The Effect of Time and Storage Conditions on the Phenolic Composition and Colour of White Wine

Food Research International 39 (2006) 220–229 www.elsevier.com/locate/foodres

The eﬀect of time and storage conditions on the phenolic composition and colour of white wine

A´ ngeles F. Recamales a, Ana Sayago a, M. Lourdes Gonza´lez-Miret b, Dolores Hernanz a,*

a Department of Analytical Chemistry, Faculty of Experimental Science, University of Huelva, Spain b Laboratory of Food Colour and Quality, Department of Nutrition and Food Science, Faculty of Pharmacy, University of Seville, Spain

Received 22 July 2005; accepted 24 July 2005

Abstract

The influence of different storage conditions on the colour and phenolic composition of young white wine was evaluated along 12 months of storage. The wine was bottled, and stored using three different conditions: position of bottles illumination and temperature variations. The results indicate that the time of storage has a significant effect (p < 0.001) on colour parameters, the majority of the phenols studied and the total phenol content. A significant decrease of phenols is detected during storage, which result in a change in the colour of the wine from pale yellow to yellow-brown. However, it can be noted that their loss was significantly higher in the wine subjected to variable temperature than in the wine stored at a constant temperature after 12 months. The principal component analysis was applied to the wine analysis data measured throughout the storage time, and the scatter plot of the samples was obtained for visual inspection. The effect of the storage time was clearly reflected in this analysis. A good differentiation among wines according to the length of storage was also obtained using linear discriminant analysis. 2005 Elsevier Ltd. All rights reserved.

Keywords: White wine; Storage; Colour; Phenolic composition

1. Introduction Neira, Hernańdez, Garcıá-Vallejo, Estrella, & Suarez, 2000). Phenolic compounds are important components of Wine is subjected to continuous changes in composi- wine. They not only contribute to their sensory charac- tion during storage. Many studies have been performed teristics of wine, such as colour, flavor and astringency in order to describe the chemical changes during bottle (Lee & Jaworsky, 1987), but may also act as antioxi- aging and their influence on the sensory perception of dants, with mechanisms involving both free-radical sca- red wine. During storage and aging of red wine, polyphe- vening and metal chelation (Benı´tez, Castro, Sańchez nolic compounds are gradually modified. Reactions Pazo, & Barroso, 2002). among anthocyanins, flavan-3-ol, proanthocyanidins The composition and concentration of phenolic in and other compounds, such as glyoxylic acid, piruvic acid, wine depend on the type of grape used for vinification, and acethaldehyde, and also between flavonols them- the procedures employed for wine-making and the chem- selves have been observed. These reactions are responsible ical reactions that occur during the aging of wine (Penã- for the appearance of new pigments (Bakker & Timber- lake, 1997; Dallas, Ricardo da Silva, & Laureano, 1996; * Corresponding author. Tel.: +34 959 219960; fax: +34 959 219942. Revilla, Pe´rez-Magarinõ, Gońzalez-San Jose´, & Beltrań, E-mail address: [email protected] (D. Hernanz). 1999), and hence for the disappearance of oligomer

