Development of temperature indicator prototype: Cardpaper coated with chitosan intelligent films

doi:10.4236/jacen.2014.31B002

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Vol.3, No.1B, 5-10 (2014) Journal of Agricultural Chemistry and Environment

http://dx.doi.org/10.4236/jacen.2014.31B002

Development of t e mperature indicat or pro t otype:

Cardpaper coated with chitosan intelligent films

Vinicius B. V. Maciel1*, Cristiana M. P. Yoshida2, Telma T. Franco1

1Department of Chemical Engineering, State University of Campinas, Campinas, Brazil;

*Corresponding Author: [email protected]

2Department of Exact and Earth Sciences, Federal University of Campinas, Diadema, Brazil

Received October 2013

ABSTRACT

An intelligent and biodegradable material pack-

aging was developed based on a natural and

thermal-sensitive pigment. Anthocyanin (ATH,

0.50 g/100g) was incorporated into chitosan

matrix films (2 g/100g) forming a chitosan intel-

ligent film (C-ATH). The system is able to indi-

cate the variation of temperature during distri-

bution and storage chain of industrial products.

The novelty of this work was an alternativ e pack-

aging material that it is biodegradable and could

inform any temperature variations on the range

of 40˚C - 70˚C, by irreversible visual colour

changes. The effects of temperature (10˚C, 30˚C

and 50˚C) and luminosity (0, 500 and 1000 l×)

were analyzed on C-ATH using an experimental

design of 2 variables, measuring the colour pa-

rameters (L*, a*, b*) and mechanical properties

(tensile strength, elongation break and Young’s

modulus) as responses. C-ATH suspensions

were applied as a coating on cardpaper surface

forming a temperature indicator prototype (TIP).

C-ATH darkened after being exposed to temper-

atures above 50˚C and luminosity of 1000 lx for

72 hours. TIP was obtained, without bubbles or

defects, with reduced water absorption capacity.

Irreversible visual colour change was verified on

TIP exposed at 40˚C independently of luminosity,

turned gradually yellow. Chitosan suspensions

containing ATH and applied as a coated on card

paper sheets could be an alternative of biode-

gradable material for packaging system that in-

dicates efficiently temperature changes. This in-

dicator system has potential application tem-

perature range of 40˚C to 70˚C, such as food,

pharmaceuticals, biological, agricultural and

others products, that are highly dependent of

storage temperature conditi ons.

KEYWORDS

Chitosan; Anthocyanin; Temperature Indicator;

Coating; Card Paper

1. INTRODUCTION

The natural polymer films application in the packaging

sector has been investigated due to their biodegradability

and ability to retard the transport of moisture, gas, fla-

vour and lipids. Films based on natural macromolecules,

have been described in literature; however, industrial ap-

plications are still scarce. Among the natural polymers,

chitosan forms resistant films with an efficient oxygen

barrier [1,2].

Intelligent packaging is designed to monitor and com-

municate information about packed product quality and

safety. Examples include time-temperature indicators,

ripeness indicators, biosensors, radio frequency identifi-

cation, etc. Colourimetric indicators can detect and moni-

tor changes in the conditions of packed products [3] by

visual colour variations .

Temperatur e greatly affects the quality and safety of

thermal-sensitive products such as food, drugs and bio-

logical compounds. Variations in temperature conditions

could promote undesirable physical and chemical dete-

riorations [4]. Time-temperatur e indicato rs (TTIs) are d e -

fined as simple, cost-effective and user-friendly devices

to monitor, record and cumulatively indicate the overall

influence of temperature traceability on the quality of the

food product from the manufacturer to the consumer [5].

TTIs could be present as small self-adhesive labels that

provide visual indications of temperature history during

distribution and storage [6]. New types of TTIs have re-

cently been studied; one example is a system based on

the growth and metabolic activ ity of a strain of Lactoba-

cillus sakei, which monitored food quality throughout the

chilled-food chain [7]. Yan et al. [8] developed a new

amyl a s e -type TTI based on the reaction between amylase

and starch solution, changing the colour from blue to

V. B. V. Maciel et al. / Journal of Agricultural Chemistry and Environment 3 (2014) 5-10

yellow after temperature exposure from 4˚C to 37˚C.

