Effect of storage time and container type on the quality of extra-virgin olive oil

Food Control 18 (2007) 521–529 www.elsevier.com/locate/foodcont

EVect of storage time and container type on the quality of extra-virgin olive oil Ana Isabel Méndez, Elena Falqué

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Química Analítica, Depto. Química Analítica y Alimentaria, Facultad de Ciencias, Universidade de Vigo, As Lagoas s/n, 32004 Ourense, Spain Received 10 April 2005; received in revised form 30 December 2005; accepted 30 December 2005

Abstract Four commercial samples of extra-virgin olive oil have been analysed in order to evaluate the inXuence of storage time on quality. The following parameters were determined after 3 and 6 months of storage: acidity, peroxide index, absorption coeYcients K270 and K230, percentage of humidity, impurity content (%), phenols content, iodine index, saponiWcation index, colour index and fatty acid content. At the same time, the eVects of container type on the deterioration in quality were studied. Each olive oil was stored in Wve diVerent containers at room temperature with the same surface area of exposition to air and light: clear PET bottle, PET bottle (covered with Al foil), glass bottle, tin, and Tetra-brik®. The results showed a gradual loss of quality during storage, especially in plastic or glass bottles. The best containers for commercial packing of extra-olive oil were tin and Tetra-brik®. © 2006 Elsevier Ltd. All rights reserved. Keywords: Extra-virgin olive oil; Storage time; Container; Chemical composition

1. Introduction Among the diVerent categories of olive oil, the “extravirgin olive oil” is outstanding in gastronomic, nutritional, therapeutic and economic importance. The other categories are generally used for cooking and in salads, but have less taste and aroma. Extra-virgin olive oil is considered to be the best olive oil for its organoleptic characteristics, for its stability and its chemical composition. It is the juice of the olive that is harvested at optimum maturity and correctly processed. It is practically the only vegetable oil that can be consumed directly in its raw state and contains important nutritional elements (fatty acids, vitamins, etc.). It should have an organoleptic score of 76.5 and a maximum acidity of 1° (EC, 1991, 1997). This excellent quality of extra-virgin olive oil is the culmination of a process that begins with the tree and Wnishes *

Corresponding author. Tel.: +34 988 387081; fax: +34 988 387001. E-mail address: [email protected] (E. Falqué).

0956-7135/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2005.12.012

in the bottle. Thus, it is necessary to care for each step of the process and of the factors that can aVect its commercial life (oxygen, light, temperature, metals, etc.) leading to a deterioration in quality as a consequence of oxidative and hydrolytic degradations (Psomiadou & Tsimidou, 2002a, 2002b). Similar to other products that are produced in a limited period of time, but that are consumed throughout the year, it must be stored, and these storage and packing conditions are going to determine the commercial life of the olive oil (Hrncirik & Fritsche, 2005; Kiritsakis & Dugan, 1984; Zanoni, Bertucciolo, Rovellini, Marotta, & Mattei, 2005). In particular, among the natural antioxidants, phenolic compounds, -tocopherol and -carotene, are reported to play a key role in preventing oxidation and have been already correlated to the storage stability of virgin olive oils (Baldiolo, Servili, Perreti, & Montedoro, 1996; Rahmani & Csallany, 1998). The eVect of some storage conditions (in darkness, diVused room light or direct sunlight, at room or elevated temperature, exposure to air and air/light, etc.) and/or packaging material (into glass and polyethylene plastic bottles, into colourless or green bottles,

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into tins, etc.) on olive oil quality (Murillo-Ramos, BonillaPolo, González-Bonillo, & Sanz-Pérez, 1997; Naz, Siddiqi, Sheikh, & Sayeed, 2005; Paganuzzi, De Lorgi, & Malerba, 1997), on olive marc oil quality (Méndez & Falqué, 2002), and on extra-virgin olive oil quality (Caponio, Bilancia, Pasqualone, Sikorska, & Gomes, 2005; de Leonardis & Macciola, 1998; Procida & Cichelli, 1999) was studied by several authors. The changes in oil quality are also reXected in the standardized quality indices, oxidative stability and tocopherol levels with the storage time (Gutiérrez & Fernández, 2002). However, other predictive studies shown that the stability of extra-virgin olive oil was not signiWcantly inXuenced by diVerent controlled bottling, transport and storage conditions in supermarkets (Pagliarini, Zanoni, & Giovanelli, 2000). Commonly, extra-virgin olive oil is usually packaged in glass, tin or plastic bottles. The primary advantages for the two Wrst ones are its impermeability to gases, but the glass and plastic bottles had some disadvantages such as to favour the photo-oxidation. This study was set up to investigate the change in extra-virgin olive oil quality, as a function of type of container and storage time, based on the analysis of parameters such as acidity, peroxide index, coeYcients K270 and K232, iodine index, colour index, saponiWcation index, impurity, humidity and volatile materials, phenol compounds and fatty acids.