0963-9969/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2005.07.009 A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229 221 proanthocyanidin from solution. These processes affect wine from Albillo grape variety during the years of stor- colour and colloidal stability (Saucier, Bourgeois, Chris- age (Pe´rez-Magarinõ & Gonza´lez-San Jose´, 2001). tiane, Roux, & Glories, 1997) and also the nutraceutical The purpose of this study was to evaluate the influ- properties (Chen & Ho, 1997; Kroon & Williamson, ence of different storage conditions (temperature, illumi- 1999). nation, position of bottles) on the colour properties and The rate of the progressive decline in anthocyan and the phenolic content of white wine during 12 months. the formation of new stable colour pigments is influ- Statistical techniques, such as analysis of variance, prin- enced by such factors as temperature, pH, sulphites cipal component analysis and linear discriminant analy- and oxygen content. The most rapid changes in the sis were used to distinguish among wines with different colour characteristics of red wine occur during the first lengths of storage. year of storage (Somers & Evans, 1986). During this time, temperature has a more important influence than oxygen concentration. Length of storage is the other 2. Material and methods factor influencing wine colour since most of the changes occurring during wine storage are time-dependent 2.1. Samples (Dallas & Laureano, 1994). In white wine, one of the main problems posed is its A total of 98 samples of bottled wine were analysed. unstable colour after bottling. Essentially, browning re- This wine was elaborated with the white grape variety sults from the oxidation of phenols to quinones, which ‘‘Zalema’’ which is exclusively grown in ‘‘Condado de in turn polymerise to form macromolecules with a typi- Huelva’’, a restricted wine-producing zone with CBO- cal yellow-brown hue (Singleton, 1987). In particular, wines, situated in the southwest of Spain. The wines are oxidative browning of white wines was shown to be produced according to traditional methods with fermen- especially related to flavanol content (Cheynier, Rigaud, tation to controlled temperatures. Due to the climatic Souquet, Barille´re, & Moutounet, 1989; Simpson, 1982). conditions of the zone (a sunny region with warm temper- Browning usually starts at the early stages of wine- atures and low rain fall), an early grape harvest was making by enzymatic reactions (Cheynier, Rigaud, performed. Souquet, Barille´re, & Moutounet, 1990), where After cold stabilization the wine was bottled in green hydroxycinnamic acid esters play a crucial role (Singlen- glass bottles of a capacity with 750 mL and stored in two ton, Timberlake, & Lea, 1978). Caffeoyltartaric acid and different conditions: (i) one set of bottles was stored in a p-coumaroyl tartaric acid were both shown to be partly open warehouse in which the bottles were sub- onverted to caffeoyltartaric acid o-quinone which then jected to temperature variations (both daily and sea- underwent further reduction and addition reactions sonal), this process is referred to as ‘‘variable’’; (ii) the involving other phenolic or non-phenolic compounds other set of bottles was stored in a cellar where the tem- (Cheynier et al., 1989, 1990; Gunata, Sapis, & Moutou- perature varied between 15 and 20 C throughout the net, 1987; Singlenton et al., 1978). year, this process is referred to as ‘‘constant’’. After fermentation, polyphenoloxidase activity de- In each set, half of the bottles were placed in a hori- creases and oxidative browning is related to polyphenol zontal position and other half in a vertical position. chemical oxidation (Singleton, 1987). Flavonols were Within each subset half of the bottles were left in the shown to play an important role in this regard (Cheynier dark and the other half in conditions of variable light. et al., 1989; Simpson, 1982) and catechin autoxidation The wine was stored for 12 months. was shown to generate the same products as enzymatic Samples (two bottles of each set) were taken at the oxidation (Oszmianski, Cheynier, & Moutounet, 1996). time of bottling, and then the same process was repeated Recent studies demonstrated a new oxidate process, con- every 2 months. verting flavonols into yellow xanthylium pigments, potentially contributing to white wine browning (Es-Safi, Guerneve´, Fulcrand, Cheynier, & Moutounet, 2000), 3. Methods which is generally expressed in an increase of absorption in the 400–500 nm (Martinez & Whitaker, 1995). 3.1. Chemical analyses However, there is little reported about the evolution of the phenolic compounds and colour during storage, Chemical parameters with enological meaning were or the effects of different conditions during the wine measured according to the methods of analysis of the white storage. Zafrilla et al. (2003) studied the change Office International de la Vigne et du Vin: ethanol, total of the phenolic composition and antioxidant activity in sulphur dioxide, total acidity, pH, volatile acidity, total ecological and conventional white wines during the first sugars, total polyphenols (AOAC Official MethodsSM, 7 months of storage in the dark. Other authors have 2003). Analyses of all the samples were made in considered the changes in some components of white duplicate. 222 A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229

