Aromatic evolution of wine packed in virgin and recycled PET bottles

Food Chemistry 176 (2015) 376–387

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Analytical Methods

Aromatic evolution of wine packed in virgin and recycled PET bottles Clara Dombre a, Peggy Rigou b, Jérémie Wirth b, Pascale Chalier a,⇑ a b

Unité Mixte de Recherche, Ingénierie des Agropolymères et Technologies Emergentes (UMR IATE), Université de Montpellier II, Place E. Bataillon, 34095 Montpellier cedex 05, France Université Montpellier 1, UMR Science Pour l’Oenologie 1083, INRA, SupAgro, 34060 Montpellier, France

a r t i c l e

i n f o

Article history: Received 20 December 2013 Received in revised form 7 July 2014 Accepted 12 December 2014 Available online 25 December 2014 Keywords: Aroma compounds PET Recycling Sorption Wine ageing Rosé

a b s t r a c t The evolution of the aromatic profile of a rosé wine packed in glass, virgin and recycled PET bottles was studied. Wine stored in PET and glass bottles was clearly differentiated after 5 months of storage but only by a limited number of compounds. More pronounced decrease of oxygen sensitive compounds such as methionol was observed in PET bottles as well as the apparition of oxidative and ageing aroma compounds such as ethyl pyruvate, furfural or dioxanes in higher concentration. Compared to virgin PET bottles, recycled PET bottles induced slight changes favouring the presence of esters and alcohols. The chemical evolution of wine was the most important phenomenon that explains the loss of flavour rather than the sorption into PET. Because of their moderate oxygen permeability, the use of virgin PET and recycled PET bottles could be adapted for short conservation of wine but detrimental to aromatic quality if long conservation is intended. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Wine is a complex matrix which composition depends on grape characteristics (variety), conditions of growth (soil, climate) and winemaking (fermentation conditions and process) (MorenoArribas & Polo, 2009; Styger, Prior, & Bauer, 2011). Microbiologically, wine is a stable product because of its acid pH and alcohol rate (10–15% v/v) but in organoleptic terms, it is a very sensitive beverage. Colour, phenolic composition and flavour of wine evolve with storage duration. Because of the acid pH of wine, its aromatic profile can be modified by acid–catalysed reactions, esterification of an organic acid and an alcohol or hydrolysis of an ester (Pérez-Prieto, López-Roca, & Gómez-Plaza, 2003). Changes can also be linked to the wine oxygen content and intake during winemaking and storage. For instance, aroma compounds, despite addition of sulphite oxide and phenols protection, undergo oxidation, which can be detrimental to wine by transforming some aroma compounds into off-flavour (Bueno, Culleré, Cacho, & Ferreira, 2010; Lee, Kang, & Park, 2011; Oliveira, Ferreira, De Freitas, & Silva, 2011). However, controlled oxygenation of wine during process, microoxygenation (Moutounet, Mazauric, Ducournau, & Lemaire, 2001) or controlled ingress of oxygen by closure during storage can be desirable (Wirth et al., 2012). Traditionally, wine is packed in glass bottles capped with a natural cork to limit oxygen intakes and preserve organoleptic quality. However, glass bottle has a ⇑ Corresponding author. Tel.: +33 (0)4 67 14 38 91; fax: +33 (0)4 67 14 45 90. E-mail address: [email protected] (P. Chalier). http://dx.doi.org/10.1016/j.foodchem.2014.12.074 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved.

negative impact on environment due to its energy cost for manufacturing and its heavy weight. Moreover, the use of natural cork may cause the development of trichloroanisole (TCA), an offflavour with an extremely low detection threshold. To limit this problem, caps companies have developed different ways to close wine bottles avoiding TCA risk and also improving oxygen intakes control. Concerning wine containers, numerous innovations were made to facilitate user consumption and to limit environmental impact, like LDPE laminated carton packs such as Tetra Brick, bag-in-boxÒ (BIB), multilayer plastics, or polyethylene terephthalate (PET) bottles. With the BIB concept, wine is contained in a bag made of a high oxygen barrier multilayer flexible film inside a cardboard box. The film allows to prevent oxidation and to preserve organoleptic qualities of wine (colour and flavour) (Hopfer, Ebeler, & Heymann, 2012). However losses of ethanol and aroma compounds by sorption in the film or permeation through the bag can occur and impact the organoleptic quality. Indeed, BIB multilayer films are usually made of polyethylene film (PE) which is well known to sorb easily aroma compounds and particularly hydrophobic ones, which can results in changing the aromatic balance of wine (Dury-Brun, Chalier, Desobry, & Voilley, 2008; Peychès-bach, Dombre, Moutounet, Peyron, & Chalier, 2012; Peychès-Bach, Moutounet, Peyron, & Chalier, 2009). This sorption phenomenon seems to be less impacting in the case of PET bottles which have good inertia properties against aroma compounds (Ducruet et al., 2007; Sajilata, Savitha, Singhal, & Kanetkar, 2007; Van Willige, Schoolmeester, van Ooij, Linssen, & Voragen, 2002). As an example, when a tomato juice is stored into PET and PE

C. Dombre et al. / Food Chemistry 176 (2015) 376–387

bottles, the comparison of limonene sorption showed that after 7 days, PE sorbed 848 lg cm3 and PET only 58 lg cm3 (Sajilata et al., 2007). Another team had worked on sorption of several aroma compounds in linear low density polyethylene (LLDPE), polycarbonate (PC) films and PET bottles. Considering ethyl-2methylbutyrate, one of the esters studied, its sorption was about 70 times and 10 times less in PET bottles than in LLDPE and PC, respectively (van Willige et al., 2002). Using PET bottles as an alternative to glass bottles presents several advantages. Due to its relatively good water, oxygen and carbon dioxide barrier properties, PET is largely used instead of glass to package soft or carbonated drinks. Its lighter weight (almost 400 g for a glass bottle against 50 g or less for a PET bottle) reduces the environmental impact during transport. Moreover, the losses of foodstuff are decreased since fewer bottles are broken during filling and storage. To our knowledge, only few scientific studies have dealt with wine packaged in PET bottles. Ough (1987) has compared oenological and sensory parameters of white, rosé and red wines packed in traditional glass and PET bottles. It has appeared that aromatic profile of wine was preserved despite a colour evolution more important in PET bottles, and a free SO2 rate that reached 0 after 12 months of storage (MS) in PET bottles against 8 mg L1 in glass bottles. Sensory evaluation has shown that red and rosé wines packed in PET bottles could be stored up to eight or nine months before they were sufficiently changed to determine lower quality than in glass bottles. Mentana, Pati, La Notte, and del Nobile (2009) have worked on two wines (red and white) stored in glass, standard PET and PET with oxygen scavenger bottles. They have studied the aroma compounds evolution and showed that after 7 MS at 15–18 °C, 18 and 7 compounds of wine packed in PET and PET with oxygen scavengers, respectively, had a concentration significantly different from those found in the wine packed in glass. Even if significant differences were evidenced between wines packed in both PET bottles, results of sensory analysis have demonstrated that wine quality was still good after 7 MS. Ghidossi et al. (2012) have studied a white wine packaged in BIB, in glass, and in monolayer or multilayer PET bottles (the multilayers contained oxygen scavengers). These bottles were stored at 20 °C during 18 months and three aroma compounds (sotolon, methional, phenylacetaldehyde) associated to the oxidative wine evolution were followed. These aroma compounds were less oxidized in glass bottles and multilayer PET bottles than in the other packages. In this study, wine in monolayer PET bottles had the same behaviour that the wine in BIB. However, compared to monolayer, multilayer PET bottles are more difficult to recycling as layers have to be delaminated prior to the recycling process. Monolayer PET is easily recyclable and bottle-to-bottle recycling of PET becomes a major prospected issue. Increasing the part of recycled polymer in the bottle manufacturing process can reduce environmental footprint, hence meeting worldwide ecological expectations. One of the major drawbacks when using recycled PET bottle is the potential presence of substances, such as aroma compounds, trapped in the polymer matrix from earlier use, and that likely will desorb in the packed food. Some aroma compounds as terpenes have already been found in recycled PET matrix (Félix, Alfaro, & Nerín, 2011). The use of recycled PET is a preferred and desirable solution because of its lower environmental footprint. However, it is important to assess the potential changes of wine aromatic profile during storage due to desorption of aromatic compounds from the recycled PET to the wine and vice versa. Even if several studies related to wine packed in PET bottles have been carried out, few of them have focused on rosé wine as well as on recycled PET bottles. Furthermore, these studies have been generally targeted on aroma profile evolution over time but the entire system, including chemical degradations in wine and molecular transfers (aroma or oxygen) through the bottle and the

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cap, has never been taken into account to describe or understand aroma compounds losses. The aim of the work presented in this article was to evaluate the impact of bottling a very sensitive wine like rosé in a lightened monolayer virgin and recycled PET bottle by studying its aromatic profile. To determine which phenomenon is the most significant in wine aroma evolution, the aromatic profile has been studied along the storage time. This evaluation has taken into account losses or gains of components due to the overall mechanisms involved as chemical reactions, oxidation, ageing and losses by transfers through polymer. Finally, an evaluation of the amount of aroma compounds lost by sorption in the PET bottle and cap has been done.