2. Materials and methods Four commercial extra-virgin olive oils have been selected: two of maximum acidity 0.7° (A1 and A2) and two others of maximum acidity 0.5° (A3 and A4). And Wve containers were evaluated: plastic bottle (transparent), opaque plastic bottle (covered with Al foil), glass bottle (transparent), tin, and Tetra-brik Aseptic®. The olive oils were acquired in a supermarket so that the amount of each variant selected had the same expiry date and a homogenous sample could be obtained. All of the selected olive oils had an expiry date exceeding the maximum duration of this investigation. The total amount of each olive oil was emptied into a sterile recipient for homogenisation and, in the minimum possible time, was transferred without headspace to the Wve containers studied in duplicates. Each of the oils was poured into 330 mL poly(ethylene) terephtalate (PET) transparent or covered, transparent glass, tin and Tetrabrik aseptic® bottles with a surface area of 250 cm2 exposed to air and light. The PET, obtained from the bottles of mineral water, was washed several times with distilled water and dried. The glass, tin and plastic-coated paperboard laminate containers, obtained from the bottles of soft drinks, were sterilized. The closed bottles were placed in the centre of a metallic shelf in a chamber with glass windows at room temperature (20–22 °C) and in an adequate space and separation to ensure equalized exposure to air and light (natural and Xuorescence lamps). These storage conditions

were selected to simulate the real conditions in a market place (illumination 10–12 h/day). The olive oils were analysed at the time of purchase and packing and after 3 and 6 months of storage at room temperature (the series of bottles were stored without opening for these times). The chemical and physical parameters (acidity, peroxide index, absorption coeYcients in UV at 232 and 270 nm, iodine index, humidity, impurity, colour index, saponiWcation index and fatty acid content) were analysed, in triplicate, following the analytical methods described in Regulations EEC/2568/91 and EEC/2472/97 of the European Union Commission, and the phenol content was determined according to the method proposed by Satue, Huang, and Frankel (1995). 3. Results and discussion To determine the eVect of the container type during the storage time on the oil quality, the results of each parameter were compared with the values obtained for the samples analysed immediately after opening the original cans (controls). The values of the initial acidity of the extra-virgin olive oils studied are below the maximum levels established by the Regulations EEC/2568/91 and EEC/2472/97 of the European Union Commission. After storing the samples for 3 months (Table 1), a similar slight increase in acidity in the Wve types of container was observed, although this was less marked in a plasticcoated paperboard laminate and tin. After 6 months the increase in acidity in all the containers was conWrmed, but to a lesser degree in a plastic-coated paperboard laminate, followed by tin can and glass bottle. The plastic bottle appears to be the container in which the hydrolytic processes of the glycerides was most intense, which could be related to the permeability of the container to oxygen and light, and less intense in the opaque plastic container (isolated from the light) than in the normal transparent container. Although the glass bottle does not allow the penetration of gases, it is sensitive to the action of light on the fatty acids, which also produces an increase in acidity. The evolution of this chemical parameter shows slightly lower values in the olive oils stored in a plastic-coated paperboard laminate than in tin containers. These results agree with the study performed by TawWk and Huyghebaert (1997) during 2 months that conWrmed the increase of acidity in olive oil over time. The initial peroxide index of the olive oils analysed (Table 1) is between 18.3 and 19.7 meq O2/kg being lower than the maximum values indicated by the EEC Regulations. After 3 months of storage it can be seen that oxidation is in advanced phases, due to the sensibility of extravirgin olive oil to photo-oxidation, although this is less notable in the A2 and A3 oil samples stored in a plasticcoated paperboard laminate and tin, as the natural pigments of the extra-virgin olive oil (chlorophylls) in the absence of light act as antioxidants, acting synergistically

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523

Table 1 Evolution of the acidity and peroxide index of extra-virgin olive oil during the storage time and in diVerent containers Container

Storage time (month)

Extra-virgin olive oil samples A1 § S.D.a

A2 § S.D.

A3 § S.D.

A4 § S.D.

Acidity (% oleic acid) Plastic Opaque plastic Glass Tin plate Tetra-brik

0 3 6 3 6 3 6 3 6 3 6

Peroxide index (meq O2/kg oil) 0 Plastic 3 6 Opaque plastic 3 6 Glass 3 6 Tin plate 3 6 Tetra-brik 3 6 a

0.31 § 0.0003 0.36 § 0.0004 0.45 § 0.0008 0.36 § 0.0089 0.44 § 0.0004 0.35 § 0.0008 0.44 § 0.0008 0.35 § 0.0094 0.44 § 0.0008 0.34 § 0.0003 0.41 § 0.0011

0.39 § 0.0004 0.43 § 0.0004 0.49 § 0.0005 0.43 § 0.0025 0.48 § 0.0005 0.42 § 0.0022 0.45 § 0.0009 0.39 § 0.0016 0.45 § 0.0005 0.39 § 0.0004 0.41 § 0.0011

0.30 § 0.0003 0.39 § 0.0027 0.46 § 0.0009 0.36 § 0.0000 0.45 § 0.0013 0.36 § 0.0008 0.45 § 0.0004 0.33 § 0.0003 0.42 § 0.0004 0.32 § 0.0006 0.41 § 0.0008

0.25 § 0.0003 0.30 § 0.0010 0.38 § 0.0014 0.29 § 0.0005 0.38 § 0.0007 0.29 § 0.0003 0.37 § 0.0007 0.28 § 0.0010 0.34 § 0.0006 0.28 § 0.0010 0.33 § 0.0003

19.7 § 0.09 16.8 § 0.16 25.5 § 0.09 17.4 § 0.29 21.4 § 0.08 22.1 § 0.08 26.9 § 0.01 21.4 § 0.07 26.3 § 0.07 22.9 § 0.09 23.4 § 0.29

19.0 § 0.12 23.3 § 0.36 34.8 § 0.08 20.1 § 0.13 14.5 § 0.15 20.2 § 0.04 23.4 § 0.01 19.7 § 0.18 23.7 § 0.03 19.2 § 0.08 21.2 § 0.11

