Comparative Evolution of Oxygen, Carbon Dioxide, Nitrogen, and

Publication Date (Web): March 10, 2014. Copyright © 2014 American ... Food chains; the cradle for scientific ideas and the target for technological i...
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Comparative Evolution of Oxygen, Carbon Dioxide, Nitrogen, and Sulfites during Storage of a Rosé Wine Bottled in PET and Glass Marie Toussaint, Jean-Claude Vidal,* and Jean-Michel Salmon UE999 Pech-Rouge, INRA, 11430 Gruissan, France ABSTRACT: The management of dissolved and headspace gases during bottling and the choice of packaging are both key factors for the shelf life of wine. Two kinds of 75 cL polyethylene terephthalate (PET) bottles (with or without recycled PET) were compared to glass bottles filled with a rosé wine, closed with the same screwcaps and stored upright at 20 °C in light or in the dark. Analytical monitoring (aphrometric pressure, headspace volume, O2, N2, CO2, and SO2) was carried out for 372 days. After the consumption of O2 trapped during bottling, the total O2 content in glass bottles remained stable. A substantial decrease of CO2 and SO2 concentration and an increase of O2 concentration were observed in the PET bottles after 6 months because of the considerable gas permeability of monolayer PET. Light accelerated O2 consumption during the early months. Finally, the kinetic monitoring of partial pressures in gas and liquid phases in bottles showed contrasting behavior of O2 and N2 in comparison with CO2. KEYWORDS: PET, glass, bottle, wine, shelf life, packaging, gas balance, oxygen, carbon dioxide, nitrogen

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at 20 °C.2 This shelf life increases with the presence of scavengers and reaches 8 months for a white wine in 18.7 cL PET bottles with 2% oxygen scavengers (without precise temperature control).5 Another study of chemical changes related to oxidation showed that a red and a white wine stored in 1 L PET bottles containing 4% oxygen scavengers at 15−18 °C in the dark for 7 months exhibited behavior close to that of glass and a better behavior than those stored in monolayer PET bottles with no oxygen scavenger.17 The performance of PET with oxygen scavengers was also demonstrated by Giovanelli (2006),18 and in some cases, depending on type of PET bottles and the storage conditions, shelf life could reach 2 years.19 PET can therefore be a good alternative for wines that are drunk young. In comparison, wine in glass bottles remains relatively stable in time because glass is not permeable: exchanges between wine and air take place exclusively through the stopper. The determination of stopper oxygen permeability has been the subject of several studies,20−22 and the authors described oxygen permeability using the oxygen transmission rate (OTR). Today, stopper OTR can be measured and is often specified by manufacturers. None of the studies mentioned above included complete monitoring of headspace and dissolved gases from bottling to the end of shelf life. They included observations of different analytical parameters (fSO2 and TSO2), wine color during storage, and partial monitoring of dissolved oxygen, sometimes completed by sensory analysis. Although CO2 is important for wine sensory properties as it enhances the perception of freshness23,24 and N2 is the main atmospheric gas, O2, N2, and CO2, in dissolved form and in gaseous form in the headspace at bottling, were not controlled or accurately measured.

INTRODUCTION The use of polyethylene terephthalate (PET) for packaging is widespread in the food and beverage industry. PET bottles have an advantage for the wine industry as they can help to reduce environmental impact and transport costs because of their lightness and strength. Life cycle analysis (LCA) of PET and glass packaging showed lower potential environmental impacts of PET than of glass.1 PET can open up new global markets for wine producers in countries where consumers display no reluctance. A drawback of PET is its moderate gas permeability, and so multilayer bottles or monolayer bottles with oxygen scavengers have been developed to improve barrier properties. The difference of gas concentrations (O2, N2, and CO2) between wine and air and between headspace and wine is the main driving force of gas exchanges. According to Fick’s laws, diffusion flux goes from regions of higher concentration to regions of lower concentration to reach a gas balance. As PET is permeable, O2, CO2, and water vapor can be diffused. One of the consequences may be a slight increase in alcohol content, as observed in a white wine stored in an 18.7 cL PET bottle at 30 °C or in a 40.0% vol alcohol solution bottled in PET.2,3 Another consequence of the increase in O2 is the rapid loss of free and total SO2 (fSO2 and TSO2).4−8 This makes wine more sensitive to oxidation, and it ages faster. The reaction between O2 and SO2 is slow in wine, but SO2 can react with wine oxidation products.9−11 It can also induce an increase in color intensity and may have an adverse impact on wine aromas, especially in rosé.8,12 Many studies have addressed the shelf life of wine in PET bottles compared to glass bottles, bag-in-box, and other packaging.13−16 As expected, the results depend on the packaging volume, the presence or absence of oxygen scavengers, and storage conditions. Ough (1987) concluded that the shelf life of a white wine in 4 L PET bottles stored at 20 °C without oxygen scavenger was 10−11 months,4 whereas Boidron (1988) estimated this shelf life to be around 40 days for a wine with 30 mg/L of fSO2 stored in 18.7 cL PET bottles © 2014 American Chemical Society

