Short communication

New pressure-activated compartmented oxygen indicator for

intelligent food packaging

Nan Young Jang & Keehoon Won*

Department of Chemical and Biochemical Engineering, Dongguk University-Seoul, 30 Pildong-ro 1-gil, Jung-gu, Seoul 100-715, Republic of

Korea

(Received 29 March 2013; Accepted in revised form 24 July 2013)

Keywords Colourimetric oxygen indicators, in-pack activation, intelligent food packaging, leak detectors, modified atmosphere packag-

ing, oxygen scavengers.

Introduction

Intelligent or smart food packaging can be defined asthe packaging system that senses, communicates andmonitors the conditions of packaged food to giveinformation about food quality, safety and the historyof a product during transport and storage. It can pro-vide great benefits for consumers and food industryand thus is becoming more important (Ahvenainen &Hurme, 1997; Brody et al., 2008; Pereira de Abreuet al., 2012). Various variables related to food qualityand safety are monitored in the intelligent packaging:temperature, carbon dioxide, oxygen, toxin and so on(De Jong et al., 2005; Nga et al., 2011; Jung et al.,2012; Vu & Won, 2013a,b). Besides other factors, oxy-gen has a significant influence on the spoilage processof several products and thus is removed in food pack-aging by modifying the atmosphere with gases such asnitrogen and/or using oxygen scavengers/oxygenabsorbers (Lee et al., 2008; Pereira de Abreu et al.,2012). However, the oxygen level in the package head-space can increase with time due to poor sealing, airpermeation through the package materials and thepackage tampered with or damaged during storageand/or transportation. As a result, the spoilage processof food is accelerated; therefore, the absence of oxygenshould be assured by sensing oxygen in the package.Whereas conventional oxygen detection methodsrequire expensive instruments and trained operators,visual oxygen indicators are cheap and also enableconsumers to notice the presence of oxygen in the foodpackage with their naked eyes (Mills, 2005). Not onlyoxygen indicators are applied to verify the effectiveness

of oxygen scavengers/oxygen absorbers, but also theyare used as seal and leak detectors with modifiedatmosphere packaging (Ahvenainen & Hurme, 1997;Smolander et al., 1997; Pereira de Abreu et al., 2012).The most widely used oxygen indicator is a colouri-

metric redox dye–based indicator, which was commer-cialised (e.g. Ageless Eye� produced by the MitsubishiGas Chemical Company, Tokyo, Japan) (Yoshikawaet al., 1979; Eaton, 2002). This type of oxygen indica-tor is typically composed of a redox dye such as meth-ylene blue and a reducing agent such as glucose in analkaline solution. In the absence of O2, methylene blueexists in its colourless reduced form (leuco-methyleneblue, kmax = 256 nm) by glucose in NaOH solution,but in the presence of oxygen, the dye is oxidised tohighly coloured form (MB, kmax = 665 nm), indicatingoxygen in the package (Obata, 1961; Mills et al.,2011). These processes can be described according tothe following equations (Adam�c�ıkov�a et al., 1999):

GluþOH� $ Glu� þH2O ð1Þ

MBþGlu� ! X� þ LMB ð2Þ

O2 þ 4LMB ! 4MBþ 2H2O ð3Þwhere Glu is glucose, X� is the oxidation productsfrom glucose, MB and LMB represent the oxidisedand the reduced form of methylene blue, respectively.However, the traditional oxygen indicators have a seri-ous drawback: they must be prepared, packaged andstored under anaerobic conditions because they reacteven to air with a high level (21%) of oxygen and stopworking in a few hours owing to the exhaustion of thereducing agent (Smolander et al., 1997; Lee et al.,2004; Mills, 2005; Pereira de Abreu et al., 2012).

*Correspondent: Fax: +82 2 2268 8729; e-mail: keehoon@dongguk.

edu

International Journal of Food Science and Technology 2014 49, 650–654

doi:10.1111/ijfs.12310

© 2013 The Authors. International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

650

To tackle this problem (i.e. the requirement ofanaerobic conditions during manufacturing and stor-age), we report a new, simple and practical approachof a pressure-activated oxygen indicator in this work.Unlike conventional oxygen indicators, the compo-nents of this oxygen indicator are physically separatedby a pressure-ruptured impervious barrier, which canbe readily broken by simple physical methods (e.g.pressing with hands). Only when the barrier is broken,each component separated in the compartments isallowed to be in contact with each other and starts towork as an oxygen indicator. The working principle ofthe pressure-activated oxygen indicator is illustrated inFig. 1. This new type of oxygen indicator is activatedonly when the package is sealed (i.e. in-pack activa-tion) and can lengthen a shelf-life even under atmo-spheric conditions. The pressure-activatedcompartmented oxygen indicator is devised and testedin this study.