3.2. Analysis of phenolic compounds field observer and standard illuminant D65, which corre- sponds to natural daylight (Wyszecki & Stiles, 1982). All individual polyphenols were analysed by high per- Within the approximately uniform colour space CIE- formance liquid chromatography. An Agilent 1100 series LAB, two colour coordinates, a* and b*, as well as light- (Palo Alto, CA, USA) chromatograph equipped with a ness, L*, are defined. Coordinate a* takes positive values diode-array detector was used. A gradient of solvent A for reddish colours and negative values for the greenish (water–acetic acid, 98:2, v/v) and solvent B (water–aceto- ones, whereas b* takes positive values for yellowish col- nitrile–acetic acid, 58:40:2, v/v/v) was applied to a re- ours and negative values for the bluish ones. L*isan versed-phase Nova-pack C18 column (30 cm · 3.9 mm approximate measurement of lightness, which is the I.D.) as follows: 0–60 min, 45% B linear; 60–70 min, property according to which each colour can be consid- 45% B isocratic; 70–75 min, 80% B linear; 75–100 min, ered as equivalent to a member of the grey scale, between washing and re-equilibration of the column. The method black and white, taking values within the range 0–100, employed possesses sufficient selectivity and sensitivity to respectively. From the CIELAB space, other parameters allow direct analysis of wines without prior sample prep- are defined, such as chroma ðCabÞ and hue (hab): aration, except filtration before injection (0.45 lm filters). 2 2 1=2 The flow was 1.0 mL/min and the temperature was Cab ¼½ða Þ þðb Þ ; hab ¼ arctanðb =a Þ. set at 20 C. The volume injected was 100 lL. Detec- Chroma ðC Þ is the attribute which allows to determine tion was performed by scanning from 200 to 700 nm. ab for each hue its degree of difference in comparison to a Identification of chromatographic peaks were carried grey colour with the same lightness, so it is considered out by comparing their retention times and spectra the quantitative attribute of colourfullness. Hue (h ) with those of standards. Quantification of phenolic ab is qualitative the attribute according to which colours compounds was carried out by area measurements at have been traditionally defined as reddish, greenish, 280 nm except rutin which was quantified at 320 nm. etc. It is the attribute which allows to distinguish a col- Quantitative assays were achieved using external cali- our with reference to a grey colour with the same light- bration curves for all standard phenols by dissolution ness. This attribute is related to the differences in of the standard solution. All analyses were repeated absorbance at different wavelengths and is considered three times and the results were expressed as mean the qualitative attribute of colour. values. Standards of phenolic compounds were from Merck 3.4. Data analysis (gallic acid, p-hydroxy benzoic acid, ferulic acid), Fluka (tyrosol, caffeic acid, p-coumaric acid, m-coumaric acid, The factors affecting the stability of the bottled wines catechin, protocatechuic acid) and Sigma (rutin). were investigated. The factors varied were storage tem- Phenolic compounds, which are not available in the perature and time, position of the bottled, and illumina- market as standards, have been identified by their retention exposure and the levels were mentioned above. tion time and spectra according to the literature. These Analysis of variance was made using general linear compounds have been assayed by assuming that their model (GLM) to determine whether mean values for molar absorptivity is the same as that of the correspond- phenolic compounds and colour parameters differed ing free standard molecule. with storage time and conditions. The means were com- pared by the least significant difference (LSD) test at a 3.3. Colour measurement significance level of 0.05. Pattern recognition (PR) techniques including principal component analysis (PCA) Colour was assessed by tristimulus colorimetry based and linear discriminant analysis (LDA) were applied on transmittance spectra with the application of the equa- on experimental standardized data to distinguish among tions proposed by the Commission Internationale de wines with different lengths of storage. Statistical analy- lÕEclariage (CIE, 1986). The spectra were registered ses were performed using the statistical package STAT- directly on the wine, using a diode array spectrophotom- ISTICA99 from Statsoft (1999). eter (Unicam 5625 UV/Vis spectrophotometer) set to measure in the visible region (k = 380–770 nm) at constant intervals (Dk = 2 nm) and integrated using the the software CromaLab (Heredia, A´ lvarez, Gonza´lez- 4. Results Miret, & Ramı´rez, 2004), which take into account the CIE recommendations. The uniform colour space CIE The study of the storage of white wine was carried 1976-(L*a*b*) (CIELAB) was used. As is required by out over 12 months. Before the storage two samples the weighted-ordinate method, the visible spectra of the were taken and analysed for chemical parameters with samples were weighted according to the characteristic fac- enological meaning. The mean values obtained in wines tor of the selected visual reference conditions: 10 visual were: pH, 3.06; density, 0.9906 g/cm3; ethanol, 11.1% A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229 223 v/v; reducing sugars, 1.0 g/L; total acidity, 5.2 g tartaric 90˚ acid/L; volatile acidity, 0.23 g acetic acid/L; SO2 total, 12 100˚ 80˚ 142.82 mg/L. 110˚ 70˚ 120˚ 60˚ 10 4.1. Colour changes

