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Constrained mixture design applied to the development of cassava starch–chitosan blown films
Journal of Food Engineering 108 (2012) 262–267
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Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Constrained mixture design applied to the development of cassava starch–chitosan blown films Franciele M. Pelissari a, Fábio Yamashita a, María A. Garcia b, Miriam N. Martino b,c, Noemi E. Zaritzky b,c, Maria Victoria E. Grossmann a,⇑ a
Departamento de Ciência e Tecnologia de Alimentos, Centro de Ciências Agrárias, Universidade Estadual de Londrina, C.P. 6001, CEP 86051-990, Londrina, PR, Brazil Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CIDCA), CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 y 116, La Plata 1900, Buenos Aires, Argentina c Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad Nacional de La Plata, 47 y 116, La Plata 1900, Buenos Aires, Argentina b
a r t i c l e
i n f o
Article history: Received 28 April 2011 Received in revised form 20 August 2011 Accepted 5 September 2011 Available online 10 September 2011 Keywords: Experimental design Biopolymers Mechanical properties Permeability Opacity
a b s t r a c t Films composed of cassava starch, chitosan and glycerol were produced by blown extrusion and employing a design for constrained surfaces and mixtures. The effects of the components of the mixture on the mechanical properties, water vapor permeability (WVP) and opacity of the films were studied. According to the models generated by the design, the concentration of starch had a positive effect in all properties. The plasticizer glycerol and its interactions with other components had a positive effect on increasing the WVP. The presence of a higher relative concentration of chitosan favored the formation of more rigid and opaque and less permeable films. In general, the concentrations of starch, chitosan and glycerol led to changes in the film properties, potentially affecting their performance. The design for constrained surfaces and mixtures proved to be a useful tool for this type of study due to the complexity of the conditions of film formation. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The growing accumulation of non-biodegradable waste together with the difficulty of recycling the majority of packaging has stimulated the development of biodegradable packaging from renewable sources. The production of packaging requires materials resistant to breakage and abrasion to protect the packaged product during handling and transport while maintaining its flexibility to adapt to eventual deformations of the product. Another important feature is the opacity of the material because low opacity indicates greater transparency, and for several products, it is important that packaging is transparent for a good visual presentation. Other times, protection against incident light is necessary, especially for products that are sensitive to degradation reactions catalyzed by light. Among the natural biopolymers, starch stands out because of its low price and availability. However, starch films present poor mechanical properties, such as fragility and excessive rigidity (Galdeano et al., 2009b; Müller et al., 2009). The addition of plasticizers reduces the stiffness of the films and increases the permeability to water vapor (Bangyekan et al., 2006; Galdeano et al., 2009b; Müller ⇑ Corresponding author. Tel.: +55 43 3371 4565; fax: +55 43 3371 4080. E-mail addresses: [email protected] (F.M. Pelissari), [email protected] (M.V.E. Grossmann). 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.09.004
et al., 2008), but one of the principal functions of packaging is to prevent moisture exchange between the product and environment. Thus, the permeability to water vapor should be as low as possible. An alternative to improve the mechanical and water vapor barrier properties of starch films is the addition of chitosan to the formulation because chitosan is more hydrophobic than starch, which favors the formation of films with greater strength and lower water vapor permeability (WVP). Chitosan is not only a compound with antimicrobial properties, but it is biodegradable, is nontoxic and has the potential for the production of biodegradable films when blended with other polymers (Aider, 2010; Bangyekan et al., 2006; Chillo et al., 2008; Devlieghere et al., 2004; Dutta et al., 2009; Pelissari et al., 2009; Xu et al., 2005). Bangyekan et al. (2006) studied the influence of chitosan and glycerol concentrations in cassava starch films produced by casting and observed that the WVP decreased with an increase in the concentration of chitosan and increased with an increase in the concentration of glycerol. According to the authors, this behavior was due to the hydrophobicity of chitosan. In another study, the addition of chitosan had a positive effect on the mechanical properties of starch films, while glycerol had a negative effect (Chillo et al., 2008). Most studies have reported the influence of chitosan and glycerol only on the properties of films produced by the casting method, but there are a few papers that have studied the effect of chitosan films produced by blown extrusion. Pelissari et al. (2011) investigated the effect of extrusion process variables (die temperature
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and screw speed) on the properties of films composed of chitosan and starch blends and concluded that an increase in the screw speed resulted in an increase in the blow-up ratio and WVP values and a decrease in the opacity, tensile strength and elongation at break of films. Low die temperatures resulted in an increase in tensile strength, elongation at break, Young’s modulus and WVP. Thus, extrusion is a viable alternative due to high productivity and both minimal space requirements and process steps compared to the method of casting. Furthermore, many traditional commercial films are produced using this process (Sothornvit et al., 2007; Thunwall et al., 2008). The objective of this study was to develop cassava starch– chitosan films by blown extrusion, using a design for constrained surfaces and mixtures, and to evaluate the effect of cassava starch, chitosan and glycerol concentrations on the mechanical, optical and water vapor barrier properties of these biodegradable films.