Materials and methods

Materials

Unless otherwise indicated, all the chemicals were pur-chased from Sigma-Aldrich (St. Louis, MO, USA) andused without any further purification. PET(12 lm)/ON(15 lm)/LLDPE(30 lm) film (oxygen permeability:29 mL/m2�24 h�atm) and LDPE film (oxygen perme-ability: 7900 mL/m2�24 h�atm) were obtained fromSunyang (Korea) and Wowpack (Korea), respectively.

Preparation of the pressure-activated compartmentedoxygen indicators

A pressure-activated compartmented oxygen indicatorwas fabricated as follows: the PET/ON/LLDPE pack-aging film (4.5 9 3 cm) was placed on the metal platewith two holes. The film on the plate was pulled by avacuum pump and thus formed two wells. Methyleneblue (MB), glucose (Glu) and sodium hydroxide

(NaOH) were added to the two wells. There are threepossible combinations to divide the three componentsof oxygen indicators into the two compartments: TypeA, B and C. In the case of Type A, 200 lL of anaqueous mixture of MB and NaOH was poured intoone well (compartment I) and 200 lL of a Glu solu-tion was into the other well (compartment II). Type Bhas MB in the compartment I and a mixture of Gluand NaOH in the compartment II; Type C has a mix-ture of MB and Glu in the compartment I and NaOHin the compartment II (see Fig. 1). The MB, Glu andNaOH concentrations in each compartment were fixedat 0.4 mM, 200 mM and 200 mM, respectively; afteractivation, they became 0.2 mM, 100 mM and 100 mM,respectively. Then, the rim of each well was tightlyheat-sealed with the oxygen-permeable LDPE film(4.5 9 3 cm) to prevent drying and leaking. However,the barrier film between the two compartments wasloosely heat-sealed so that it could be opened easily(see Fig. 1).

Activation of the oxygen indicator and colourmeasurement

The unactivated oxygen indicators (Type A, B and C)were stored at 4, 20 or 45 °C under atmospheric con-ditions for 12 h, during which time the colour of eachcompartment was monitored. To test the pressure-acti-vated compartmented oxygen indicator, the C-typeindicator that had been stored at 4 °C was activated(i.e. it was pressed with a hand) and then placed in agas cell under ambient conditions. To the cell was con-tinuously supplied a mixed gas of O2 and N2 (0.2, 1, 5,10 or 21% oxygen) produced using an automatic gasmixing system (Sehwa Hightech Co., Korea) composedof a static mixer and two mass flow controllers (KoflocModel 3660, Japan); one (10 sccm) was connected toan oxygen cylinder, and the other (500 sccm) was to anitrogen cylinder. The oxygen concentration in the gascell was checked using an oxygen sensor (CheckPointII, PBI-Dansensor, Denmark). The gas cell containing

Figure 1 Schematic diagram and working

principle of the pressure-activated

compartmented oxygen indicator. MB and

Glu are methylene blue and glucose,

respectively.

© 2013 The Authors

International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

International Journal of Food Science and Technology 2014

Pressure-activated oxygen indicator N. Y. Jang and K. Won 651

the activated oxygen indicator was incubated at roomtemperature. All the experiments were carried out atleast in triplicate, and the data were presented with themean and the standard deviation.

The colours of the oxygen indicators were measuredusing a portable spectrophotometer (CM-2600d,Konica Minolta, Tokyo, Japan), which measures thespectral distribution of reflectance of samples and cal-culates colour, with the SCI mode (specular compo-nent included), which evaluates total appearanceindependent of surface conditions. The colours wereexpressed as L* (lightness), a* (redness/greenness) andb* (yellowness/blueness) (Korifi et al., 2013); theL*a*b* colour space (also referred to as CIELAB) isthe most widely used due to the uniform distributionof colours (Wu & Sun, 2013). The colour changes withtime were determined numerically as the index of totalcolour change, DE:

DE ¼ ½ðDL�Þ2 þ ðDa�Þ2 þ ðDb�Þ2�1=2 ð4Þ

where DL*, Da* and Db* are differences in L*a*b*between controls and samples (Adekunte et al., 2010;Licciardello & Muratore, 2011; Pathare et al., 2013).The controls were samples at time = 0, and the colourmeasurement was performed on 3–4 points for eachsample.

