SUMMARY OF THE DOCTORAL THESIS by Pacos

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									UNIVERSITY OF CRAIOVA
FACULTY OF CHEMISTRY
DISCIPLINE OF PHYSICAL CHEMISTRY AND TECHNOLOGY




   SUMMARY OF THE DOCTORAL
           THESIS



SCIENTIFIC COORDINATOR:
PROF.UNIV.DR.MIRCEA PREDA



                         DOCTORAND:
                   ING.VALENTINA DANISOR




                     2005
    MINISTERY OF EDUCATION AND RESEARCH


       UNIVERSITY OF CRAIOVA
        FACULTY OF CHEMISTRY
    DISCIPLINE OF PHYSICAL CHEMISTRY AND
                 TECHNOLOGY




OXIDO-REDUCTION PROCESSES
   PRODUCED BY OXYGEN
  PENETRATION INTO WINE



SCIENTIFIC COORDINATOR:
PROF.UNIV.DR.MIRCEA PREDA



                         DOCTORAND:
                   ING.VALENTINA DANISOR




                   2005
                         SUMMARY OF THE DOCTORAL THESIS

                                                  Table of Contents
Introduction........................................................................................................................1
Chapter One: Processes of oxidation and reduction in wines.......................................3
        1.1. The mechanism of oxidation in wines………………………………………4
        1.2. The oxido-reductant potential of wine………………………………………9
                  1.2.1. The redox-buffer effect………………………………………....9
                  1.2.2. The variation of the redox potential of wine..............................11
Chapter Two: Ionic Equilibriums..................................................................................14
         2.1. Tartaric precipitations..................................................................................17
                   2.1.1. The states in which tartaric acid is found in wine and the
                             equilibriums among them............................................................18
                   2.1.2. The inhibition and stimulation of the precipitation of acid
                            potassium- tartrate in wine............................................................20
         2.2. Ferric precipitations.....................................................................................22
                  2.2.1 The white crushing........................................................................22
                                2.2.1.1. States of iron in wine...................................................23
                                2.2.1.2. States of phosphoric acid in wine................................26
                                2.2.1.3. The mechanism of formation and precipitatio n of
                                             ferric phosphate...........................................................27
                                 2.2.1.4. Factors influencing white crushing.............................29
                   2.2.2. The black crushing......................................................................31
                   2.2.3. The stabilization of wine as to ferric precipitations....................32
          2.3. Precipitation due to copper.........................................................................34
Chapter Three: The influence of the wine oxidation and reduction state on its
                   organoleptic characteristics................................................................39
          3.1. The color of wine........................................................................................40
          3.2. The aroma and bouquet of wine..................................................................42
          3.3. Modifications of taste and smell.................................................................44
Objectives of the doctoral thesis.....................................................................................48
Chapter four: The utilized work methods.....................................................................49
         4.1. Determination of characteristics of physical and chemical composition....49
         4.2. Methods of appreciating the color of wines................................................51
                    4.2.1. Intensity of color.........................................................................51
                    4.2.2. Tint (nuance) of color.................................................................51
          4.3. Global and sub -class determination of phenolic compounds.....................52
                    4.3.1. Determination of total polyphenols............................................52
                    4.3.2. Determination of polyphenols by sub-classes............................52
          4.4. Determination of redox potential................................................................54
          4.5. Evaluation methods of astringency of red wines........................................56
Chapter Five: The influence of the redox potential on the quality of wines from the
                elaboration stage up to their maturation and aging............................58
          5.1. Experimental scheme..................................................................................59
         5.2. Evolution of the oxido-reductant potential during alcoholic
               fermentation................................................................................................63
                  5.2.1. Material used and work method...................................................64
                  5.2.2. Results obtained...........................................................................65
         5.3. Evolution of the oxido-reductant potential during the formation and
