The phenolic chemistry and spectrochemistry of red sweet wine-making and oak-aging

Food Chemistry 152 (2014) 522–530

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The phenolic chemistry and spectrochemistry of red sweet wine-making and oak-aging M. Figueiredo-González a, B. Cancho-Grande a, J. Simal-Gándara a,⇑, N. Teixeira b, N. Mateus b, V. De Freitas b a b

Nutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, E-32004 Ourense, Spain ´mica, Departamento de Quı ´mica e Bioquı ´mica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal Centro de Investigação em Quı

a r t i c l e

i n f o

Article history: Received 9 October 2013 Received in revised form 26 November 2013 Accepted 3 December 2013 Available online 9 December 2013 Keywords: Sweet wines Naturally grape dehydration process Fortification with spirits Aging Vitis vinifera L. cv Garnacha Tintorera Phenolic content Proanthocyanidins HPLC

a b s t r a c t A natural sweet wine (NSW) was made with dried grapes from Vitis vinifera L. cv Garnacha Tintorera. A fortified sweet wine (FSW) was also obtained: the maceration-alcoholic fermentation of Garnacha Tintorera must was stopped by addition of ethanol 96% (v/v). UV/Vis spectrophotometry and HPLC/DAD-ESI/ MS were applied to determine, respectively, the evolution of colour and phenolic compounds in Garnacha Tintorera based-sweet wines during aging. In sweet wines, aging decreased a⁄ (red/green), colour saturation and lightness and increased b⁄ (yellow/blue), and hue angle. Most of the phenolic compounds determined, such as anthocyanins, esters of hydroxycinnamic acids, flavan-3-ols monomers, oligomers and polymers decreased in both sweet wines during aging. On the contrary, hydroxybenzoic and hydroxycinnamic acids and vitisins increased after one year of aging. Despite that both terminal and extension subunit compositions show very small changes, mean degree of polymerisation of proanthocyanidins decline slightly as aging progressed in both sweet wines. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Sweet wines are traditionally elaborated in Galicia (the N.W. corner of Spain). The Denomination of Origin (DO) Valdeorras, one of the five DOs in Galicia, wants to promote the production and marketing of new sweet wines. The following red wines were examined in this work. The first one, a naturally sweet wine (NSW) was made with dried grapes Vitis vinifera L. cv Garnacha Tintorera; this cultivar is a teinturier variety which has excellent potential to produce wines from raisined grapes. The second one, a fortified sweet wine (FSW); the maceration-alcoholic fermentation of Garnacha Tintorera must was stopped by addition of ethanol 96% (v/v). Additionally, both sweet wines were subjected to aging process in French oak barrels. The colour changes during wine maturation are usually attributed to anthocyanin polymerisation reactions with other phenolic compounds, such as flavan-3-ol monomers. The formation of these polymeric pigments by direct and/or mediated by acetaldehyde reactions can usually lead to the loss of colouring matter if the polymerised pigments reach high molecular weight (Alañón et al., 2013). The cycloaddition process between anthocyanins and some yeast metabolites such as vinylphenol, pyruvic acid, ⇑ Corresponding author. E-mail address: [email protected] (J. Simal-Gándara). 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.12.018

acetaldehyde leading to more stable pigments, structurally allied to pyranoanthocyanins, is described as other type of reactions established in wines (Atanasova, Fulcrand, Cheynier, & Moutounet, 2002). The formation of these pigments remains in solution and therefore they hardly are lost in the precipitates of colouring matter. Recently, it has been detected the formation of hydroxyphenylpyranoanthocyanins such as pinotin A in wines during the aging process (Rentzsch, Schwarz, Winterhalter, & Hermosín-Gutiérrez, 2007). Instead, Oliveira, De Freitas, Silva, and Mateus (2007) detected a new class of blue anthocyanin-derived pigments isolated from Port wines, namely portisins (formed from anthocyanins– pyruvic acid adducts and vinyl phenols) and a new family of turquoise blue anthocyanin-derived pigments (Oliveira et al., 2010). The physical and chemical characteristics of wood are also important quality factors in the wine aging process, since they affect the wood-wine interaction phenomena, such as oxygen-diffusion, compound extraction from wood, and oxidation processes in wines (Hernández, Estrella, Dueñas, De Simón, & Cadahía, 2007). Although the quality of sweet wine is determined essentially by aroma compounds, colour and phenolic compounds are also significant sensory attribute of wines. The preservation of the optimal chromatic characteristics during the aging process is the main problem of this type of dessert wine, more than the maintenance of aromatic compounds. Therefore, evolution of colour and phenolic compounds during aging process was established in Pedro

M. Figueiredo-González et al. / Food Chemistry 152 (2014) 522–530

Ximénez wines (Chaves, Zea, Moyano, & Medina, 2007; López de Lerma, Peinado, Moreno, & Peinado, 2010; Serratosa, LopezToledano, Medina, & Merida, 2011); in Sherry wines (Fabios, Lopez-Toledano, Mayen, Merida, & Medina, 2000; García-Moreno & García-Barroso, 2002; García-Parrilla, Heredia, and Troncoso, 1999; Ortega, Mayen, Merida, & Medina, 2008; Schwarz, Rodríguez, Guillén, & Barroso, 2012); and Port wines (Mateus & De Freitas, 2001; Oliveira, De Freitas, Silva, & Mateus, 2007; Oliveira et al., 2010; Romero & Bakker, 1999). In order to obtain a good-quality sweet wine, the aim of this work was to evaluate the colour and phenolic composition from different Garnacha Tintorera-red sweet wines during the aging process. By this way, with the understanding of the evolution of colour-responsible phenolic pigments during aging in red sweet wines obtained under different practices, it could be possible to optimise the best conditions to obtain a sweet aged wine based on their colour and taste balance. In addition, this research may also contribute to the listing of technical support information for the others Geographic indications of origin of sweet wines, since it is the first detailed study on Garnacha Tintorera based-sweet wines during the aging process.