For the study of the colour in this work the system 8 CIE 1976-(L*a*b*) (CIELAB) has been selected. The analysis of variance was applied for testing the signifi- b* cance of the effects of storage time and conditions on 6 these variables. The results showed that only the time of storage has a significant influence (p < 0.001) on the 4 studied parameters (Table 1). 0 months 2 months Fig. 1 shows the distribution of the wines grouped 4 months according to the time of storage in the (a*b*) colour 2 6 months 8 months plane, in which the colour points are represented regard- 10 months ing the axes green-red (a*+a*) and blue-yellow 12 months 0 (b*+b*). It can be observed that most of the samples -6 -4 -2 0 2 4 6 are located inside a defined area between the 90 and the a* 120 of hue angle (hab) that belongs to the medium yel- Fig. 1. Colour diagram (a*,b*). low or with a very slight tendency to the green. Also, this grouping is given in a very near area to the origin of coordinates, with low values of chroma ðCabÞ, that is The increases of the chroma ðCabÞ and decreases of with a high proportion of white light transmitted by the hue (hab) are the characteristic changes in wines dur- the samples. These data, besides the high levels of light- ing storage. During the storage, an evolution in the val- ness (L*) near to 100% of quantity of transmitted global ues of the two colour coordinates (a* and b*) are light, determine the final colour in the category of the observed. The value of a* (red component) displays pale yellow. initially a reduction from 0.86 to 1.47, but soon it

Table 1 Inﬂuence of conditions and storage time on colour parameters (CIELAB)a Source of variation L* a* b* Cab hab Storage period (months) 0 99.76c 0.86c 3.38c 3.49c 105.71c 2 98.41c 0.21c 3.32c 3.60c 102.70c 4 98.98c 0.91c 3.17c 3.29c 107.07c 6 99.28c 0.77c 3.61c 3.69c 104.11c 8 101.67d 1.49c 2.45c 2.91c 147.77d 10 99.69c 1.27c 3.40c 3.67c 112.10e 12 102.95d 4.07d 7.77d 8.81d 63.42f b Signiﬁcance *** *** *** *** ***

Temperature Variable 99.79 0.02 4.06 4.37 108.82 Constant 100.54 0.18 3.85 4.29 103.58 Signiﬁcanceb ns ns ns ns ns

Exposition Light 100.27 0.27 3.83 4.18 102.91 Dark 100.05 0.07 4.08 4.48 109.48 Signiﬁcanceb ns ns ns ns ns