18.6 § 0.23 23.8 § 0.99 30.0 § 0.04 20.5 § 0.10 19.2 § 0.02 22.4 § 0.19 22.1 § 0.08 18.7 § 0.28 23.1 § 0.01 18.7 § 0.08 21.8 § 0.03

18.3 § 0.08 12.2 § 0.10 20.5 § 0.49 13.8 § 0.06 15.5 § 0.05 17.5 § 0.07 21.6 § 0.07 17.6 § 0.13 16.4 § 0.15 17.4 § 0.01 16.6 § 0.11

S.D.: standard deviation of three replicates.

with the phenol antioxidants (Interesse, Ruggiero, & Vitagliano, 1971), inhibiting the initiation stage of auto-oxidation. An increase in the peroxide index (propagation phase) is produced in all the samples at 6 months, as, once autooxidation is started, it does not stop until all the free radicals that are formed are inactivated (Kiritsakis, 1992). The less signiWcant evolution of the peroxides during the period of analysis is very similar in the plastic-coated paperboard laminate and in the tin container. The opaque plastic, as in the two previous types of container, protects the olive oil from the light, but its permeability to oxygen accelerates the auto-oxidation process, acting as a catalyst. The oxidation reactions appear in more advanced stages than in the plastic-coated paperboard laminate and tin containers, and the propagation or degradation stage of oxidation is observed. This takes place simultaneously, due to the presence of oxygen that favours the formation and decomposition of the hydroperoxides, originating other volatile compounds with lower molecular weights that are responsible for the disagreeable smell and taste of the olive oil (Angerosa, Di Giacinto, & De Mattia, 1993; Solinas, Angerosa, & Cucurachi, 1985). In the glass and plastic bottles, the action of light on the olive oil is favouring photo-oxidation, although in both containers, the pigments of the olive oil (chlorophylls and pheophytins) have an oxidising eVect (Interesse et al., 1971; Khan & Shadidi, 1999; Procida & Cichelli, 1999). In addition, the permeability to oxygen is an inXuence in the plastic bottle, for which reason, at 6 months, the olive oil shows

a higher degree of oxidation and an increase in the peroxide index is produced in all the samples. The initial values of the coeYcients K270 and K232 are between 0.15 and 0.17 for K270, and between 2.06 and 2.45 for K232, within the limits permitted by the legislation. In Fig. 1 it can be seen that after 3 months of storage, primary and secondary oxidation increases in all the samples. However, the olive oils stored in a plastic-coated paperboard laminate and in tin containers show lower levels of absorbance at 270 nm than in the other containers and there is a lesser degree of oxidation (primary and secondary) in the plastic-coated paperboard laminate. After 6 months of storage the increase of these coeYcients in all the samples and in any type of container is conWrmed. The lesser oxidative alteration in the containers stored in the dark could be related to the antioxidant eVect of the natural pigments in the dark (Rahmani & Csallany, 1998), acting synergistically with the phenols. But the opaque plastic allows the entrance of oxygen and, once the irreversible auto-oxidation reactions begin, they are forming hydroperoxides that simultaneously degrade other compounds. An increase in oxidation also occurs in the samples stored in glass and PET plastic containers, due to the increase in the number of compounds resulting from the degradation of the hydroperoxides, which is conWrmed by an increase of the coeYcient K270 (Gasparoli, Taormina, & Fedeli, 1991; OlíasJiménez & Gutiérrez-González-Quijano, 1970). But, compounds susceptible to primary oxidation are still found in the samples, corroborated by the values of the coeYcient

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A.I. Méndez, E. Falqué / Food Control 18 (2007) 521–529

Plastic

Opaque Pl.

Glass

Tin plate

Tetra Brik

4.000

K-232

3.000 2.000 1.000 0.000 0

3

6

3

6

3

6

3

6

3

6

Storage time (months)

A1

A3

A2

A

A4

Plastic

Opaque Pl.

Glass

3

3

Tin plate

Tetra Brik

0.300

K-270

0.250 0.200 0.150 0.100 0

3

6

3

6

6

6

3

6

S torage time (months) B

A1

A2

A3

A4

Fig. 1. Evolution of the absorption coeYcients K232 (A) and K270 (B) of extra-virgin olive oils during storage time and in diVerent containers.

K232, which increases in all the samples stored in glass and plastic containers. Higher values of coeYcient K232 are found in the olive oils stored in plastic bottles than in the rest of the containers. This could be due to the joint action of light and the permeability of this type of container to oxygen, which catalyses the oxidation reaction. As a result the olive oil in this type of container shows a higher oxidative rancidity level after 3 months of storage. At the end of the period of sample analysis, the number of characteristic compounds of secondary oxidation continues to increase, with an evolution in the diVerent types of container similar to that already explained for up to 3 months of storage. The initial content in humidity and volatile compounds do not exceed the maximum value tolerated for extra-virgin olive oil. Percentage of humidity increases with storage time, above all in olive oils stored in normal and opaque plastic bottles, followed by glass, tin, and plastic-coated paperboard laminate. The least increase with respect to the initial value is produced in this latter container (Table 2). The evolution of this parameter is a danger for the conservation of extra-virgin olive oil as this could acquire a strange taste or smell and, moreover, other processes of alteration could be induced in the product (Civantos, 1999). In this sense, the olive oils stored in plastic bottles (normal