2. Materials and methods 2.1. Sweet wines Red grapes of Vitis vinifera L. cv Garnacha Tintorera were harvested in Valdeorras (Ourense, N.W. Spain). Two vinification experiments were performed at the experimental cellar belonging to DO Valdeorras Regulatory Council: (a). Garnacha fortified sweet wine (NSW) This wine is a naturally sweet wine made with Garnacha Tintorera grapes harvested and dehydrated in 2011 such as follows. Red grapes were harvested at optimum ripening stage, and were left in plastic boxes for 3 months to carry out the drying process in order to concentrate sugars under natural conditions of temperature and relative humidity. Bunches of grapes were placed in a single layer in each box and checked weekly, removing the spoiled grapes manually for the purpose of getting the best conditions of raisining. In December, at first, the grapes were crushed in the traditional manner. Then the pressing of the resulting paste was completed using a hydraulic press of 25 kg and the must was placed in a metallic fermentation vessel (25 L). After 24 h, Saccharomyces cerevisiae Fermol Super 16 (AEB Group) yeasts were inoculated. One week later, the alcoholic fermentation began and it lasted one month at room temperature (around 18–20 °C). At the end of the fermentation, the wine was subjected to aging process during one year in French oak barrels (b). Garnacha fortified sweet wine (FSW) This wine is a fortified sweet wine made with Garnacha Tintorera grapes harvested at 2011 such as follows. Red grapes were crushed again in the traditional manner and placed in a metallic fermentation vessel (25 L) to which was added SO2 at a 40 mg L1concentration. After 24 h, S. cerevisiae commercial yeasts were inoculated. When it reached an alcohol content of 7.5° of alcohol, the maceration-alcoholic fermentation was stopped by addition of ethanol 96% (v/v). Afterwards this wine was subjected to aging process during one year in French oak barrels.

2.2. Characterisation of the colour fraction Colour measurements were taken after centrifugation of the wines for 15 min at 3000 rpm and using quartz cells of 1 mm path length.

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2.2.1. Colorimetric indexes Absorbances at 420, 520, 620 nm were measured to assess the wine colour by chromatic parameters such as % red, % yellow and % blue, colour intensity (CI), tonality (T), according to Glories (1984). 2.2.2. CIELAB space The wine colour was also assessed by the CIELAB space (OIV, 2000). CIELab colour parameters were determined by measuring the transmittance of the must every 10 nm over the visible spectrum (from 380 to 770 nm), using the illuminate D65 (daylight source) and 10° standard observer (perception of a human observer). The parameters that define the CIELab space are: rectangular coordinates such as red/green colour component (a⁄), yellow/blue colour component (b⁄) and lightness (L⁄); and the cylindrical coordinates such as chroma (Cab⁄) and hue angle (hab). 2.3. Characterisation of the phenolic content 2.3.1. Analytical standards, reagents and materials Malvidin-3-O-glucoside chloride, catechin, epicatechin, resveratrol, and gallic, 3,5-dihydroxybenzoic, protocatechuic, vanillic, syringic, p-coumaric and caffeic acids were purchased from Sigma Aldrich (St. Louis, MO, USA). B1, B2, B4, B6, C1, B3, B5, B7, B8, and B2-gallate were previously isolated in the laboratory. Individual stock solutions of each compound were prepared in methanol. Different working standards solutions were prepared by appropriate dilution in 12% (v/v) ethanol in water and then stored in dark vials at 80 °C. Solvents (water, methanol, acetone and ethyl acetate) of HPLC grade and other inorganic reagents (formic, hydrochloric, acetic, trifluoroacetic and ascorbic acids, phloroglucinol, sodium acetate anhidro, sodium hydroxide and sodium bisulphite) were purchased from Sigma Aldrich. The sorbent material used for SPE was: Oasis MCX cartridges (500 mg, 6 mL size) from Waters Corp (Milford, MA, USA); StrataX-A 33u Polymeric Strong Anion sorbent (60 mg, 3 mL size) and Strata C18-E (2 g, 12 mL size) from Phenomenex (Torrance, CA, USA) and gel TSK Toyopearl HW-40(S) (250  25 mm) from Tosoh, Japan. 2.3.2. Extraction procedures Extraction of these groups of polyphenols was performed according to procedures described by Figueiredo-González, Regueiro, Cancho-Grande, and Simal-Gándara (2014). 2.3.2.1. No flavonoids. Ethanol of wine samples were previously evaporated under a stream of nitrogen and reconstituted with water. 3 mL of the reconstituted wine (adjusted to pH 7 with sodium hydroxide) was loaded into a MCX cartridge previously activated with 5 mL of methanol followed by 5 mL of water. The sorbent was washed with 5 mL 0.1 M hydrochloric acid followed by 5 mL of water. The no flavonoid fractions were eluted with 15 mL of methanol. The eluate was evaporated down (35 °C, 10 psi) and and then reconstituted in 12% (v/v) EtOH. The ethanolic extract was passed through a filter of 0.45 lm pore size prior to HPLC/DAD-ESI/MS analysis. 2.3.2.2. Anthocyanins. Ethanol of wine samples were previously evaporated under a stream of nitrogen and reconstituted with water. 2 mL of the reconstituted wine was loaded into a Strata C18 cartridge, previously activated with 10 mL of methanol followed by 10 mL of water. The sorbent was dried by blowing N2 for 30 min. After washing with of 20 mL of ethyl acetate, the anthocyanin fraction was eluted with 30 mL of 0.1% (v/v) trifluoroacetic acid in methanol. The eluate was evaporated down (35 °C, 10 psi)