The mean thickness of each film was determined from an average of 10 random measurements.
2. Materials and methods
2.5. Water vapor permeability (WVP)
2.1. Materials
The WVP was determined by gravimetry according to ASTM E96-00 (2000) with modifications. The pre-conditioned film (64% relative humidity, 25 °C for 48 h) was placed on the circular opening (diameter of 60 mm) of the permeability capsule with silicone grease to ensure that humidity migration occurred only through the film. The inside of the capsule was completely filled with calcium anhydride (CaCl2 – 0% relative humidity), and the system was placed in a desiccator containing a saturated sodium chloride solution (NaCl – 75% relative humidity). The desiccator containing the films was placed in a BOD oven at 25 °C. Each formulation was assayed twice. The samples were weighed 10 times at intervals of 12 h. The mass gain (m) was graphically determined as a function of time (t) using the angular coefficient (m/t) and calculating the water vapor permeation ratio (WVPR) with the following equation:
The raw materials used in this study were native cassava starch (19% amylose) (Indemil, Paranavai, PR, Brazil), glycerol (Nuclear, Diadema, SP, Brazil) and chitosan (average molecular weight of 100–300 kDa) (Acros Organics, Geel, Belgium). 2.2. Film production The films were processed in a pilot single screw extruder (BGM, model EL-25, Brazil) equipped with a screw diameter (D) of 25 mm and a screw length of 28 D, four heating zones, and die with two 3 mm diameter holes for the production of pellets. For the production of tubular films, the same extruder was used, with five heating zones, 50 mm film-blowing die with internal air for the formation of the film ‘‘bubble’’. The components of the formulations (starch, chitosan and glycerol) were mixed with a mixer (model Ciranda Classic, Arno, Brazil) at the lowest speed (approximately 780 rpm) for 5 min. In the first stage of the extrusion process, the mixtures were extruded and pelletized twice to obtain good homogenization with a temperature profile of 120/120/120/110 °C and a screw speed of 35 rpm (Fig. 1a). Next, the reprocessed pellets were used to manufacture the film by blown extrusion with a temperature profile of 120/120/120/120/130 °C and 35 rpm screw speed (Fig. 1b). 2.3. Thickness The thickness of the films was measured using a manual micrometer (Mitutoyo, São Paulo, Brazil) with an accuracy of 0.0001 mm.
2.4. Mechanical properties The tensile properties were determined with a texture analyzer (Stable MicroSystems, model TATX2i, England) according to the standard method D882-02 (ASTM, 2002), taking an average of five determinations in each case. The samples were cut parallel to the film flow into 25.4 mm wide and 100 mm long strips using a scalpel, and fit to the tensile grips. The initial grip separation was set at 50 mm and the crosshead speed at 8.3 mm/s. The parameters determined were the following: tensile strength (MPa), elongation at break (%), and Young’s modulus (MPa). For analysis, the samples were conditioned for 48 h in glass desiccators with a relative humidity of 64% and a temperature of 25 °C.
WVPR ¼
m 1 t A
ð1Þ
where: m/t is the angular coefficient of the curve (g water/s), and A is the sample permeation area (m2). Water vapor permeability (WVP) was determined with the following equation:
WVP ¼
WVPR t spðRH1 RH2 Þ
ð2Þ
where: t is the mean sample thickness (m), sp is the water vapor saturation pressure at the assay temperature (Pa), RH1 is the relative humidity of the chamber, and RH2 is the relative humidity inside the capsule.
Fig. 1. Film production by extrusion: (a) acquisition of pellets and (b) formation of tubular film.