Received: Revised: Accepted: Published: 2946

November 29, 2013 February 28, 2014 March 9, 2014 March 10, 2014 dx.doi.org/10.1021/jf405392u | J. Agric. Food Chem. 2014, 62, 2946−2955

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This study was a part of the Novinpak project. The first objective of the latter was to develop a monolayer PET bottle containing recycled PET (RPET) and suitable for wine. In addition, this bottle had to be light and suitable for incorporation in present industrial recycling and recovery processes. The second objective concerned gas management during bottling (dissolved oxygen (DO2), headspace or gaseous oxygen (HspO2), and dissolved carbon dioxide (DCO2)) that ensured satisfactory conservation of rosé wine. Indeed, the oxygen content of headspace and wine during bottling can be the equivalent of several months of O2 ingress through packaging.25,26 The management of both dissolved and headspace gases during bottling and the choice of packaging are the key factors in the control of the quality and shelf life of wine. Bottling is the last step before selling wine, and O2 trapped during bottling is consumed by wine and has consequences on wine aging.6,25,27−29 The final objective of the project was to be able to ensure the good conservation of the organoleptic quality of wine by gas management during bottling and oxygen ingress management during storage. Several research teams and companies worked on this project in order to attain these objectives. Wine color and aroma evolution were studied, and sensory evaluation was performed. Life cycle analyses of glass and PET bottles were compared. Inertness, food contact suitability, and the barrier properties of PET were also studied. These studies are not reported in the present paper. Our study examines the limits of a standard monolayer PET bottle for wine packaging, with regard to the three main gases present in headspace and in wine (O2, CO2, N2) and their exchanges with air in order to propose monolayer packaging for the wine targeted and its required shelf life. The impact on wine aging during 372 days of storage and SO2 content are also examined. To the best of our knowledge, this is the first complete gas balance study for PET and glass bottles in time.

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Table 1. Summary of Analyses Performed during Storage* no. of bottles/ procedure

dates of analyses (days after bottling)

analyses

method

DO2 (mg/L) converted in (mg/bt)

polarography

3

luminescence

3

HspO2 (% (v/v)) converted in (mg/bt)

micro gas chromatography luminescence

3

DCO2 (mg/L)

volumetry

3

Paphro (hPa)

pressure potentiometer FTIR

3 3

0 (12 < n < 18), 35, 91, 162, 278, 372 1, 7, 15, 21 and approx each month from 0 to 372 0 (12 < n < 18), 35, 91, 162, 278, 372 1, 7, 15, 21 and approx each month from 0 to 372 0 (12 < n < 18), 35, 91, 162, 278, 372 0 (12 < n < 18), 35, 91, 162, 278, 372 0, 35, 91, 162, 278, 372

FTIR enzymatic colorimetric

3 3 3

0 0, 35, 91, 162, 278, 372 0, 35, 91, 162, 278, 372

alcohol (%), TA (g/L H2SO4), pH RS (mg/L) VA (g/L H2SO4) fSO2 (mg/L), TSO2 (mg/L)

3

*

At least 3 bottles per procedure were analyzed for each analysis. At t = 0, “n” represents the number of bottles analyzed per procedure. To monitor bottling homogeneity throughout the process, dissolved and headspace gases were measured in a larger number of bottles (12 < n < 18).

beginning and the end of bottling is higher than during the rest of the process.27,30 Certain bottling parameters, kind of bottles, headspace and wine volume, and gas management are summarized in Table 2. Bottles were stored upright for 12 months in a thermostatically controlled room (20 ± 0.7 °C) with a relative humidity (RH) of 68 ± 9% (monitored but not controlled). Half of the bottles were stored in light (400 Lux) 24 h a day and 7 days a week and the other half stored in the dark (packed in cardboard boxes). Determination of Headspace and Wine Volume with Unfilled Level. O2 trapped in headspace directly determines consumption by wine after bottling.28 To be able to compare procedures, the same screwcap was used whatever the packaging and the headspace volume/wine volume ratios (Hspvol/winevol) were as close as possible in each procedure. The unfilled level, directly related to headspace and wine volumes, was set before bottling. Different unfilled levels and volumes of reverse osmosis water (22 °C) were tested by Sidel Blowing Service (Le Havre, France) on several bottles of each procedure. It appeared that correlation between Hspvol measured and the unfilled level was good (R2 ≈ 0.98, data not shown). Experiments conducted at UEPR indicated the accuracy and reproducibility of this method for wine (data not shown). To achieve the closest Hspvol/winevol in all procedures, the headspace level at 20 °C was set at 46 mm for PET bottles and 60 mm for glass bottles. As a result, the wine volume was not exactly the same for each packaging type (Table 2). Noninvasive Analyses. On line O2 monitoring was performed using a PreSens luminescent probe (PreSens Precision Sensing GmbH, Regensburg, Germany) and PSt3 O2-sensitive optical spots (PreSens Precision Sensing GmbH; oxygen range, 0−22 mg/L; limit of detection, 15 μg/L; accuracy, ±1% at 100% air-saturation and ±0.15% at 1% air-saturation) integrated at four checkpoints on the bottling line and at the top and bottom of the preparation and filler tank. In bottles, DO2 and HspO2 were also measured using this method.22 Data acquisition was performed using PST3v541 software (PreSens Precision Sensing GmbH). Analytical monitoring was performed on 19 dates of analyses after bottling (Table 1). The system measured oxygen partial pressure (PO2) in hPa. It could also express the values in mg/L or in % (v/v) according to the phase studied, temperature, and pressure. Headspace was measured in % (v/