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and then reconstituted in 12% (v/v) EtOH. The ethanolic extract was passed through a filter of 0.45 lm pore size prior to HPLC/DAD-ESI/MS analysis. 2.3.2.3. Flavan-3-ol monomers, oligomers and polymers. Flavan-3-ol monomers (catechin, epicatechin and gallocatechin) were extracted following the procedure a. However analysis of polymers is particularly complex, due to the great structural diversity resulting from the number of hydroxyl groups, their position on the aromatic nuclei, the stereochemistry of asymmetrical carbons in the pyran cycle, as well as the number and type of bonds between the basic units. The polymeric composition is based in a previous extraction also by the procedure a followed by a lysis of the polymer by breaking the interflavane bond in a mild acid medium leading to a reaction with phloroglucinol (procedure b). In particular, flavan-3-ols oligomeric were extracted by the procedure c. a. Flavan-3-ol monomers extraction 2 mL of wine was adjusted to pH 1.0 with a drop of concentrated hydrochloric acid, transferred to a 5 mL test tube containing 800 mg sodium bisulphite and stirred for 20 min. This bleached wine was diluted 1:1 with ultrapure water and 2 mL were loaded into a mixed-mode anion exchange/reversed phase SPE cartridge Strata-X-A, previously activated with 2 mL 75% (v/v) acetone in water followed by 4 mL water. After washing with 4 mL water, flavan-3-ols monomers and polymers were eluted with 8 mL 75% (v/v) acetone in water, whereas anthocyanins and organic acids were still retained through anion exchange interactions. This eluate was evaporated down (35 °C, 10 psi) and then reconstituted in 200 lL methanol. In order to quantify monomeric flavan-3-ols, 50 lL of this methanolic extract were filled up to 500 lL with 2.5% (v/v) acetic acid in water, filtered by 0.20 lm and analysed by HPLC/DAD-ESI/MS. b. Acid-catalysed degradation in presence of phloroglucinol A solution containing 0.2 M hydrochloridric acid, 50 mg mL1 phloroglucinol and 10 mg mL1 L-ascorbic acid was prepared in methanol as phloroglucinolysis reagent. 100 lL methanolic wine extract were allowed to react with 200 lL phloroglucinol solution in a water bath for 40 min at 50 °C. Afterwards, the reaction was cooled down and quenched by the addition of 2.7 mL of 15 mM sodium acetate aqueous solution. The reaction mixture was then purified by SPE using a Strata-X-A cartridge SPE previously conditioned with 2 mL 75% (v/v) acetone in water followed by 4 mL water. The cartridge was washed with 4 mL water and the phloroglucinolysis products were eluted with 8 mL 75% (v/v) acetone in water. This eluate was evaporated to dryness on a rotary evaporator at 35 °C, reconstituted in 500 lL 2.5% (v/v) acetic acid in water, filtered by 0.20 lm and analysed by HPLC/DAD-ESI/MS. c. Flavan-3-ol oligomers 20 mL of wine were extracted with ethyl acetate (20 mL). The aqueous phase was eliminated. The organic phase containing the oligomeric flavan-3-ols was recovered. This extraction was repeated three times. All the organic extracts were collected, evaporated to dryness on a rotary evaporator (35 °C, 10 psi) and reconstituted in MeOH (2 mL). The extract was loaded into a gel TSK Toyopearl HW-40 (S) column (250  25 mm) at 0.8 mL min1 using MeOH as the eluant during 2.5 h to obtain fraction A and then over another 2.5 h, to obtain fraction B containing oligomeric flavan-3-ols. The eluate was evaporated down (35 °C, under vacuum) and then reconstituted in 12% (v/v) EtOH. The ethanolic extract was passed through a filter of 0.45 lm pore size prior to HPLC/UV–Vis analysis. 2.3.3. HPLC/DAD-ESI/MS analysis Polyphenols were identified according to the HPLC/DAD-MS procedures described by Figueiredo-González et al. (2014). HPLC

measurements were made by using a Thermo Separation-Products (TSP):P2000 binary pump equipped with a TSP AS1000 autosampler, a TSP SCM1000 vacuum membrane degasser. An analytical column, Phenomenex C18 Luna (150  3 mm, i.d., 5 lm), with a guard column, Pelliguard LC-18 (50  4.6 mm i.d., 40 lm; Supelco, Bellefonte, PA) was used for separation of anthocyanins, phenolic acids and resveratrol. An analytical column, Phenomenex C18 Luna (150  3 mm, i.d., 3 lm) was used for separation of flavan-3-ol monomers and polymers and two analytical columns Merck Lichrospher reverse phase based on C18 ODS (250  4.6 mm, i.d. 5 lm) were used for separation of oligomeric flavan-3-ols. UV–Vis spectra were scanned from 200 to 600 nm on a diode array detector UV6000LP. For confirmation purposes, the HPLC–DAD system was coupled to a TSQ Quantum Discovery triple-stage quadrupole mass spectrometer from Thermo Fisher Scientific (Waltham, MA). The mass spectrometer was operated in the negative electrospray ionization (ESI) mode under the following specific conditions: spray voltage 4000 V, capillary temperature of 250 °C, sheath gas and auxiliary gas pressure of 30 and 10 units, collision energy 25 eV and tube lens offset 110. The detection was accomplished in the full-scan mode, from m/z 100 to 1700, and in the full-scan MS/MS mode.

2.3.3.1. Phenolic acids and resveratrol. Ethanolic extract (20 lL) was injected into the column and eluted at 35 °C. Mobile phase A and B were 0.2% formic acid aqueous solution and methanol, respectively, and the flow rate was 0.6 mL/min. The following linear gradient was used: 0–5 min, 97% A, and 3% B; 40 min, 70% A, and 30% B; 50–53 min, 50% A, and 50% B; 55–65 min, 5% A, and 95% B; 68–80 min, 97% A, and 3% B. DAD detection wavelength of 280, 320 and 309 nm were selected for hydroxybenzoic acids, hydroxycinnamic acids and resveratrol, respectively.