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2.6. Opacity The opacity was assessed according to the HunterLab method (1997) by means of a BYK Gardner colorimeter (model Spectroguide 45/0 gloss, Geretsried, Germany) at a 10° angle and illuminant D65 (daylight). The film opacity (Y) was calculated as the ratio between the opacity of a sample placed under a black pattern (Yb) and the opacity of a sample placed under a white pattern (Yw) (Eq. (3)) on an arbitrary scale (between 0% and 100%). Measurements were made in triplicate and the results were presented as mean values:
Y¼
good handling characteristics, and the thicknesses varied between 190 and 230 lm. The proportions of the components in each test and the results of the film properties are presented in Table 2. According to the analysis of variance (Table 3), the models generated for the different properties were significant (p 6 0.05) and yielded values of R2 P 0.84. The significant lack of fit of the model to the Young’s modulus (p 6 0.05) was due to the low value of the pure error (data not shown), which does not affect the predictive ability of this model. 3.1. Mechanical properties
Yb 100 Yw
ð3Þ
2.7. Experimental design A design for constrained surfaces and mixtures (Statsoft, 2004) was used because it is not possible to produce films with, for example, 100% glycerol. When these experimental limitations occur, it is necessary to adjust the mixture design for conditions in which it can perform the measurements, reducing the original scale, but ensuring that the correct distribution of the experiments is obeyed. This can be done through the pseudo-components, which are combinations of the original components, used to reset the coordinates of mixtures in relation to the experimental space to be effectively studied (Barros Neto et al., 2007). The restrictions for each component were determined in preliminary experiments (data not shown): starch (70–82%), chitosan (0–5%) and glycerol (18–25%). Chitosan concentrations greater than 5% were not used due to its high cost. The following responses were evaluated: tensile strength, elongation at rupture, Young’s modulus, WVP and opacity. The design is presented in Table 1. The coefficients of the models adjusted for each response were estimated by the Scheffé canonical models. The models were subjected to analysis of variance (ANOVA) to assess the level of significance, the coefficient of determination (R2) and the lack of fit of the model. The program Statistica 7.0 (StatSoft, 2004) was used to generate the experimental design and mathematical models, as well as for construction of the graphs. 3. Results and discussion All the films produced in accordance with the mixture design presented a homogeneous surface with no bubbles or cracks and
The concentrations of starch and chitosan had a positive linear effect on the tensile strength of the films (Table 3), i.e., proportionately higher concentrations of both chitosan and starch increased the tensile strength of the films. The interaction between these two components and between chitosan and glycerol, although not significant, contributed to the model fit, with coefficients of the same order of magnitude than the linear effect of chitosan. These interactions were antagonistic (negative), which contributed to the decrease in film resistance. The response surface presented in Fig. 2a shows that the highest concentrations of starch and chitosan (with consequent reduction of crude glycerol) induce the formation of more resistant films. An increase in the values of tensile strength of the biodegradable films with increasing concentrations of starch and chitosan is attributed to the formation of intermolecular hydrogen bonding between –NH2 groups present in the structure of chitosan and the –OH groups of cassava starch (Xu et al., 2005). The ordered crystalline structure of the starch molecules is disorganized by the gelatinization process that occurs during extrusion, resulting in the exposure of –OH groups that quickly form hydrogen bonds with the –NH2 group of chitosan (Bourtoom and Chinnan, 2008). As the chitosan concentration in the films increases, the number of –NH2 groups also increases. Bourtoom and Chinnan (2008) and Shen et al. (2010), working with films from rice starch and sweet potato starch, respectively, found that the tensile strength of the films also increased with increases in the concentrations of chitosan. According to the authors, these films, produced by casting, presented tensile strength values ranging from 27.5 to 38.1 MPa for the rice starch–chitosan film and from 32 to 44 MPa for the sweet potato starch–chitosan film, while that of cassava starch–chitosan produced by extrusion in this study presented values between 0.85 and 2.71 MPa. The difference between the results is due to a greater concentration of
Table 1 Experimental design for the study of the properties of films composed of cassava starch, chitosan and glycerol, in real proportions of the components in the mixture and in pseudo-components. Experimental
Proportion of the components in the ternary mixture In pseudo-componentsa
In real concentrations
1 2 3 4 5 6 7 8 9b 10b 11b a b
Starch (%)
Chitosan (%)
Glycerol (%)
Starch (x1)
Chitosan (x2)
Glycerol (x3)
82.0 70.0 77.0 75.0 78.5 73.5 79.5 72.5 76.0 76.0 76.0
0.0 5.0 5.0 0.0 0.0 5.0 2.5 2.5 2.5 2.5 2.5
18.0 25.0 18.0 25.0 21.5 21.5 18.0 25.0 21.5 21.5 21.5
1.000 0.000 0.583 0.417 0.708 0.291 0.792 0.209 0.500 0.500 0.500
0.000 0.417 0.417 0.000 0.000 0.417 0.208 0.208 0.208 0.208 0.208
0.000 0.583 0.000 0.583 0.292 0.292 0.000 0.583 0.292 0.292 0.292
Calculated based on the following equations: x1 = (Cstarch 0.70)/0.12, x2 = (Cchitosan 0.00)/0.12, x3 = (Cglycerol 0.18)/0.12. Replicates of the central point.