2. Materials and methods 2.1. Chemicals and wine The aroma compounds selected for the sorption study were isoamyl acetate (molar mass. 130 g mol1; density. 0.876 g cm3; vapour pressure. 747 Pa), isoamyl alcohol (molar mass. 130 g mol1; density. 0.876 g cm3; vapour pressure. 747 Pa), octanoic acid (molar mass. 88 g mol1; density. 0.809 g cm3; vapour pressure. 635 Pa), ethyl octanoate (molar mass. 172 g mol1; density. 0.867 g cm3; vapour pressure. 30 Pa), hexanoic acid (molar mass. 116 g mol1; density. 0.927 g cm3; vapour pressure. 21 Pa), hexyl acetate (molar mass. 144 g mol1; density. 0.870 g cm3; vapour pressure. 185 Pa), ethyl hexanoate (molar mass. 144 g mol1; density. 0.869 g cm3; vapour pressure. 221 Pa), isobutanol (molar mass. 74 g mol1; density. 0.803 g cm3; vapour pressure. 1200 Pa), methionol (molar mass. 106 g mol1; density. 1.030 g cm3; vapour pressure. 21 Pa), 2-phenylethanol (molar mass. 122 g mol1; density. 1.017 g cm3; vapour pressure. 10 Pa) purchased from Sigma–Aldrich, France, and hexanol (molar mass. 102 g mol1; density. 0.812 g cm3; vapour pressure. 126 Pa) from Prolabo, France. Dichloromethane, and 4-nonanol, the internal standard were provided by Sigma–Aldrich, France. Anhydrous sodium sulphate was provided by MERCK, France. Wine used was a Rosé Cinsault from South of France supplied by UCCOAR – Val d’Orbieu (Carcassonne, France). Wine pH was 3.3, its ethanol content was about 12.6% (v/v), its total acidity was 3.4 g L1, and volatile acidity 0.17 g L1. After bottling, free SO2 was about 36 mg L1 and total SO2 about 130 mg L1.

2.2. Packaging, filling and storage condition The experiments were carried out with glass bottles, virgin polyethylene terephthalate bottles (PET) and 100% recycled polyethylene terephthalate bottles (rPET) supplied by SIDEL Blowing Service (France). The OTR of PET and rPET bottles was equal to 1.97 and 1.63 103 cm3 m2 day1 at 23 °C and 60% HR, respectively. Bottles can contain 0.75 L of wine. The weight of both PET bottles was 38 g, thickness around 350 lm for bottle body, increasing until 470 lm in the lower part and 700 lm in the top of the bottle shoulder. The same kind of closure was used for PET and glass bottles: a polypropylene cap with a multilayer connective joint (Novatwist™ from Novembal) with an Oxygen transmission rate OTR of 6.72 106 cm3 m2 day1 at 23 °C and 60% HR. Bottling was performed by the experimental Unit of Pech Rouge (INRA, Gruissan, France). Bottles were filled using a ‘‘Perrier filler’’ equipped with a WineBraneÒ filtration system (INOXPA) (membrane porosity 1 lm for pre-filtration and 0.65 lm for final filtration). Caps were installed manually with a Zalkin TM3. Then, they were stored under a 400 lux light, at 20 °C for 12 months.

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2.3. Extraction and analysis of wine aroma compounds Concentration of aroma compounds in wine was measured just after filling (t0) and after 3, 5, 9 and 12 MS at 20 °C. Aroma compounds were extracted by liquid–liquid method using dichloromethane as solvent. The extraction was carried out twice on 100 mL of wine, using the same volume of dichloromethane (25 mL). The mix was shaken by magnetic stirring during 20 min at 500 rpm and the phases were separated by centrifugation during 30 min at 6000 rpm. Known quantity of 4-nonanol, the internal standard (100 lL of a solution at 2.17 mg mL1), was added before extraction. The resulting organic phase was dried using anhydrous sodium sulfate. Semi-quantitative determination was performed using Gas Chromatography–Mass Spectrometry (GC–MS). The GC–MS used was an Agilent 1530 coupled to a quadrupole mass spectrometer (5973 MSD Hewlett Packard) equipped with a ZBWAX column (30 m  0.25 mm, 0.25 lm). Helium was used as carrier gas with a flow rate of 1 mL min1. The oven temperature stayed 3 min at 60 °C, then was raised by 3 °C min1 to 250 °C and was kept at 250 °C for 10 min. Injector was maintained at 245 °C. Injection was done in splitless mode and the split was opened at 1 min after injection with a 1:10 ratio to avoid losses of the most volatiles compounds. The electron impact (EI) energy was 70 eV and the quadrupole temperature was set at 250 C. Detection was carried out in full scan mode covering a mass range (m/z) of 30–300 amu. A response factor equal to 1 toward the internal standard (4-nonanol), was adopted for this semi-quantitative analysis. The results were expressed in mg of equivalent 4-nonanol L1. Three replicates were made for each experiment. 2.4. Analysis of sorbed aroma compounds The amount of sorbed aroma compounds in virgin and recycled PET bottles was measured before filling and after 3, 5, 9 and 12 MS at 20 °C. The method used was quantitative: an internal standard was added to the sample and a calibration curve was realized for each studied aroma compound. The response factor of each selected compound has been determined and used to quantify the amount sorbed compounds (2-phenylethanol; 0.88, ethyl hexanoate; 1.0, ethyl octanoate; 1.01, hexanoic acid; 1.18, hexanol; 0.92, hexyle acetate; 0.95, isoamyl acetate; 1.06, isoamyl alcohol; 0.79, Isobutanol; 0.74, methionol; 1.56, octanoic acid; 0.98). Wine aroma compounds trapped in PET bottles and multilayer connective joint cap were extracted with dichloromethane (provided by Sigma–Aldrich) by contact during 12 h under magnetic stirring (250 rpm). Known quantity of internal standard (10 lL of a 6.81 mg mL1 of 4-nonanol) was added at the beginning of the extraction. The resulting organic phase was dried using anhydrous sodium sulphate and concentrated under a nitrogen flow to approximately 2 mL. Extracts were analysed by Gas Chromatography (GC), a Varian 3800 GC equipped with a DB-WAX column (30 m  0.25 mm, 0.25 lm) and a flame ionization detector (FID; hydrogen = 30 mL min1, air = 300 mL min1, nitrogen = 30 mL 1 min ). Hydrogen was used as carrier gas with a flow rate of 2 mL min1. The oven temperature stayed 3 min at 60 °C, then was raised by 3 °C min1 up to 245 °C and was kept at 245 °C for 20 min. Injector and detector temperatures were 250 °C and 300 °C, respectively. Injection was done in split mode with a 1:20 ratio. Three replicates were made for each experiment. An extraction of virgin and recycled PET bottles without wine contact was realized to take account of aroma compounds potentially sorbed before experiment. 2.5. Statistical analysis Each experiment was repeated three times and the results reported were the means of the three trials. The one way analyses

of variance (ANOVA) were performed using XLSTAT 2012.4.03 software (Addinsoft 1995–2012). Tukey’s test was used to compare modalities at level of significance P < 0.1. Principal component analyses (PCA) were performed using the same software in order to find the possible differentiation between wines according to time elapsed and package used. 3. Results and discussion 3.1. Aroma compounds evolution during storage 3.1.1. Aroma compounds of wine just before storage Just after filling (t = 0) the aromatic profile of the rosé wine was determined by a semi-quantitative method using 4-nonanol as an internal standard. The results are presented in Table 1. 36 aroma compounds were detected in the rosé wine for a total amount of 122.4 mg L1. Alcohols were the major class, with a total amount of 96.6 mg L1. Among the 12 alcohols identified, the 2 majors were isoamyl alcohol and 2-phenylethanol, representing 64% and 28% of the total alcohol amount, respectively. 14 esters (ethyl and acetates) were detected for a total amount of 15.0 mg L1. 6 acids were identified for a total amount of 9.5 mg L1. Finally 3 lactones and one ketone at low concentration were also present. As previously stated, the high concentration of esters and higher alcohols strongly contributed to the fruity notes of rosé wine (Masson & Schneider, 2009). 3.1.2. Aroma compounds evolution The evolution of aroma compounds of a rosé wine packed in glass, virgin PET and recycled PET bottles was followed during 12 MS at 20 °C. This included losses and gains of aroma compounds due to the overall mechanisms involved such as chemical reactions as esterification, hydrolysis, oxidation, ageing and losses by transfers through the polymers (bottle and cap). Those specific losses and gains are presented in this section while losses by sorption will be detailed in a specific one. The analysis of aromatic profile was realized at time 0 and after 3, 5, 9 and 12 MS. For sake of clarity, Table 1 presents the concentration of each aroma compounds only at time 0, 5 and 12 MS. In order to discriminate wine packages, ANOVA analyses were realized on aroma compounds concentration at each time (Table 1). 3.1.2.1. Esters. Esters contribute to the fruity flavour of wine and their evolution has a strong olfactive impact on wine. They can be formed during storage by esterification of an organic acid and an alcohol, or degraded by hydrolysis. These reactions depend on the equilibrium between the esters and the corresponding acids. 3.1.2.1.1. Ester losses. Four esters were strongly degraded, up to 50% of losses at 5 MS and from 70% up to 90% of losses after 12 MS (Table 1). Among them, ethyl 4-hydroxy-butanoate was faster degraded in glass between 0 and 9 MS, and then its concentration was stable between 9 and 12 MS. A difference between the two PETs was noted, with lower amount of this compound found in recycled PET. A decrease of this ester had already been reported during wine ageing (Schneider & Baumes, 1998). Isoamyl acetate was the most degraded ester with 84% of losses for wine in glass and recycled PET and 86% of losses for wine in virgin PET. No correlation between isoamyl acetate and isoamyl alcohol was observed since the concentration of alcohol also decreased, suggesting that other reactions occurred. Hexyl acetate decreased regularly during storage in all bottles: losses were about 40% after 3 MS, 55% after 5 MS and 65% after 9 MS. The low concentration and an important standard deviation of this aroma compound after 12 MS avoid drawing conclusion.

