Seediscussions,stats,andauthorprofilesforthispublicationat:https://www.researchgate.net/publication/227603117
Freeaminoacidsandvolatilecompoundsin
vinegarsobtainedfromdifferenttypesof
substrate
ArticleinJournaloftheScienceofFoodandAgriculture·March2005
DOI:10.1002/jsfa.2016
CITATIONS
READS
14
67
6authors,including:
EvaValero
JuanCMauricio
UniversidadPablodeOlavide
UniversityofCordoba(Spain)
42PUBLICATIONS647CITATIONS
87PUBLICATIONS1,487CITATIONS
SEEPROFILE
Allin-textreferencesunderlinedinbluearelinkedtopublicationsonResearchGate,
lettingyouaccessandreadthemimmediately.
SEEPROFILE
Availablefrom:JuanCMauricio
Retrievedon:17September2016
Journal of the Science of Food and Agriculture
J Sci Food Agric 85:603–608 (2005)
DOI: 10.1002/jsfa.2016
Free amino acids and volatile compounds
in vinegars obtained from different types
of substrate
Eva Valero,1 Teresa M Berlanga,1 Pedro M Roldán,1 Carlos Jiménez,2
Isidoro Garcı́a2 and Juan C Mauricio1∗
1 Departamento
de Microbiologı́a, Edificio ‘Severo Ochoa’, Facultad de Ciencias, Universidad de Córdoba, Campus Universitario de
Rabanales, 14071 Córdoba, Spain
2 Departamento de Ingenierı́a Quı́mica, Edificio ‘Marie Curie’, Facultad de Ciencias, Universidad de Córdoba, Campus Universitario de
Rabanales, 14071 Córdoba, Spain
Abstract: The present work reports on the free amino acids and volatile compounds in vinegars obtained
from different types of raw materials (cider, white wine and red wine). Based on the amino acid contents
of three types of vinegar and of the substrates from which they were obtained, the profile of the nitrogensupplying compounds and their uptake for the acetic acid bacteria were very similar. The most important
amino acid in terms of supply and uptake was found to be L-leucine. L-Proline proved also important in
the wine vinegars, however it was not depleted as L-leucine. The different acetification reactions involved
were found to yield acetoin, and plus 1,1-diethoxyethane in the wine vinegars.
 2004 Society of Chemical Industry
Keywords: acetification; amino acids; cider; red wine; vinegar; volatile compounds; white wine
INTRODUCTION
Vinegar is a solution of acetic acid obtained by
a fermentation process from a variety of raw
materials (especially white and red wines, alcohol,
apple juice, honey, malted barley, etc). Major
wine-making countries are also usually important
producers of vinegar, which they obtain from wine
and other alcohol-containing substrates formed in
previous fermentations. Vinegar thus obtained exhibits
enhanced sensory properties1 and is therefore more
suitable for direct human consumption; in many cases,
it is subjected to aging in casks in order to further
improve its final properties.2 – 4
The fermentation process that leads to the formation
of vinegar essentially involves the conversion of
ethanol into acetic acid. The microbes that effect
such transformation are acetic acid bacteria from the
genus Acetobacter and Gluconobacter.2,5 Free amino
acids present in the medium are known to be the main
sources of nitrogen for these bacteria. Because the
initial substrate comes from a previous fermentation
effected by yeasts,6 it is essential to ensure that
enough available nitrogen (and in an appropriate
form) is present for acetic acid fermentation to take
place.
The amino acid contents of grape musts used to
make wines and of wines subjected to subsequent
biological aging have been evaluated in depth,7 – 11 to
avoid potential deficits in some essential compounds
or their shortage, which might bring alcoholic
fermentation to a premature halt.12,13 This is of
potentially greater interest in the acetification process,
which involves the fermentation of a medium resulting
from a previous alcoholic fermentation and a series
of physico-chemical operations such as flocculation
and filtration that are intended to stabilize musts
and wines, and that can decrease the amino acid
concentrations in these media.14 Similar studies
on analysis of amino acids have been conducted
on the characterization of vinegars,15 – 18 and the
chemical and biochemical transformations in sherry
vinegar during the different aging stages3 have been
described.