               maturation of wines.....................................................................................70
                  5.3.1. The stage of wine formation........................................................70
                  5.3.2. The maturation stage....................................................................75
                  5.3.4. Material used and work method...................................................78
                  5.3.5. Results obtained...........................................................................79
         5.4. The evolution of the oxido-reductant potential during the aging of red
               wines; its influence on the quality of wines...............................................94
                  5.4.1. Material used and work method...................................................95
                  5.4.2. Results obtained...........................................................................96
                              5.4.2.1. The oxido-reductant potential of the wines kept in
                                            wood vessels................................................................96
                              5.4.2.2. The oxido-reductant potential of bottled wines after
                                           one year......................................................................102
         5.5. Conclusions..............................................................................................105
Chapter Six: The influence of the redox systems formed by sulphur
              compounds on the quality of wines.......................................................110
          6.1. Sulphilation of wines...............................................................................110
          6.2. Material used and work method...............................................................113
          6.3. Results obtained.......................................................................................113
                   6.3.1. The influence of SO 2 on the oxido-reductant potential............115
                  6.3.2. The influence of SO 2 on the wine color intensity and tint
                             after the alcoholic fermentation is finished...............................117
                  6.3.3. The influence of SO 2 on the wine antocyans and color
                             intensity, six month after they were obtained...........................121
                   6.3.4. The influence of SO 2 on the content of total polyphenols........123
          6.4. Conclusions.............................................................................................125
Chapter seven: The influence of the redox systems of iron and copper
                 on the quality of red irons..................................................................127
          7.1. Material used and work method..............................................................127
           7.2. Results obtained......................................................................................130
                    7.2.1. The influence of iron ions........................................................130
                   7.2.2. The influence of copper ions....................................................139
                   7.2.3. Modifications of color characteristics of young red
                              wines that undergo blue - gluing treatement..............................144
           7.3. Conclusions ............................................................................................148
Chapter Eight: The influence of the redox systems formed out of
                 phenolic-type substances with ortodihydroxi-groupings
                 and the redox systems formed by antocyans/antocyanides
                 on the quality of wines........................................................................150
          8.1. Material used and work method..............................................................152
           8.2. Results obtained......................................................................................153
                   8.2.1. The influence of maceration conditions on the content of
                              phenolic compounds in red wines............................................153
                   8.2.2. The effect of extra-SO 2 on the content of phenolic
                              compounds in red wines...........................................................159
                   8.2.3. The influence of the content of polyphenols on the
                              development of malolactic fermentation.................................160
          8.3. Conclusions.............................................................................................161
Chapter Nine: General conclusions..............................................................................164
Bibliography...................................................................................................................177
Key words: acetaldehyde, antocyans, depectil, sulphur dioxide, maceration
duration, enzymes, non-reducing extract, alcoholic fermentation, wine
formation, ethanol index, UV (I 280) index, HCl index, polyphenol index,
color intensity, wine aging, wine maturation, total polyphenols, tanninic
polyphenols, non-tanninic polyphenols, aromatic polyphenols, non-aromatic
polyphenols, blue polymers, brown polymers, red polymers, tint, oxido-
reduction potential, decanting, oxido-reduction processes, tannin, Ultrazyin
100, wine, vinification, Vinozyin G, astringency, iron, copper, potassium
ferric cyanide.