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F.M. Pelissari et al. / Journal of Food Engineering 108 (2012) 262–267 Table 2 Responses of the dependent variables for the films prepared with different concentrations of starch, chitosan and glycerol.
a b
Experimental
Proportions of the components (%)a
Dependent variablesb
x1
x2
x3
Y1
Y2
Y3
Y4
Y5
1 2 3 4 5 6 7 8 9 10 11
82.0 70.0 77.0 75.0 78.5 73.5 79.5 72.5 76.0 76.0 76.0
0.0 5.0 5.0 0.0 0.0 5.0 2.5 2.5 2.5 2.5 2.5
18.0 25.0 18.0 25.0 21.5 21.5 18.0 25.0 21.5 21.5 21.5
2.45 ± 0.20 0.85 ± 0.08 2.54 ± 0.01 1.08 ± 0.03 1.97 ± 0.10 2.06 ± 0.21 2.71 ± 0.25 0.99 ± 0.05 1.33 ± 0.05 1.38 ± 0.03 1.53 ± 0.05
21.95 ± 1.98 25.81 ± 2.01 23.07 ± 1.67 34.74 ± 1.20 34.50 ± 0.92 35.44 ± 3.74 22.56 ± 4.29 51.26 ± 1.27 57.40 ± 2.18 62.15 ± 2.83 74.04 ± 2.67
140.36 ± 5.30 14.76 ± 2.75 72.34 ± 5.17 30.76 ± 2.89 63.34 ± 4.65 36.44 ± 3.61 106.64 ± 5.76 22.98 ± 2.41 51.58 ± 3.95 51.50 ± 4.63 51.08 ± 4.58
1.39 ± 0.16 1.99 ± 0.23 1.00 ± 0.01 2.22 ± 0.06 2.11 ± 0.09 1.72 ± 0.08 1.36 ± 0.30 2.14 ± 0.16 1.84 ± 0.05 1.80 ± 0.00 1.79 ± 0.06
44.10 ± 2.14 36.01 ± 0.51 51.25 ± 1.13 28.68 ± 2.04 31.82 ± 2.07 43.71 ± 0.14 46.38 ± 2.35 31.83 ± 0.73 32.98 ± 1.69 33.97 ± 0.79 33.87 ± 0.62
x1 = Starch, x2 = chitosan, x3 = glycerol. Y1 = Tensile strength (MPa), Y2 = elongation at rupture (%), Y3 = Young’s modulus (MPa), Y4 = WVP 1010 (g/Pa m s), Y5 = opacity (%), ±standard deviation.
Table 3 Regression coefficients of the response variables and analysis of variance of the polynomial models.a Coefficients
Linear b1 b2 b3 Quadratic b12 b13 b23
Response variablesb Y1
Y2
Y3
Y4
Y5
2.55*** 6.08* 0.09
14.65 241.38* 37.66
137.01*** 5.61 32.16**
1.46*** 0.46 1.98***
44.69*** 112.24** 44.29**
5.46
184.74***
6.78
450.15* 206.86* 615.66*
1.98* 2.64*
84.73* 64.77* 148.76*
0.92 0.11
0.84 0.39
0.99 0.00
0.97 0.08
Cubic b123 R2c Lack of fit
97.28 0.98 0.07
a Y = b1x1 + b2x2 + b3x3 + b12x1x2 + b13x1x3 + b23x2x3 + b123x1x2x3, x1 = starch, x2 = chitosan, x3 = glycerol. b Y1 = Tensile strength (MPa), Y2 = elongation at rupture (%), Y3 = Young’s modulus (MPa), Y4 = WVP 1010 (g/Pa m s), Y5 = opacity (%). c Coefficient of determination. * p 6 0.05. ** p 6 0.01. *** p 6 0.001.