Based on this, the difficulty or impossibility of
ensuring acetic fermentation from some alcoholic
substrates led us to believe that one potential origin of
the problem might be the shortage of amino acids as
nitrogen sources for the process. We thus undertook
the present preliminary study, in which we determined
the content of 23 amino acids, urea and ammonium
∗
Correspondence to: Juan C Mauricio, Departamento de Microbiologı́a, Facultad de Ciencias, Universidad de Córdoba, Campus
Universitario de Rabanales, Edificio C-6 s/n, 14071 Córdoba, Spain
E-mail: [email protected]
Contract/grant sponsor: Spanish Ministry of Science and Technology; contract/grant number: AGL2002-01712
(Received 2 October 2003; revised version received 9 July 2004; accepted 10 August 2004)
Published online 26 November 2004
 2004 Society of Chemical Industry. J Sci Food Agric 0022–5142/2004/$30.00
603
E Valero et al
ions of various types of vinegars and the substrates
from which they were obtained.
Concentrations of volatile compounds of vinegars have been thoroughly investigated.3,4,19 – 25 The
volatile fraction of vinegars mainly comprises alcohols
and esters, which are very important in the vinegar
quality. Major volatile compounds have been determined by gas chromatography with or without previous neutralization.4,21,24 – 28 Some aroma compounds
and organic acids are considered to be responsible
for the differentiation of wine vinegars produced from
different wine substrates and different acetification
methods.25
The aim of the study described here was to evaluate
the concentrations of free amino acids and some
volatile compounds in vinegars obtained from different
types of raw materials.
MATERIALS AND METHODS
Microorganisms
The inoculum used was a mixed culture of fully
active acetic acid bacteria from the genus Acetobacter
and Gluconobacter from industrial fermentation tanks.
Total biomass concentration was 2 × 108 cell ml−1 .
Fermentable substrates
Three fermentable media were used for acetification
process: white wine, red wine and cider. The wines
used had an ethanol content of 12 ± 0.5 ◦ GL and an
initial acidity of 0.3%, expressed as acetic acid, and the
cider had an initial alcohol content of 6.3 ± 0.5 ◦ GL
and an initial acidity of 0.14%. The initial contents
in free amino acids, ammonium ion, urea and volatile
compounds are shown in Figs 1 and 2 for the three
substrates.
ASSM-N
NH4+
Urea
L-Asp
L-Ser
L-Met
L-Lys
L-Asn
L-Tyr
L-Orn
L-Gln
L-Ile+Phe
L-Cist
L-Trp
L-His
L-Gly
L-Val
L-Leu
L-Cys
L-Ala
L-Glu
L-Thr
GABA
L-Arg
L-Pro
CIDER
ASSM-N
NH4+
Urea
L-Asp
L-Ser
L-Met
L-Lys
L-Asn
L-Tyr
L-Orn
L-Gln
L-Ile+Phe
L-Cist
L-Trp
L-His
L-Gly
L-Val
L-Leu
L-Cys
L-Ala
L-Glu
L-Thr
GABA
L-Arg
L-Pro
WHITE WINE
ASSM-N
NH4+
Urea
L-Asp
L-Ser
L-Met
L-Lys
L-Asn
L-Tyr
L-Orn
L-Gln
L-Ile+Phe
L-Cist
L-Trp
L-His
L-Gly
L-Val
L-Leu
L-Cys
L-Ala
L-Glu
L-Thr
GABA
L-Arg
L-Pro
RED WINE
0
2
4
6
8
10
12
Nitrogen concentration (mM)
Figure 1. Nitrogen concentration (mM) from ammonium ions, urea and free amino acids of the vinegars (bold column) and the substrates (unfilled
column) from which they were obtained (cider, white wine and red wine). ASSM-N: assimilable nitrogen.
604
J Sci Food Agric 85:603–608 (2005)
Free amino acids and volatile compounds in vinegars
CIDER
Acetoin
Isoamyl alcohols
Isobutanol
Propanol
1,1-diethoxyethane
Ethyl acetate
Acetaldehyde
WHITE WINE
Acetoin
Isoamyl alcohols
Isobutanol
Propanol
1,1-diethoxyethane
Ethyl acetate
Acetaldehyde
RED WINE
Acetoin
Isoamyl alcohols
Isobutanol
Propanol
1,1-diethoxyethane
Ethyl acetate
Acetaldehyde
0
50
100
150
200
Concentration (mg l-1)
Figure 2. Concentrations (mg l−1 ) of acetoin, isoamyl alcohols,
isobutanol, propanol, 1,1-diethoxyethane, ethyl acetate and
acetaldehyde in the vinegars (bold column) and the substrates
(unfilled column) from which they were obtained.