      The technological processes of obtaining wine can be conducted through oxido-
reduction reactions that may ameliorate the final product. For this reason it s very i
important for the technology specialist to know and direct the oxido-reduction processes
in the grapes-wine system.
      The oxido-reduction processes that can take place from as early as the alcoholic
fermentation stage (the stage when no antioxidant protection of the must or must
processing is ensured) have great importance on its oenology because they determine the
quality of wines. The importance and effect of these processes are evident as to the
duration of grapes treatments as well as to the duration of wine formation and maturation.
      Beside limpidity, smell and taste, color plays an important role in appreciating the
quality of red wines. In order to obtain red wines of a good quality, different technologies
are used by which the extraction of phenolic compounds is stimulated from grapes skins,
especially from the colored ones. The rachis, which contains astringent polyphenols with
a grassy taste, unfavorable to high-quality wines, is eliminated through grapes
dechistering.
      Vinification is in itself a biotechnological process in which the administration of
industrial enzymatic compounds makes up for the absence or insufficiency of the natural
enzymatic activity; for the oenologist these products represent a new performant means
whose utilization is based on a technology well-adapted to grapes that are considered
noble raw matter.
      Knowing the nature and structure of the macromolecules forming the colloidal
system of the must and of wine opens up new possibilities for the use of industrial
enzymes. The enzymatic modifications of grapes, musts or wines are evident not only in
decantation and filtration, but also in the procedures of extraction (color, aromas and
stabilization).
        The experimental variants of wines produced for the current doctoral study and
presented in this thesis have been elaborated between 2001 and 2002, during the
processing of grapes for the record wines at ICDVV Valea Calugareasca under the
following technological working conditions: sulphitation, pressing, declustering,
administration of enzymes and selected yeasts, pumping the must in the maceration-
fermentation containers, decanting from pomace, completion of alcoholic fermentation,
decanting wine from yeast.
      After decantation from the fermentation deposit, wines have been subjected to
sulphitation with SO 2 concentrations that matched the type of wine.
      The wine was stored in vessels 50l in adequate places at temperatures of 10-13°C.
In January and April, respectively, decantations 2 and 3 were made and the respective
SO2 corrections, in order to maintain a free SO2 concentration of about 35 mg/l over the
whole period up to the beginning of the conditioning process.
       The experimental variants had the aim to put into relief a series of factors that have a
direct influence on the quality of wines. They focused on the utilization of enzymes in
different doses, different SO2 doses being applied to grapes or at grapes pressing, as well
as different periods of maceration.
      The phenolic compounds represent the majority of O2 consuming substances in red
wine, which participate in many oxido-reduction reactions. These compounds contribute
to color, aroma, astringency and bitterness directly or indirectly, being also involved in
the browning reactions both in grapes and in wine. The aging of wines in wooden vessels
increases the range of the oxidable phenolic substances through the extraction of these
compounds from wood.
      The measurements of the oxido-reductant potential have great importance in the
elaboration of wine, especially of the red wine. Moreover when it is aged in a wooden
vessel (barometric ) the wine passes through oxidation processes that modify the
characteristics of its polyphenolic content, and have direct influences on its organoleptic
properties.
      In Chapter Five, “The influence of the redox potential on the quality of wines
from the elaboration stage up to their maturation and aging”, data are presented that
were obtained in the period 2001-2003, related to the determination of the oxido-
reductant potential during the alcoholic fermentation, formation, maturation and aging of
wines.
      The current analyses of the physical-chemical composition were made after the
methods standardized in our country-STAS-while the determinations of the oxido-
reductant potential were made by means of a millivoltmetre, which was also used to
measure the differences of potential between the electrodes of platinum and calomel.
      The oxido-reductant potential was determined during the alcoholic fermentation for
the variants:
     • “witness” (variant with no enzymes, no SO2 or modified pH)
     • with different doses of enzymes
     • the same dose of enzyme + different doses of SO2
     • with modified pH by adding calcium carbonate or tartaric acid