2.3.3.2. Anthocyanins. Ethanolic extract (20 lL) was injected into the column and eluted at 35 °C. Mobile phase A and B were 5% formic acid aqueous solution and methanol, respectively, and the flow rate was 1 mL/min. The following linear gradient was used: 0–5 min, 90% A, and 10% B; 15 min, 80% A, and 20% B; 30 min, 70% A, and 30% B; 50 min, 60% A, and 40% B; 51–56 min, 5% A, and 95% B; 57–70 min, 90% A, and 10% B.

2.3.3.3. Flavan-3-ol monomers and polymers. Acetic acid extract (20 lL) was injected into the column and eluted at 30 °C. Mobile phase A and B were 0.1% formic acid aqueous solution and 95% acetonitrile (in 5% mobile phase A), respectively, and the flow rate was 0.4 mL/min. The linear gradient used was as follows: 0–2 min, 98% A, and 2% B; 20–22 min, 90% A, and 10% B; 40 min, 80% A, and 20% B; 50–53 min, 60% A, and 40% B; 58 min, 40% A, and 60% B; 62–65 min, 15% A, and 85% B; 70–80 min, 98% A, and 2% B. HPLC chromatograms were registered at 280 nm.

2.3.3.4. Flavan-3-ol oligomers. Methanolic extract (20 lL) was injected into the columns and eluted at 25 °C. Mobile phase A and B were 2.5% acetic acid aqueous solution and 80% acetonitrile (in 20% mobile phase A), respectively, and the flow rate was 1 mL/min. The linear gradient used was as follows: 0–5 min, 93% A, and 7% B; 5–90 min, 80% A, and 20% B; 95 min, 0% A, and 100% B; 95–105 min, 0% A, and 100% B; 106–110 min, 93% A, and 7% B. HPLC chromatograms were registered at 280 nm.

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M. Figueiredo-González et al. / Food Chemistry 152 (2014) 522–530 Table 1 Colour fraction in fortified sweet wine (FSW) and naturally sweet wine (NSW) with the aging process (unaged, 6-six months and 12-twelve months). 6-FSW

12-FSW

NSW

6-NSW

12-FSW

31 ± 0.73 57 ± 0.82 11 ± 0.05 55 ± 0.52 2.9 ± 0.24

33 ± 0.01 52 ± 0.55 11 ± 0.08 60 ± 0.27 2.6 ± 0.56

36 ± 0.66 50 ± 0.47 11 ± 0.09 63 ± 0.82 2.4 ± 0.02

37 ± 0.67 48 ± 0.72 13 ± 0.02 80 ± 0.54 2.5 ± 0.50

38 ± 0.21 46 ± 0.30 13 ± 0.05 82 ± 0.75 2.3 ± 0.24

39 ± 0.41 44 ± 0.52 14 ± 0.18 85 ± 0.81 2.1 ± 0.38

55 ± 0.21 23 ± 0.55 23 ± 0.45 60 ± 0.17 28 ± 0.49

55 ± 0.34 23 ± 0.56 23 ± 0.66 59 ± 0.44 27 ± 0.09

53 ± 0.54 24 ± 0.42 24 ± 0.02 57 ± 0.51 25 ± 0.34

50 ± 0.23 25 ± 0.46 26 ± 0.62 55 ± 0.47 26 ± 0.57

48 ± 0.51 25 ± 0.21 26 ± 0.35 54 ± 0.74 24 ± 0.05

47 ± 0.20 26 ± 0.02 27 ± 0.43 51 ± 0.52 21 ± 0.48

3. Results and discussion 3.1. Characterisation of the colour fraction from Garnacha Tintorera based-sweet wines with the aging process Colour fraction in fortified sweet wine (FSW) and naturally sweet wine (NSW) during aging process show in Table 1. 3.1.1. Colorimetric indexes During the aging process, the red component showed a drop from 57 to 50 in fortified sweet wine (FSW) and from 48 to 44 in naturally sweet wine (NSW) meanwhile the yellow component showed an increase from 31 to 36 in FSW and 37 to 39 from in NSW. Consequently tonality also increased in FSW (from 55 to 63) and NSW (from 80 to 85). This trend was similar to other red wines made from other varieties such as Tinto Fino and Cabernet Sauvignon (Pérez-Magariño & González-SanJosé, 2004), Tempranillo, Merlot and Cabernet Sauvignon (Cadahía, Fernández de Simón, Sanz, Poveda, & Colio, 2009) and Tempranillo (Fernández de Simón, Hernandez, Cadahía, Dueñas, & Estrella, 2003). The blue component is kept constant in both sweet wines. In an oxidative process such as aging in barrel, the percentage of red decrease mainly due to the loss of free anthocyanins (Pérez-Magariño & González-SanJosé, 2006). By contrast, the percentage of yellow increase due to the formation of orange–yellow pigments during aging (Pérez-Magariño & González-SanJosé, 2004). In particular the flavan-3-ols, although initially are colourless, gradually turn brown due to oxidation, contributing to the yellow component. The increase in tonality could be due to the formation of polymeric pigments that produce colour stabilization over aging time (Alañón et al., 2013). The colour intensity decreased slightly for FSW from 2.9 to 2.4 and for NSW from 2.5 to 2.1, in the same way as previously found by other authors (Fernández de Simón et al., 2003; Pérez-Magariño & González-SanJosé, 2004). The decline in colour intensity may be due to the formation of insoluble polymeric pigments, which are within precipitated dyestuff fraction in aged wines (Alañón et al., 2013). 3.1.2. CIELab coordinates The coordinate a⁄ (red/green) decreased in both sweet wines due to the decrease in the content of anthocyanin by their interaction with other compounds of wines under oxidative conditions. Saturation (Cab⁄) also decreased in both sweet wines with aging time due to the formation of polymerised pigments, as a result of a more complex mixture of pigments involved in burgundy colour of red wine (Alañón et al., 2013). The coordinate b⁄ (yellow/blue) and hue (hab) increased slightly in both sweet wines with aging time due to the formation of yellow–orange pigments during this process (Pérez-Magariño &