Fermentation conditions
The vinegars were obtained in a Frings turbine
fermenter (capacity 8 l) at 31 ◦ C. The fermenter was
operated in a semi-continuous manner, using a loading
time of about 4 h. The fermentation rate was 0.3%
acetic acid h−1 . The air flow-rate used was 101 h−1 l−1
fermentation broth.
Analyses
Free amino acids in both types of wine, cider and the
resulting vinegars were conducted according to Botella
et al.29 Vinegar samples were previously adjusted
to pH 5 with 4 M NaOH, with provision for the
dilution factor. Amino acids were quantified from
the absorbances at 254 nm of their dansyl derivatives,
which were previously isolated by high-performance
liquid chromatography on a Spectra-Physics P200
HPLC instrument equipped with an SP 8450 UV–vis
detector and a 15 × 0.4 cm reversed-phased column
packed with Spherisorb ODS2 resin of 5 µm particle
size obtained from Tracer Analı́tica (Barcelona, Spain)
and thermostated at 25 ◦ C. A volume of 20 µl of
5 mmol l−1 norleucine was used as internal standard.
J Sci Food Agric 85:603–608 (2005)
Urea and ammonium ion were determined by
the enzymatic method (urea/ammonia UV-method,
Boehringer-Mannheim, Germany).
Acetaldehyde, 1,1-diethoxyethane, ethyl acetate,
propanol, isobutanol, isoamyl alcohols and acetoin
were determined by gas chromatography (GC), using
2.5 µl injections of a distillate containing the internal
standard (993 mg ml−1 4-methyl-2-pentanol in 14%
v/v ethanol). Gas chromatography was performed on a
Hewlett-Packard 5890 Series II chromatograph with a
split/splitless injector and an FID detector, furnished
with a CP-WAX fused silica capillary column (50 m ×
0.25 mm, 0.25 µm film thickness) and interfaced to
an HPCHEM 3365 data station. Chromatographic
conditions were as follows: initial temperature,
50 ◦ C for 15 min; program rate, 4 ◦ C min−1 ; final
temperature, 190 ◦ C; injector temperature, 270 ◦ C and
detector temperature, 300 ◦ C. Helium was used as the
carrier, and a column head pressure of 15 psi and a
flow split ratio of 1:70 were also employed.
Reagents from Sigma-Aldrich and Merck were
employed to prepare the standard dissolutions of
volatile compounds. Thus, identifications were confirmed for components by comparison of retention
indices of pure compounds analyzed under identical conditions, and quantification was based on the
response factors calculated from standard solutions
that were subjected to the same process as the samples.
All experiments were carried out in triplicate, then
all results reported herein are the average of all three
independent experiments; the error bars represent
standard deviations.
RESULTS AND DISCUSSION
Figure 1 shows the nitrogen concentration (mM) from
free amino acids, urea and ammonium ions of the
three substrates and the resulting vinegars obtained in
this study. The wines contained the largest amounts
of total assimilable nitrogen. However, except for Lproline, the profile of the compounds that supplied
assimilable nitrogen for the acetic acid bacteria was
similar for all the cases.
The principal amino acids in terms of abundance
were L-proline, except in cider, and L-leucine. The
present results are consistent with those obtained by
Polo et al 18 in a study on the free amino acid and
nitrogen contents in Spanish vinegars; they found that
the total nitrogen contents of wine vinegars exceeded
those of cider vinegars and the former contained a
high concentration of L-proline that could be used to
assess possible adulteration. Erbe and Brückner16 also
reported that vinegars manufactured from grape must
contained L-proline as the major amino acid.
Figure 1 shows the availability of the different nitrogen sources and provides an estimate of the nitrogen
consumed by acetic acid bacteria in each case. As with
the wine yeasts used in alcoholic fermentation30,31 and
the biological aging of fino wines,10 where they tend
to consume specific amino acids, acetic acid bacteria
605
E Valero et al
also appear to use specific amino acids to a greater
extent than others. Thus, yeasts use L-arginine, Lglutamic acid, L-glutamine, L-aspartate, L-asparagine,
L-threonine and L-serine during the alcoholic fermentation of grape must.32 Acetic acid bacteria exhibited a
parallel between the availability and total consumption
of the following amino acids: L-aspartic acid, Lmethionine, L-glycine, L-valine, L-leucine, L-alanine,
L-glutamic acid and L-arginine. This was not the case
with other amino acids such as L-lysine, L-histidine, Lcysteine, L-threonine and L-proline; the uptake of the
latter was substantial in absolute terms, but amounted
to only 50% of the initial content.