Table 1 Aroma compound evolution during storage at 20 °C (expressed in lg L1 eq 4-nonanol) in wine stored in glass, virgin and recycled PET. Code

Compound

t0

t5

t9

Glass Esters

Acids

Recycled PET

Glass

91 251 279 1751 108 696 91 1273 326 165 3521 2409 555 9582 1526 34 97 nd nd nd nd nd nd 22.8

A A A A A A A A A A A A A A A B A

83 244 244 1498 105 603 92 1195 392 139 3418 2569 462 11,702 1417 104 152 nd nd nd nd nd nd 2026

AB A B A A A A A A A A A AB A A A A

75 198 189 1196 89 704 14 1232 458 195 4098 3932 717 10,305 2026 48 194 60 nd nd 556 74 234 26.6

A A A A A A A A A B A A A A A A B A

Virgin PET

Recycled PET

Glass

68 184 192 1117 80 666 31 1179 366 205 3859 3948 751 10,841 2060 48 225 55 nd nd 589 180 235 26.9

B A A A A A A AB A A A A A A A A A AB

67 191 193 1159 82 653 30 1081 380 191 3837 3731 722 11,275 1974 44 213 48 nd nd 602 173 226 26.9

B A A A A A A B A AB A A A A A A A B

42 129 159 556 nd 568 107 1087 383 214 3391 4578 761 10,851 72 38 500 48 23 2481 23 128 211 26.4

A A AB AB

1,3PM 1,3-Propanediol monoacetate 2PA 2-Phenylethyl acetate E4HB Ethyl 4-hydroxy-butanoate IA Isoamyl acetate HA Hexyl acetate EH Ethyl hexanoate E2HB Ethyl 2-hydroxy butyrate EO Ethyl octanoate ED Ethyl decanoate EPL Ethyl phenyl-lactate EL Ethyl lactate DM Diethyl malate EHG Ethyl hydroxy glutarate ME Monoethyl succinate DS Diethyl succinate Gl Glycine, N-acetyl-, ethyl ester DT Diethyl tartrate I3M Isopropyl-3-methyl butanoate E2HI Ethyl 2-hydroxy isovalerate E3MB Ethyl 3-methylbutyl butanedioate EB Ethyl butanoate Epy Ethyl pyruvate EP Ethyl pyroglutamate Total (mg/L)

189 ± 5 456 ± 13 919 ± 16 3545 ± 66 239 ± 10 622 ± 12 97 ± 6 971 ± 30 253 ± 22 101 ± 10 2309 ± 60 694 ± 32 210 ± 13 4413 ± 462 nd nd nd nd nd nd nd nd nd 15.0 ± 0.5

81 215 175 1768 128 689 80 1225 320 160 3482 1343 196 2028 1376 35 88 nd nd nd nd nd nd 13.4

B A C A A A A A A A A A B A A B A

2PE 2-Phenylethanol c3HO Cis-3-hexen-1-ol 1B 1-Butanol I Isobutanol c2,3B Cis-2,3-butanediol t2,3B Trans-2,3-butanediol IAO Isoamyl alcohol M Methionol 1P 1-Propanol BA Benzylalcohol H Hexanol 3M1P 3-Methyl 1-pentanol 2,6D4 2,6-Dimethyl-4-heptanol t3HO Trans-3-hexen-1-ol T Tyrosol 4M2P 4-Methyl-2-pentanol 4V 4-Vinylguaiacol Total (mg/L)

27,601 ± 766 136 ± 7 157 ± 14 4601 ± 305 500 ± 34 104 ± 24 61,455 ± 2303 296 ± 44 707 ± 80 61 ± 12 906 ± 50 35 ± 5 nd nd nd nd nd 96.6 ± 2.4

2328 119 136 3384 534 138 66,310 233 384 52 872 64 125 25 315 31 55 96.1

B A A A A A A A B C A B A A A A B

24,046 126 136 3431 642 158 37,386 215 452 57 882 68 121 28 840 29 52 68.7

B A A A A A B A A B A AB A A A A B

21,825 111 117 3160 507 103 46,023 215 376 95 853 70 101 32 762 41 153 74.5

A A A A A A B A B A A A A A A A A

19,454 133 154 4176 105 175 38,312 309 619 0 1049 75 729 34 693 32 39 66.1

A A A A A A A A A A A A A A C A A

19,196 130 140 3874 106 178 36,969 213 550 0 974 68 692 34 855 30 38 64.0

A A A A A A A B A A B B A A B A A

19,737 123 160 3935 101 162 36,416 201 635 0 922 66 690 29 929 39 37 64.2

A A A A A A A B A A B B A A A A A

16,184 122 118 2817 198 42 30,690 286 12 0 911 69 172 32 883 nd nd 52.5

A A A A A B B A A

Hac Hexanoic acid Oac Octanoic acid Dac Decanoic acid Bac Butanoic acid IBac Isobutyric acid IVac Isovaleric acid 2Hac 2-Hexenoic acid Total (mg/L)

2287 ± 55 4514 ± 135 1106 ± 132 220 ± 14 139 ± 12 nd nd 8.3 ± 0.2

1658 1671 912 169 152 196 nd 4.8

A B A A A A

2153 4044 976 231 139 268 nd 7.8

A A A A A A

2098 4063 1137 196 110 225 nd 8.2

A A A A A A

2106 4161 1102 238 150 283 58 8.1

A A A A A A A

2102 4146 1149 238 140 263 63 8.1

A A A A A B A

2114 4114 1137 244 173 267 62 8.1

A A A A A B A

2108 3857 1000 237 152 266 173 7.8

A A A A A A A

A B A

A A A

A A A

A A A A A A A A A A A A B B A B C A

AB A A A A

Virgin PET

Recycled PET

44 124 167 511 nd 537 106 1081 402 196 3353 3271 601 10,508 54 46 200 60 28 2498 23 201 140 24.1

A AB A B

38 111 141 579 nd 608 108 1095 330 131 3696 3754 509 7769 31 20 46 58 31 2490 43 218 34 21.9

A B B A

15,362 120 122 2663 204 67 30,308 219 9 0 844 66 161 26 571 nd nd 50.7

A A A A A A B B A

15,692 126 123 2947 206 29 34,297 197 18 0 968 73 169 26 170 nd nd 55.0

A A A A A C A B A

2092 3687 1191 257 164 239 158 7.8

A AB A A A A B

2046 3197 678 243 150 250 138 6.7

A B B A A A C

A A A A A A AB AB A A A B A AB A B B AB

B A A A A

A A A B A A B B B A A C A A A A A B

C. Dombre et al. / Food Chemistry 176 (2015) 376–387

Alcohols

t12

Virgin PET

A A A A B

(continued on next page) 379

A B B A A

A B C

A A AB A A

964 542 65 1.57 134 48 8 96 28 0.31 A A A

A AB A B B

924 843 179 1.95 150 79 36 92 33 0.39 A A B

A A A

980 813 113 1.91 133 64 47 15 13 0.27 B A A

A A A

969 691 85 1.75 150 64 41 nd nd 0.26 A A A

A B A

1019 725 84 1.83 161 68 47 nd nd 0.28 AB A A

A A A

1092 764 87 1.94 163 49 51 nd nd 0.26 A A A

A B B

803 526 82 1.41 123 100 81 nd nd 0.30 A A A

Miscellaneous

672 ± 6 473 ± 33 101 ± 6 1.25 ± 0.03 149 ± 10 nd nd nd nd 0.15 ± 0.01 gB c-Butyrolactone 4CgB 4-Carbethoxy-c-butyrolactone g5HH c-5-Hydroxy-hexalactone Total (mg/L) A Acetoin 2PEA 2-Phenyl-ethyl-acetamide AV Acetovanillone cD Cis-dioxane tD Trans-dioxane Total (mg/L) Lactones

nd: not detected, A, B, C: different letters mean significant difference between packages.