Results and discussion

First of all, we examined whether the pressure-acti-vated oxygen indicator changed in colour under aero-bic conditions before activation. The three types ofcompartmented oxygen indicators were stored underatmospheric conditions at different temperatures for

12 h, and the colour of each compartment wasmonitored. At the beginning, every compartment I wasblue because of MB oxidised by atmospheric oxygen,whereas every compartment II was colourless. Whenthe nonactivated oxygen indicators were stored at4 °C, all types of oxygen indicators showed little col-our change even if they were exposed to oxygen (datanot shown). At 20 °C, the Type B and C oxygen indi-cators did not display noticeable colour changes; how-ever, the colour of the Type A compartment Icontaining MB and NaOH changed with time fromblue to violet as shown in Fig. 2a. This may be attrib-uted to the decay of MB in the alkaline solution.Alkali must be used to create sugar anions to reduceblue MB to colourless LMB (eqns 1 and 2); the rateof MB reduction was dependent on NaOH concentra-tion (Adam�c�ıkov�a et al., 1999). It is known that underalkaline conditions, MB decomposes through hydroly-sis of the dimethylamino group and demethylation,and consequently, the spectrum of MB changes(Singhal & Rabinowitch, 1967; Mills et al., 2011). Theabsorption spectrum of MB shows a long-wavelengthmaximum at 665 nm (a-band) and a short-wavelengthshoulder at 608–610 nm (b-band), which are ascribedto the monomeric and dimeric forms, respectively. Thespectral shape depends on MB concentration, that is.,an increase in the dye concentration causes a decreasein the monomer band (a-band) and a development ofthe more energetic band (b-band) (Ghanadzadeh et al.,2008). When MB was in NaOH solution (0.5 M) at20 °C for 129 min, both a- and b-bands loweredwhereas the absorbance at 580 nm rose (i.e. the colourchanged), and the MB decomposition followed thefirst-order kinetics with respect to NaOH concentra-tion (Adam�c�ıkov�a et al., 2000).

Time (h)

ΔE

0

5

10

15

20

25

30

Time (h)0 2 4 6 8 10 120 2 4 6 8 10 12

ΔE

0

5

10

15

20

25

30Type A, compartment I (MB + NaOH)Type A, compartment II (Glu)Type B, compartment I (MB)Type B, compartment II (Glu + NaOH)Type C, compartment I (MB + Glu)Type C, compartment II (NaOH)

(a) (b)

Figure 2 Colour changes during storage of the three types of oxygen indicators (before activation) under atmospheric conditions (a) at 20 °Cand (b) at 45 °C.

© 2013 The Authors

International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

International Journal of Food Science and Technology 2014

Pressure-activated oxygen indicator N. Y. Jang and K. Won652

The storage temperature of the oxygen indicatorswas increased; the three types of pressure-activatedoxygen indicators were placed in a 45 °C oven, andtheir colours were monitored for 12 h. The increase intemperature brought about twice the larger colourchange in the compartment I of the A-type oxygenindicator as shown in Fig. 2b. It appears that thehigher temperature can accelerate the MB decay in thealkaline solution. Not only Type A but also Type Boxygen indicator exhibited a significant colour change:the compartment II to contain Glu and NaOH turnedorange/brown. This is due to glucose degradation byalkali, which is a well-known phenomenon. Muchresearch has been conducted to understand the alka-line degradation of monosaccharides in aqueous solu-tion (Corbett & Liddle, 1961; Moulik et al., 1978).Glucose undergoes various degradation reactions,

which can be enhanced at high temperature. The deg-radation products are primarily composed of manysaccharinic (≤ C6) acids. Higher molecular weightcompounds (> C6 acids) and diverse nonacidic andcyclic unsaturated carbonyl compounds are alsoformed in minor amounts (Yang & Montgomery,1996). Glucose degradation under alkaline conditionsis accompanied by colour formation (Eggleston &Vercellotti, 2000).Among the three types, only the Type C oxygen

indicator turned out to be kept unchanged in colourwhen stored at 4, 20 and 45 °C under aerobic condi-tions, showing the highest stability. This is becauseMB and glucose, which are degraded by alkali, arephysically separated from NaOH; therefore, the TypeC oxygen indicator was employed for further study.For reference, 12 h after activating the three types ofoxygen indicators that had been stored at 45 °C for12 h, we measured their colour changes (DE) underambient conditions and found that the C-type oxygenindicator exhibited a higher DE value than the othertwo types (data not shown).We examined whether the compartmented oxygen