and opaque) are the ones that show a major variation and, therefore, are the riskiest for conserving the quality of the olive oil until it is consumed. The percentage of impurities of all the initial samples is below the level established by EEC Regulations. The evolution of this parameter in the diVerent containers is shown in Table 2 and reXects an increase with storage time, although to a diVerent degree according to the container used. In normal and opaque plastic there is a greater increase of impurities, duplicating in almost all the samples after 3 months of storage, followed by glass and tin containers. The olive oil stored in a plastic-coated paperboard laminate shows the least variation of this parameter. The degree in which the impurities increase in each sample can be related to the degree of oxidation. The olive oil stored in plastic (normal and opaque) shows the highest level of rancidity, followed by those stored in glass, tin and plastic-coated paperboard laminate. As a consequence of oxidation, the content in oxidised compounds, fatty acids, and impurities increases, which result in a deterioration of the organoleptic characteristics of the extra-virgin olive oil (Angerosa et al., 1993). Initially a markedly high content of phenols is found in the extra-virgin olive oils (with the exception of A1 that

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525

Table 2 Evolution of the humidity (%), impurity (%) and phenol content (ppm gallic acid) of extra-virgin olive oil during the storage time and in diVerent containers Container

Storage time (month)

Extra-virgin olive oil samples A1 § S.D.a

A2 § S.D.

A3 § S.D.

A4 § S.D.

% Humidity Plastic Opaque plastic Glass Tin plate Tetra-brik

0 3 6 3 6 3 6 3 6 3 6

0.06 § 0.0001 0.07 § 0.0002 0.09 § 0.0001 0.07 § 0.0005 0.09 § 0.0001 0.07 § 0.0006 0.08 § 0.0005 0.07 § 0.0001 0.08 § 0.0005 0.07 § 0.0005 0.08 § 0.0001

0.07 § 0.0005 0.08 § 0.0003 0.09 § 0.0005 0.08 § 0.0001 0.09 § 0.0001 0.08 § 0.0005 0.09 § 0.0006 0.07 § 0.0001 0.08 § 0.0001 0.07 § 0.0009 0.08 § 0.0001

0.07 § 0.0004 0.08 § 0.0001 0.09 § 0.0006 0.07 § 0.0014 0.09 § 0.0004 0.07 § 0.0007 0.08 § 0.0001 0.07 § 0.0010 0.08 § 0.0008 0.07 § 0.0006 0.08 § 0.0005

0.07 § 0.0001 0.08 § 0.0001 0.10 § 0.0005 0.08 § 0.0006 0.09 § 0.0001 0.08 § 0.0008 0.09 § 0.0004 0.08 § 0.0004 0.09 § 0.0001 0.08 § 0.0004 0.09 § 0.0006

0 3 6 3 6 3 6 3 6 3 6

0.017 § 0.0001 0.010 § 0.0002 0.012 § 0.0001 0.009 § 0.0003 0.012 § 0.0003 0.008 § 0.0001 0.011 § 0.0001 0.007 § 0.0001 0.011 § 0.0001 0.007 § 0.0001 0.010 § 0.0001

0.006 § 0.0003 0.010 § 0.0001 0.013 § 0.0017 0.009 § 0.0002 0.011 § 0.0006 0.008 § 0.0002 0.010 § 0.0001 0.008 § 0.0003 0.010 § 0.0001 0.007 § 0.0003 0.009 § 0.0002

0.005 § 0.0003 0.008 § 0.0003 0.011 § 0.0004 0.008 § 0.0002 0.011 § 0.0001 0.007 § 0.0002 0.010 § 0.0001 0.007 § 0.0001 0.009 § 0.0003 0.006 § 0.0004 0.008 § 0.0001

0.006 § 0.0001 0.013 § 0.0003 0.019 § 0.0003 0.012 § 0.0002 0.018 § 0.0002 0.010 § 0.0001 0.015 § 0.0001 0.009 § 0.0001 0.015 § 0.0003 0.008 § 0.0003 0.014 § 0.0004

285 § 0.01 160 § 0.01 39 § 0.01 164 § 0.01 49 § 0.04 172 § 0.01 66 § 0.01 175 § 0.01 70 § 0.01 176 § 0.01 74 § 0.01

519 § 0.01 360 § 0.05 120 § 0.04 387 § 0.01 176 § 0.01 429 § 0.01 194 § 0.07 476 § 0.00 241 § 0.05 489 § 0.01 267 § 0.03

549 § 0.01 451 § 0.06 139 § 0.01 466 § 0.01 210 § 0.07 475 § 0.01 217 § 0.01 477 § 0.01 250 § 0.01 478 § 0.01 265 § 0.05

433 § 0.01 303 § 0.01 108 § 0.06 305 § 0.01 113 § 0.01 310 § 0.01 165 § 0.05 320 § 0.01 172 § 0.00 324 § 0.01 173 § 0.01

% Impurity Plastic Opaque plastic Glass Tin plate Tetra-brik

Phenol content (ppm gallic acid) 0 Plastic 3 6 Opaque plastic 3 6 Glass 3 6 Tin plate 3 6 Tetra-brik 3 6 a

S.D.: standard deviation of three replicates.

shows a content of 285 ppm, much lower than the other olive oils) with values similar to those found by Vázquez, del Valle, and del Valle (1976), Satue et al. (1995) and Barranco, Fernández-Escobar, and Rallo (1999). This high concentration of phenols in the extra-virgin olive oils could be related to the production process and its aptitude for being consumed directly without the necessity of being previously reWned (GutWnger, 1981; Satue et al., 1995; Vázquez, Janer del Valle, & Janer del Valle, 1973). The lower concentration in which it appears in sample A1 (Table 2) could be due to the dependence of this parameter on diVerent factors: agronomic (variety, cultivation system, environmental factors, date of harvesting), extraction system used (COI, 1987; Montedoro & Garofolo, 1984; Vázquez et al., 1976), and inclusively could be related to the plastic container used in the commercialisation of this particular extra-virgin olive oil, as they are normally commercialised stored in glass bottles.