A B B

899 615 34 1.55 145 48 36 nd nd 0.23 A A A

C 21 nd nd nd 0.02 nd nd nd nd 0.00 ± 0.00 F Furfural V Vanillin 5HF 5-Hydroxymethylfurfural P Phenylacetaldehyde Total (mg/L) Aldehydes

t0 Compound Code Table 1 (continued)

878 603 79 1.30 144 40 33 nd nd 0.22

96 6 35 15 0.15 A A A A 90 90 64 22 0.27 56 47 38 17 0.16 A A A 84 45 37 nd 0.2 A A A 56 67 28 nd 0.2 B 36 nd nd nd 0.04 A

Glass Virgin PET

40 nd nd nd 0.04

t9

Glass

Recycled PET t5

A A B

76 67 40 nd 0.2

Glass Virgin PET

Recycled PET

t12

B B B A

Virgin PET

A C B A

C. Dombre et al. / Food Chemistry 176 (2015) 376–387

Recycled PET

380

Nevertheless, we could notice that hexyl acetate continued to decrease. The evolutions of ethyl hexanoate and ethyl octanoate were not linear. Both seemed to first increase during 9 MS and then decrease. After 12 MS, about 10% of losses were observed in glass and virgin PET bottles for ethyl hexanoate and 10% of gain for ethyl octanoate. Increase and decrease could be explained by acid production due to oxidation from longer chain fatty acids and ester formation followed by subsequent hydrolysis of the ester to maintain equilibrium (Lee et al., 2011). However, the link between oxidation and ester decrease is not clearly established (Ugliano, 2013) even if decrease of fatty acid ester was observed when wine was in contact with oxygen. 3.1.2.1.2. Ester gains. Ethyl decanoate increased by 55% in glass and virgin PET bottles but less in recycled PET (almost 30%) after 12 MS (Table 1). This ester could be formed by esterification of the decanoic acid with ethanol. However, decanoic acid losses were higher in the recycled PET bottles than in the other bottles. This increase was in contradiction with the lowest formation of ester in these bottles. As previously described, decanoic acid could be oxidized in shorter chain fatty acids. Then a strongest oxidation of decanoic acid could occur in recycled PET resulting in a lowest ethyl decanoate formation. Ethyl decanoate has pleasant fruity notes and its increase can impact the aromatic quality of wine. With a detection threshold of about 200 lg L1 (Ferreira, Lopez, & Cacho, 2000), its initial Odour Activity Value (OAV) was about 1.3, which was just enough to be detected. OAV is classically used to estimate the sensory contribution of an aroma compound to the overall flavour of a wine (Cacho, Moncayo, Palma, Ferreira, & Culleré, 2012). It is calculated by dividing the concentration of the aroma compound by its odour threshold in simulated wine. A compound with an OAV > 1 can play a major role on odour perception because its concentration is above its odour threshold. After 12 MS in glass and virgin PET, the OAV of ethyl decanoate was doubled thus supposing to increase the fruity perception whereas for recycled PET its effect was less pronounced. For ethyl lactate, known for its buttery, creamy and coconut notes, the increase reached a maximum of 40% after 5 MS, and the evolution was similar in glass and PET bottles. The same phenomenon was observed in white wine after 12 MS at 15 °C in glass bottle (with a much higher increase) (Cejudo-Bastante, Hermosín-gutierrez, Castro-Vazquez, & Perez-Coello, 2011). Diethyl-malate and ethyl hydroxyglutarate strongly increased during the storage but more moderately in PET bottles (180% and 400%, respectively) than in glass bottles (250% and 550%, respectively) after 12 MS. No data are available concerning ethyl hydroxylglutarate odour threshold but Simpson (1980) mentioned that diethyl-malate is known for its high flavour threshold. Thus, despite its high increase during storage, its odour impact on wine is limited. 3.1.2.1.3. New esters. Between 0 and 5 months, 3 esters were formed (Table 1). Among those, diethyl succinate appeared during storage of wine in glass and PET bottles. A large amount was formed after 5 MS but its concentration decreased between 9 and 12 MS. It might be due to equilibrium with monoethyl succinate, its potential precursor. The increase of diethyl succinate was used as a marker for the degree of ageing of red or white in Madeira wine (Câmara, Alves, & Marques, 2006). The formation of diethyl tartrate was higher in glass than in PET bottles and notable differences could be observed between both PET. This ester was formed by esterification of tartaric acid. It seemed that its production was affected by the barrier properties of the packages. Between 5 and 12 MS, 6 new esters were formed. Among those, isopropyl-3-methylbutanoate (or isopropyl isovalerate) was in

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C. Dombre et al. / Food Chemistry 176 (2015) 376–387 Table 2 Comparison between bottles modalities after 12 months of storage: aroma compounds which discriminate wine in virgin PET and glass bottles and wine in virgin and recycled PET. Comparing virgin pet and glass bottles

Comparing virgin and recycled pet bottle

>in virgin PET

>in glass

>in virgin PET

>in recycled PET

Ethyl pyruvate

Diethyl tartrate Methionol

Diethyl tartrate

Ethyl butanoate Ethyl pyruvate Isoamyl acetate Hexanol

Isopropyl-3-methyl butanoate Trans-2,3-butanediol

Ethyl 4-hydroxybutanoate Ethyl decanoate

5-Hydroxymethyl furfural Furfural

Monoethyl succinate

Vanillin

Tyrosol 2-Hexenoic acid

Trans-2,3-butanediol

c-5-Hydroxy hexalactone Cis-dioxane Trans-dioxane

Isoamyl alcohol

Overall, ester concentration was rising during time. After 12 MS, the amount of ester was increased by 76% for wine stored in glass bottles, 61% for wine stored in virgin PET bottles, and 46% for wine stored in recycled PET bottles. At 12 MS, the presence of three esters was clearly specific to wine packed either in glass or in both PETs bottles (Table 2): diethyl tartrate, higher in glass bottles, ethyl pyruvate and isopropyl 3 methyl butanoate higher in PET bottles. Differences between both PETs were due to ethyl 4-hydroxybutanoate, ethyl decanoate, monoethyl-succinate, and diethyl tartrate in higher amount in virgin than in recycled PET, and to ethyl butanoate, ethyl pyruvate, and isoamyl acetate in stronger amount in recycled than in virgin PET. Ethyl pyruvate is known to appear during oxidation; hence it could be used as a marker because of its higher quantity in PET bottles and more specifically in recycled PET bottles. 3.1.2.2. Alcohols. Alcohols can be degraded during storage by oxidation, involved in esterification, or formed after hydrolysis of acetates and other esters.

Decanoic acid 5-Hydroxymethyl furfural Vanillin 4-Carbetoxy-cbutyrolactone c-5-Hydroxy hexalactone 2-Phenyl ethyl acetamide

higher concentration after 12 MS in virgin and recycled PET bottles than in glass bottles. This ester has apple and pineapple notes. Amount of ethyl butanoate was 2 times higher in recycled PET. This aroma compound provides banana and strawberry notes to wine. Its detection threshold in a 10% ethanol solution (v/v) is about 20 lg L1 (Guth, 1997). With an OAV in glass and virgin PET bottles equal to 1 but equal to 2 in recycled PET, the fruity notes of wine packed in recycled PET could be improved compared to the other packages. Ethyl pyroglutamate was found at very low concentration in recycled PET compared to virgin PET and glass bottles, indicating a poor protection of this compound in recycled PET bottles. This is in contradiction with the increase of ethyl pyroglutamate observed by Schneider and Baumes (1998) in oxidized wine. Ethyl pyruvate has increased twice more in recycled and virgin PET than in glass bottles. The formation of this aroma compound could be explained by oxidation of ethyl lactate (Del Álamo, Nevares, & Cárcel, 2006).

3.1.2.2.1. Alcohol losses. Numerous alcohols decreased similarly after 5 MS in glass and PET bottles. At 12 MS their losses varied between 10%, as for cis-3-hexen-1-ol, and 100% as for benzyl alcohol and 1-propanol. However, the esters, aldehydes or acids corresponding to those alcohols were not detected. Alcohol can be first oxidized to form an aldehyde, which is then further oxidized to form an acid. The extraction method used was not specific enough to correctly extract aldehydes and consequently the analysis is not quantitative. It is possible that oxidation occurred differently between both types of packaging but the method did not allow differentiating them. The decrease of one major alcohol, 2-phenylethanol, may be explained by the apparition of the corresponding aldehyde between 5 and 12 MS. Again, because the method of extraction and analysis was only semi-quantitative it was not possible to establish a stoichiometric link between the concentrations of those two compounds. In the same way, the presence of aldehydes formed from other alcohols was not evidenced. Another major alcohol, the isoamyl alcohol was lost at 50% except in the wine stored in recycled PET for which the smallest decrease (44%) was observed. This loss cannot be correlated to isoamyl acetate formation since this ester decreased during storage, suggesting that other reactions were involved such as their oxidation into aldehydes. Detection threshold of isoamyl alcohol (banana notes) is 30 mg L1 (Ferreira et al., 2000), thus its initial OAV was equal to 1.8 and decreased to 1.0 in glass and virgin PET bottle and to 1.1 in recycled PET. This is barely above the

Table 3 Physico-chemical characteristics and quantity sorbed after 12 months storage in bottle and cap of selected aromas compounds. (a and b mean significant difference). Quantity sorbed (102 lg/g)

Physico-chemical characteristics

* 1 2 3

Aroma compound

Log P

Detection threshold (lg L

2-Phenylethanol* Ethyl hexanoate* Ethyl octanoate* Hexanoic acid* Hexanol Hexyl acetate Isoamyl acetate* Isoamyl alcohol* Isobutanol* Methionol Octanoic acid*

1.36 2.83 3.90 1.72 1.86 2.83 2.26 1.22 0.76 0.40 2.74

100,002 143 53 30,002 80,002 15,001 302 300,003 400,002 10,003 5003

1

)

dPET/aroma 4.1 4.3 7.3 4.3 5.7 13.0 4.4 6.2 8.8 nd 4.3

Aroma which had reach sorption equilibrium after 12 months of storage. Coelho, Coimbra, Nogueira and Rocha (2009). Guth (1997). Ferreira et al., (2000).