       All additions were made to the must, before the alcoholic fermentation.
       The determinations of the oxido-reductant potential were made during the alcoholic
 fermentation for the “witness” variant and the experimental technological va riants
 generally showed the same tendency of prominent decrease during the stage of
 tumultuous fermentation. This stage is characterized by a degradation of sugars
 accompanied by an abundant release of CO2 and a proliferation of the O2-consuming
 yeasts.
        At the stage of slow fermentation of CO2 release is reduced and a slow diffusion of
 O 2 from air begins, which modifies the balance between oxidation and reduction, slight
 increases of the oxido-reductant potential being observed.
       It was observed that both in the first and the seventh day of alcoholic fermentation,
 the highest values of the oxido-reductant potential (414 and 368 mV, respectively) were
 registered with the “witness” variant that did not received any supplement of anti-oxidant
 substances, for color-extraction or modification of pH.
       This process endorses the assertion that the enzymatic preparations extract from the
 grapes skins a series of phenolic compounds that behave similarly to the antioxidant
 substances which lead to the decrease of the oxido-reductant potential of wines.
      The prominent decrease of the redox potential during the stage of tumultuous
fermentation could be correlated to the activity of yeasts that are great O2 consumers. In
this way it is evidenced once more that yeasts are biochemical catalysts and regulators of
the oxido-reduction processes. In the technology of obtaining red wines, the fermentation
takes place in the presence of solid parts (skin, pulp and seeds). In this situation the
possibilities of internal regulation of the oxido-reduction processes are much more
accelerated due to the natural redox systems of grapes consisting of tannins, coloring
substances, nitrogenous substances, etc.
      The low values of the redox potential registered at the variants with enzymatic
preparations administered to the must are due to the increased content of reductant
substances contained in the skin, pulp and seeds, which were extracted in a greater
proportion than from the “witness”.
      These data demonstrate that as the process of fermentation advances and the
temperature rinses, the release of the resulted carbon dioxide prevents the penetration of
oxygen from the air and makes the values of the oxido-reductant potential decrease.
      Moreover it is supposed that at higher temperatures (24-25°C) the oxido-reductant
potential also decreases due to the enzymes that intensify the processes of polyphenolic
compounds extraction from the solid parts of red grapes, which have an anti-oxidant
role.
      The release of carbon dioxide, which remained undissolved after fermentation,
continues during the stage of wine formation. The intensity of gas release gets lower and
lower, because both the gas contend and the temperature decrease, which increases the
solubility of carbon dioxide in wine.
      As it slows down, the CO2 release impedes less and less the O2 penetration in wine.
Due to this process there is subsequent increase of the redox potential, which becomes
evidently higher than during fermentation. Small CO 2 quantities remain in wine, which
contributes to its rich and fresh taste: 100-300 mg CO 2 per liter in red wines. Moreover
the presence of carbon dioxide in young wines protects them against oxidation, namely it
limits the penetration of oxygen from air into the wine.
       For all variants the determination of the oxido-reductant potential, ten days after
alcoholic fermentation, showed an increase of the oxido-reductant potential as a
consequence of the open decanting, when there was contact with air.
        The global transformations taking place at the maturation stage are also related to
the modification of the redox potential of wine and to the shift of position in the oxido-
reduction equilibriums, which favors the oxidation of some wine components (alcohols,
aldehydes, phenolic compounds, metal ions, etc.) and the formation of some precipitates
(ferric phosphate, complex combinations of iron and phenolic compounds). At the same
time, the presence of oxygen determines the start of some enzymatic oxidation reactions
and a certain limit it creates favorable conditions for the development aerobian micro-
organisms (acetic bacteria, leavens of barms).
      In order to observe how the oxido-reductant potential evolves in wines at the
maturation stage, red wines from Valea Calugareasca were studied. They were from the
2001 crop obtained from the varieties Cabernet Sauvignon and Merlot, out of the
variants that differed as to the duration of maceration-fermentation (maceration duration:
24 hours, 7 days, 14 days and 21 days of prolonged maceration, after the alcoholic
fermentation was finished).
       According to their quality characteristics, the wines obtained were grouped in two