These natural antioxidants provide the olive oil with certain characteristics at a chemical, organoleptic, and health level. At a chemical level, there is a correlation between the total polyphenols content and the stability of the olive oil against oxidation (Monteleone, Caporale, Carlucci, & Pagliarini, 1998; Tsimidou, Papadopaulos, & Boskou, 1992; Vázquez et al., 1976). They are also related to the sensorial characteristics of the virgin olive oil (COI, 1987). Thus, bitterness is considered to be a positive attribute in virgin olive oil and is directly related to the content in polyphenols (Jiménez et al., 1994; Uceda, Jiménez, Hermoso, & Frías, 1994). There was a sharp decrease in phenol contents in all the samples during storage, as a consequence of the hydrolysis and oxidation of these compounds (Cinquanta, Esti, & La Note, 1997), which involves a loss of stability and a deterioration of the sensorial properties and, therefore, of the commercial quality of the olive oil. The degradation of these

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A.I. Méndez, E. Falqué / Food Control 18 (2007) 521–529

Table 3 Evolution of the iodine index and saponiWcation index of extra-virgin olive oil during the storage time and in diVerent containers Container

Storage time (month)

Extra-virgin olive oil samples A1 § S.D.a

Iodine index (g I2/100 g oil) 0 Plastic 3 6 Opaque plastic 3 6 Glass 3 6 Tin plate 3 6 Tetra-brik 3 6 SaponiWcation index (mg KOH/g oil) 0 Plastic 3 6 Opaque plastic 3 6 Glass 3 6 Tin plate 3 6 Tetra-brik 3 6

A3 § S.D.

A4 § S.D.

82.41 § 0.14 80.74 § 0.18 77.68 § 0.18 81.16 § 0.05 77.98 § 0.04 81.33 § 0.10 78.53 § 0.16 81.25 § 0.13 78.65 § 0.28 81.46 § 0.21 79.03 § 0.01

84.89 § 0.03 82.46 § 0.05 77.50 § 0.05 82.71 § 0.02 77.89 § 0.04 82.94 § 0.02 78.60 § 0.02 83.07 § 0.12 78.86 § 0.05 83.52 § 0.11 79.35 § 0.07

85.69 § 0.31 84.40 § 0.17 80.28 § 0.09 84.52 § 0.01 80.55 § 0.01 84.05 § 0.03 80.81 § 0.01 84.17 § 0.22 82.82 § 0.09 84.70 § 0.17 82.84 § 0.07

87.93 § 0.02 80.95 § 0.01 77.54 § 0.32 81.34 § 0.21 78.01 § 0.01 81.28 § 0.27 78.19 § 0.09 81.60 § 0.03 79.14 § 0.11 81.83 § 0.21 79.69 § 0.14

190.45 § 0.16 188.20 § 0.10 185.13 § 0.11 188.49 § 0.44 185.80 § 0.06 188.59 § 0.23 185.75 § 0.12 188.73 § 0.12 185.65 § 0.01 189.19 § 0.28 187.11 § 0.11

189.40 § 0.16 187.10 § 0.03 181.40 § 0.03 186.73 § 0.05 182.28 § 0.01 188.34 § 0.25 183.45 § 0.12 187.29 § 0.10 183.70 § 0.11 187.53 § 0.23 184.46 § 0.28

188.60 § 0.18 186.59 § 0.01 183.49 § 0.23 186.39 § 0.40 184.39 § 0.01 186.97 § 0.14 184.65 § 0.10 185.45 § 0.27 184.52 § 0.01 185.72 § 0.01 185.01 § 0.01

192.35 § 0.23 190.71 § 0.14 186.00 § 0.10 191.07 § 0.01 187.00 § 0.01 190.48 § 0.25 187.22 § 0.30 191.17 § 0.35 187.42 § 0.01 191.40 § 0.28 187.56 § 0.11

S.D.: standard deviation of three replicates.

natural antioxidants is notable in the A1 sample of olive oil; in which the initial concentration is reduced to one seventh (284 to 38 ppm) after 6 months storage. The initial value of the iodine index of the samples is very homogenous (Table 3), varying between 82.41 and 87.93 g I2/100 g oil. After 3 months of storage a slight decrease is observed in a similar manner in all the containers tested. However, after 6 months of storage, the variation of this parameter is conWrmed, not only with respect to the temperature and storage time (TawWk & Huyghebaert, 1997), but also with respect to the type of container, showing a sharper decrease with respect to the initial value in plastic (normal and opaque), followed by glass and tin containers. Plastic-coated paperboard laminate is again the container in which the extra-virgin olive oil is least aVected by degradation of the double bonds that could be a consequence of oxidation. The saponiWcation index of the samples at the beginning of the investigation is within the range Wxed by EEC Regulations and the homogeneity of the results is noticeable, showing values of between 188.60 and 192.35 mg KOH/g oil (Table 3). After 3 months of storage a slight decrease of this parameter is observed to a similar degree in the diVerent types of containers, which is conWrmed after 6 months in all the containers. Although, in the olive oils stored in plastic bottles (normal and opaque), the decrease is such that A2 and A3 show a saponiWcation index at the limit or below the level permitted by the legislation. On the contrary, the samples stored in a plastic-coated paperboard laminate still

Colour index

a

A2 § S.D.