MATERIALS AND METHODS

A Cinsault rosé wine was bottled at Pech Rouge Experimental Unit (INRA, UEPR, Gruissan) in 75 cL colorless glass and PET bottles. Gas management in the bottling line used achieved homogeneous bottling with negligible losses of CO2 and a low DO2 content.26,27 Two PET bottles were studied: a 38 g standard PET bottle (PET38) and a 38 g 100% recycled PET bottle (PET38R). Different methods were used to measure fSO2, TSO2, and headspace and dissolved gases (O2, CO2, N2) for one year as described in Table 1. Analyses were scheduled throughout bottle storage to characterize the changes in the wines. A PreSens probe was used for frequent measurement of HspO2 and DO2 in the same three bottles for 372 days (noninvasive analyses). However, it was not possible to measure HspCO2, HspN2, or DCO2 using this method. We therefore used other methods such as polarography and gas chromatography (invasive analyses) to measure all these parameters (gas balance) in three different bottles on several dates. Experimental Bottling. The line was first purged with N2 from preparation tank to head filler machine (to HspO2 < 1% (v/v)). The preparation tank was filled by gravity with rosé wine. The wine was sparged with N2 gas until DO2 reached 0.3 mg/L. DCO2 was then regulated with CO2 gas using a porous injector bolted to the bottom of the preparation tank until DCO2 reached 1 g/L. DCO2 was monitored by sampling in the preparation tank using a Carbodoseur (DujardinSalleron laboratories, Noizay, France). Wine was forced into the circuit by N2 to the filler tank through the filtration skid using overpressure of 150 kPa applied to the preparation tank. Bottles were blanketed before filling. Filled bottles were placed in the capping machine, where a screwcap was crimped. To achieve good bottling homogeneity, we discarded the first three and the last three bottles as DO2 at the 2947

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Table 2. Bottling Parameters at t = 0* vol (mL) unfilled level (mm) instrument no. of samples PET38 PET38R GLASS

46 46 60

Hsp

20.5 20.5 19.4

wine

742.4 742.4 751.4

(Hspvol/winevol) (%)

DO2 (mg/bt)

HspO2 (mg/ bt)

2.76 2.76 2.58

Orbisphere 12 < n < 18 1.37 ± 0.20 1.66 ± 0.10 1.19 ± 0.29

PreSens n=6 4.05 ± 0.48 4.28 ± 0.32 4.46 ± 0.32

TO2 (mg/ bt)

DCO2 (mg/ bt)

5.42 5.94 5.65

Carbodoseur 12 < n < 18 623 ± 20 601 ± 37 617 ± 24

HspCO2 (mg/ bt) μGC 12 < n 4.08 ± 4.03 ± 3.51 ±

< 18 1.94 2.06 0.95

*

Averages and standard deviations of bottling parameters: “n” represents the number of samples per analysis. TO2 is the sum of DO2 measured by Orbisphere probe and HspO2 measured by PreSens spots.

v) and converted into milligrams per bottle (mg/bt) according to Hspvol, using eq 1: HspO2 =

MO2 HspO2 ′ × Hspvol × T + 273.15 100 VM × 273.15

The methods used to determine alcohol content (% vol), total and volatile acidity (TA and VA: g/L H2SO4), pH, and free and total SO2 (fSO2 and TSO2: mg/L) are reported in Table 1. Calculation of Gas Flow Directions inside the Bottle and between Bottle and Air. In glass bottles, exchanges with air can only take place through the screwcap. As monolayer PET is gas-permeable, exchanges can also take place through the bottle wall as well. In general, as soon as a difference in the concentration of a chemical species appears in an environment, matter flows appear to reach balance. In our case, diffusion was the main driver for gas exchange between bottle and air and between headspace and wine. To determine gas exchange direction between bottle and air, we used the comparison of partial pressure of each gas in the headspace (PHspO2, PHspCO2, PHspN2) and the partial pressure of each dissolved gas (PDO2, PDCO2, PDN2) with the partial pressure of each gas in air at RH 68% (as monitored in our experiment). The partial pressure of each gas was expressed in hPa using results of the headspace composition in a bottle given by μGC in % (v/v). We consider that the air in the headspace was water vapor saturated. Oxygen partial pressure in headspace is given by eq 4:

(1)