chitosan in the films produced by casting (20–45%). Moreover, in the casting process, the formation of hydrogen bonds between starch and chitosan is increased due to protonation of the amino group ðNHþ 3 Þ resulting from the use of acid to solubilize the chitosan (Xu et al., 2005). Galdeano et al. (2009a) studied the effect of the production process on the properties of oat starch films. Films produced by casting showed a tensile strength of 15 MPa, while those produced by extrusion showed a tensile strength of only 2 MPa. Both used glycerol as a plasticizer. According to the authors, during extrusion, the starch chains may be degraded when exposed to high temperature and shear stress, thus decreasing the mechanical strength of the films. The concentration of chitosan showed a negative linear effect on the elongation at rupture of the films, but the chitosan–starch, starch–glycerol and chitosan–glycerol interactions had a positive effect (Table 3), i.e., there was a synergistic effect between the components, resulting in a maximum elongation in the region near the central point, slightly shifted towards higher levels of glycerol (Fig. 2b). Moving away from this region and moving toward increasing concentrations of chitosan and decreased concentrations of starch or glycerol, it was verified that there was a reduction in elongation. The films with greater glycerol content and without
chitosan presented an elongation of 35%. However, when using maximum and minimum concentrations of chitosan and glycerol, respectively, this value fell to 23%. The reason for this behavior is primarily linked to reducing the plasticizer content but could also be attributed to a potential increase in the crystallinity of starch caused by chitosan. Xu et al. (2005) observed that the crystalline structure of waxy starch (high in amylopectin) in the composition of the films was apparently caused by adding chitosan, while Bourtoom and Chinnan (2008) also observed similar results with rice starch–chitosan films. The concentrations of starch and glycerol had a positive linear effect on the Young’s modulus of the films, but the starch–glycerol interaction presented a negative effect (Table 3). The greatest values of the Young’s modulus were obtained, especially for higher starch concentrations, with a tendency to form more rigid films (Fig. 2c). While films without chitosan and with lower glycerol content showed a Young’s modulus of 140 MPa, this value decreased to 20 MPa when the maximal concentrations of chitosan and glycerol were employed. The conditions employed during the manufacturing process of the films, such as high temperature, pressure and shear force of the extruder, allowed the approximation of the starch chains, favoring the formation of a denser and more rigid matrix. Several studies have reported that increasing the concentration of glycerol in the films decreases the Young’s modulus (Alves et al., 2007; Mali et al., 2004; Sobral et al., 2001). The authors reported that the addition of the plasticizer made the matrix of the films less dense, facilitating the movement of the polymer chains and enhancing the flexibility of the films. 3.2. Water vapor permeability (WVP) The concentrations of starch and glycerol presented a positive linear effect on the WVP of the films. Moreover, the starch–glycerol and chitosan–glycerol interactions also had a positive effect (Table 3). The greatest WVP values (2.22 1010 g/Pa m s) were obtained for high concentrations of starch and glycerol (Fig. 3). The effects of these compounds on WVP are in agreement with results reported by other authors (Alves et al., 2007; Bangyekan et al., 2006; Chillo et al., 2008; Mali et al., 2004). The increased WVP values at high concentrations of glycerol might be related to changes in the network structure of starch, which can become less dense due to the plasticizing effect of glycerol (Arvanitoyannis and Biliaderis, 1998; Mali et al., 2004). The films also exhibited greater WVP values with an increasing concentration of starch, which may be attributed to the greater number of free hydroxyl groups and a consequent increase in hygroscopicity. However, the increased number of interactions between chitosan and starch (hydrogen bonding) along with the increased chitosan
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Fig. 2. Quadratic response surface models of the mechanical properties of the films, in terms of pseudo-components: (a) tensile strength (MPa), (b) elongation of rupture (%) and (c) Young’s modulus (MPa). The area highlighted between the points indicates the experimentally analyzed region.
Fig. 3. Surface response for the quadratic model of the WVP variable (1010 g/Pa m s), in terms of pseudo-components. The area highlighted between the points indicates the experimentally analyzed region.
Fig. 4. Surface response for the special cubic model of the opacity variable (%), in terms of pseudo-components. The area highlighted between the points indicates the experimentally analyzed region.