Position Horizontal 99.90 0.13 4.06 4.40 100.90 Vertical 100.43 0.07 3.85 4.26 111.49 Significanceb ns ns ns ns ns a Data followed by different letters for each column and source of variation are significantly different by LSD test. b ns, *, **, ***, not significant and significance at p < 0.05, 0.01 and 0.001, respectively. 224 A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229 increases sharply in the last two months of the test to able temperature than those stored at a constant temper- reach value of 4.07. However, the values of b* practi- ature. Ferulic acid, caffeic acid, p-coumaric acid and cally remain constant until the 10th month in which it compound 1 levels also increased with storage time, experiences a sharp increase, reaching the value 7.77. but in these cases the temperature effect is not Therefore, the global result is an increase of the a* significant. and b* values, resulting in a change in the colour of After 12 months of storage, the samples show signif- the wine from pale yellow to yellow-brown. icant losses of phenolic compounds relative to initial values. Caftaric acid, m-coutaric acid and ethyl caffeate are 4.2. Changes in phenolic compounds during storage the compounds that exhibited a lower pronounced concentration reduction (14.67–9.32, 0.58–0.28, 0.69– In the analysis of individual phenolic contents, 17 0.42 mg/L, respectively). Catechin levels also diminish phenols were identified and quantified as follows: with time which is according to other authors. This de- hydroxycinnamic acid (caftaric acid, p-coutaric acid, crease occurred mainly in the last 2 months. Wine that coutaric acid glucoside, fertaric acid, m-coutaric acid, was stored for 10 months has a mean concentration of caffeic acid, ferulic acid, p-coumaric acid, m-coumaric catechin of 1.31 mg/L and after 12 months the catechin acid, ethyl caffeate, ethyl p-coumarate), benzoic acids was not detected. Simpson (1982) has reported that cat- (p-hydroxybenzoic acid, ethyl galate), flavonoids (cate- echins and procyanidins have a strong influence on the chin, rutin), tyrosol, as well as an unknown compound susceptibility of white wines to browning, because fla- (compound 1), this phenol which has an absorption van-3-ols may suffer oxidations and polymerizations. spectra similar to p-hydroxy benzoic acid spectra, so it The profiles of changes in the concentration of cou- was quantified as this acid. taric acid glucosides, as well as p-hydroxybenzoic acid Table 2 shows the mean for the phenolic compound and ethyl gallate were very similar. Their contents pro- contents of the white wine. This table reports the effect gressively decrease, and from the eighth month they in- of different conditions during the storage of the wine crease slightly. With regard to the tartaric ester of the white. It can be seen that the temperature (variable/con- ferulic acid, their concentration decreases, and from stant) has a significant influence on the total phenols the sixth month increases, this increase being slightly content (expressed as mg/l gallic acid) and the light higher for samples stored at a constant temperature than exposure on the tyrosol and caftaric acid concentration, at a variable temperature (32% and 7%, respectively). at the 5% significance level. The factor of position (hor- While m-coumaric acid and ethyl p-coumarate levels izontal/vertical) of the bottles has no effect on any of the also diminish until the sixth month and after practically compounds studied, as can be observed in Table 2. do not change. The decrease encountered for coutaric With regard to the evolution of the total phenols, a acid glucosides content (1.44–0.47 mg/L) may be due significant decrease is detected during storage, as has to the hydrolysis in the acidic wine medium, while oxida- been shown in earlier work (Benı´tez et al., 2002). This tion processes may have been responsible for the de- decrease occurred mainly in the last 4 months and is re- crease in concentration of hydroxycinnamic derivatives lated to the changes of colour observed in the wine. (Garcıá Parrilla, Heredia, & Troncoso, 1999). However, it can be noted that their loss was significantly Among the flavonols studied only the rutin could be higher in the wine subjected to daily and seasonal tem- detected and quantified in the wines. Their content also perature variations (8.26%) than in the wine stored at diminishes and could not be detected after 6 months of a constant temperature (4.42%) after 12 months. storage. The study of individual behaviour of phenolic compounds indicates that the content of most of the pheno- 4.3. Multivariate analysis lic compounds identified in the wines studied diminishes with time, with the exception of tyrosol, caffeic acid, Another objective of this work was to check the abil- ferulic acid, p-coumaric acid and compound 1. Recent ity of the phenolic compounds and colour variables to experimental evidence indicates that storage conditions differentiate among wines with different lengths of stor- are expected to strongly affect the content of phenols, age. For this reason, several pattern recognition (PR) since they can undergo modifications during storage, techniques including principal component analysis mainly due to hydrolysis, oxidations and complexations (PCA) and linear discriminant analysis (LDA) have (Zafrilla et al., 2003). Other factors such as light and been applied on experimental standardized data. temperature can contribute to the degradation of pheno- Applied to our data set, PCA revealed that the first lic compounds (Cheynier & Fulcrand, 2003). Hydrolysis four principal components explain 70% of total variance (enzymatic or not) is mainly responsible for the increase (Table 3). A plot of the scores of PC1 versus PC2, i.e., of simpler compounds, such as tyrosol and free phenolic the projection of the samples along the directions iden- acids. So, in the same conditions of light, the amount of tified by the first two PCs, is reported in Fig. 2.Itis tyrosol is 1.4 times higher in the wines stored at a vari- apparent that samples are grouped in a similar way to Table 2 Influence of conditions and storage time on phenolic compounds (mg/L)a Source of Total Caftaric Coutaric acid p-Coutaric Tyrosol p-Hydroxybenzoic Catechin m-Coutaric Fertaric acid variation polyphenols acid glucoside acid acid acid Storage period (months) 0 231.05c 14.67c 1.44c 0.76c 22.60c 1.16c 1.42c 0.58c 1.19c 2 220.00c 11.14c 1.59c 1.83d 8.88d 1.25c 1.30c 0.56cd 0.95c 4 244.80d 11.11c 0.56d 1.09d 11.01d 0.72cd 1.52c 0.65d 0.93c 6 234.86d 8.33d 0.44d 0.95e 10.78d 0.31e 1.02c 0.32e 0.64d 8 228.60c 8.33d 0.33d 1.36e 10.40d 0.26e 0.98c 0.36e 0.71d 10 216.41c 8.21d 0.37d 1.04e 11.20d 0.41e 1.31c 0.33e 0.68d A c d d e e cf e cd ´ 12 216.51 9.32 0.47 1.61 13.21 0.79 nd 0.28 0.85 220–229 (2006) 39 International Research Food / al. et Recamales .F. b Significance *** *** ** * * *** *** *** ***