HspO2 is headspace oxygen (mg/bt), HspO2′ is headspace oxygen (% (v/v)), Hspvol is headspace volume (mL), T is wine temperature (°C), MO2 is the molar mass of oxygen (32 g/mol), and VM is the molar volume (22.414 L/mol). DO2 values were measured in mg/L and converted into mg/bt as the volume of wine in the bottle was known. Invasive Analyses. DO2 was measured using an Orbisphere 31110A polarographic probe equipped with a 25 μm 2956A membrane (Hach Ultra Analytics, Trappes, France). The membrane range of O2 measurement was 0.25 Pa to 50 kPa (limit of detection, 1 μg/L; accuracy, 0.02 μg/L). The probe was connected to an Orbisphere Moca 3600 single channel microprocessor analyzer for oxygen measurements. Results were expressed in mg/L and converted into mg/bt according to the volume of wine. At t = 0, the Orbisphere probe was used to measure DO2 in bottles because the response time of PreSens spots in liquid is greater than in gas. As a result, measurement of DO2 should take place at least 40 min after bottling with the PreSens probe, whereas it can be measured immediately after bottling with the Orbisphere probe (Table 2). HspO2, headspace CO2 (HspCO2), headspace N2 (HspN2), and aphrometric pressure (Paphro) were measured by gas chromatography (μGC, micro GC CP4900, Varian, Les Ullis, France) (accuracy = 0.25%). A specific sampling system was set up, consisting of a peek tube with a needle, a Genie 170 membrane to prevent any liquid contamination, a four-way valve to purge the needle or to load the sample into the injectors, and an electronic manometer to measure the internal pressure of the sample (Paphro). After the piercing of the screwcap, the internal pressure was monitored and then the sample was pumped for 30 s through the circuit to ensure satisfactory clearance. A 400 μL sample was then injected in the columns. The results were expressed in % (v/v) and converted into mg/bt using eq 2:

Hspgas =

PHspO2 =

⎛ ⎞ 6690.9 − 4.681 × ln(T + 273.15)⎟ Pw(T ) = exp⎜52.57 − ⎝ ⎠ T + 273.15 (5) Equation 6 was deduced from eqs 4 and 5 and used to calculate oxygen partial pressure in the headspace using HspO2′:

PHspO2 =

⎛ HspO2 ′ ⎛ 6690.9 × ⎜Ptot − exp⎜52.57 − ⎝ ⎝ 100 T + 273.15 ⎞⎞ − 4.681 × ln(T + 273.15)⎟⎟ ⎠⎠

(6)

Similarly we calculated PHspN2 (partial pressure of N2 in headspace) and PHspCO2 (partial pressure of CO2 in headspace) using HspN2′ (headspace N2 in (% (v/v))) and HspCO2′ (headspace CO2 in (% (v/ v))). We calculated the partial pressure of O2 in air at RH 68% (PO2atm) using eq 7 (pressure in hPa):

(2)

Hspgas is gas headspace (mg/bt), Hspgas′ is gas headspace (% (v/v)), Hspvol is headspace volume (mg/L), Mgas is the molar mass of gas (O2, 32 g/mol; CO2, 44 g/mol; or N2, 28 g/mol), R is the universal gas constant (8.314 J/mol/K), T is headspace temperature (°C), and Ptot is total pressure (hPa), the sum of atmospheric and aphrometric pressure of the day 3

Ptot = Patm + Paphro

(4)

PHspO2 is the partial pressure of O2 in headspace (hPa), HspO2′ is headspace O2 measured by μGC (% (v/v)), Ptot is total pressure (hPa) (eq 3), and Pw(T) is the saturated water vapor pressure (hPa). The saturated water vapor pressure at a known temperature can be expressed using Campbell’s eq 5 in this form (T expressed in °C):

Hspgas′Ptot Hspvol × 10−6 ⎛ R ⎞ ⎜ × 103⎟(273.15 + T ) ⎝ Mgas ⎠

HspO2 ′ × (Ptot − Pw(T )) 100

PO2atm = (Patm − 0.68Pw(T )) × 0.2095

(3)

(7)

Likewise, we calculated the partial pressure of N2 and CO2 in air at RH 68% (PN2atm, PCO2atm) using eqs 8 and 9:

DCO2 was measured by sampling in the preparation tank or bottles. Determination was performed using a Carbodoseur (repeatability 90 mg/L).31 Results were expressed in mg/L and converted into mg/bt.

PN2atm = (Patm − 0.68Pw(T )) × 0.7808 2948

(8)

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Figure 1. HspO2 and DO2 for PET and glass bottles during storage time in light (a, b) and in the dark (c, d). Averages and standard deviations are calculated from 3 bottles per procedure. Data were analyzed by analysis of variance (ANOVA) at 372 days, followed by Newman−Keuls multiple comparison tests (α = 0.05). Similar letters denote no significant differences between the tested groups. HspO2 and DO2 values were obtained by PreSens, except for DO2 at t = O where values were obtained by using an Orbisphere probe. Dotted lines with squares, triangles, and diamonds indicate HspO2 of PET38, PET38R, and glass bottles respectively. Continuous lines with squares, triangles, and diamonds indicate DO2 of PET38, PET38R, and glass bottles respectively.