categories:
    • wines that evolved normally during maturation
    • wines that depreciated to a certain extent
     Most of the wines evolved normally during maturation. In the second group there
were the “Witness” wines that were macerated without any supplement of pectolitical
enzymes and of SO 2 .
     Organoleptically, these wines (the “Witness” wines) were qualitatively belong the
wines made from grapes or must treated with SO2 .
     During maturation the “Witness” wines became darker, had a higher rate of
antocyans decrease (an average of approximately 20 mg per month) and high instability.
     The totality of the organoleptic and composition characteristics of the wines
produced through extending the maceration period by 7, 14 up to 21 days after the
alcoholic fermentation was finished, proved that this extension is not justified. Moreover
the quality of wines was not improved, as it had been expected while the vinification
space was uselessly occupied. During the wine aging there occur a series of condensation
on reactions in which tannins are invollved. If in the condensation products there are also
antocyans molecules, their color can be from red to brick red or violet red. In defining
the color, the oxygen can have an important role, if it is present in limited quantities.
     Tannins have a very important role in the evolution of wines, because they are
easily oxidable, and play the role of redox buffer, which protects the other wine
compounds. In certain conditions tannins can transform into insoluble products.
      By polymerization of tannins there are obtained products with large molecules,
whose color can vary from yellow to intense orange; these products modify both the tint
of the wine color and their astringency.
       During the processes of maturation and aging of wines the phenolic compounds
pass through complex processes of degradation, oxidation and condensation, this
influencing the quality of wines. The chromatic characteristics of wines are modified
significantly, characteristics which are defined by color intensity and tint.
      The evolution of the wines kept in wood vessels was influenced both by their initial
composition and the size of the vessel. In smaller vessels the oxygen penetrated through
the wood staves into the wine more easily than in larger vessels.
     Analyses showed that after three years, the values of the oxido-reduction potential
were lower than the initial values, for all the wines kept in wood vessels.
      The highest value of the oxido-reduction potential (305 mV) was recorded for the
wine that had been kept in the smallest vessel (1815 l).
      The transformations of the phenolic compounds in the wines kept in bottles (that are
oxygen-proof) are less evident than in the wines kept in wood vessels.
     The evolution of the oxido-reduction potential was also different in bottled wines as
compared to the wines kept in wood vessels.
        The differences that appeared in the analysis of bottled wines, after a year, were
dependent on the initial composition of each kind of wine, which was influenced by the
vinification procedure.
     The wines kept in bottles remained young, fresh, with a higher content of
antocyans.
       The wines kept in bottles, as compared to the “Witness” samples (before bottling),
presented, after a year, a decrease of the oxido-reduction potential, due to the
consumption of the oxygen from the empty space in the bottle and of the oxygen
incorporated on bottling.
      For all the 12 samples of wine that were analyzed, the decreases of the oxido-
reduction potential were more or less significant according to the type of wine.
     The multitude of factors related to the different compositions of the 12 wines
obtained through various technological operations, made it for the value of the oxido-
reduction potential to vary from one wine to another, within limits of up to 22 mV.
      In Chapter Six “The influence of the redox systems formed by sulphur
compounds on the quality of wines”, the action of SO2 on the quality of wines was
studied. To this purpose wines were analyzed, namely the wines from the experimental
variants of the varieties Cabernet Sauvignon and Merlot obtained in 2002. The analysis
was made both in the absence and presence of SO 2 in the vinification of grapes.
       The results obtained in these experiments lead to the hypothesis that the HSO3 - and
     2-
SO3 ions, which are present in the must or wine due to their affinity to oxygen,
combined with it. In this way all the wines obtained, having a supplement of SO2 added
to the primary vinification, were protected against oxidation (in case that this hypothesis
accepted, it would mean that the oxygen present in the must or wine might be transferred
to oxidable substances through the action of oxidizers and the obtained wine might be
oxid ized).
      The vinification lacking sulphitation contributed to obtaining intensely colored