Kato, Yoshida, Reis, Melo and Franco [9] developed a

fast and colorimetric indicator system by combining chi-

tosan as a three-dimensional biopolymer matrix and ferr-

ous sulfate (FeSO4) as a colorimetric indicator of hydro-

gen sulfide (H2S) gas. Maciel, Yoshida and Franco [10]

developed an intelligent and biodegradable temperature

indicator packaging material based on a natural and heat-

sensitive pigment and chitosan solution dispersing on

card paper.

In this study, the objective was to develop an intelli-

gent and biodegradable alternative packaging material

based on a natural polymer, chitosan, and thermal-sensi-

tive pigment (anthocyanin, ATH) that visually change the

colour after temperature exposition in a specific range.

The efficiency response of this system was analysed by

the changes in colour parameters. The mechanical prop-

erties were measured.

2. MAT ERIALS AND METHODS

2.1. Materials

Chitosan (Primex, Iceland; d egree of acetylation (DA)

of 18% and molecular weight (Mw) of 238,000 g∙mol−1),

acetic acid (Synth, Brazil), anthocyanin (Christian Hansen,

Brazil ) and card paper tri plex TP 250 g∙m−2 ( Suzano Pa pel

e Celulose Ltd., Brazil) were used.

2.2. Chitosan Intelligent Films (C-ATH)

Film suspensions were pr epared by dispe rs ing chitosa n

(2.00 g/100g) in aqueous acetic acid [10]. The stoichio-

metric amount of acetic acid was calculated from sample

weight, taki ng int o acco unt t he val ue of DA to ac hieve the

protonation of all the NH2 sites [2] . T he sus pensi ons we re

homogenized by magnetic stirring at room temperature

for 45 minutes. The ATH (0.50 g/100g) was added to the

filmogenic suspension and homogenized. Aliquots of 9.0

mL were poured into Petri dishes (9.5 cm) and dried at

room t emperature for 36 hours a nd then ke pt at 28 ˚C in an

incubator with forced air circulation for 24 hours. As the

mass suspension used to cast the C-ATH was kept con-

stant, the total solid content per gram of dried films was

28.2 g∙m−2.

2.2.1. Experimental Design

The experimental design was applied to study the tem-

perature and luminosity effects on the colour of C-ATH

(Table 1). The luminosity range was from dark exposure

(0 l×) to simulation of supermarket light (1000 l×). The

time of exposure to temperature and luminosity condi-

tions established was 72 hours.

2.2.2. Mechanical Properties

Tensile strength (TS), elongation at break (ε) and

Tabl e 1 . Values range used in experimental design of two va-

riables.

Variables −1 0 +1

Temperature (oC) 10 30 50

Luminosity (lx) 0 500 1000

Young’s Modulus (E) were determined on C-ATH based

on ASTM Standard method D882 [11]. Films were cut

into 25.4 × 100.0 mm strips and preconditioned at 50%

relative humidity (RH) and 25˚C ± 2˚C for 48 hours.

Measurements were made using a TA.XT2 texture ana-

lyzer (Stable Micro Systems, Godalming, UK). The ini-

tial grip separation was set at 50 mm and crosshead

speed at 1 mm∙s−2. There were at least ten replicates per

experiment. F ilm thickness was measured using a micro-

meter (Mitutoyo Mfg Co. Ltd., Japan) and measurements

were taken at five random positions on the film, using

the average values to calculate film properties.

2.2.3. Scanning Electron Microscopy (SEM)

SEM analysis was performed on fractured cross-sec-

tions and the surface of gold-sputtered C-ATH films us-

ing a LEO 440i scanning electron microscope (LEO

Electron Microscopy Ltda., England), operating at 10 kV

and 100 pA [10]. Chitosan films (CF) without anthocya-

nin was studied as reference.