Plastic

80 70 60 50 40 30 20 10 0

Opaque Pl.

Glass Tin plate

Tetra Brik A1 A2 A3 A4

0

3 6

3

6

3

6

Storage time (month)

3

6

3

6

Fig. 2. Evolution of the colour index of extra-virgin olive oils during storage time and in diVerent containers.

show levels that are within the limits established by EEC Regulations. The colour index is identiWed using the A.B.T. scale of indexes (Fig. 2). After 3 months of storage there is no variation in colour. However, at the end of the investigation, a change was produced in the colour of the samples when plastic or glass bottles had been used for storage, showing an intensiWcation of the A.B.T. indexes and a brownish colour. This could be a consequence of the interaction of the natural pigments with the light, fundamentally the chlorophylls that degrade with photo-oxidation to produce pheophytins, and the appearance of other compounds resulting from advanced oxidation (Kiritsakis, 1992; Mínguez, Rejano, Gandul, Sánchez, & Garrido, 1990). All these are produced to a greater

A.I. Méndez, E. Falqué / Food Control 18 (2007) 521–529

degree in the extra-virgin olive oil stored in plastic or glass bottles than in plastic-coated paperboard laminate or tin containers (Olías-Jiménez & Gutiérrez-González-Quijano, 1971). The modiWcation of the colour index means deterioration in the organoleptic value of the extra-virgin olive oil (Garrido, Gandul, Gallardo, & Mínguez, 1990) and a loss in the commercial importance of the product, because it is one of the sensorial parameters that make it attractive to the purchaser. The initial content of fatty acids of all the samples is within the established limits. The isomers that are detected in extra-virgin olive oils are “cis” isomers, as the detection of “trans” isomers would mean that the olive oil had been submitted to high pressures or temperatures (Civantos, 1999). The high percentage of oleic acid is noticeable, which is the predominant acid (Tables 4a and 4b). The analyses performed after 3 months of storage show that the percentage of fatty acids analysed has not varied with respect to the initial composition. Neither were signiWcant variations observed after 6 months storage, although the fatty acids margaric, margaroleic, and gadoleic were not detected, despite minimal amounts (<0.30%) in the initial samples and after 3 months of storage. A slight decrease in the percentage of oleic acid is produced, which is supposed to be the consequence of the degree of oxidation in the samples (Frega, Mozzon, & Lercker, 1999). This was noted fundamentally in the olive oils stored in plastic bottles (normal and opaque) and above all in oil sample A1 with an initial content of 76.3% that fell to 73.3%. The percentage of polyunsaturated fatty acids remains more or less constant throughout the period of investigation.

527

4. Conclusion The physical–chemical parameters analysed in the diVerent samples of extra-virgin olive oil at the beginning of the investigation are within the limits established by the legislation, but vary during the storage period and according to the container employed. The principal cause of the deterioration of the extra-virgin olive oil during storage is the oxidation and hydrolysis reactions and the products resulting from these, loss of natural antioxidants, variation in the content of natural pigments – fundamentally chlorophylls and carotenes – increase of rancidity, increase of impurities, etc. This loss of extra-virgin olive oil quality is very more marked the Wrst 3 months of storage, and afterwards remained almost constant. With respect to storage time, the acidiWcation and oxidative rancidity of the olive oil increases during the storage period. The degree of unsaturation tends to decrease as the expiry date becomes closer and, although the percentage of fatty acids remain constant until 3 months of storage, after 6 months an increase in the degree of saturation and a decrease in the characteristic fatty acid (oleic) is observed as a consequence of its oxidation. All of the physical–chemical parameters analysed changed during 6 months resulting in a deterioration in quality of this food product. With respect to the type of container, it is seen that the traditional container (plastic bottle) in which some extra-virgin olive oils are packaged commercially is not the most adequate for storage as, after 3 months, the oil has lost more stability compared to the other containers as a consequence

Table 4a Evolution of fatty acid content (% § S.D.a) of extra-virgin olive oil during the storage time and in diVerent containers % Initial

Plastic

0 month

3 months

6 months

Opaque plastic

Glass

3 months

3 months

6 months

Tin plate 6 months

3 months

Tetra-brik 6 months

3 months

6 months

A1 oil sample Palmitic 10.3 § 0.1 Palmitoleic 0.8 § 0.0 Margaric 0.1 § 0.1 Margaroleic 0.1 § 0.0 Estearic 4.1 § 0.1 Oleic 76.3 § 0.1 Linoleic 5.0 § 0.1 Linolenic 0.7 § 0.1 Araquic 0.4 § 0.1 Gadoleic 0.2 § 0.1

10.6 § 0.7 10.6 § 0.2 0.8 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.0 ND 3.1 § 0.1 4.7 § 0.1 75.3 § 0.1 73.3 § 0.4 6.2 § 0.1 6.5 § 0.4 0.6 § 0.0 0.8 § 0.1 0.4 § 0.1 0.7 § 0.1 0.2 § 0.1 ND