PCO2atm = (Patm − 0.68Pw(T )) × 0.0003

bibliographical references on wine. For dissolved gases, we were able to measure DCO2 and DO2 as described above, but we could not measure DN2. It was estimated using eq 11 based on Dalton’s law (3% is an estimate for water, ethanol, and the vapor pressure of noble gases):

(9)

We compared PHspgas with Pgasatm to identify gas flow directions between bottle and air 10 (pressures in hPa):

Hspgas% =

PHsp

gas

Pgasatm

PDN2 = 0.97 × Ptot − PDO2 − PDCO2

× 100 (10)

(11)

DO2 was given using Orbisphere probe in mg/L and was used to calculate partial pressure of O2 dissolved in wine (hPa). The solubility of oxygen in water was used here and can be described by the Bunsen absorption coefficient α(T) (eq 12):32

Hspgas% is expressed as the gas saturation percentage in air at RH 68%. As long as Hspgas% is below 100% (respectively above 100%), gas from the air tends to diffuse through the bottle wall into the headspace to reach equilibrium (respectively headspace gas tends to diffuse from bottle to air). Furthermore, we were interested in exchanges in the bottle between headspace and wine. O2, N2, and CO2 are present in the headspace and are also dissolved in the wine. These exchanges are governed by both Fick’s law and Henry’s law: the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. To calculate the pressure of dissolved gases (PDgas), we used formulas that took into account O2 and N2 dissolution in water, for lack of

PDO2 =

DO2 × 1013.25 α(T ) × 1000 ×

32 22.41 ×

T + 273.15 273.15

(12)

PDO2 is the partial pressure of dissolved O2 (hPa), DO2 is oxygen concentration (mg/L), T is temperature (°C), and α(T) is the Bunsen absorption coefficient (mL(O2)/mL), that determines the partition between gas and liquid phases (eq 13) (T expressed in °C): 2949

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RESULTS AND DISCUSSION Bottling. Results showed inter- and intraprocedure homogeneity (Table 2). HspO2 formed the major part of total oxygen content (TO2) (HspO2 ≈ 75% TO2) because of the low wine level (wine volume of 742.4 mL instead of 750 mL). Furthermore, average DO2 was 1.38 mg/bt whereas average HspO2 was higher (4.27 mg/bt). Another study conducted at UEPR showed that HspO2 could reach 0.38 mg/ bt to 3.58 mg/bt according to Hspvol, the kind of stopper, and the use of inert gas, whereas average DO2 was 3.91 mg/bt.28 TO2 was between 5.40 mg/bt and 5.95 mg/bt. However these results could have been lower if the headspace had been flushed with N2 before capping and PET bottles had a wine volume of 750 mL. Average DCO2 was 615 mg/bt (≈800 mg/L), and HspCO2 formed less than 1% of the total carbon dioxide content (TCO2) at bottling. Evolution of Headspace and Dissolved Oxygen. Figures 1a and 1b represent HspO2 and DO2 evolution for PET and glass bottles during storage in light. O2 decreased in both graphs whatever the packaging because of consumption by wine.28 This decrease was not linear and was faster during the first month.6,25 After 3 months, it increased for PET but remained stable for glass, and at 12 months, HspO2 and DO2 were 0.59/0.59, 0.63/0.64, and 0.07/0.07 mg/bt respectively for PET38, PET38R, and glass. The Newman−Keuls multiple comparison test showed that differences between procedures were significant (α = 0.05) for HspO2 and DO2 between PET and glass (for DO2 there was no difference between PET and RPET). Figures 1c and 1d represent HspO2 and DO2 during storage in the dark. We found the same behavior as previously. However, O2 consumption was slower: on day 7, HspO2 and DO2 values were higher than in light, and this was still the case after 372 days. The estimated average rate of TO2 consumption in 7 days in light was 0.49 ± 0.02 mg/bt/d (PET and glass), whereas it was 0.25 ± 0.03 mg/bt/d in the dark (Table 3). Data

α(T ) × 103 = 48.998 − 1.335T + 2.755 × 10−2 × T 2 −4

− 3.220 × 10

−6

3

× T + 1.598 × 10

×T

4

(13) As this solubility was given for dissolved oxygen in water, we used it for wine as well. DCO2 was given by Carbodoseur methodology in mg/L, and the partial pressure of dissolved CO2 (PDCO2) was then calculated. The formula according to the OIV Reference Method at 20 °C (OIV, 2008) was used for calculations and applications in wine. Equation 14 takes into account the temperature correction factor as proposed by Liger-Belair.33

PDCO2

⎛ DCO2 ⎜ =⎜ ⎜ exp 2984 × 1 − ⎝ 293.15

(

1 T + 273.15

)

⎞ 1 1 ⎟ × × ⎟ ⎟ 0.01951(0.86 − 0.01E)(1 − 0.00144 × RS) 100 ⎠ (14) PDCO2 is the partial pressure of dissolved CO2 (hPa), DCO2 is CO2 concentration (mg/L), T is wine temperature (°C), E is the alcohol content (12.6% vol alcohol), and RS is the residual sugar in wine (0.23 g/L). As explained for eq 10, if we compare PDgas (partial pressure of dissolved gases) with Pgasatm (partial pressure of gas in air at RH 68%), we can understand the direction of gas flows between wine and air (eq 15) (pressures are expressed in hPa).