2.3. Temperature Indicator Prototype (TIP)

Sheets of card paper (0.045 m2) were coated with C-

ATH suspensions. The C-ATH suspension was spread on

the card paper surface using 80 µm wire bar coater (TKB

Erichsen, Brazil). The coated paper sheets were dried in

an oven at 1 50 ˚C for 90 s.

2.3.1. Water Absorption—Cobb Test

Water absorption capacity was determined in accor-

dance with standard ASTM D3285 [12]. T441om-90.27

The weight gain was measured using Mettler AE 163

analytical scales. The results are expressed in g m−2.

There were at least 15 replicates per experiment. Sam-

ples were preconditioned at 50 % RH and 25 °C for 48

hours in a desiccator.

2.3.2. Taber Stiffness

Taber stiffness was determined using standard method

ASTM D5342 [1 3]. Uncoated and coated cardpaper

sheets were cut into samples of 38 × 70 mm2 in the ma-

chine direction (MD) and the cross-machine direction

(CD) using a guillotine (Regmed, Brazil). Taber stiffness

was measured at an angle of 15˚ using Taber stiffness

equipment (model RI 5000, Regmed, Brazil). Results are

expressed in mN. There were at least 15 replicates per

V. B. V. Maciel et al. / Journal of Agricultural Chemistry and Environment 3 (2014) 5-10

experiment. Samples were preconditioned at 50% RH

and 25˚C for 48 hours in a desiccator.

2.4. Colour Response Efficiency

Measurement

The colour parameters (L*, a*, b*) of C-AT H a n d T I P

were measured at different periods of times after tem-

perature and luminosity exposition. A Chroma Meter CR

400 colourimeter (Konica Minolta, Japan) was used. The

parameter L* represents the lightness of colours from 0

(dark) to 100 (light), a* is a measure of gr eenness/redness

and b* is the grade of blueness/yellowness. Both a* and

b* scales range from −60 to +60. The transformation of

a* and b* into geometric values (hue angle – hab) for C-

ATH is a better predictor variable of sensory perception

in experimental design application. The hab (0˚ - 360˚)

was obtained by arctan b*/a* and was used to expres s the

characteristic/dominant colour [14]. According to several

authors [1 4,15] this conversion is necessary to obtain

results in the experimental design due to interaction be-

tween parameters a* and b*, where a change in one usu-

ally does not occur without changing the other. The C-

ATH was exposed to experimental design conditions and

the TIP was exposed to a range of temperatures (10˚C -

70˚C) and 0 and 1000 l×. There were three replicates per

experiments.

2.5. Statistical Analysis

Statistical analysis was carried out with the Statistic

version 7.0 program (Statistic Inc., USA) and differences

between the means were detected by the Tukey multiple

comparison test.

3. RESULTS AND DISCUSSIO N

Initially C-ATH was obtained to evaluate the colour

response efficiency of the system as temperature indica-

tor. Homogeneous, transparent, dark violet films were

obtained and following drying, were easily removed

from the support plates, forming a flexible and resistant

matrix.

3.1. Experimental Design

The colour parameters L* and hab of C-ATH were

characterized after 72 h under exposure to temperatures

and luminosities (Table 2).

The effects of temperature and luminosity on colour

variations of C-ATH were significant for a confidence

level of 90% for parameters L* and hab (Figure 1). The

initial purple colour of the films gradually turned dark.

Increasing the temperature from 10˚C to 50˚C, parame-

ters L* and hab increased to 5.02 and 3.40, respectively.

Although increasing the luminosity from 0 to 1000 l×, a

Table 2. Matrix of experimental design 22, colour parameters

and mechanicals properties of C-ATH films.