compound

dLDPE/aroma 13.3 9.2 10.7 12.3 13.9 10.6 8.1 14.4 17.2 nd 9.3

compound

In PET bottle

In rPET bottle

In multilayer joint

60.4 ± 2.9a 17.1 ± 0.2a 16.9 ± 0.9a 12.6 ± 0.1a 3.7 ± 0.3b 3.9 ± 0.4a 15.5 ± 2.6a 47.7 ± 1.5a <0.017 1.2 ± 0.0b 38.8 ± 0.1b

58.7 ± 3.0a 16.1 ± 1.8a 11.2 ± 2.0b 12.1 ± 0.2b 6.5 ± 0.6a 3.0 ± 0.3b 14.4 ± 1.3a 45.2 ± 5.6a <0.017 5.2 ± 0.4a 42.3 ± 1.2a

1370 ± 63 32 ± 21 7500 ± 674 2085 ± 135 78 ± 25 68 ± 34 481 ± 48 3976 ± 148 <0.017 69 ± 85 762 ± 124

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detectable odour threshold and could influence negatively the sensorial profile. Methionol decreased by 30% in virgin and recycled PET bottles and remained unchanged (considering the standard deviation) in glass bottles after 12 MS. This aroma compound, synthesized by yeast during fermentation, is well known to be very sensitive to oxidation. Oxidized methionol produces methional (Escudero, Hernández-Orte, Cacho, & Ferreira, 2000). Thus, methionol was only oxidized in PET bottles for which oxygen transfer was assumed. Consequently, this aroma compound can be considered as an oxidation marker. Methionol exhibits boiled potato notes and its odour threshold is very high (1000 lg L1 – Table 3). Its odour impact is negligible because its OAV was initially below 1. However, methional, its oxidation product, is considered as an off-flavour with cooked potatoes and cabbage flavour notes. Moreover, its odour threshold is very low, about 0.5 lg L1 (Escudero et al., 2000). Methional could not be chemically detected because the extraction and analysis methods are not adapted to the quantification of this aldehyde. However, after 12 MS, wine packed in PET bottles may contain methional concentration that could be sensorially detected by consumers because of its very low odour threshold. 2,3-Butanediol is the major di-alcohol found in wine and is a by-product of fermentation, probably formed from pyruvic acid or oxidised to form acetoin. Cis-2,3-butanediol and trans-2, 3-butanediol strongly decreased but no relation could be established with the acetoin concentration that remained unchanged during storage (Table 1). Surprisingly, the trans isomer was present at different concentration depending on the package. These diols can be implied in acetals formation (Schneider & Baumes, 1998) which might explain their fall during storage. Hexanol was rather stable during storage but was found at higher concentration in wines bottled in recycled PET than in virgin PET. Hexanol can be oxidized in hexanal but also produced from hydrolysis of hexyl acetate (Lee et al., 2011). This aroma compound provides appreciated herbaceous notes to wine (Welke, Manfroi, Zanus, Lazarotto, & Alcaraz Zini, 2012). However, in the studied wine, hexanol concentration was below its perception threshold value before and after 12 MS. This alcohol should not have a significant impact on wine aromatic profile. 3.1.2.2.2. New alcohols. Between 0 and 5 MS, 5 news alcohols appeared in wine. Among those, tyrosol, or 4-(2-hydroxyethyl)phenol, was formed slower in glass than in both PET bottles but it was found in lower quantity in both PET bottles after 12 MS. This aroma compound is very sensitive to oxidation phenomenon (Proestos et al., 2005) and could act as a protector of other aroma compounds against oxidation. This may explain its presence at very low amounts in PET bottles and most specifically in recycled PET. Overall, alcohol concentration decreased over time. After 12 MS, the decrease of alcohols was about 45% for all bottles modalities. Only two alcohols, 2,3-butanediol, and methionol, allowed differentiating the wine packed in glass bottles to the one packed in PET. Hexanol and isoamyl alcohol concentrations were significantly lower in wine stored in virgin PET than in recycled PET. The difference observed for these two aroma compounds suggests a lowest protection of alcohol against oxidation in virgin PET bottles than in recycled PET bottles, opposite to esters protection. 3.1.2.3. Acids. Acids can be esterified or oxidized in shorter acids and they are formed by hydrolysis of esters, oxidation of aldehydes and reduction of alcohols during storage (Moreno-Arribas & Polo, 2009). 3.1.2.3.1. Acid losses. The decay of hexanoic acid reached 10% after 12 MS, with the same behaviour in all bottles modalities. This acid decreased between 0 and 3 MS (about 20%) but increased

again after 3 MS in PET bottles and after 5 MS in glass bottles. This behaviour can be correlated to that of ethyl hexanoate showing an increase followed by a decrease in concentration. As previously shown, decanoic acid losses were higher in recycled PET than in the other bottles. A stronger oxidation of decanoic acid into lower fatty acids could occur in recycled PET thus resulting in lowest ethyl decanoate formation. 3.1.2.3.2. Acid gains. After 12 MS, 2 acids increased by 10–20%: butanoic acid, which could be formed from ethyl butanoate hydrolysis, and isobutyric acid, which could be formed by isobutanol oxidation that decreased during storage (Styger et al., 2011). No differences were found between packaging for these 3 acids. 3.1.2.3.3. New acids. Only two acids appeared during storage of wine in glass and PET bottles. Between 0 and 5 MS, isovaleric acid was formed in the same manner in all bottles modalities. This acid could be formed from isoamyl alcohol and thus, its formation partially explains the decrease of this alcohol (Styger et al., 2011). Between 5 and 12 MS, 2-hexenoic acid appeared in higher quantity in virgin PET than in recycled PET. Overall, acid concentration was stable during time. Losses and gains were rather equivalent. Acid losses were slightly higher (+15%) in recycled PET than in virgin PET and glass due to decanoic acid decrease. 3.1.2.4. Aldehydes. No aldehydes were found initially in the studied wine. It is possible that some aldehydes couldn’t be detected because the methodology used for extraction and analysis was not adapted. SFP or SPME and derivatisation with PFBHA should be carried out to quantify aldehydes (Zapata, Mateo-Vivaracho, Cacho, & Ferreira, 2010). One aldehyde, furfural appeared between 3 and 5 MS. From 5 MS, furfural amount was twice higher in virgin and recycled PET than in glass bottle. The same trend was followed between 5 and 12 MS. Furfural is an off-flavour of wine, formed by the Maillard reaction involving ascorbic acid (Marauja, Blair, Olsen, & Wenze, 1973). But as Maillard reactions are not favoured at acid pH, its formation can also be explained by acid catalysed degradation of pentose. Although the activation of sugar transformation by oxygen was not demonstrated (Cutzach-billard, 1999) it has noticed that furfural is an ageing marker found in wine when it is exposed to oxidation (Schneider & Baumes, 1998) in agreement with our results. The odour threshold of furfural in 11% ethanol solution (v/v) is about 14.1 mg L1 (Ferreira et al., 2000). Because furfural amount in the studied wine was lower than 0.1 mg L1, it has no impact on organoleptic quality of wine, as already reported by Simpson (1980). Between 5 and 12 MS, 3 aldehydes were formed. Vanillin, an aromatic aldehyde, which can be an important powerful aroma in wine, was found at 5 months in glass and recycled PET bottles but not in virgin PET bottles. After 12 MS, quantity of vanillin was twice higher in virgin PET bottles than in glass bottles and ten times lower in recycled PET bottles than in virgin PET bottles. This result suggests that vanillin is an intermediate product that can be simultaneously formed and degraded. Vanillin can be formed from 4-vinylguaiacol and its formation seemed to be partially correlated to 4-vinylguaiacol decrease. Vanillin can also be oxidized in acid and it allows suggesting that wine packed in recycled PET was more oxidized than virgin PET. Important quantities of 5-hydroxymethyl furfural were found in virgin PET bottles (10 times more than in glass bottles). Just like furfural, this aroma compound is a product of Maillard type reaction, sugar dehydration in acid medium and caramelization (Pereira, Albuquerque, Ferreira, Cacho, & Marques, 2011). With a detection threshold determined in beer around 20 mg L1 (reported by Simpson, 1980), its impact on organoleptic quality of wine should be negligible.