Dgas% =

PDgas Pgasatm

Article

× 100 (15)

Dgas% is expressed as the percentage of gas saturation in air at RH 68% (% (sat)). Equations 10 and 15 are also used to deduce the direction of gas exchanges between headspace and wine. As long as Dgas% is below Hspgas% (respectively above), gas tends to dissolve from the headspace into the wine (respectively to diffuse from wine to headspace).25,28 Wine. The wine was a Cinsault rosé “Vin de Pays d’Oc” (12.6% vol alcohol; RS, 0.23 g/L; TA, 3.40 g/L H2SO4; VA, 0.17 g/L H2SO4; pH, 3.28; free and total SO2, 36 and 130 mg/L, respectively). Bottling Raw Materials. PET bottles were 75 cL colorless Bordeaux bottles supplied by Sidel. The OTRs of PET38 and PET38R bottles were respectively 0.0637 ± 0.0008 and 0.0527 ± 0.0009 mg/ bt/day. Glass bottles were 75 cL colorless Bordeaux bottles (BSN Glasspack SA, Villeurbanne, France). PET and glass bottles were capped with Novatwist 30H60 screwcaps (Novembal, Edison, NJ, USA) with Saranex seals (OTR: 0.0016 mg/cap/day). These caps were made of PE (polyethylene) and PP (polypropylene) and were 100% recyclable. The OTR values mentioned above were measured using a Mocon Ox-Tran 2/20 (Mocon, Minneapolis, MN. Tests were carried out by Sidel on an entire bottle at 23 °C (RH 60%), and the test gas was ambient air. Tests were performed on five bottles per procedure. Bottles of pure N2 and pure CO2 (food quality, purity ≥99.9%, Air Liquide, France) were used to manage gases during bottling as described above. Bottling Line. The bottling line used consisted of three components: (1) a filtration skid with one preparation tank (105 L), 2 cartridge housings for 1 μm prefiltration, and 0.65 μm filtration membrane cartridges; (2) a single head filler MTB 1/1 (Perrier, Le Cheylard, France) with a 46 L tank; (3) a single head capping machine (TM3, Zalkin, Rueil-Malmaison, France). Data Analysis. Statistical analyses were performed with analysis of variance (ANOVA) and Newman−Keuls multiple comparisons test (α = 0.05) using XLSTAT version 2007.1 program (Addinsoft, Paris, France).

Table 3. Estimated Average Rates of TO2 Consumption between 0 and 7 Days for PET and Glass Bottles Stored in Light and in the Dark* TO2 consumption rate (mg/bt/d) PET38 PET38R glass

light

darkness

0.49 ± 0.02 a 0.44 ± 0.01 a 0.44 ± 0.02 a

0.25 ± 0.03 b 0.28 ± 0.02 b 0.25 ± 0.05 b

*

TO2 consumption rate is an average of oxygen consumption for the first 7 days calculated with the following formula: TO2 consumption rate = (TO2t=0 − TO2t=7)/7. Averages and standard deviations were based on 3 bottles per procedure. Data were analyzed by ANOVA followed by Newman−Keuls multiple comparison tests (α=0.05). Similar letters denote no significant differences between the tested groups.

were analyzed by Newman−Keuls multiple comparison tests, and there was a statistical difference (α = 0.05) between O2 consumption rate in light and O2 consumption rate in the dark. Furthermore, a transient increase in DO2 was observed between 7 and 20 days. This means that, during this time, the rate of oxygen dissolution in wine was higher than consumption. This phenomenon was observed by Dimkou et al. (2011) for wine samples in glass bottles closed with a screwcap.6 The increase was not observed for wine stored in 2950

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Table 4. fSO2 during Storage Time for PET and Glass Bottles* fSO2 (mg/L) PET38 PET38R glass

0b

35b

162b

278b

372b

37 ± 1 a 36 ± 1 a 38 ± 1 a

24 ± 2 a 24 ± 2 a 26 ± 1 a

11 ± 0 b 11 ± 1 b 28 ± 1 a

3±1b 3±0b 19 ± 4 a

3±1b 3±2b 19 ± 1 a

*

Averages and standard deviations are based on 6 bottles per procedure (3 bottles in light + 3 bottles in the dark), except for glass bottles at 162 days (n = 4). Data were analyzed at each date by ANOVA followed by Newman−Keuls multiple comparison tests (α = 0.05). Similar letters denote no significant differences between the tested groups. bTime (d).