indicator could be activated with pressure and functionas a colourimetric oxygen indicator. The fragile barrierof the Type C oxygen indicator was ruptured by press-ing with a bare hand, and each component separatedin the two compartments was allowed to mix. Thismixing made the blue colour of methylene blue disap-pear; this is because MB was reduced to leuco-methy-lene blue (colourless) by the reducing sugar (i.e.glucose in the NaOH solution). After the activation,the oxygen indicator was placed in a gas cell withvarying concentrations of oxygen, and its colour wasmonitored using the portable spectrophotometer. Fig-ure 3a indicates that the colour of the oxygen indica-tor changed with time (it turned blue); the extent ofthe colour change increased with oxygen concentrationas shown in Fig. 3b (Eaton, 2002). This clearly showsthat the pressure-activated oxygen indicator devised inthe present study successfully works as a colourimetricoxygen indicator.

Conclusions

A pressure-activated oxygen indicator has been pro-posed for the first time. The three components (i.e.methylene blue, glucose, and NaOH) were physicallyseparated into two compartments. When the oxygenindicator (Type C), in which an aqueous mixture ofMB and Glu is in one compartment and NaOH solu-tion in the other compartment, was stored at 4, 20 and45 °C, it was kept unchanged in colour even in the air.Upon rupture of the barrier to separate the two com-partments, the pressure-activated oxygen indicatorbegan to function; it turned blue depending on oxygen

Time (h)

ΔE

0

5

10

15

20

2521% O210%5%1%0.2%

Oxygen concentration (%)

0 5 10 15 20 25

0 5 10 15 20 25

ΔE a

fter 2

4 h

0

5

10

15

20

25

(a)

(b)

Figure 3 (a) Colour changes of the Type C oxygen indicator (after

activation) with time under the environment with varying concentra-

tions of oxygen. (b) Dependence of the colour change on oxygen

concentration.

© 2013 The Authors

International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

International Journal of Food Science and Technology 2014

Pressure-activated oxygen indicator N. Y. Jang and K. Won 653

concentration. The new, simple and practical oxygenindicator has advantages over traditional oxygen indi-cators: it does not require anaerobic conditions andlacks degradation of dyes and reducing sugars byalkali during preparation and storage. This pressure-activated colourimetric oxygen indicator with a longshelf-life can be applied to verify that all oxygen isremoved with oxygen scavengers/oxygen absorbers andcan be used as seal and leak detectors with modifiedatmosphere packaging; it will be essential for intelli-gent food packaging.

Acknowledgments

This research was supported by the AgricultureResearch Center (ARC, 710003-03-3-SB120) programof the Ministry for Food, Agriculture, Forestry andFisheries, Korea.

References

Adam�c�ıkov�a, L., Pavl�ıkov�a, K. & �Sev�c�ık, P. (1999). The methyleneblue-D-glucose-O2 system. oxidation of D-glucose by methyleneblue in the presence and the absence of oxygen. International Jour-nal of Chemical Kinetics, 31, 463–468.

Adam�c�ıkov�a, L., Pavl�ıkov�a, K. & �Sev�c�ık, P. (2000). The decay ofmethylene blue in alkaline solution. Reaction Kinetics and CatalysisLetters, 69, 91–94.

Adekunte, A.O., Tiwari, B.K., Cullen, P.J., Scannell, A.G.M. &O’Donnell, C.P. (2010). Effect of sonication on colour, ascorbicacid and yeast inactivation in tomato juice. Food Chemistry, 122,500–507.

Ahvenainen, R. & Hurme, E. (1997). Active and smart packagingfor meeting consumer demands for quality and safety. Food Addi-tives and Contaminants, 14, 753–763.

Brody, A.L., Bugusu, B., Han, J.H., Sand, C.K. & Mchugh, T.H.(2008). Innovative food packaging solutions. Journal of Food Sci-ence, 73, R107–R116.

Corbett, W.M. & Liddle, A.M. (1961). The alkaline degradation ofglucose and of some of its acetyl derivatives. Journal of the Chemi-cal Society, 531–538.

De Jong, A.R., Boumans, H., Slaghek, T., Van Veen, J., Rijk, R. &Van Zandvoort, M. (2005). Active and intelligent packaging forfood: is it the future? Food Additives and Contaminants, 22,975–979.