Based on the results, the most important amino acid
in terms of nitrogen supply and uptake was L-leucine,
which must thus be the principal source of nitrogen
for acetic acid bacteria. The proportion of this amino
acid used by the bacteria was 100% of that available
in the three types of vinegar; also, the amino acid
supplied 56, 30 and 44% of the total nitrogen used by
the bacteria in the production of vinegar from cider,
white wine and red wine, respectively. L-Leucine and
L-proline in combination supplied 50, 53 and 74%,
respectively, of the total amount of nitrogen used by
the cider, white wine and red wine, respectively. It
should be noted that the cider produced L-proline
during its fermentation.
The typical amino acid uptake during the fermentation of must to wine11 suggests that L-leucine is not a
preferential target for wine yeasts; in fact, it can even be
released by these during fermentation, which accounts
for the high concentration of this amino acid relative to
others found in the substrates of acetic fermentation.
Also, the use of this amino acid by acetic acid bacteria
testifies to the complementariness between both types
of microorganisms in the biological oxidation process
of the initial carbohydrates to the final acids.
Based on the total assimilable nitrogen contents,
acetic acid bacteria in the three types of vinegar use
nearly 50% of this element; nitrogen is thus no limiting
factor for the acetic fermentation in the present study,
and this is especially apparent if one takes into account
that some amino acids, while assimilable by the
bacteria, were not fully used.
Of special interest as regards nitrogen sources for
the fermentation process was the presence of little urea
in the medium; even in those cases where the results
were significant with provision for any potential errors,
the concentration of this compound decreased during
acetification. Urea and ethanol are known to be the
main sources of ethyl carbamate,7,33,34 a carcinogenic
compound.35 It is therefore important to control the
formation of urea among the fermentation products of
ethanol-containing media.8,36
The quality of a vinegar is determined by the raw
materials and acetification process employed in its
production; vinegar quality is especially related to its
chemical composition. Thus vinegar flavor depends on
the constituents formed during the fermentation of the
substrate and during the stock or the aging. Vinegars
produced from different substrates and different acetification methods have been characterized according
to some aroma compounds and organic acids.19,25,37
Morales et al 24 studied the changes in chemical composition occurring during the acetification of sherry
wine by submerged culture and observed significant differences for ethanol, acetic and lactic acids
and some volatile compounds (methanol, 1-propanol,
2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl1-butanol, acetoin, acetaldehyde, ethyl acetate and
ethyl lactate). In the present study, the concentrations in some volatile compounds and the differences
in their concentrations between the vinegars and the
substrates from which they were obtained are shown
in Figs 2 and 3, respectively. All the compounds
studied evolved similarly. As expected, acetoin was
produced in the acetification of the three types of
substrate,24,38 but particularly in the cider vinegar,
Acetoin
Isoamyl alcohols
Isobutanol
Propanol
1,1-diethoxyethane
Ethyl acetate
Acetaldehyde
-200
-150
-100
-50
0
50
100
150
Differences in concentrations (mg l-1)
Figure 3. Differences in concentrations (mg l−1 ) of acetoin, isoamyl alcohols, isobutanol, propanol, 1,1-diethoxyethane, ethyl acetate and
acetaldehyde upon acetification between the vinegars and the substrates (bold column, red wine; single grid line column, white wine; double grid
line column, cider).
606
J Sci Food Agric 85:603–608 (2005)
Free amino acids and volatile compounds in vinegars
where it was found in amounts doubling those in
the wine vinegars. These latter additionally produced
1,1-diethoxyethane, which was present at higher concentrations in the vinegar from red wine. Palacios et al 3
reported that acetoin concentration also increases significantly during the biological and physicochemical
phases of sherry vinegar aging. All other compounds
examined (higher alcohols, ethyl acetate and acetaldehyde) were fully or partially consumed in the three
cases, which is in accordance with Morales et al.24
Higher alcohols decreased also during the aging process of sherry vinegar,3 in contrast to ethyl acetate
and acetaldehyde that generally increase during sherry
vinegar aging.3,4
ACKNOWLEDGEMENTS
The authors wish to acknowledge funding of this
research (AGL2002-01712) by the Spanish Ministry
of Science and Technology and would also like to
thank Vinagres y Salsas, SA (Córdoba, Spain) for
their invaluable help and information.
