and seeds measured separately by protein precipitation after acetone extraction and removal of the solvent. This procedure served as a measure of the tannin in the fruit at harvest, including acetone extractable tannin in the skin and seeds and bound tannin in the skin. After racking the wine made from the fruit, the volume of the lees was measured and a sample of the solid lees material was collected. A measured amount of the lees material was extracted with aqueous acetone. The acetone solution and the insoluble material from the lees were assayed for tannin by protein precipitation. After the acetone treatment to remove the extractable tannins, a weighed aliquot of the insoluble lees material was retained and subjected to the acid butanol procedure for proanthocyanidin analysis. This provided a measure of the amount of tannin bound to the solid lees material. The combined procedure provided a measure of bound and extractable tannin in the lees. Pomace samples were collected from each of the three lots and the total amount of tannin in the pomace was determined. The wine volume after racking was measured and aliquots of the wine were retained for tannin determination by protein precipitation. The outcome of this experiment was that we obtained estimates for the amount of tannin in the fruit at harvest, and in each of the fractions after fermentation; wine, pomace, and gross lees. By also measuring the amount of bound tannin in the insoluble material from fruit, lees and pomace after acetone extraction we were able to account for all of the tannin in the fruit and describe how it was partitioned among the different components at the end of fermentation. PARTICIPANTS: Ms. Jenny Schultz was the individual that worked on this project. This opportunity provided training in experimental winemaking, phenolics in grape berries and all of the components that result from winemaking. TARGET AUDIENCES: The target audiences for this work are winemakers that are concerned with red wine fermentations. Making the results known to this target audience will highlight the importance in bound tannins to the overall process of tannin extraction from fruit during winemaking. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The major outcome from this research is that compared to fruit there appears to be an increase in the amount of tannin in the pomace and lees that is not extractable with acetone. Prior to this work it was not possible to account for all of the tannin in the fruit by measuring only the soluble fractions after fermentation. It was important to include measurements for the bound or non-extractable in order to account for all of the tannin that entered the fermentation. Another outcome was that we were able to show that the bound tannin increases during fermentation. It is thought that this increase in non-extractable tannin represents tannin from the skin and seeds that becomes attached to the insoluble matrix of the berry such that after fermentation it is no longer extractable with acetone. While the mechanism for this phenomenon is unknown, it represents a significant portion of the extractable tannin in fruit at harvest. The major impact of this work will be in helping us understand how tannin is partitioned during winemaking. Understanding the winemaking parameters that influence this phenomenon should enable winemakers to more carefully control tannin extraction during red wine fermentations.
Publications
- No publications reported this period
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Experiments were conducted to compare the level of phenolic compounds such as tannin and anthocyanins with amino acids that are closely related to the biochemical pathways that lead to the phenolics. We studied Merlot fruit grafted onto two different rootstocks (101-14 and 1103P) grown at Oakville California in the Napa Valley. We measured the level of up to 31 amino acids, including the protein amino acids and several non-protein amino acids, as well as the level of free ammonium. Berries were peeled and the skin, seeds and mesocarp were assayed separately after extraction in either 80% ethanol for amino acids or 70% acetone for phenolic components. Amino acids and phenolics were measured in the skin and mesocarp of grape berries one week after veraison and again at harvest. The objective was to assess the level of the direct precursor amino acid (phenylalanine) and amino acids thought to be involved in ammonium recycling required as a result of ammonia liberation from the phenylalanine ammonia lyase reaction at the beginning of phenolic biosynthesis. Berry samples were also assayed for tannin, anthocyanins and iron reactive phenolics, keeping skin and mesocarp tissue separate as described for the amino acid anaylsis. This was done so that we could assess the amount of phenolics that accumulated in the skin and mesocarp tissue compared to the level of the precursor amino acid (phenylalanine) and the ammonia recycling system (ammonia, glutamate and glutamine) during the ripening phase of berry development. PARTICIPANTS: Some of the work carried out in this project was done by an undergraduate student from the University of Geisenheim, Germany. This project provided training in experimental design, sample processing, amino acid analysis and phenolic analysis of grape berries. TARGET AUDIENCES: This work was presented at the annual meeting of the American Society for Enology and Viticulture in June 2008. The target audience was grape growers and winemakers and the efforts were designed to show the dynamic nature of phenolic biosynthesis in grape berries, skins in particular) during the ripening period. Growers and winemakers often think of the phenolic end products without fully considering their relationship to the amino acid precursor (phenylalanine) and related amino acids in the fruit. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Fruit from the two rootstocks showed about two-fold differences for most, but not all of the amino acids assayed at each sample date. Fruit from 101-14 rootstock had the lower level of amino acids whereas fruit from 1103-P had higher amino acid levels. The rootstocks did not appear to have a significant effect on the concentration of tannin and iron-reactive phenolics in the fruit and at harvest the level of anthocyanins in the fruit from the two rootstocks was nearly identical. However, because the amino acid composition of the fruit was different and the level of phenolics was similar, the relative rate of amino acid turnover in fruit from the two rootstocks was calculated to be quite different. In the case of phenylalanine, one week after veraison the level in fruit from 101-14 rootstock was 15 nmoles per gram of skin fresh weight (SFW) whereas in the fruit from 1103-P the level was 28 nmoles/g SFW. Glutamine levels were 117 nmoles/g SFW in the 101-14 rootstock and 230 nmoles/g SFW in fruit from 1103-P. During the first week of ripening (after the beginning of color change) the fruit procured 14 micro moles of anthocyanin in the 101-14 fruit and 9.49 micro moles in the fruit from 1103-P. Knowing the amount of anthocyanin produced and the relative amounts of amino acids in the skin tissue enabled us to estimate the mean time required for turnover of the phenylalanine and glutamine pools in the skin tissue. Our estimates were 21.5 and 60.2 minutes for phenylalanine in the 101-14 and 1103-P rootstocks respectively. The glutamine turnover was slower (167 minutes and 489 minutes respectively) because of the larger glutamine pools compared to phenylalanine. The outcome of this information was a change in our knowledge of how the level of amino acid precursors of phenolics (phenylalanine) in grape skins is related to the amount of phenolics produced right after the beginning of ripening (anthocyanins in this case). We also gained knowledge of how the level of amino acids related to ammonia recycling (glutamine) compared to the level of the precursor amino acid (phenylalanine) and the amount of anthocyanins produced during ripening.
Publications
- No publications reported this period
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