10.3 § 0.1 10.6 § 0.3 0.8 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.0 ND 4.1 § 0.1 4.5 § 0.3 76.5 § 0.1 73.5 § 0.1 5.0 § 0.1 6.5 § 0.1 0.7 § 0.0 0.7 § 0.2 0.4 § 0.0 0.6 § 0.0 0.2 § 0.1 ND

10.5 § 0.3 10.7 § 0.2 0.8 § 0.1 0.8 § 0.1 0.1 § 0.0 ND 0.1 § 0.1 ND 4.0 § 0.1 4.3 § 0.1 76.0 § 0.1 75.1 § 0.1 5.0 § 0.0 3.7 § 0.1 0.7 § 0.1 0.7 § 0.1 0.4 § 0.1 0.5 § 0.1 0.2 § 0.0 ND

10.3 § 0.1 10.5 § 0.1 0.8 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.0 ND 4.1 § 0.1 4.7 § 0.1 76.6 § 0.1 75.0 § 0.1 4.9 § 0.0 5.2 § 0.1 0.6 § 0.1 0.6 § 0.1 0.4 § 0.1 0.5 § 0.1 0.2 § 0.1 ND

10.5 § 0.1 10.7 § 0.1 0.9 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.0 ND 3.9 § 0.01 4.3 § 0.1 76.0 § 0.2 75.4 § 0.1 5.0 § 0.1 5.4 § 0.2 0.7 § 0.1 0.7 § 0.1 0.4 § 0.1 0.5 § 0.0 0.2 § 0.1 ND

A2 oil sample Palmitic 12.1 § 0.1 Palmitoleic 0.9 § 0.0 Margaric 0.1 § 0.1 Margaroleic 0.2 § 0.1 Estearic 2.9 § 0.0 Oleic 72.4 § 0.1 Linoleic 7.9 § 0.0 Linolenic 0.7 § 0.1 Araquic 0.4 § 0.1 Gadoleic 0.3 § 0.1

12.0 § 0.1 12.2 § 0.1 0.9 § 0.1 1.4 § 0.1 0.1 § 0.0 ND 0.2 § 0.1 ND 3.0 § 0.1 3.7 § 0.3 72.3 § 0.1 70.5 § 0.3 7.9 § 0.1 7.9 § 0.1 0.7 § 0.0 0.8 § 0.1 0.4 § 0.1 0.6 § 0.1 0.3 § 0.0 ND

12.2 § 0.0 12.2 § 0.3 1.0 § 0.1 1.4 § 0.1 0.1 § 0.1 ND 0.2 § 0.1 ND 2.9 § 0.1 3.8 § 0.1 72.2 § 0.1 70.8 § 0.1 7.9 § 0.1 7.9 § 0.1 0.6 § 0.0 0.8 § 0.1 0.4 § 0.1 0.6 § 0.1 0.3 § 0.1 ND

12.2 § 0.1 12.2 § 0.1 1.0 § 0.0 1.3 § 0.1 0.1 § 0.0 ND 0.2 § 0.1 ND 3.0 § 0.1 3.7 § 0.1 72.4 § 0.1 71.0 § 0.1 7.8 § 0.0 7.9 § 0.0 0.6 § 0.0 0.8 § 0.1 0.4 § 0.1 0.5 § 0.1 0.3 § 0.0 ND

12.2 § 0.3 12.2 § 0.1 0.9 § 0.1 1.3 § 0.1 0.1 § 0.1 ND 0.2 § 0.1 ND 2.9 § 0.1 3.5 § 0.1 72.3 § 0.2 71.4 § 0.1 7.8 § 0.1 7.8 § 0.1 0.6 § 0.0 0.8 § 0.1 0.4 § 0.0 0.5 § 0.0 0.3 § 0.0 ND

12.2 § 0.1 0.9 § 0.1 0.1 § 0.0 0.2 § 0.1 2.9 § 0.1 72.3 § 0.1 7.8 § 0.2 0.6 § 0.0 0.4 § 0.1 0.3 § 0.0

ND: not detected. a S.D.: standard deviation of three replicates.

12.2 § 0.1 1.3 § 0.1 ND ND 3.5 § 0.3 71.5 § 0.2 7.9 § 0.1 0.7 § 0.1 0.5 § 0.1 ND

528

A.I. Méndez, E. Falqué / Food Control 18 (2007) 521–529

Table 4b Evolution of fatty acid content (% § S.D.a) of extra-virgin olive oil during the storage time and in diVerent containers % Initial

Plastic

0 month

3 months

6 months

Opaque plastic

Glass

3 months

3 months

6 months

Tin plate 6 months

3 months

Tetra-brik 6 months

3 months

6 months

A3 oil sample Palmitic 11.9 § 0.1 Palmitoleic 0.9 § 0.1 Margaric 0.1 § 0.1 Margaroleic 0.2 § 0.1 Estearic 3.1 § 0.0 Oleic 72.8 § 0.1 Linoleic 7.6 § 0.1 Linolenic 0.7 § 0.1 Araquic 0.4 § 0.1 Gadoleic 0.2 § 0.0

11.8 § 0.1 11.8 § 0.1 0.9 § 0.1 1.1 § 0.1 0.1 § 0.0 ND 0.2 § 0.0 ND 3.0 § 0.1 3.9 § 0.1 72.8 § 0.1 71.8 § 0.1 7.6 § 0.0 7.7 § 0.1 0.7 § 0.0 0.7 § 0.1 0.4 § 0.0 0.6 § 0.1 0.3 § 0.1 ND