REFERENCES
1 Carnacini A and Gerbi V, L’aceto di vino, un prodotto da
tutelare e da valorizzare. Indust Bevande 21:465–477 (1992).
2 Tesfaye W, Morales ML, Garcı́a-Parrilla MC and Troncoso AM, Wine vinegar: technology, authenticity and quality
evaluation. Trends Food Sci Technol 13:12–21 (2002).
3 Palacios V, Valcárcel M, Caro I and Pérez L, Chemical and
biochemical transformations during the industrial process
of sherry vinegar aging. J Agric Food Chem 50:4221–4225
(2002).
4 Morales ML, Tesfaye W, Garcı́a-Parrilla MC, Casas JA and
Troncoso A, Evolution of the aroma profile of sherry wine
vinegars during an experimental aging in wood. J Agric Food
Chem 50:3173–3178 (2002).
5 Caro I, Palacios VM and Perez L, Kinetic models for the acetic
acid fermentation. Rec Res Dev Biotechnol Bioeng 1:203–211
(1998).
6 Ciani M, Wine vinegar production using base wines made with
different yeast species. J Sci Food Agric 78:290–294 (1998).
7 Ough CS, Influence of nitrogen compounds in grapes on
ethyl carbamate formation in wines. In Proceedings of the
International Symposium on Nitrogen in Grapes and Wines, Ed
by Rantz J, Seattle, WA, pp 165–171 (1991).
8 Monteiro FF and Bisson LF, Nitrogen supplementation of
grape juice. I. Effect on amino acid utilization during
fermentation. Am J Enol Vitic 43:1–10 (1992).
9 Monteiro FF and Bisson LF, Nitrogen supplementation of
grape juice. II. Effect on amino acid and urea release following
fermentation. Am J Enol Vitic 43:11–17 (1992).
10 Mauricio JC and Ortega JM, Nitrogen compounds in wine
during its biological aging by two flor film yeasts: An approach
to accelerated biological aging of dry Sherry-type wines.
Biotechnol Bioeng 53:159–167 (1997).
11 Valero E, Millán C, Ortega JM and Mauricio JC, Concentration
of amino acids in wine after the end of fermentation by
Saccharomyces cerevisiae strains. J Sci Food Agric 83:830–835
(2003).
12 Bely M, Sablayrolles JM and Barre P, Automatic detection of
assimilable nitrogen deficiencies during alcoholic fermentation in oenological conditions. J Ferment Bioeng 70:246–252
(1990).
13 Monteiro FF and Bisson LF, Biological assay of nitrogen content of grape juice and prediction of sluggish fermentations.
Am J Enol Vitic 42:47–57 (1991).
J Sci Food Agric 85:603–608 (2005)
14 Ayestarán BM, Ancı́n MC, Garcı́a AM, González A and Garrido JJ, Influence of prefermentation clarification on nitrogenous contents of musts and wines. J Agric Food Chem
43:476–482 (1995).
15 Kutlán D and Molnár-Perl I, New aspects of the simultaneous
analysis of amino acids and amines as their o-phthaldialdehyde
derivatives by high-performance liquid chromatography.
Analysis of wine, beer and vinegar. J Chromatogr A
987:311–322 (2003).
16 Erbe T and Brückner H, Chiral amino acid analysis of vinegars
using gas chromatography-selected ion monitoring mass
spectrometry. Z Lebensm Unters Forsch A 207:400–409 (1998).
17 Erbe T and Brückner H, Studies on the optical isomerization of
dietary amino acids in vinegar and aqueous acetic acid. Eur
Food Res Technol 211:6–12 (2000).
18 Polo MC, Suárez MA and Llaguno C, Aportación al estudio de
los vinagres españoles. I. Contenido en aminoácidos libres
y nitrógeno total. Rev Agroquı́m Tecnol Alim 16:257–263
(1976).
19 Natera R, Castro R, Garcı́a-Moreno MV, Hernández MJ and
Garcı́a-Barroso C, Chemometric studies of vinegars from
different raw materials and processes of production. J Agric
Food Chem 51:3345–3351 (2003).