Eaton, K. (2002). A novel colorimetric oxygen sensor: dye redoxchemistry in a thin polymer film. Sensors and Actuators B: Chemi-cal, 85, 42–51.

Eggleston, G. & Vercellotti, J.R. (2000). Degradation of sucrose, glu-cose and fructose in concentrated aqueous solutions under constantpH conditions at elevated temperature. Journal of CarbohydrateChemistry, 19, 1305–1318.

Ghanadzadeh, A., Zeini, A., Kashef, A. & Moghadam, M. (2008).Concentration effect on the absorption spectra of oxazine1 and

methylene blue in aqueous and alcoholic solutions. Journal ofMolecular Liquids, 138, 100–106.

Jung, J., Puligundla, P. & Ko, S. (2012). Proof-of-concept study ofchitosan-based carbon dioxide indicator for food packaging appli-cations. Food Chemistry, 135, 2170–2174.

Korifi, R., Le Dr�eau, Y., Antinelli, J.-F., Valls, R. & Dupuy, N.(2013). CIEL*a*b* color space predictive models for colorimetrydevices–analysis of perfume quality. Talanta, 104, 58–66.

Lee, S.-K., Mills, A. & Lepre, A. (2004). An intelligence ink for oxy-gen. Chemical Communications, 1912–1913.

Lee, K.-E., Kim, H.J., An, D.S., Lyu, E.S. & Lee, D.S. (2008).Effectiveness ofmodified atmosphere packaging in preserving a preparedready-to-eat food.Packaging Technology and Science, 21, 417–423.

Licciardello, F. & Muratore, G. (2011). Effect of temperature andsome added compounds on the stability of blood orange marma-lade. Journal of Food Science, 76, C1094–C1100.

Mills, A. (2005). Oxygen indicators and intelligent inks for packag-ing food. Chemical Society Reviews, 34, 1003–1011.

Mills, A., Hazafy, D., Parkinson, J., Tuttle, T. & Hutchings, M.G.(2011). Effect of alkali on methylene blue (CI Basic Blue 9) andother thiazine dyes. Dyes and Pigments, 88, 149–155.

Moulik, S.P., Basu, D. & Bhattacharya, P.K. (1978). Effects of vari-ous conditions on the alkaline degradation of D-fructose andD-glucose. Carbohydrate Research, 63, 165–172.

Nga, M., Audorff, H., Reichstein, W. et al. (2011). Performance of aphotochromic time-temperature indicator under simulated freshfish supply chain conditions. International Journal of Food Scienceand Technology, 46, 297–304.

Obata, H. (1961). Photoreduction of methylene blue by visible lightin the aqueous solution containing certain kinds of inorganic saltsII. photobleached product. Bulletin of the Chemical Society ofJapan, 34, 1057–1063.

Pathare, P.B., Opara, U.L. & Al-Said, F.A.-J. (2013). Colour mea-surement and analysis in fresh and processed food: a review. Foodand Bioprocess Technology, 6, 36–60.

Pereira de Abreu, D.A., Cruz, J.M. & Paseiro Losada, P. (2012).Active and intelligent packaging for the food industry. FoodReviews International, 28, 146–187.

Singhal, G.S. & Rabinowitch, E. (1967). Changes in the absorptionspectrum of methylene blue with pH. Journal of Physical Chemis-try, 71, 3347–3349.

Smolander, M., Hurme, E. & Ahvenainen, R. (1997). Leak indica-tors for modified-atmosphere packages. Trends in Food Science andTechnology, 8, 101–106.

Vu, C.H.T. & Won, K. (2013a). Bioinspired molecular adhesive forwater-resistant oxygen indicator films. Biotechnology Progress, 29,513–519.

Vu, C.H.T. & Won, K. (2013b). Novel water-resistant UV-activatedoxygen indicator for intelligent food packaging. Food Chemistry,140, 52–56.

Wu, D. & Sun, D.-W. (2013). Colour measurements by computervision for food quality control–A review. Trends in Food Scienceand Technology, 29, 5–20.

Yang, B.Y. & Montgomery, R. (1996). Alkaline degradation of glu-cose: effect of initial concentration of reactants. CarbohydrateResearch, 280, 27–45.

Yoshikawa, Y., Nawata, T., Goto, M. & Fujii, Y. (1979). Oxygenindicator. US Patent 4169811.

© 2013 The Authors

International Journal of Food Science and Technology © 2013 Institute of Food Science and Technology

International Journal of Food Science and Technology 2014

Pressure-activated oxygen indicator N. Y. Jang and K. Won654