Temperature Variable 220.89 9.29 0.59 1.24 10.86 0.69 1.04 0.44 0.83 Constant 232.84 9.53 0.67 1.39 10.97 0.56 0.99 0.40 0.75 b Signiﬁcance ** ns ns ns ns ns ns ns ns

Exposition Light 226.15 8.76 0.58 1.16 9.72 0.61 1.02 0.39 0.76 Dark 227.58 10.05 0.67 1.46 12.11 0.64 1.02 0.44 0.82 b Signiﬁcance ns * ns ns * ns ns ns ns

Position Horizontal 227.95 9.51 0.61 1.17 11.41 0.66 1.07 0.42 0.80 Vertical 225.78 9.31 0.65 1.45 10.42 0.60 0.97 0.42 0.78 Signiﬁcanceb ns ns ns ns ns ns ns ns ns

Source of Caffeic acid Ethyl Ferulic Compound 1 p-Coumaric m-Coumaric Ethyl Ethyl Rutin variation galate acid acid acid caffeate p-coumarate Storage period (months) 0 0.92c 1.73c 0.54c 199.49c 0.06 0.12c 0.69c 0.13c 0.84c 2 1.85c 1.35c 0.76c 189.12c 0.20 0.53d 0.76d 0.36d 0.82c 4 2.51d 1.17d 1.11d 202.44 c 0.41 0.28d 0.65c 0.28de 0.75d 6 1.52c 0.99d 0.87cd 159.67d 0.30 0.15e 0.53c 0.16ef nd 8 2.19e 1.01d 0.97cd 163.72d 0.37 0.21e 0.56c 0.17f nd 10 2.08e 1.10d 0.91cd 162.20d 0.77 0.20e 0.57c 0.17f nd 12 2.39e 1.22d 2.00e 218.48e 0.20 0.18e 0.42e 0.15f nd b Significance ** *** *** *** ns *** *** *** **

Temperature Variable 2.12 1.15 1.08 182.85 0.47 0.26 0.58 0.22 0.27 Constant 2.06 1.14 1.13 182.36 0.28 0.26 0.59 0.21 0.26 Signiﬁcanceb ns ns ns ns ns ns ns ns ns (continued on next page) 225 226 A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229

Table 3 Variance explained by the ﬁrst PCs

Rutin PC Eigenvalue Explained Cumulative variance (%) variance (%) 1 8.13 35.35 35.35 2 3.96 17.25 52.60 3 2.43 10.59 63.19 4 1.54 6.70 69.90 -coumarate Ethyl p

our classification. Moreover, an interesting feature can be pointed out: such groups are arranged along the direction of PC1, in a way that reflects their storage Ethyl caffeate time, that is, samples that have been a shorter time in bottles have higher scores, and those which have been bottled for a longer time have lower scores on PC1. The loadings, i.e., the coefficients that define the weight of each original variable in the PCs, can then be investigated in order to understand which chemical com- -Coumaric

m acid pounds are responsible for the ranking of samples on the basis of storage time on the first PC. A comparison of scores and loadings for PC1 allows the identification of the compounds having a higher influence on this feature; analytes with highly positive loadings on PC1 should be regarded as compounds whose concentration -Coumaric