different wines, those stored in PET generally contain less SO2 than those stored in glass. Evolution of Headspace and Dissolved Carbon Dioxide. The results shown in Table 5 were obtained using

light, probably because of faster O2 consumption than dissolution from headspace to wine. DO2 was subsequently close to minimum on the 14th day in light but did not reach minimum in darkness before the 60th day, meaning that after the consumption of initial DO2, O2 consumption was limited by the diffusion from headspace into wine for bottles stored in light. At 12 months, HspO2 and DO2 were 0.68/0.68, 0.76/ 0.72, and 0.04/0.02 mg/bt respectively for PET38, PET38R, and glass. PET38 and PET38R exhibited similar but statistically different behavior. Evolution of SO2. Table 4 represents losses of fSO2 during storage. As there were no significant differences between storage in light and in the dark (data not shown), values represent averages at each month. Similar profiles were obtained for TSO2 (data not shown). At bottling, fSO2 was higher than 30 mg/L, and after one month, around 30% of initial fSO2 had been lost, whatever the packaging. In the early stages of storage, fSO2 decrease was consistent with other studies6,7 and was associated with the oxygen present at bottling, especially with HspO2, which represented, in our case, 75% of TO2 at t = 0. These results showed the importance of managing O2 and SO2 at bottling: the results would have been better if the headspace had been flushed by N2 just before capping.6 In wine, the reaction between oxygen and SO2 is extremely slow.9 Sulfites react with the products of wine oxidation and in particular with the hydrogen peroxide that is produced when polyphenols are oxidized.10,11 Finally, after 162 days, fSO2 in PET reached around 10 mg/L. It is widely accepted that below this limit wine is not protected anymore. Godden et al. (2001) showed that, below this concentration, the sensory perception of a Semillon wine was affected by oxidized aroma, in contrast with wines that retained higher concentrations of SO2, and had higher scores for citrus and fruity aromas.8 After one year, wine in glass bottles had still 19 ± 1 mg/L of fSO2. Data were analyzed by Newman−Keuls multiple comparison tests at 372 days and the difference between PET and glass was significant (α = 0.05). These results corroborated those found in an experiment conducted on a Sauvignon Blanc wine using 75 cL glass bottles containing 6.26 mg/bt of TO2 just after closure and stored at 17.1 °C, where fSO2 losses were 44% after one month.25 Another study showed that, for a white wine packed in 3 L PET containers and stored 12 months at 20 °C, fSO2 fell from 30 to 12 mg/L in the first month, then, to less than 4 mg/L after 12 months (similar results were found for rosé and red wines), whereas fSO2 in glass fell from 30 to 14 mg/L in the first month and then to 10 mg/L after 12 months.4 The same behavior was observed for 18.7 cL PET bottles with 2% oxygen scavenger and stored at 20−25 °C: in a white wine, the initial fSO2 was 36 mg/L and then decreased to 9 mg/L at 12 months, in contrast with 18 mg/L in glass bottles.5 After 12 months of storage of

Table 5. TCO2 during Storage Time for PET and Glass Bottles* TCO2 (mg/bt)

PET38 PET38R glass

CO2 losses (%)

0**

162**

372**

0− 162**

0− 372**

627 ± 19 a 605 ± 37 a 621 ± 25 a

498 ± 10 b 478 ± 23 c 590 ± 15 a

370 ± 0 b 357 ± 30 b 633 ± 33 a

21 21 5

41 41 −2

*

The results were obtained using a Carbodoseur for DCO2 and the μGC for HspCO2 (TCO2 = HspCO2 + DCO2). Averages and standard deviations are based on 6 bottles per procedure (3 bottles in light + 3 bottles in the dark). Data were analyzed at each date by ANOVA followed by Newman−Keuls multiple comparison tests (α = 0.05). Similar letters denote no significant differences between the tested groups. **Time (d).

a Carbodoseur for DCO2 and μGC for HspCO2. As there were no differences between storage in light or away from light (data not shown), values are averages for each month. At 162 days, TCO2 losses were 21% for PET38 and PET38R. Finally, after 372 days, TCO2 decreased by more than 40% for PET, whereas it remained almost stable for glass bottles. This decrease could have consequences on the perception of the wine.24 LonvaudFunel (1976) showed that, for a red wine with different low DCO2 contents (below 600 mg/L), differences can be detected by an untrained jury.23 Furthermore the diffusion of O2 in wine is facilitated when the CO2 concentration decreases.34 In our experiment, HspCO2 represented less than 4% of TCO2 at any time during storage. It appeared that DCO2 was very close to TCO2 and could be compared directly with it. DCO2 losses were observed in different wines stored in 75 cL PET bottles with no special barrier to prevent CO2 permeation,15,19 and also in 25 cL PET bottles where the DCO2 content decreased in wine whose initial DCO2 was more than 100 mg/L.2 Evolution of Other Parameters. There were no significant differences in alcohol content, residual sugars, TA, VA, and pH after 372 days of storage (data not shown). Direction of Gas Flows inside the Bottle and between Bottle and Air. As results for PET38R were close to those for PET38, and as there were no fundamental differences between storage in light or in the dark, the results for glass and PET38 bottles stored in light are presented here. Figure 2a covers glass bottles and represents HspO2% and DO2%. These values were calculated using eqs 4 to 15 cited previously. As HspO2% and DO2% were below 100% saturation, O2 tended to permeate into the bottle from air to reach 2951