González-SanJosé, 2004). This increase was quite small, which could indicate that aged wines still have a red colour with violet hues similar to unaged wines. These results disagree with Chaves et al. (2007) who observed a decrease in wines made from the Pedro Ximenez variety, possibly because the aging period tested was much higher than that proposed in this paper. The lightness (L⁄) decreased as aging progressed, in FSW from 28 to 25 and in NSW from 26 to 21, in accordance with previous results described in Pedro Ximenez (Serratosa et al., 2011) and Sherry wines (Schwarz et al., 2012). This could be the result of the development of browning reactions leading to the formation of polymers of reddish brown in the wines (Chaves et al., 2007). As can be seen in Fig. 1, colorimetric indexes and CIELab coordinates was similar in both sweet wines and during the aging process; only tonality was higher in NSW compared to FSW. 3.2. Characterisation of the phenolic content from Garnacha Tintorera based-sweet wines with the aging process No flavonoid and flavonoid concentration in fortified sweet wine (FSW) and in naturally sweet wine (NSW), with the aging process, show in Table 2 a and b, respectively.

COLOUR FRACTION 90

60

FSW (mg L-1)

Colorimetric indexes Yellow (%) Red (%) Blue (%) Tonality (%) Intensity CIELab coordinates a⁄ b⁄ hab Cab⁄ L⁄

FSW

30

0 0

30

60

NSW (mg

90

L-1)

Fig. 1. Colorimetric indexes: red component (red colour); yellow component (yellow colour); tonality (orange colour) and CIELab coordinates: a⁄ (blue colour); b⁄ (green colour) and L⁄ (violet colour) of FSW (axis Y) and NSW (axis X) (unaged-}, six-h, and twelve-4months of aged). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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Table 2 No flavonoids (a) and flavonoids (b) (mg L-1) in fortified sweet wine (FSW) and naturally sweet wine (NSW) with the aging process (unaged, 6-six months and 12-twelve months). (a) NO FLAVONOIDS

FSW

6-FSW

12-FSW

NSW

6-NSW

12-FSW

Phenolic acids Hydroxybenzoic acids Gallic acid Hydroxybenzoic acid Protocatechuic acid Vanillic acid Syringic acid P Hydroxybenzoics

15 ± 0.77 3.4 ± 0.10 1.3 ± 0.27 8.2 ± 0.06 2.8 ± 0.09 32

22 ± 1.15 2.6 ± 0.11 3.9 ± 0.22 11 ± 0.09 6.7 ± 0.53 46

24 ± 0.17 2.4 ± 0.41 4.3 ± 0.54 12 ± 0.61 7.7 ± 0.92 50

5.0 ± 0.73 0.1 ± 0.05 5.1 ± 0.28 13 ± 0.35 16 ± 1.70 40

7.6 ± 0.80 0.1 ± 0.06 7.1 ± 0.31 14 ± 0.15 17 ± 1.52 46

8.6 ± 0.01 0.1 ± 0.07 8.1 ± 0.84 15 ± 0.24 18 ± 1.69 50

Hydroxycinnamic acids c-Caftaric Caffeic acid c-Coutaric t-Coutaric p-Coumaric acid P Hydroxycinnamics

59 ± 0.55 1.6 ± 0.12 2.6 ± 0.25 22 ± 0.55 2.2 ± 0.21 87

57 ± 0.54 1.9 ± 0.06 2.4 ± 60.01 20 ± 2.70 2.5 ± 0.05 84

53 ± 0.58 2.0 ± 0.01 2.2 ± 0.04 19 ± 0.04 3.4 ± 0.01 80

4.6 ± 0.93 14 ± 0.85 0.4 ± 0.07 0.7 ± 0.20 2.9 ± 0.17 23

1.4 ± 0.07 20 ± 1.15 0.3 ± 0.03 0.5 ± 0.14 6.9 ± 0.81 29

1.1 ± 0.17 23 ± 2.51 0.3 ± 0.02 0.4 ± 0.04 7.5 ± 0.60 32

Stilbene t-Resveratrol Total

0.4 ± 0.04 119

0.2 ± 60.01 130

0.1 ± 60.01 130

nd 63

nd 75

nd 82

(b) FLAVONOIDS ANTHOCYANINS 3-O-glucosides Malvidin Peonidin Petunidin Delphinidin Cyanidin Pelargonidin P Glucosides

210 ± 1.25 95 ± 0.07 15 ± 0.87 10 ± 1.05 2.9 ± 0.27 0.3 ± 60.01 333

12 ± 0.64 5.1 ± 0.30 0.4 ± 0.06 0.4 ± 60.01 0.3 ± 0.01 0.1 ± 60.01 19

7.3 ± 0.10 2.5 ± 0.51 0.3 ± 0.02 0.3 ± 0.02 0.2 ± 0.01 0.1 ± 0.02 10

46 ± 2.48 26 ± 1.49 2.2 ± 0.27 0.6 ± 0.19 2.0 ± 0.16 nd 77

6.7 ± 0.03 3.9 ± 0.27 0.4 ± 0.03 0.3 ± 0.03 0.4 ± 0.13 nd 12

4.3 ± 0.30 2.8 ± 0.03 0.2 ± 0.03 0.2 ± 60.01 0.2 ± 0.03 nd 8

3-O-(6-O-p-coumaroyl)glucosides Malvidin Peonidin Petunidin Delphinidin Cyanidin P Coumaroyls