Tests

Independent Var iables Properties

Temperature Luminosity L* hab (˚) ε TS E

(˚C) (lx) (%) (MPa ) (GPa)

1 −1 (10) −1 (0) 45.52 274.13 3.21 60.71 3.12

2 +1 (50) −1 (0) 48.73 307.29 2.91 66.51 3.15

3 −1 (10) +1 (1000) 45.16 298.08 3.61 60.62 2.50

4 +1 (50) +1 ( 1 000 ) 45.85 323.19 3.38 50.04 2.71

5 0 (30) 0 (500) 45.77 312.29 2.56 67.64 3.14

6 0 (30) 0 (500) 45.70 311.45 2.53 67.67 3.14

7 0 (30) 0 (500) 46.09 312.01 2.56 67.63 3.14

(a)

(b)

Figure 1. Effect of temperature and luminosity on variat ions in

colour of C-ATH: (a) Parameter L* and (b) Parameter hab.

-3.25

-4.17

5.02

p=,1

T em perature by Luminosity

Lumi nosity

T emperature

-0.47

2.33

3.40

p=,1

T em perature by Luminosity

Luminosity

Temperature

V. B. V. Maciel et al. / Journal of Agricultural Chemistry and Environment 3 (2014) 5-10

process of discolouration was observed with the reduc-

tion in L*. The combined temperature and luminosity

decreased the L* in 3.25 the C-ATH became lighter.

Shaked-Sachray, Weiss, Reuveni, Nissim-Levi and

Oren-Shamir [16] studie d th e co mbin ed effect of elevated

temperatures and metal concentrations on the accumula-

tion of ATH in aster flowers and observed that the an-

thocyanin degraded and became discoloured at higher

temperatures (higher than 30˚C). Significant changes in

b* values were also found by Alighourchi and Barzegar

[17] for anthocyanins in pasteurised pomegranate juice

stored at 4˚C, 20˚C and 37˚C for 210 days. In their study,

L*, a* and b* values decreased and the most significant

colour change was observed after storage at 20˚C and

37˚C. This change was attributed to the degradation of

anthocyanin. According to Lauro and Francis [18], the

anthocyanins could change with temperature, light, oxy-

gen, presence of sugars and enzyme, pH and presence of

proteins and metal ions [19-22], producing polymers

with decreased stability.

Temperature and luminosity had not affected ε and TS

significantly (Table 2). For E, only the luminosity had a

slightly significant effect (p ≤ 0.1). Increasing luminosity

from 0 to 1000 l×, E decreased in order to 19.9% at 10˚C

and 14.0% at 50˚C. These results are indicating that

flexibility and s trength of ATH-CF were maintained sim-

ilar to the initial condition.

The good mechanical properties of CF and ATH-CF

could be related with the microstructures (Figure 2). A

compact and cohesive structure without pores or cracks

was observed in CF (Figure 2(a)). No significant differ-

ence was observed between CF and ATH-CF structures

(Figure 2(b)). ATH was entrapped in the tridimensional

matrix forming a uniform structure films. Yoshida,

Oliveira-Junior and Franco [1] found similar results for

CF and CF with palmitic acid.

3.2. Film Card Paper System (TIP)

C-ATH suspensions were applied as a coating on card

paper surface forming TIP system. The TIP drying proc-

ess time was 90 s, which was faster than the total film dry-

ing process (60 h) that could be a commercial adv antage.

C-ATH suspensions formed a homogeneous card pa-

per coating without bubbles or defects. The systems were

submitted to different temperature and luminosity condi-

tions during 72 hours. An irreversible and gradual change

in colour exposition of the TIP was visually observed

after 72 hours at different temperature and luminosity

conditions (Figure 3 ). A more pronounced colour change

was observed after luminosity exposition. Studying the

colour stability of berry anthocyanin, Rein [19] found

that the exposition at higher luminosities accelerated

ATH discolouration. The parameter b* values increased

(a) (b)

Figure 2. SEM Micrographs for (a) CF, (b) C-ATH containing

0.25% ATH.

(a)

(b)

Figure 3. The visual and b* colour parameter changes on TIP

system exposed to different temperatures and luminosities: (A)

0 l× and (b) 1000 l×.

in TIP after 0 and 1000 l× exposition.