concentration reduces the availability of hydrophilic groups, thereby decreasing the rate of water vapor permeation (Chillo et al., 2008; Xu et al., 2005). Thus, with the maximum content of chitosan and minimum content of glycerol, the WVP was reduced to 1.00 1010 g/Pa m s. Similar results were found by Vásconez et al. (2009) and Shen et al. (2010) in films of cassava starch and sweet potato starch, respectively. The cassava starch–chitosan films plasticized with glycerol had higher WVP values than films of low-density polyethylene (LDPE) (0.0036 1010 g/Pa m s) (Shellhammer and Krochta, 1997) and of oat starch plasticized with glycerol and produced by casting (0.042 1010 g/Pa m s) and extrusion (0.22 1010 g/Pa m s) (Galdeano et al., 2009a). However, these values were lower when compared with the WVP of other biodegradable films, for example,
wheat gluten plasticized with glycerol (7.00 1010 g/Pa m s) and amylose (3.80 1010 g/Pa m s) (Gennadios et al., 1994) and also similar to the WVP films of cellophane (0.84 1010 g/Pa m s) (Shellhammer and Krochta, 1997) and methylcellulose films (0.50 1010 g/Pa m s) (Turhan and Sahbaz, 2004). 3.3. Opacity The concentrations of starch, glycerol and chitosan showed a positive linear effect on the opacity of the films, though all the binary interactions were negative (Table 3). Fig. 4 indicates that the highest opacity values were principally obtained at high chitosan concentrations. These results suggest that the presence of chitosan might result in more opaque and darker films, possibly because of
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the yellowish color of chitosan. Similar results, based on the assessment of color, were found by Bourtoom and Chinnan (2008) and Chillo et al. (2008). 4. Conclusions The design of constrained surfaces and mixtures proved to be a useful tool in studying the development of biodegradable films due to the complexity of the linear effects, such as the interactions between components of the mixture. The concentrations of starch, chitosan and glycerol and their interactions influenced the mechanical and optical properties, as well as the water vapor barrier properties of the films. The addition of relatively small amounts of chitosan increases the mechanical resistance and decreases the WVP of starch films, which are promising results for the use of such films in food packaging. The models generated by the experimental design allow for the production of films with the desired characteristics within the limits studied and might also indicate a more promising direction for new formulations. Acknowledgements The authors thanks the financial support provided by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Secretaria de Estado da Ciência, Tecnologia e Ensino Superior do Paraná (SETI-PR). References Aider, M., 2010. Chitosan application for active bio-based films production and potential in the food industry: review. LWT-Food Science and Technology 43, 837–842. Alves, V.D., Mali, S., Beléia, A., Grossmann, M.V.E., 2007. Effect of glycerol and amylose enrichment on cassava starch film properties. Journal of Food Engineering 78, 941–946. Arvanitoyannis, I., Biliaderis, C.G., 1998. Physical properties of polyol-plasticized edible films made from sodium caseinate and soluble starch blends. Food Chemistry 62 (3), 333–342. ASTM, 2000. Standard test methods for water vapor transmission of material (E9600). In: Annual Book of ASTM Standards. American Society for Testing and Materials, Philadelphia, PA. ASTM, 2002. Standard test method for tensile properties of thin plastic sheeting (D882-02). In: Annual Book of ASTM Standards. American Society for Testing and Materials, Philadelphia, PA. Bangyekan, C., Aht-Ong, D., Srikulkit, K., 2006. Preparation and properties evaluation of chitosan-coated cassava starch films. Carbohydrate Polymers 63, 61–67. Barros Neto, B., Scarmínio, I.S., Bruns, R.E., 2007. Planejamento e otimização de experimentos. Unicamp, Campinas, pp. 390–392. Bourtoom, T., Chinnan, M.S., 2008. Preparation and properties of rice starch– chitosan blend biodegradable film. Food Science and Technology 41, 1633– 1641.
267
Chillo, S., Flores, S., Mastromatteo, M., Conte, A., Gerschenson, L., Del Nobile, M.A., 2008. Influence of glycerol and chitosan on tapioca starch-based edible film properties. Journal of Food Engineering 88, 159–168. Devlieghere, F., Vermeulen, A., Debevere, J., 2004. Chitosan: antimicrobial activity, interactions with food components and applicability as a coating on fruit and vegetables. Food Microbiology 21, 703–714. Dutta, P.K., Tripathi, S., Mehrotra, G.K., Dutta, J., 2009. Perspectives for chitosan based antimicrobial films in food applications. Food Chemistry 114, 1173–1182. Galdeano, M.C., Grossmann, M.V.E., Mali, S., Bello-Perez, L.A., García, M.A., ZamudioFlores, P.B., 2009a. Effects of production process and plasticizers on stability of films and sheets of oat starch. Materials Science and Engineering C 29, 492–498. Galdeano, M.C., Mali, S., Grossmann, M.V.E., Yamashita, F., García, M.A., 2009b. Effects of plasticizers on the properties of oat starch films. Materials Science and Engineering C 29, 532–538. Gennadios, A., Weller, C.L., Gooding, C.H., 