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Figure 2. Comparison of Hspgas% and Dgas% with saturation of each gas in air at RH 68% for glass bottles stored in light. Hspgas were measured using the μGC, DO2 was measured using the Orbisphere, DCO2 was measured using the Carbodoseur, and DN2 was calculated as described previously (eq 11). For panels a, b, and c respectively, solid squares indicate DO2%, DCO2%, and DN2% and striped squares indicate HspO2%, HspCO2%, and HspN2%.

equilibrium. Furthermore, whatever the date of analyses, DO2% was lower than HspO2%, so O2 tended to dissolve in wine.28 During the first month, HspO2% and DO2% decreases were due to wine oxygen consumption (as seen in Figure 1). After three months, DO2 content was very low and remained stable at around 0.1 mg/bt (0.12 mg/L), corresponding to PDO2 ≈ 1 hPa (PHspO2 ≈ 2 hPa). These results were consistent with those found of Vidal and Moutounet (2006) in which DO2 reached value of 0.06 mg/L in a rosé wine after 150 days of storage at 20 °C.28 Figure 2b concerns CO2. As HspCO2% and DCO2% were far above 100% saturation, CO2 tended to diffuse from the bottle. In contrast with O2, HspCO2% was lower than DCO2% and so CO2 tended to diffuse from the wine to the headspace. After one month, HspCO2% and DCO2% remained stable for PHspCO2 (≈460 hPa) and PDCO2 (≈560 hPa), showing that diffusion through screwcaps is negligible in glass bottles. Finally, N2 displayed the same behavior as O2 (Figure 2c). N2 was below 100% saturation, and so it tended to permeate into the bottle, and as DN2% was below HspN2%, N2 dissolved in wine in the first month and then equilibrium was nearly attained for PHspN2 (≈640 hPa) and PDN2 (≈520 hPa). Figure 3 is for PET38. In the first month, O2 consumption by wine was the dominant factor in oxygen kinetics, but after 3

months both HspO2% and DO2% increased (Figure 3a). This meant that wine O2 consumption became slower than O2 ingress. Between 91 and 372 days, PHspO2, (respectively PDO2) increased from 11 hpa (respectively 7 hPa) to 28 hpa (respectively 25 hPa). For CO2 (Figure 3b), during first month, a phase of equilibrium between HspCO2% and DCO2% was observed like for glass bottles before PHspCO2 and PDCO2 decreased by respectively 148 hPa (0.24 mg/L) and 171 hPa (235 mg/L) between 91 and 372 days. Finally for N2, differences with glass bottles could be seen after 1 month (Figure 3c): HspN2% and DN2% increased. Between 91 and 372 days, PHspN2 (respectively PDN2) increased slightly from 607 hPa (respectively 480 hPa) to 616 hPa (respectively 561 hPa). These results could be compared with those of Paphro (Table 6). Standard deviations showed that there was substantial variability within each procedure. It was observed for PET bottles that Paphro decreased from 41 ± 33 hPa to −68 ± 21 hPa during one year of storage. For glass bottles, Paphro decreased but remained positive. As standard deviations were substantial, it was difficult to make a conclusion although a decrease of Paphro for PET bottles could be expected: eq 11 cited previously can be used for partial pressure in bottle headspace: 0.97(Paphro + Patm) = PHSO2 + PHSCO2 + PHSN2 2952

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dx.doi.org/10.1021/jf405392u | J. Agric. Food Chem. 2014, 62, 2946−2955

Journal of Agricultural and Food Chemistry

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Figure 3. Comparison of Hspgas% and Dgas% with saturation of each gas in air at RH 68% for PET38 bottles stored in light. Hspgas were measured using the μGC, DO2 was measured using the Orbisphere, DCO2 was measured using the Carbodoseur, and DN2 was calculated as described previously (eq 11). For panels a, b, and c respectively, solid squares indicate DO2%, DCO2%, and DN2% and striped squares indicate HspO2%, HspCO2%, and HspN2%.

Table 6. Paphro during Storage Time for PET and Glass Bottles* Paphro (hPa) **

**

1 PET38 PET38R PET average glass

30 55 41 167

± ± ± ±

162**

91 38 22 33 19

−3 17 7 94

± ± ± ±

−5 13 4 111

19 9 18 19

± ± ± ±

17 10 16 6

278** −48 −44 −46 79

± ± ± ±

32 15 24 28

372** −76 −59 −68 84

± ± ± ±

19 20 21 29

*

Paphro is measured by μGC. Averages and standard deviations are based on 6 bottles per packaging (3 bottles in light + 3 bottles in the dark), except for PET38R bottles at 1 day (n = 5). **Time (d).

Patm varied slightly during one year (