40 ± 1.58 21 ± 1.05 2.1 ± 1.02 0.7 ± 0.04 1.3 ± 0.02 65

0.8 ± 0.08 0.4 ± 0.06 0.2 ± 60.01 nd nd 1.5

0.3 ± 0.01 0.4 ± 0.02 0.1 ± 60.01 nd nd 0.8

5.9 ± 0.10 4 ± 0.05 0.3 ± 60.01 0.1 ± 60.01 0.4 ± 0.01 11

0.7 ± 0.10 0.3 ± 0.06 0.1 ± 60.01 nd nd 1.0

0.4 ± 0.06 0.2 ± 0.01 0.1 ± 60.01 nd nd 0.6

3-O-(6-O-acetyl) glucosides Malvidin Peonidin Petunidin Delphinidin Cyanidin P acetyls

7.8 ± 1.23 7.0 ± 0.72 1.2 ± 0.30 0.5 ± 0.07 0.3 ± 0.10 17

0.4 ± 0.22 1.4 ± 0.13 0.2 ± 0.01 nd 0.2 ± 0.04 2.2

0.3 ± 60.01 0.7 ± 0.14 0.2 ± 0.02 nd 0.1 ± 60.01 1.6

0.2 ± 60.01 0.3 ± 0.01 0.2 ± 0.02 0.1 ± 0.01 0.3 ± 0.06 1.2

0.1 ± 0.01 0.2 ± 60.01 nd nd nd 0.3

0.06 ± 60.01 0.08 ± 60.01 nd nd nd 0.2

3-O-(6-O-caffeoyl) glucosides Malvidin Peonidin P Caffeoyls

0.5 ± 0.02 0.4 ± 0.01 0.8

nd nd

nd nd

0.3 ± 0.04 0.2 ± 0.02 0.5

nd nd

nd nd

Vitisins Vitisin A Vitisin B Vitisin A coumaroyl Vitisin A acetyl P Vitisins Total

12 ± 0.47 3.7 ± 0.06 2.1 ± 0.02 0.5 ± 60.01 18 433

20 ± 0.06 7.3 ± 0.52 3.8 ± 0.51 0.9 ± 0.03 32 54

19 ± 0.13 6.8 ± 0.55 3.6 ± 0.62 0.8 ± 0.02 30 43

1.8 ± 0.25 1.3 ± 0.15 0.5 ± 0.03 0.1 ± 0.03 4 93

1.7 ± 0.31 0.9 ± 0.18 0.5 ± 0.01 0.1 ± 0.02 3 16

1.8 ± 0.15 0.7 ± 0.09 0.6 ± 60.01 0.1 ± 0.02 3 12

FLAVAN-3-OLS Monomers Gallocatechin Catechin Epicatechin P Monomers

6.5 ± 0.04 40 ± 0.08 27 ± 0.07 73

5.8 ± 0.04 22 ± 0.06 8.4 ± 1.07 36

5.4 ± 0.03 17 ± 0.34 5.7 ± 0.15 28

2.2 ± 0.28 16 ± 60.01 3.0 ± 0.14 21

1.8 ± 0.14 16 ± 60.01 2.4 ± 0.21 20

0.9 ± 0.28 15 ± 60.01 1.8 ± 0.21 18

Oligomers B1 + B3 B4 B2 B6 B8 C1 B2-Gallate B7 B5 P Oligomers

214 ± 1.81 23 ± 0.22 41 ± 0.35 1.7 ± 0.02 0.4 ± 0.04 0.7 ± 60.01 8 ± 0.26 1.5 ± 0.07 0.6 ± 0.02 290

86 ± 0.81 10 ± 0.44 14 ± 0.71 1.0 ± 60.01 0.3 ± 0.01 0.6 ± 0.18 3.1 ± 0.14 0.5 ± 60.01 0.6 ± 60.01 116

54 ± 0.02 3.7 ± 0.05 7.6 ± 0.41 0.5 ± 0.01 nd nd 1.4 ± 0.13 nd nd 66

37 ± 1.25 5.3 ± 0.72 9.4 ± 1.60 1.1 ± 0.01 nd 0.4 ± 0.01 1.9 ± 0.22 0.3 ± 0.10 nd 55

34 ± 1.12 4.1 ± 0.46 6.8 ± 0.04 1.2 ± 60.01 nd nd 2.9 ± 0.34 0.2 ± 0.02 nd 50

24 ± 0.10 3.4 ± 0.01 5.6 ± 0.10 0.8 ± 0.01 nd nd 1.2 ± 0.08 nd nd 35

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M. Figueiredo-González et al. / Food Chemistry 152 (2014) 522–530 Table 2 (continued) (a) NO FLAVONOIDS

⁄

FSW

6-FSW

12-FSW

NSW

6-NSW

12-FSW

Polymers P Polymers

322 ± 3.94

147 ± 2.32

108 ± 1.52

121 ± 5.5

110 ± 3.95

88 ± 0.91

mDP aMW Procyanidins (% PC) Prodelphinidins (% PD) Galloilated (% G)

2.9 743 76 24 1.0

2.6 733 78 21 0.9

2.2 651 80 19 0.8

3.0 908 45 54 1.1

3.2 969 42 56 0.9

2.6 797 39 60 1.3

nd, not detected.