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Surprisingly, phenylacetaldehyde, formed by the oxidation of 2phenylethanol, was found in the same amount in all bottles modalities. Phenylacetaldehyde is usually described as a marker of oxidation (Silva Ferreira, Guedes de Pinho, Rodrigues, & Hogg, 2002) and differences between wine glass and PET were expected as described for white wine (Ghidossi et al., 2012). The absence of oxygen ingress in our case can be explained by the strong concentration of 2-phenylethanol and the presence of compounds which are more sensitive to oxygen than this alcohol. At 12 months, aldehydes were the less represented aroma class of compounds. Apart from phenylacetaldehyde, all the aldehydes allowed to differentiate the wines packed in glass and in PET bottles. 5-hydromethyl furfural and vanillin differentiated wines packed in both PETs. 3.1.2.5. Lactones. Lactones are cyclic molecules formed by esterification of an acid and an alcohol function belonging to the same molecule. Volatile lactones of fermentative origin are found in wine as c-butyrolactone the most known. Lactones provide to wine buttery, coconut (butyrolactone) and herbaceous (hexalactone) notes (Moreno-Arribas & Polo, 2009; Schneider & Baumes, 1998). In the wine at t0, three lactones were detected for a total amount about 1.2 mg L1. The amount of c-butyrolactone increased from 25% to 40% of its initial quantity after 5 and 12 MS, respectively. This aroma compound had the same behaviour in all modalities. 4-Carbethoxy-c-butyrolactone also increased after 5 MS, reaching 15% of gain for wine in recycled PET and 70% for virgin PET and glass bottles after 12 MS. This aroma compound was found in higher quantities in sweet fortified wines after oxidation (Schneider & Baumes, 1998). This statement is in contradiction with the strong increase observed in glass bottles which is supposed to be less prone to oxidation. Therefore, increase must be due to the type of wine and storage time. The c-5-hydroxy-hexalactone concentration increased by 12% in glass bottles, 78% in virgin PET bottles but decreased by 35% in recycled PET bottles. This aroma compound is found in Madera wine and derives from c-hexalactone, one of the compounds used to define sensory characteristics of wine ageing (Câmara et al., 2006). 3.1.2.6. Other aroma compounds. Acetoin was rather stable during storage. This aroma compound could be transformed in diacetyl and formed from 2,3-butanediol (Moreno-Arribas & Polo, 2009). Because of the diminution of 2,3-butanediol, an increase of acetoin was expected but diacetyl amount could not be detected in this experiment. Therefore, it is difficult to conclude on the behaviour of this aroma compound. Between 0 and 5 MS, 2 aroma compounds appeared; the 2-phenyl-ethyl-acetamide and the acetovanillone that were present in highest amount in recycled PET bottles after 5 MS. Both were stable between 5 and 12 MS in glass and virgin PET bottles but their quantities strongly decreased in recycled PET bottles. Between 5 and 12 MS, two new aroma compounds were formed the cis and trans dioxane. The amounts of cis dioxane and trans dioxane were respectively 6 times and 2 times higher in PET bottles than in glass bottles. These aroma compounds are formed by acetalization of glycerol and ethanal (Câmara et al., 2006; Schneider & Baumes, 1998), and are frequently found in Madera wine or ‘‘cooked wine’’ like sherries or French ‘‘vin jaune’’, but also in high quantity in oxidized wine (Câmara et al., 2006). However, it was reported that cis and trans dioxane do not impact aroma at the concentrations found in sweet fortified wine (Schneider & Baumes, 1998). Thus, these acetals can be considered as markers of oxidation that have no impact on the aromatic quality of wine.

We demonstrated that the evolution of aroma compounds could be explained in part by chemical reactions (oxidation, acid–catalysed reactions, ageing) that occur in the wine matrix. However, the use of plastic bottles to package wine makes possible the loss of aroma compounds by sorption of volatile compounds on the polymer matrix. 3.2. Sorption of aroma compounds in bottles and joint caps Mentana et al. (2009) had studied the aromatic changes of a wine stored in PET bottles, but they did not take into consideration the impact of aroma compounds sorption on the polymer. In this study, we measured the aroma compounds sorption in virgin and recycled PET bottles and in sealing joint caps during storage at 20 °C in order to determine if losses by transfer through plastic significantly impacted the aromatic quality of wine. These analyses were realized on the same bottles and at the same time period (3, 5, 9 and 12 MS) as for the aromatic profile evolution. We selected 11 aroma compounds classically found in rosé wine that are characterized by different physico-chemical properties (Table 3), and that are likely to sorb into polymer matrix. Nevertheless, we verified that no other compounds that those 11 selected had a strong sorption into the material, and we identified and quantified compounds that were present in PET before use, and most specifically for the rPET. The ability of aroma compounds to pass through polymer matrix is identified as a succession of steps, which take place from packaged food to external environment or from environment to food (Sajilata et al., 2007). First, molecules are sorbed in a gas form into the polymer, which is named molecule solubilisation. This step depends on the molecule concentration, temperature, pressure and affinity for the polymer. Then, because of the concentration gradient on both sides of the polymer film, molecule diffuses. Diffusion depends on molecule size, temperature and concentration gradient. At last, the molecule is desorbed on the other side of the polymer, the desorption being faster when the molecule is more volatile. The sequence of all phenomena is called permeation. In the studied system, sorption equilibrium is difficult to reach. Because one face of PET is in contact with wine and the other face with environment, diffusion through PET and external desorption phenomenon were also important. Aroma compounds sorption into packaging depends on their affinity toward the polymer (Sajilata et al., 2007). The potential affinity between packaging and volatile organic compounds can be theoretically evaluated by calculating the difference between Hansen solubility parameters of aroma compounds (dDmaterial/aroma) (Table 3) and PET material (dd = 19.4 MPa1/2; dp = 3.5 MPa1/2; dh = 8.6 MPa1/2) (Chandra & Koros, 2009). The affinity was calculated using Hildebrand theory by Eq. (1): 2

dDPET=Aroma ¼ ðddPET  ddAroma Þ þ ðdpPET  dpAroma Þ2 þ ðdhPET  dhAroma Þ

2

ð1Þ

This evaluation accounts for the overall solubility parameter including the dispersive (d), polar (p), and hydrogen (h) bonding contributions. The lowest the Dd, the highest is the affinity between the polymer and the aroma compound. On this basis, aroma compounds can be classified as those showing a strong affinity (dDPET/aroma < 4.5), medium affinity (5 < dDPET/aroma > 10) and low affinity (dDPET/aroma > 10) (Table 3). 3.2.1. Sorption of aroma compound in PET bottles 3.2.1.1. Sorption results in virgin PET. The total amount of aroma compounds sorbed was strongly increased between 0 and 5 MS for both PETs (data not shown). After 5 months, the total amount of most of the volatile compounds sorbed was slowed down

C. Dombre et al. / Food Chemistry 176 (2015) 376–387

because sorption equilibrium was almost reached (82 lg bottle1). Table 3 shows the results obtained after 12 MS for each aroma compounds studied. Nevertheless, over the 11 aroma compounds studied, only 8 reached equilibrium after 12 MS (Table 3), i.e., a stable concentration in the polymer. 2-Phenylethanol, isoamyl alcohol and octanoic acid were the most sorbed compounds with a concentration exceeding 0.25 lg g1. It can be noticed that the 2-phenylethanol and octanoic acid showed the same affinity for PET in regard to their Hansen solubility parameters but relatively to their concentrations, the 2-phenylethanol was sorbed at lower amount in PET. Although, isoamyl alcohol has theoretically a weak affinity for PET, its concentration in wine during the 12 MS remained important compared to other aroma compounds, explaining its strong sorption into PET. The Hansen solubility parameter was one of the parameter used to explain sorption but its estimation can lead to large uncertainties as previously stated (Peychès-Bach et al., 2009). Ethyl hexanoate, ethyl octanoate, isoamyl acetate and hexanoic acid were sorbed at the same rate. Except for ethyl octanoate, these aroma compounds were present at low quantities in wine after 12 MS but their affinity for PET were important. Ethyl octanoate is estimated to be less affine to PET than others but its concentration in wine was superior. Hexyl acetate reached its equilibrium with a concentration lower than 0.05 lg L1 probably because of its really low affinity for PET. Between 5 and 9 MS, isoamyl acetate slightly desorbed from the polymer matrix. Indeed, over time, this ester was hydrolysed in wine and can then be desorbed to restore equilibrium. The same phenomenon was also described by Peychès-bach et al. (2012) for ethyl esters such as ethyl hexanoate and ethyl butyrate in an alcoholic model solution in contact with a polyethylene film. This phenomenon seemed to depend on the aroma affinity for the polymer matrix. Two aroma compounds started to sorb later than the others and did not reach their equilibrium at the end of the experiment. Hexanol started to sorb between 3 and 5 MS and methionol between 9 and 12 MS. Another alcohol, isobutanol, did not sorb during the experiment. Methionol and isobutanol are really polar aroma compounds and showed poor affinity for PET, thus explaining their low sorption. Table 3 shows that only small differences exist between recycled and virgin PET at 12 MS. Isoamyl acetate, isoamyl alcohol, and ethyl hexanoate had the same behaviour in both PET. After 12 MS, hexyle acetate and ethyl octanoate had more sorbed into virgin PET than into recycled PET (respectively 23% and 34% more). Hexanol was not found in virgin PET at 5 MS whereas it was sorbed by recycled PET. After 12 MS, this alcohol was twice more sorbed in recycled (+43%) than in virgin PET. Similarly, methionol started to sorb between 9 and 12 MS and was present in higher amount in recycled PET than in virgin PET (77%) after 12 MS. For these two aroma compounds, equilibrium was not reached and it might explain the differences between packages. Octanoic acid sorbed slightly more in recycled PET than in virgin PET after 12 MS (+8%). Hexanoic acid and 2-phenylethanol were more sorbed in recycled PET after 5 MS (respectively 29% and 17% more), but it was not the case after 12 MS. 3.2.1.2. Sorption model determination. Sorption of aroma compounds in polymer depends on the polymer characteristics (glassy or rubbery at ambient temperature, crystallinity), aroma compound characteristics as polarity or affinity, and on the nature of matrix (as presence of ethanol or pH) (Peychès-bach et al., 2012; Sajilata et al., 2007). Most of the studies focused on aroma compounds in simplified or model solutions, or with aroma compounds all at similar concentrations (Chandra & Koros, 2009; Dury-Brun et al., 2008; van Willige et al., 2002). In this study, the system was real and consequently more complex because of the presence

of numerous aroma compounds at different amounts. Therefore, we tried to explain sorption phenomenon, by proposing a linear regression between the sorption of aroma compounds that had reached equilibrium and different parameters which can influence. The selected parameters were density, vapour pressure, polarity expressed by the log P, which is the ratio between solubility in octanol and in water, affinity for PET calculated from Hansen parameters and the residual concentration of aroma compounds after 12 MS. The results of this analysis showed a strong correlation (almost 70.3%) between aroma compounds concentration in wine at 12 MS and the amount sorbed. By way of contrast, no high correlation could be established between affinity (43%) or polarity (10%) and amount sorbed as it would have been expected and suggested in the literature (Sajilata et al., 2007). This statistical analysis made it possible to derive a model predicting the quantity of a given aroma sorbed after 12 MS that takes into account all the parameters (Eq. (2)):