p acid decreases with storage time, while analytes with highly negative loadings tend to increase. The most important compounds are esters: caftaric acid, coutaric acid glucoside, m-coutaric acid, ethyl galate and ethyl-p- coumarate, and some acids: p-hidroxybenzoic acid, all with positive loading values on PC1. This assumption is in accordance with the literature. Phenolic compounds Compound 1 are directly related to the browning phenomenon of white wines (Singleton & Essau, 1969) because they can be easily oxidized to quinones and polymers (Cacho, 1997; Sapis, Macheix, & Cordonnier, 1983a; Sapis,

acid Macheix, & Cordonnier, 1983b). The main phenols found in white grape juices and wines are hydroxycinnamic esters which can be both oxidation substrates

< 0.05, 0.01 and 0.001, respectively. Nd: not detected. and browning precursors (Cheynier, Osse, & Rigaud, p 1988; Romeyer, Sapis, & Macheix, 1985). Also the second principal component seems to con- tain information on the difference between the seven groups. Wine from the first sample and from samples with 2, 4 and 6 months in a bottle is situated at the right of the plot with negative values of PC2. The most important variables in this case are b* value and chroma ðCabÞ. In order to observe the contribution of the com- Caffeic acid Ethyl galate Ferulic nsns ns ns nspounds ns ns and colour ns parameters ns studied ns ns to the differenti- ns ns ns ns ns ns ns ation among the wines with different lengths of storage, , not significant and significance at the results are subjected to a discriminant analysis. *** , b b Matrix data are divided into training and evaluation **

, set; the training set was used to build the model, and * the evaluation set to test its performance. The cross Data followed by differentns, letters for each column and source of variation are significantly different by LSD test. a b validation method was used to test the computed Exposition LightDarkSignificance 1.93 2.25 1.09 1.19 1.04 1.16 176.15 189.06 0.43 0.32 0.25 0.26 0.55 0.61 0.22 0.20 0.26 0.26 Source of variation Position HorizontalVerticalSignificance 2.14 2.03 1.16 1.13model. 1.07 1.13 184.46 180.75 0.45 0.30 0.26 0.25 0.57 0.59 0.23 0.20 0.26 0.26 A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229 227

2.5

2.0

1.5

1.0

0.5

0.0 PC 2 (19.78%) -0.5 control 2 months -1.0 4 months 6 months 8 months -1.5 10 months 12 months -2.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 PC 1 (31.27%)

Fig. 2. Scores plot of the samples using the two ﬁrst principal components obtained by PCA.

Table 4 Discriminant power (F-value) of the variables selected and coefficients of discriminant functions Variable F-valuea Standardized coefficients Root 1 Root 2 Root 3 Root 4 Rutin 1480.774 1.192 0.114 0.825 0.032 Coutaric acid glucoside 39.778 0.622 0.537 0.810 0.253 Ferulic acid 10.623 0.159 0.868 0.145 0.699 b* 7.702 0.293 0.279 0.684 0.750 Eigenvalue 461.131 5.918 4.062 0.131 Cum.Prop 0.978 0.991 0.999 1.000 a Significant at p < 0.001.

Fig. 3. Scatterplot of canonical variates. 228 A´ .F. Recamales et al. / Food Research International 39 (2006) 220–229

Forward stepwise method selected rutin, coutaric tion on the phenolic composition and quality of Grenache and acid glucoside, ferulic acid and b* as the variables of Chardonnay wines. American Journal of Enology and Viticulture, highest discriminant capacity (according to FisherÕs 40, 36–42. Cheynier, V., Rigaud, J., Souquet, J. M., Barille´re, J. M., & test). Table 4 lists the discriminant power and stan- Moutounet, M. (1990). Must browning in relation to the behaviour dardized coefficient for the five functions obtained, of phenolic compounds during oxidation. American Journal of which allow to obtain a correct global classification Enology and Viticulture, 41, 346–349. of 100% using the training set and 87.5% using predic- Cheynier, V. F., & Fulcrand, H. (2003). Oxidacioń de los polifenoles tion set. Fig. 3 shows the graphical representation of en los mostos y los vinos. In C. Flanzy (Ed.), Enologıá: Fundamentos Cientı´ficos y Tecnolo´gicos (2nd ed.) 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