3.2.1. Phenolic acids and resveratrol Hydroxybenzoic acid concentration increased as aging progressed. Before this process, the average concentration in FSW was 32 mg L1 and 40 mg L1 in NSW. After one year of aging, the concentration increased to 50 mg L1 for both sweet wines. These results are in agreement with those reported by Cadahía et al. (2009) who also noted an increase in the concentration of hydroxybenzoic acids and their derivatives in wines made from different cultivars aged in French oak for 12 months. This fact could be explained because the gallic acid and its dimer, ellagic acid, and other benzoic acids, such as syringic and vanillic, can be present in oak wood and they can be transferred to the wine during the aging period (Cadahía et al., 2009). In particular, gallic acid concentration doubles after one year of aging. This could be explained not only by the compounds extraction from the wood, but also by hydrolysis of gallic tannins during the aging process (García-Parrilla et al., 1999). The hydroxycinnamic acid esters such as t-caftaric and c- and tcoutaric acids decreased throughout aging process in both sweet wines. This fact could be due to slow hydrolysis process of esters for the generation of their corresponding free acids. This behaviour was not observed by García-Moreno and García-Barroso (2002) under oxidative aging of ‘‘oloroso wines’’, which showed a constant evolution of hydroxycinnamic acid esters, except for the caftaric acid which showed a strong decrease. A different behaviour was observed for the free forms: in NSW there was an increase of caffeic and p-coumaric acids from 14 to 23 and from 2.9 to 7.5 mg L1, respectively; in FSW from 1.6 to 2 mg L1 of caffeic acid and from 2.2 to 3.4 mg L1 of p-coumaric acid. These results agreed with those provided by Cadahía et al. (2009) who observed an increase in the concentrations of hydroxycinnamic acids in three different wines during aging. The increase observed in free forms was not proportional to the loss of the corresponding esters. In addition to the hydrolysis process, other processes such as the formation of hydroxyphenyl-pyranoanthocyanins developed by direct reaction between free hydroxycinnamic acids and anthocyanins (Rentzsch et al., 2007), and/or co-pigmentation processes (Monagas, Gómez-Cordovés, & Bartolomé, 2005) can be registered. Wine contact with wood (which may contain p-coumaric and/or caffeic acid) could also contribute to the increase of such acids. Other authors explain that p-coumaric acid can also increase as a result of the disappearance of coumaroyl anthocyanins during aging process (Monagas et al., 2005). The t-resveratrol, present only in fortified sweet wine, showed a mean concentration of 0.4 mg L1 at the beginning of aging, but this concentration decreased to 0.1 mg L1 after one year of aged. Barrera-García et al. (2007) found that this decrease could be originated by an oak wood absorption mechanism. 3.2.2. Anthocyanins Anthocyanin content at the beginning of aging process in FSW was 433 mg L1 and in NSW was 93 mg L1. The low anthocyanin content in NSW compared to FSW could be ascribed during the

grape drying process, anthocyanin concentration decrease due to reaction with other phenols, enzymatic reactions by production of quinonas via coupled oxidation reactions and/or condensation between quinones and/or non-enzymatic reactions by production of polymers from anthocyanin monomers (Figueiredo-González, Cancho-Grande, & Simal-Gándara, 2013). After six months of aging, the anthocyanin concentration decreased to 54 and 16 mg L1 in both sweet wines, respectively. After one year of aging, the anthocyanin content decreased to 43 mg L1 in FSW and to 12 mg L1 in NSW. These results were also obtained by Mateus and De Freitas (2001) who observed in the Port wine after a year of aging a decrease between 80% and 90% of glucoside derivatives. Other derivatives such as malvidin and peonidin-3-caffeoylglucoside, minor before starting the aging process, completely disappeared after 6 months in oak, in both sweet wines. This fact could be ascribed because anthocyanin derivatives gradually react with other phenolic compounds of wine. It should be noted that the phenomenon of co-pigmentation may eventually contribute to the colour of young wines between 30% and 50%. During aging, since the monomeric anthocyanins decrease, copigmentation process also decreases. Some authors postulate copigmentation decrease up to 20–34% after three months and almost negligible after nine months of aging due to this process being a possible first in the formation of more stable compounds resulting from condensation of anthocyanins with flavan3-ols (Boulton, 2001; Hermosín-Gutiérrez, Sánchez-Palomo, & Vicario-Espinosa, 2005). Other reactions can be produced between anthocyanins with low molecular weight compounds such as pyruvic acid, vinylphenol, or glyoxylic acid, resulting ‘‘new pigments’’ namely pyranoanthocyanins. Unlike the classical polymeric anthocyanin-flavan-3-ol pigments that tend to precipitate, pyranoanthocyanins are much more stable and responsible for wine colour during aging process because they have higher red–orange colour intensity than their monomeric anthocyanins (Atanasova et al., 2002). The main piranoanthocyanins in wines are vitisins formed by reaction between anthocyanins and yeast metabolites. Vitisin A, derived from the reaction of malvidin-3-O-glucoside with pyruvic acid, was higher in FSW than the NSW. This fact could be ascribed because during stop fermentation, the pyruvic acid concentration is expected to be higher than when the fermentation is allowed to go to end (Mateus & De Freitas, 2001). Additionally, the high ethanol content of this wine increases the solubility of these pigments. During the aging process, vitisins increased in fortified sweet wine (from 18 to 30 mg L1). This fact could be due to ellagitannins from wood, convert oxygen into reactive species, and the oxygendiffusion through the pores of the wood, may have favored the formation of vitisins. These results agree with those reported by Alañón et al. (2013) who reported an increase in vitisins after six months aging in barrel. Alcalde-Eon, Escribano-Bailón, Santos-Buelga, and Rivas-Gonzalo (2006) also observed an increase in vitisins with aging process, differing with Mateus and De Freitas (2001) who

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M. Figueiredo-González et al. / Food Chemistry 152 (2014) 522–530

Extension units

observed in port wines after one year of aged, a decrease of 15–25% of vitisin A and 15–30% and 30–45% of acetyl and coumaroyl vitisin A, respectively. In NSW vitisin concentration remained constant (4 to 3 mg L1). In particular, only vitisin B, derived from the reaction of malvidin-3-O-glucoside with acetaldehyde, decreased with aging. This fact was also observed by other authors, who detected a rapid decrease in vitisins B after eight months of aging in oak (Alcalde-Eon et al., 2006).