20 Anklam E, Lipp M, Radovic B, Chiavaro E and Palla G, Characterisation of Italian vinegar by pyrolysis-mass spectrometry and a sensor device (‘electronic nose’). Food Chem
61:243–248 (1998).
21 Charles M, Martin B, Ginies C, Etievant P, Coste G and
Guichard E, Potent aroma compounds of two red wine
vinegars. J Agric Food Chem 48:70–77 (2000).
22 Del Signore A, Chemometric analysis and volatile compounds
of traditional balsamic vinegars from Modena. J Food Eng
50:77–90 (2001).
23 Giordano L, Calabrese R, Davoli E and Rotilio D, Quantitative
analysis of 2-furfural and 5-methylfurfural in different Italian
vinegars by headspace solid-phase microextraction coupled
to gas chromatography-mass spectrometry using isotope
dilution. J Chromatogr A 1017:141–149 (2003).
24 Morales ML, Tesfaye W, Garcı́a-Parrilla MC, Casas JA and
Troncoso AM, Sherry wine vinegar: physicochemical changes
during the acetification process. J Sci Food Agric 81:611–619
(2001).
25 Morales ML, González GA, Casas JA and Troncoso A, Multivariate analysis of commercial and laboratory produced sherry
wine vinegars: influence of acetification and aging. Eur Food
Res Technol 212:676–682 (2001).
26 Troncoso AM and Guzmán M, Volatile components in Andalusian vinegars. Z Lebensm Unters Forsch 185:130–133 (1987).
27 Garcı́a-Parrilla MC, Heredia FJ and Troncoso AM, Sherry wine
vinegars: phenolic composition changes during aging. Food
Res Int 32:433–440 (1999).
28 Blanch GP, Tabera J, Sanz J, Herraiz M and Reglero G, Volatile
composition of vinegars. Simultaneous distillation-extraction
and gas chromatographic-mass spectrometric analysis. J Agric
Food Chem 40:1046–1049 (1992).
29 Botella MA, Pérez-Rodrı́guez L, Domecq B and Valpuesta V,
Amino acid content of fino and oloroso Sherry wines. Am J
Enol Vitic 41:12–15 (1990).
30 Jiranek V, Langridge P and Henschke PA, Amino acid and
ammonium utilization by Saccharomyces cerevisiae wine yeasts
from a chemically defined medium. Am J Enol Vitic 46:75–83
(1995).
31 Ough CS, Huang Z, An D and Stevens D, Amino acid uptake by
four commercial yeasts at two different temperatures of growth
and fermentation: Effects on urea excretion and reabsorption.
Am J Enol Vitic 42:26–40 (1991).
32 Feuillat M, Charpentier C and Mauhean A, Los compuestos
nitrogenados, in Enologı́a: Fundamentos Cientı́ficos y Tecnológicos, Ed by Flanzy C. AMV Ediciones, Mundi-Prensa,
Madrid, pp 97–113 (2000).
33 Ough CS, Crowell EA and Mooney LA, Formation of ethyl
carbamate precursors during grape juice (chardonnay)
607
E Valero et al
fermentation. I. Addition of amino acid, urea and ammonia:
effects of fortification on intracellular and extracellular
precursors. Am J Enol Vitic 39:243–249 (1988).
34 Monteiro FF, Trousdale EK and Bisson LF, Ethyl carbamate
formation in wine: use of radioactively labeled precursors to
demonstrate the involvement of urea. Am J Enol Vitic 40:1–8
(1989).
35 Inai K, Arihiro K, Takeshita Y, Yonehara S, Tachiyama Y,
Khatum N and Nishisaka T, Quantitative risk assessment of
carcinogenicity of urethane (ethyl carbamate) on the basis
of long-term oral administration to B6C3F1 mice. Japan J
Cancer Res 82:380–385 (1991).
608
36 Mauricio JC, Millán MC, Moreno J and Ortega JM, Changes
in the urea concentration during controlled wine aging
by two flor veil-forming yeasts. Biotechnol Lett 17:401–406
(1995).
37 Benito MJ, Cruz M, Sánchez MS, Sarabia LA and Iñiguez M,
Typification of vinegars from Jerez and Rioja using classical
chemometrics techniques and neural network methods.
Analyst 124:547–552 (1999).
38 Llaguno C and Polo MC, El Vinagre de Vino. CSIC, Madrid
(1991).
J Sci Food Agric 85:603–608 (2005)