Colour change on the TIP could be associated with

ATH molecules chemical structure. Thermal degradation

can produce changes in ATH structures that depend on

the severity and heating conditions. The mechanisms of

ATH degradation are still relatively unknown. Chemical

V. B. V. Maciel et al. / Journal of Agricultural Chemistry and Environment 3 (2014) 5-10

structures and the presence of other organic acids have a

strong influence [22]. Markakis, Livingstone and Fillers

[23] suggested that the pyrylium ring of ATH opens,

forming a chalcone structure as a first degradation step.

Chalcone is derived from three acetates and one cin-

namic acid. It has a yellow pigmentation and is a pre-

cursor of the biosynthesis of flavonoid. Adams [24] re-

ported that ATH could decompose upon heating into a

chalcone structure and be further transformed into a cou-

marin glucoside derivative by the loss of the B-r ing.

The ATH discolouration was observed in blue flowers

[16], pomegranate juice [17], vegetables extracts [25]

and fruits purees [26] after exposure to temperatures

higher than 30˚C. The discolouration process is usually

accelerated with luminosity [23].

3.3. Properties of TIP

The grammage, water absorption capacity and Taber

stiffness results for uncoated and coated card paper are

shown in Table 2. The C-ATH coating did not signifi-

cantly change the grammage of card paper. Water resis-

tance is an important property which can determine the

behaviour of card paper in various applications. The wa-

ter absorption of the TIP decreased significantly applying

C-ATH coating.

According to Aider [27], chitosan films have the abil-

ity to avoid moisture loss or water absorption and could

act as a reinforcement layer. Bordenave, Grelier, Picha-

vant and Coma [28] studied the potentiality of bioactive

food packaging based on ch ito san -coated papers and

show that chitosan film improved the water absorption of

paper despite the very low amount of total solids. The

incorporation of chitosan as a papermaking additive in

paper and paperboard production or as a surface coating,

had previously been investigated [29-32]. Different con-

centrations of chitosan were app lied as a coating additive

in paper and paperboard making, and it was observed

that when increased chitosan concentration from 0.1 to

0.75% (w/w), the water absorption decreased significant-

ly [29]. The greaseproof paper coated with chitosan films

did not provide an extra barrier against water absorption

[30]. The Taber stiffness values were statistically differ-

ent when applied C-ATH coating on card paper surface

as compared to uncoated card paper (Table 3). The resis-

tance and flexiblility of C-ATH strengthened the cellu-

lose fiber interbonds. Chitosan films had a positive im-

pact on the mechanical properties of coated pap er [32 ].

4. CONCLUSION

An efficient and irreversible temperature indicator ma-

terial was obtained for a specific range (from 40˚C to

70˚C) using biodegradable materials (chitosan, card pa-

per and ATH). The TIP changed the colour from violet to

yellow after temperature exposition. Luminosity acceler-

Table 3. Grammage, Cobb Test and Taber stiffness of TIP [10].

Samples Grammage Water absorption

Taber Stiffness (mN.m)

(g∙m−2) (g∙m−2) CD MD

Uncoated

cardpaper 252.71 ± 1.88a

45.48 ± 1.76a 5.60 ± 0.16a

12.97 ± 0.21a

TIP system

253.17 ± 1.71a

35.41 ± 1.66b 6.43 ± 0.17b

14.15 ± 0.09b

a, b, cMeans in the same column with different superscripts differ signifi-

cantly (p ≤ 0.05) in accordance with Tukey’s test.

ated the ATH molecule degradation. The advantages of

this temperature indicator were the simple man ufacturing

process, use of natural compounds that are food safety

contact, the biodegradability and low cost. This ind icator

system has potential applications in different areas such

as food, pharmaceuticals, biological, agricultural and

others products, that are highly dependent of storage

temperature conditions.

ACKNOWLEDGEMENTS

The financial support of CNPq, FAPESP, CA PES and Suzano Papéis

e Celulose Ltd.

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