11.7 § 0.1 11.7 § 0.1 0.9 § 0.1 1.1§ 0.1 0.1 § 0.0 ND 0.2 § 0.0 ND 3.1 § 0.1 3.7 § 0.1 73.1 § 0.1 72.4 § 0.4 7.6 § 0.1 7.7 § 0.1 0.7 § 0.0 0.7 § 0.1 0.4 § 0.0 0.6 § 0.1 0.3 § 0.0 ND

12.1 § 0.1 11.7 § 0.4 0.9 § 0.1 1.0 § 0.1 0.1 § 0.1 ND 0.2 § 0.1 ND 3.0 § 0.0 3.6 § 0.4 72.6 § 0.1 72.3 § 0.4 7.5 § 0.1 7.6 § 0.0 0.7 § 0.0 0.7 § 0.0 0.4 § 0.0 0.5 § 0.1 0.3 § 0.1 ND

11.8 § 0.1 11.8 § 0.2 0.9 § 0.1 1.1 § 0.1 0.1 § 0.0 ND 0.2 § 0.1 ND 3.1 § 0.1 3.3 § 0.2 73.0 § 0.2 72.5 § 0.2 7.6 § 0.1 7.7 § 0.1 0.7 § 0.0 0.7 § 0.1 0.4 § 0.1 0.5 § 0.1 0.3 § 0.1 ND

11.7 § 0.1 11.6 § 0.0 1.0 § 0.0 1.0 § 0.1 0.1§ 0.0 ND 0.2 § 0.0 ND 3.1 § 0.0 3.2 § 0.0 73.1 § 0.1 73.0 § 0.1 7.6 § 0.1 7.6 § 0.1 0.7 § 0.0 0.7 § 0.1 0.4 § 0.1 0.5 § 0.1 0.3 § 0.1 ND

A4 oil sample Palmitic 10.8 § 0.2 Palmitoleic 0.8 § 0.1 Margaric 0.1 § 0.0 Margaroleic 0.1 § 0.0 Estearic 3.3 § 0.1 Oleic 77.5 § 0.2 Linoleic 4.2 § 0.1 Linolenic 0.7 § 0.0 Araquic 0.4 § 0.1 Gadoleic 0.2 § 0.0

10.5 § 0.2 10.7 § 0.0 0.7 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.1 ND 3.3 § 0.1 3.8 § 0.1 77.6 § 0.4 76.2 § 0.1 4.2 § 0.1 4.4 § 0.1 0.6 § 0.1 0.7 § 0.1 0.4 § 0.1 0.6 § 0.1 0.2 § 0.0 ND

10.6 § 0.1 10.7 § 0.1 0.8 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.1 ND 3.3 § 0.1 3.7 § 0.1 77.7 § 0.3 76.5 § 0.2 4.2 § 0.1 4.4 § 0.1 0.7 § 0.1 0.7 § 0.1 0.4 § 0.1 0.6 § 0.1 0.2 § 0.1 ND

10.6 § 0.1 10.7 § 0.1 0.8 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.1 ND 3.6 § 0.1 3.6 § 0.1 77.4 § 0.3 77.0 § 0.1 4.1 § 0.1 4.3 § 0.1 0.7 § 0.0 0.7 § 0.1 0.5 § 0.0 0.6 § 0.1 0.3 § 0.0 ND

10.5 § 0.1 10.6 § 0.1 0.7 § 0.1 0.9 § 0.1 0.1 § 0.0 ND 0.1 § 0.1 ND 3.3 § 0.1 3.5 § 0.1 77.7 § 0.2 77.4 § 0.1 4.1 § 0.1 4.2 § 0.0 0.6 § 0.0 0.7 § 0.1 0.4 § 0.1 0.5 § 0.1 0.2 § 0.1 ND

10.8 § 0.2 10.6 § 0.1 0.8 § 0.1 0.9 § 0.1 0.1 § 0.1 ND 0.1 § 0.0 ND 3.3 § 0.1 3.5 § 0.1 77.7 § 0.2 77.3 § 0.2 4.1 § 0.1 4.3 § 0.0 0.6 § 0.1 0.7 § 0.1 0.4 § 0.1 0.4 § 0.1 0.2 § 0.0 ND

ND: not detected. a S.D.: standard deviation of three replicates.

of the action of oxygen and light that induce a rapid deterioration in plastic bottles. Likewise, acidiWcation, an increase in impurities, loss of the phenolic fraction, etc. is favoured. The storage of extra-virgin olive oil in plastic bottles, but isolated from light (covered with aluminium foil), allows the conservation of its properties for longer than in the traditional plastic bottle, which suggested that the light transmission on the PET bottle, during this initial storage time, is unimportant compared to oxygen permeability. Although after 6 months of storage deterioration is similar, due to its permeability to oxygen. Glass acts as a barrier to oxygen, which cannot pass through it, avoiding the loss of certain components that deteriorate in its presence, but it does allow the direct action of light on the olive oil, producing oxidative rancidity even earlier than in the opaque plastic container, as a consequence of its sensibility to photo-oxidation. Although most of the extra-virgin olive oils are packaged commercially in glass bottles as an indicator of high quality, this container does not maintain throughout its commercial life, the sensorial and nutritive attributes for which the product is so much appreciated. The plastic-coated paperboard laminate and tin containers are possibly the least used commercially at the present time. However, they would be the most appropriate for maintaining the quality of extra-virgin olive oil, at least during 6 months. Both, in common, protect against light and gases, but the Tetra-brik Aseptic® conserves the initial characteristics of the product much better than any of the containers.

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