Q ¼ 87:0 þ 5:8  103  VP  7:8  102  Dd þ 9:8  104  C þ 93:0  D þ 3:9  Log P

ð2Þ

With Q the quantity of an aroma compound sorbed after 12 MS (lg bottle1), VP the vapor pressure of the aroma compound (Pa), Dd the affinity of aroma compound for the PET (MPa1/2), C the concentration of aroma compound in wine after 12 MS (lg bottle1), D the density of the aroma compound (g cm3). Fig. 1 shows the experimental value of Q in function of predicted values. The good linearity with R2 = 0.93 confirms the interest of the prediction equation. To validate the model, a model solution containing the 11 aroma compounds, 12% ethanol (v/v), salts and tartaric acid (from Sigma–Aldrich) was prepared and placed in contact with virgin PET in a well closed and hermetic flask at 20 °C under stirring. A same polymer/liquid ratio as in wine bottles was used and sorption in PET was measured after 7, 14, 30, 60 days. Due to short contact time and despite the stirring, over the 11 compounds studied, only the 2-phenylethanol and octanoic acid, the compounds most affine for PET, reached equilibrium after 60 days of contact. Using Eq. (2), an amount of 38.3 lg bottle1 was predicted for 2-phenylethanol against 39.0 lg bottle1 for the measured value, and 13.3 lg bottle1 for octanoic acid against 14.0 lg bottle1 for the real amount sorbed. It revealed an error from 2% up to 6% between the predicted value and experimental results, which is very satisfying.

25

20

15

Q

384

10

5

0 -5

0

5

10

15

20

-5

Pred(Q) Fig. 1. Predictive model to the aroma compound sorption in virgin PET.

25

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The same linear regression was done with aroma compounds sorbed in recycled PET using affinity parameter of PET. Indeed, it was demonstrated that crystallinity (Xc) and glass transition temperature (Tg) of virgin and recycled PET were similar (data not shown). Results were almost the same as for virgin PET, with a slightly weaker linearity (R2 = 0.86), which can explain by the small difference between both packaging. 3.2.2. Sorption of aroma compounds in screw cap Screw cap was made up of a multilayer connective joint with a polyethylene (PE) layer in contact with food and a polypropylene screw cap. The connective joint was not in direct contact with wine because of the upright storage of the bottles but only in indirect contact with the volatile compounds present in the headspace. PE is an apolar polyolefin and this kind of polymer is known to absorb a larger quantity of aroma compounds than polyesters like PET (van Willige et al., 2002). Table 3 shows results at 12 MS for each aroma compound studied. For 6 of them, desorption phenomenon were observed between 5 and 12 months. 2-phenylethanol only reached its sorption equilibrium after 12 MS, while the others were still increasing. Ethyl octanoate was the most sorbed compound in PE joint because of its apolar character and affinity for PE (Table 3). This aroma is well known for its ability to sorb in this kind of polymer (Licciardello, Del Nobile, Spagna, & Muratore, 2009). Sorbed amount of ethyl octanoate increased twice much between 5 and 12 MS. Despite their polar character and their low affinity for PE (Table 3), isoamyl alcohol and 2-phenylethanol sorbed a lot in the joint, both of them being found at high quantities in the wine after 12 MS (Table 1). 2-Phenylethanol was less sorbed than isoamyl alcohol because of its low volatility, which was an important criterion in this experiment because wine headspace contacted with cap joint. Hexanoic acid, although it is rather polar and less volatile showed high sorption in the cap because of its relatively high quantity in wine after 12 MS. Octanoic acid is apolar and its affinity for PE is important, consequently it was sorbed in high amount between 3 and 9 MS. However, an important desorption occurred after 9 MS, may be to compensate its decrease in wine. Isoamyl acetate and ethyl hexanoate are very apolar, showing a great affinity for PE and a high volatility, but their sorption were limited by their low amount in wine after

12 MS. Methionol, hexanol and isobutanol were slightly or not sorbed because of their high polarity and their low affinity for PE. Total amount of aroma compounds sorbed was about 72 lg joint1. This amount is very important compared to the total amount sorbed in PET bottle (about 82 lg bottle1) and the joint cap of 6 cm2 in contact with head space sorbed almost 90% of the total amount sorbed by the package including a 580 cm2 of PET bottle in contact with wine. Therefore, regarding sorption phenomenon of aroma compounds, the sensitive point of wine packaging system is the connective joint cap. 4. Discussion Fig. 2 shows the repartition of losses due to sorption in cap and bottle and those due to mechanism such as chemical degradation, for the 11 aroma compounds studied in rosé wine packed in PET bottle during 12 MS. For both studied PETs, losses seem to be mainly due to wine ageing. Indeed, losses by sorption did not exceed 2% of the initial quantity, except for ethyl octanoate (almost 4.5%). This study demonstrates that when comparing wine packaging in PET bottles and in glass bottles the oxygen intake through the polymer is a major concern compared to losses by sorption in the bottle. Considering aroma profile evolution, new compounds appeared independently to the wine packaging type (glass, virgin or recycled PET bottles). During the storage of the rosé wine, 7 aroma compounds appeared between 3 and 5 MS (only one ageing wine aroma, furfural), 6 aroma compounds between 5 and 9 MS (including a furfural derivative, 5-hydroxymethyl furfural and ethyl pyruvate) and 4 others between 9 and 12 MS (including markers of ageing as dioxanes and oxidation as phenylacetaldehyde). These new compounds were not specific to a package but some of them as diethyl tartrate, ethyl pyruvate and vanillin allowed to differentiate the package because of their concentration. Total amount of aroma compounds at t0 was about 122.5 mg L1. After 12 MS, glass bottles had lost 26% of their initial amount, virgin PET 28% and recycled PET 29%. At this time, the three packages could be distinguished because of the evolution of some specific compounds (Table 2). However, for a different storage time, other compounds could be implied in the characterisation of wine packed

Virgin PET Oac

Recycled PET

81.7

M

17.9

73.9

I

26.0

57.9

IAO

41.8

49.3

IA

50.7

14.4

85.3

0.37

Oac

0.16

M

66.6

32.7

0.67

0.36

I

64.0

35.6

0.36

0.02

IAO

0.25

IA

28.8

70.8

44.2

55.8

93.2

6.6 0.21

H

Hac

91.5

8.0 0.54

Hac

2.28

EO

97.8

1.69

EH

97.8

0.14

2PE

97.7

EH

86.3

2PE

12.0

55.7

0%

20%

44.2

40%

60%

80%

100%

0.02

83.4

16.3

H

EO

0.41

0.23 0.34

99.7

10.0 0.54

89.4

2.16 0.6

56.9

0%

20%

43.0

40%

60%

80%

Non degradated aroma compound

Non degradated aroma compound

Losses from wine ageing

Losses from wine ageing

Losses from sorpon (bole + cap)

Losses from sorpon (bole + cap)

1.60 0.13

100%

Fig. 2. Repartition (in %) of aroma compounds losses (losses by sorption and losses due to wine ageing) in PET. bottles after 12 months storage at 20 °C.