50

%

40 30 20 10 0 FSW

6- FSW

12- FSW

% EGC

%C

NSW

6- NSW

%EC

12- NSW

%ECg

Terminal units

40

%

30 20 10 0 FSW

% EGC

6- FSW

12- FSW

% GC

%C

NSW

6- NSW 12- NSW

% EC

% ECg

Fig. 2. Proanthocyanindin composition of extension and terminal units in FSW and NSW with the aging process (unaged, 6-six months and 12-twelve months). C, catechin; EC, epicatechin; GC, gallocatechin; EGC, epigallocatechin; and ECg, epicatechin 3-O-gallate.

3.2.3. Flavan-3-ol monomers, oligomers and polymers The concentration of flavan-3-ol monomers in both sweet wines after one year of aging was determined being catechin the main monomer, followed by epicatechin and gallocatechin. With aging there was a decrease from 73 to 28 mg L1 in FSW and from 21 to 18 mg L1 in NSW as a consequence of the reactions involved these monomers. Total flavan-3-ol polymers (or proanthocyanidins) decreased in FSW from 322 to 108 mg L1 and from 121 to 88 mg L1 in NSW. These results are in agreement with wines made from Cabernet Sauvignon (Chira, Jourdes, & Teissedre, 2012). Two principal processes are responsible for the loss of proanthocyanidins. The first one is the classical acid-catalysed C–C bond-breaking during aging process (Haslam, 1980) and the second one is the precipitation of some high molecular weight polymers that is accompanied by a loss of the colouring matter and a decrease in astringency (Llaudy et al., 2006). In disagreement with these results are those provided by Serratosa et al. (2011) who observed an increase in tannin content in Pedro Ximénez sweet wines during aging process. The mean degree of polymerisation of these polymers (mDP) decreased with aging in the FSW from 2.9 to 2.2 and from 3.0 to 2.6 for NSW as it was previously described by other authors (Chira et al., 2012), indicating that high molecular weight flavan-3-ols might be easier to be degraded or transformed (Sun & Spranger, 2005).

Fig. 3. Phenolic content (mg L1) of anthocyanins (red colour); phenolic acids (yellow colour); monomeric flavan-3-ol (blue colour); oligomeric flavan-3-ol (green colour) and polymeric flavan-3-ol (violet colour) of FSW (axis Y) and NSW (axis X) with the aging (unaged-}, six-h, and twelve-4months of aged). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

M. Figueiredo-González et al. / Food Chemistry 152 (2014) 522–530

The composition of proanthocyanidins was determined in both sweet wines (see Fig. 2). The extension units identified were epigallocatechin (EGC), (+)-catechin (C), ()-epicatechin (EC) and epicatechin-3-O-gallate (ECG). Terminal units were identified as epigallocatechin (EGC), gallocatechin (GC), (+)-catechin (C), ()-epicatechin (EC) and epicatechin-3-O-gallate (ECG). EC was the major extension subunit accounting for between 35% (FSW) and 40% (NSW) of total subunits, followed by C (FSW: 7%; NSW: 8%), EGC (FSW and NSW: 3%), and ECg (FSW: 0.1–0.6% and NSW: 1%). Among the terminal subunits (see Fig. 2), EGC was the predominant monomer in both sweet wines (FSW: 30%; NSW: 24%), followed by C (FSW: 16%; NSW: 15%), EC (FSW: 7%; NSW: 5%), GC (FSW: 3%; NSW: 2%), and ECg (in FSW and NSW at 0.2%). The composition of proanthocyanidins was similar in both sweet wines and they showed no significant changes throughout the aging process. It appears that only both terminal and extension units of catechin and epicatechin increased slightly through aging process. The concentration of B-type procyanidins (dimers resulting from the condensation of two units of flavan-3-ols) and C-type trimer (two interflavan bonds of B-type dimers) in both sweet wines were examined during aging. The main dimers found in both sweet wines studied were B1 + B3 > B2 > B4. The same way that their monomer derivatives, oligomeric flavan-3-ols also decreased from 290 to 66 mg L1 in FSW and from 55 to 35 mg L1 in NSW. The high disappearance rate of dimeric procyanidins in comparison with that of momeric flavan-3-ols is mainly attributed to the acid-catalysed C–C bond-breaking of procyanidins during aging (Haslam, 1980). Previous studies have confirmed similar decreases in catechin, epicatechin and dimeric derivatives (such as B2 and B3) in Rioja wines aged in French oak (Fernández de Simón et al., 2003). Actually, Glories (1978) noted that, during this process, the corresponding percentage of dimeric flavan-3-ols tends to zero after several years of aging. In general, as can be seen in Fig. 3, total phenolic compound concentration was higher in FSW compared to NSW. Furthermore, both sweet wines are rather different in the phenolic profile at the beginning of the aging process but after 1-year aging process in oak barrels these differences were minimized.

4. Conclusion In general, colour evolved towards yellow–brown colour with aging of red sweet wines. In both sweet wines hydroxybenzoic and hydroxycinnamic acids increased because they can be present in oak wood and can be transferred to the wine during the aging period. However, anthocyanin, flavan-3-ol monomer, oligomer and polymer concentrations decreased with aging process because it is influenced by the effects of polimerization, condensation and/ or oxidation reactions. In particular, vitisins increased and exhibit orange tones that play an important role during aging because these relatively small molecules remain in solution. All these processes produced colour stabilization. Total polyphenol index was determined in both wines. Although the concentration of various individual phenolic compounds decreased markedly, the fact that the level of total polyphenol index remained nearly constant during wine aging in FSW and NSW may indicate that native phenolic compounds apparently disappeared were converted to other phenolic forms. The results obtained in this work gave useful information to understand better the sensorial quality of new Garnacha Tintorera-based sweet wines (NSW and FSW) produced in Galicia (N.W. Spain). Further studies are needed in the evolution and stabilization of these sweet wines.

529

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