wines, as a consequence of the decoloring effect of SO2, while the greatest decrease in
the content of antocyans was recorded during its evolution. The wine was pleasant, but
had a more intense color (polymeric pigments) with a lower lever of total polyphenols
and antocyans. This lack of equilibrium was manifest in a less pleasant bitterish taste.
     In Chapter Seven “The influence of the redox systems of iron and copper on the
quality of red wines”, the aim was to illustrate the way in which the iron and copper
ions influence the color of red wines. To this purpose, in 2003 three different wines of
the 2002- crop were chosen (Cabernet Sauvignon, Feteasca Neagra, and Pinot Noir),
which received a supplement of those ions. For each of the three kinds of wine, five
variants were prepared, by adding C u2+and Fe3+ ions in different doses.
      It is also presented the mode in which complex blue gluing influenced the color and
the organoleptic qualities of the young red wines obtained with different enzymatic
preparations at ICDVV Valea Calugareasca in 2003.
       Chapter Eight is entitled “The influence of the redox systems formed out of
substances of phenolic- type with orthodihydroxides and of the redox systems
formed by antocyans / antocyanides on the quality of wines”. In this chapter observed
the mode in which some technological operations of vinification influence the content of
phenolic compounds, e. q. antocyans, total polyphenols, tannins, etc. The analysis was
done on the wines from the experimental variants (the varieties Merlot and Cabernet
Sauvignon, the 2001 crop) obtained by maceration with or without pectolitic enzymes,
with or without sulphitation of the grapes or must. Determinations were made of the
color intensity and the content in polyphenolic compounds.
One of he most important sensory attribute of a red wine is its astringency, which, in
most cases, is estimating through tasting the product. This appreciation must be done by
a group of expert tasters and is not always an objective one. There is also the possibility
of other estimations made by determining the Gelatine Index “Glories” or by a new
method developed by a group of Spanish researchers. In order to see which of the
methods is better, I made a comparative study of these two methods. The results were
presented in a scientific paper presented at the Scientific Session at ICDVV Valea
Calugareasca in 2003. They were also discussed in an article submitted for publication to
the Chemistry Journal.
      Chapter nine presents the conclusion to these studies, some of them being as
follows: “The value of the oxido-reductant potential is one of the reference elements in
the appreciation of the quality of wines, beside other characteristics of the physical-
chemical composition”:
    • The determinations of the oxido-reduction potential during the alcoholic
          fermentation showed that the potential decreased in all variants by almost 100
                           n
    mV (from 296 mV i the must before the alcoholic fermentation to 200 mV,
    approximately, after the alcoholic fermentation ended).
•   The oxido-reductant potential evolves differently during wine aging depending
    on the kind of vessel in which this process takes place.
•   By aging in bottles, the wines have a lower oxido-reductant potential than when
    aging in wood vessels.
•   The supplementation with Cu2+and Fe3+ ions to red wines leads to the formation
    of complex combinations with phenolic substances, which leads to a series of
    modifications of the aroma and composition characteristics.
•   In all the studied cases, enriching wines with metal ions had as an effect the
    decrease in the percentage of monomeric pigments, and the increase in the
    percentage of polymeric pigments.
•   Although the presence of iron and copper in wine determines the decrease in the
    content of antocyans and total phenols, an increase was recorded in the coloring
    intensity in parallel with the acetaldehyde content in wines.
•   The color intensity decreased in all the variants of wines that passed through the
    treatment of blue gluing.
•   The treatment of blue glu ing stimulated the polymeric pigments, which led to a
    decrease in the content of tannins and total polyphenols
•   The treatment of blue gluing plays an importance role in the increase of the
    organoleptical qualities and of the physical chemical stability of wines.
•   Through the technology of vinification both the quantity of extracted phenolic
    compounds and their quality are influenced.
•   The wines obtained through maceration with enzymatic preparation were in
    equilibrium, harmonious, refined, pleasant, and delicate.
•   The utilization of some moderate doses of pectolitic enzymes (1-1,5g /100 Kg of
    grapes) contributed to obtaining intensely colored wines with a greater content of
    polyphenolic compounds, which enhanced the organoleptical qualities of wines.

								
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