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C. Dombre et al. / Food Chemistry 176 (2015) 376–387

Variables (axes F1 et F2 : 59.79 %)

Observaons (axes F1 et F2 : 59.79 %)

1 8 2,3B 1P

I 1B

EB

0.5

4V 2PE IA HA 1,3PM IAO 2PA BA

F2 (19.62 %)

0.25

t9 - Glass

A

t9 - PET

4

EL

H

Dac

c3HO M

E4HB

0

EO

t9

6

2,6D4H

2,3B

AV EP EDgB Gl Aac t3HO EPL Oac EHG Hac V MEIVac T 2PEA IBac I3M 3M1P DT BacDM F 4CgB

-0.25

g5HH

Epy

5HF

2

t0

0

t9 - rPET

t5 - PET

t5 - Glass t5 - rPET t0

t3 - PET

t12

t3 - rPET

-2

t3 - Glass

t3

-4

2Hac

-0.5

t5 F2 (19.62 %)

0.75

DS 4M2P

EH

t12 - Glass

cD tD E2HI P E3MB

-0.75 E2HB

-6

t12 - rPET

t12 - PET

-8

-1 -1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

F1 (40.17 %)

F1 (40.17 %)

Fig. 3. Principal component analysis of wine aroma compounds comparing wine in glass, virgin and recycled bottles after 12 months storage at 20 °C. (see Table 2 for code of aroma compounds).

in a specific material. Indeed, the wine permanently evolves. After 5 MS, wine in glass bottles and PET bottles can be differentiated on the base of 3 compounds: benzyl alcohol, ethyl-4-hydroxybutanoate with different evolution and furfural which appears. To conclude and to illustrate wine evolution, a Principal Component Analyses (PCA) was performed with data of aroma compounds concentrations after t0, 3, 5, 9 and 12 MS and for the three kinds of bottles studied. The two principal components explained together almost 60% of the total variance (Fig. 3). The first component (PC1), retaining 40% of the variance, confirms a strong evolution of wine between 0 and 12 MS independently to the packaging type. The second component (PC2), retaining 20% of the variance differentiated t9 and t12 by the apparition of news aroma compounds as dioxanes. PC1 appears to be related to the evolution of the aroma profile and the apparition of new compounds, markers of wine ageing, explains PC2. This statistical analysis shows that differences between packaging are less impacting aroma profile than evolution during time. However, a sensorial analysis of the wine stored during 9 months, done by an internal wine expert jury of INRA (UMR, SPO Montpellier), has clearly spotted differences between wine in PET and glass bottles and between virgin and recycled PET. Specific red fruit notes were found in wine stored in both PETs, probably because of the higher amount in PET than in glass of esters such as ethyl pyruvate (fruity and old rum), isopropyl-3methyl butanoate (fruity, pineapple) or isoamyl acetate (fruity, banana, walnut) and of a lactone, c-5-hydroxy-hexalactone (fruity). Spicy notes were also reported and furfural and 5-hydroxymethylfurfural could be responsible. Opposite to wine in PET bottles, mushroom and sulphur notes characterized wine in glass bottle. Methionol, with its cabbage and boiled potatoes notes could contribute to this differentiation. Moreover, by sensorial analysis, wine in virgin PET is described as amylic whereas in recycled PET, the wine was characterized by nut and honey notes. However no differences were observed related to the isoamyl alcohol, isoamyl acetate or phenylacetaldehyde concentration between the wines packed in virgin and recycled PET. However, as other differences of the aromatic profile occurred, it can be suggested that some predominant notes are enhanced

by the presence of some other compounds as previously described (Lytra, Tempere, de Revel, & Barbe, 2012). As shown in Table 2, virgin PET is characterized by oxidation and ageing markers as 5-hydroxymethyl furfural, c-5-hydroxyhexalactone, while recycled PET is characterised by some aroma compounds contributing to green and fruity notes of rosé wine such as hexanol and ethyl butanoate. To conclude about aroma compounds evolution, even if global losses seem to be very similar in all bottles modalities, the formation of new compounds and the evolution of some aroma compounds can differentiate the modalities and such compounds may have a non-negligible impact on wine flavour. 5. Conclusion This study has demonstrated that rosé wine packed in PET bottles evolves with differences compared to wine packed in glass bottles. Eleven wine compounds allowed to distinguish both packaging after 12 MS. Oxidative and ageing aroma compounds appeared in higher amount in PET than in glass bottles due to oxygen ingress through matrix packaging. Methionol, a wine aroma compound sensitive to oxygen, was better preserved in glass than in PET bottles. The use of recycled compared to virgin PET bottles induced some changes in aromatic profile: ageing aroma compounds were predominant in virgin PET bottles whereas esters and alcohols, with fruity and green notes, were less degraded in recycled PET bottle. However, a sensory analysis is needed to highlight an eventual perceptible difference between wines packed in recycled or virgin PET bottles. Losses of flavours were essentially due to chemical reactions, as the sorbed amount of aroma compounds in virgin and recycled PET was too weak to impact organoleptic quality of wine. This study suggests that the use of virgin and recycled PET in light monolayer bottles could be a great alternative to package wine during a short period of time (6 months). This should be fairly well adapted for rosé wine, which is not a ‘‘vin de garde’’ and is often consumed in the year of production. To maintain the aromatic quality during a longer duration, the inclusion of an oxygen scavenger in PET could be an innovating alternative while preserving the recyclability of the PET bottles.

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Acknowledgments This work was carried out with the financial support of Bpi France (Hérault, France), the FEDER (Fonds Européen de Développement Regional) and the Languedoc-Roussillon Region (France), in the context of an FUI project named NOVINPAKÒ. The authors would like to thank the associated companies and their project holders, Marie-Hélène Lemaistre and Yann Pernel from SIDEL Blowing Service (Le Havre, France), Perrine Languet from UCCOAR-Val d’Orbieu (Carcassonne, France) and Alain Bobe from Pure Environnement (Montpellier, France). The authors also acknowledge the UE Pech Rouge (INRA, Gruissan, France), the UMR SPO (Science pour l’Oenologie, INRA, Montpellier, France), the UMR PBS (Polymères Biopolymères Surfaces, Rouen, France) and the IRSTEA (Institut national de Recherche en Sciences et Technologies pour l’Environnement et l’Agriculture, Montpellier) for their participation and help. References Bueno, M., Culleré, L., Cacho, J., & Ferreira, V. (2010). Chemical and sensory characterization of oxidative behavior in different wines. Food Research International, 43(5), 1423–1428. http://dx.doi.org/10.1016/j.foodres. 2010.04.003. Cacho, J., Moncayo, L., Palma, J. C., Ferreira, V., & Culleré, L. (2012). Characterization of the aromatic profile of the Italia variety of Peruvian pisco by gas chromatography-olfactometry and gas chromatography coupled with flame ionization and mass spectrometry detection systems. Food Research International, 49(1), 117–125. http://dx.doi.org/10.1016/j.foodres.2012.07.065. Câmara, J. S., Alves, M. A., & Marques, J. C. (2006). Changes in volatile composition of Madeira wines during their oxidative ageing. Analytica Chimica Acta, 563(1–2), 188–197. http://dx.doi.org/10.1016/j.aca.2005.10.031. Cejudo-Bastante, M. J., Hermosín-gutierrez, I., Castro-Vazquez, L. I., & Perez-Coello, M. S. (2011). Hyperoxygenation and bottle storage of chardonnay white wines: Effects on color-related phenolics, volatile composition, and sensory characteristics. Journal of Agricultural and Food Chemistry, 59, 4171–4182. Chandra, P., & Koros, W. J. (2009). Sorption of lower alcohols in poly(ethylene terephthalate). Polymer, 50(17), 4241–4249. http://dx.doi.org/10.1016/ j.polymer.2009.06.066. Coelho, E., Coimbra, M. A., Nogueira, J. M. F., & Rocha, S. M. (2009). Quantification approach for assessment of sparkling wine volatiles from different soils, ripening stages, and varieties by stir bar sorptive extraction with liquid desorption. Analytica Chimica Acta, 635(2), 214–221. http://dx.doi.org/10.1016/ j.aca.2009.01.013. Cutzach-billard, I. (1999). Etude sur l ’arôme des vins doux naturels non muscatés au cours de leur élevage et de leur vieillissement, son origine, sa formation. Revue des Oenologues et des Techniques Vitivinicoles et Oenologiques, 94, 13–17. Del Álamo, M., Nevares, I., & Cárcel, L. M. (2006). Redox potential evolution during red wine aging in alternative systems. Analytica Chimica Acta, 563(1–2), 223–228. http://dx.doi.org/10.1016/j.aca.2005.11.017. Ducruet, V., Vitrac, O., Saillard, P., Guichard, E., Feigenbaum, A., & Fournier, N. (2007). Sorption of aroma compounds in PET and PVC during storage of a strawberry syrup. Food Additives and Contaminants, 24(11), 1306–1317. Dury-Brun, C., Chalier, P., Desobry, S., & Voilley, A. (2008). Properties of treated papers and plastic film influencing ethyl ester transfer. Journal of Food Engineering, 88(1), 114–125. http://dx.doi.org/10.1016/j.jfoodeng.2008.01.020. Escudero, A., Hernández-Orte, P., Cacho, J., & Ferreira, V. (2000). Clues about the role of methional as character impact odorant of some oxidized wines. Journal of agricultural and food chemistry, 48(9), 4268–4272. Retrieved from http:// www.ncbi.nlm.nih.gov/pubmed/10995348. Félix, J. S., Alfaro, P., & Nerín, C. (2011). Pros and cons of analytical methods to quantify surrogate contaminants from the challenge test in recycled polyethylene terephthalate. Analytica Chimica Acta, 687(1), 67–74. http:// dx.doi.org/10.1016/j.aca.2010.12.013. Ferreira, V., Lopez, R., & Cacho, J. F. (2000). Quantitative determination of the odorants of young red wines from different grape varieties. Journal of the Science of Food and Agriculture, 80, 1659–1667. Ghidossi, R., Poupot, C., Thibon, C., Pons, A., Darriet, P., Riquier, L., et al. (2012). The influence of packaging on wine conservation. Food Control, 23(2), 302–311. http://dx.doi.org/10.1016/j.foodcont.2011.06.003. Guth, H. (1997). Quantitation and sensory studies of character impact odorants of different white wine varieties. Journal of agricultural and food chemistry, 45, 3027–3032. Hopfer, H., Ebeler, S. E., & Heymann, H. (2012). The combined effects of storage temperature and packaging type on the sensory and chemical properties of chardonnay. Journal of agricultural and food chemistry, 60, 10743–10754.

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