1994. Measurements errors in water vapor permeability of highly permeable, hydrofilic edible films. Journal of Food Engineering 21, 395–409. HUNTERLAB, 1997. Universal Software Versions 3.2 and Above. User’s Manual. Hunter Associates Laboratory, Reston, VA. Mali, S., Grossmann, M.V.E., García, M.A., Martino, M.N., Zaritzky, N.E., 2004. Barrier, mechanical an optical properties of plasticized yam starch films. Carbohydrate Polymers 56, 129–135. Müller, C.M.O., Laurindo, J.B., Yamashita, F., 2009. Effect of cellulose fibers addition on the mechanical properties and water vapor barrier of starch-based films. Food Hydrocolloids 23, 1328–1333. Müller, C.M.O., Yamashita, F., Laurindo, J.B., 2008. Evaluation of the effects of glycerol and sorbitol concentration and water activity on the water barrier properties of cassava starch films through a solubility approach. Carbohydrate Polymers 72, 82–87. Pelissari, F.M., Grossmann, M.V.E., Yamashita, F., Pineda, E.A.G., 2009. Antimicrobial, mechanical, and barrier properties of cassava starch–chitosan films incorporated with oregano essential oil. Journal of Agricultural and Food Chemistry 57, 7499–7504. Pelissari, F.M., Yamashita, F., Grossmann, M.V.E., 2011. Extrusion parameters related to starch/chitosan active films properties. International Journal of Food Science and Technology 46, 702–710. Shellhammer, T.H., Krochta, J.M., 1997. Whey protein emulsion film performance as affected by lipid type amount. Journal of Food Science 62 (2), 390–394. Shen, X.L., Wu, J.M., Chen, Y., Zhao, G., 2010. Antimicrobial and physical properties of sweet potato starch films incorporated with potassium sorbate or chitosan. Food Hydrocolloids 24, 285–290. Sobral, P.J.A., Menegalli, F.C., Hubinger, M.D., Roques, M.A., 2001. Mechanical water vapor barrier and thermal properties of gelatin based edible films. Food Hydrocolloids 15 (6), 423–432. Sothornvit, R., Olsen, C.W., McHugh, T.H., Krochta, J.M., 2007. Tensile properties of compression-molded whey protein sheets: determination of molding condition and glycerol-content effects and comparison with solution-cast films. Journal of Food Engineering 78, 855–860. STATSOFT, 2004. STATISTICA for Windows – Computer Program Manual. Statsoft Inc., Tulsa. Thunwall, M., Kuthanova, V., Boldizar, A., Rigdahl, M., 2008. Film blowing of thermoplastic starch. Carbohydrate Polymers 71, 583–590. Turhan, K.N., Sahbaz, F., 2004. Water vapor permeability, tensile properties and solubility of methylcellulose-based edible films. Journal of Food Engineering 61 (3), 459–466. Vásconez, M.B., Flores, S.K., Campos, C.A., Alvarado, J., Gerschenson, L.N., 2009. Antimicrobial activity and physical properties of chitosan–tapioca starch based edible films and coatings. Food Research International 42, 762–769. Xu, Y.X., Kim, K.M., Hanna, M.A., Nag, D., 2005. Chitosan–starch composite film: preparation and characterization. Industrial Crops and Products 21, 185–192.
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Constrained mixture design applied to the development of cassava starch–chitosan blown films Franciele M. Pelissari a, Fábio Yamashita a, María A. Garcia b, Miriam N. Martino b,c, Noemi E. Zaritzky b,c, Maria Victoria E. Grossmann a,⇑ a
Departamento de Ciência e Tecnologia de Alimentos, Centro de Ciências Agrárias, Universidade Estadual de Londrina, C.P. 6001, CEP 86051-990, Londrina, PR, Brazil Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CIDCA), CONICET, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 y 116, La Plata 1900, Buenos Aires, Argentina c Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad Nacional de La Plata, 47 y 116, La Plata 1900, Buenos Aires, Argentina b
a r t i c l e
i n f o
Article history: Received 28 April 2011 Received in revised form 20 August 2011 Accepted 5 September 2011 Available online 10 September 2011 Keywords: Experimental design Biopolymers Mechanical properties Permeability Opacity
a b s t r a c t Films composed of cassava starch, chitosan and glycerol were produced by blown extrusion and employing a design for constrained surfaces and mixtures. The effects of the components of the mixture on the mechanical properties, water vapor permeability (WVP) and opacity of the films were studied. According to the models generated by the design, the concentration of starch had a positive effect in all properties. The plasticizer glycerol and its interactions with other components had a positive effect on increasing the WVP. The presence of a higher relative concentration of chitosan favored the formation of more rigid and opaque and less permeable films. In general, the concentrations of starch, chitosan and glycerol led to changes in the film properties, potentially affecting their performance. The design for constrained surfaces and mixtures proved to be a useful tool for this type of study due to the complexity of the conditions of film formation. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The growing accumulation of non-biodegradable waste together with the difficulty of recycling the majority of packaging has stimulated the development of biodegradable packaging from renewable sources. The production of packaging requires materials resistant to breakage and abrasion to protect the packaged product during handling and transport while maintaining its flexibility to adapt to eventual deformations of the product. Another important feature is the opacity of the material because low opacity indicates greater transparency, and for several products, it is important that packaging is transparent for a good visual presentation. Other times, protection against incident light is necessary, especially for products that are sensitive to degradation reactions catalyzed by light. Among the natural biopolymers, starch stands out because of its low price and availability. However, starch films present poor mechanical properties, such as fragility and excessive rigidity (Galdeano et al., 2009b; Müller et al., 2009). The addition of plasticizers reduces the stiffness of the films and increases the permeability to water vapor (Bangyekan et al., 2006; Galdeano et al., 2009b; Müller ⇑ Corresponding author. Tel.: +55 43 3371 4565; fax: +55 43 3371 4080. E-mail addresses: [email protected] (F.M. Pelissari), [email protected] (M.V.E. Grossmann). 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.09.004
et al., 2008), but one of the principal functions of packaging is to prevent moisture exchange between the product and environment. Thus, the permeability to water vapor should be as low as possible. An alternative to improve the mechanical and water vapor barrier properties of starch films is the addition of chitosan to the formulation because chitosan is more hydrophobic than starch, which favors the formation of films with greater strength and lower water vapor permeability (WVP). Chitosan is not only a compound with antimicrobial properties, but it is biodegradable, is nontoxic and has the potential for the production of biodegradable films when blended with other polymers (Aider, 2010; Bangyekan et al., 2006; Chillo et al., 2008; Devlieghere et al., 2004; Dutta et al., 2009; Pelissari et al., 2009; Xu et al., 2005). Bangyekan et al. (2006) studied the influence of chitosan and glycerol concentrations in cassava starch films produced by casting and observed that the WVP decreased with an increase in the concentration of chitosan and increased with an increase in the concentration of glycerol. According to the authors, this behavior was due to the hydrophobicity of chitosan. In another study, the addition of chitosan had a positive effect on the mechanical properties of starch films, while glycerol had a negative effect (Chillo et al., 2008). Most studies have reported the influence of chitosan and glycerol only on the properties of films produced by the casting method, but there are a few papers that have studied the effect of chitosan films produced by blown extrusion. Pelissari et al. (2011) investigated the effect of extrusion process variables (die temperature
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and screw speed) on the properties of films composed of chitosan and starch blends and concluded that an increase in the screw speed resulted in an increase in the blow-up ratio and WVP values and a decrease in the opacity, tensile strength and elongation at break of films. Low die temperatures resulted in an increase in tensile strength, elongation at break, Young’s modulus and WVP. Thus, extrusion is a viable alternative due to high productivity and both minimal space requirements and process steps compared to the method of casting. Furthermore, many traditional commercial films are produced using this process (Sothornvit et al., 2007; Thunwall et al., 2008). The objective of this study was to develop cassava starch– chitosan films by blown extrusion, using a design for constrained surfaces and mixtures, and to evaluate the effect of cassava starch, chitosan and glycerol concentrations on the mechanical, optical and water vapor barrier properties of these biodegradable films.
The mean thickness of each film was determined from an average of 10 random measurements.
2. Materials and methods
2.5. Water vapor permeability (WVP)
2.1. Materials
The WVP was determined by gravimetry according to ASTM E96-00 (2000) with modifications. The pre-conditioned film (64% relative humidity, 25 °C for 48 h) was placed on the circular opening (diameter of 60 mm) of the permeability capsule with silicone grease to ensure that humidity migration occurred only through the film. The inside of the capsule was completely filled with calcium anhydride (CaCl2 – 0% relative humidity), and the system was placed in a desiccator containing a saturated sodium chloride solution (NaCl – 75% relative humidity). The desiccator containing the films was placed in a BOD oven at 25 °C. Each formulation was assayed twice. The samples were weighed 10 times at intervals of 12 h. The mass gain (m) was graphically determined as a function of time (t) using the angular coefficient (m/t) and calculating the water vapor permeation ratio (WVPR) with the following equation:
The raw materials used in this study were native cassava starch (19% amylose) (Indemil, Paranavai, PR, Brazil), glycerol (Nuclear, Diadema, SP, Brazil) and chitosan (average molecular weight of 100–300 kDa) (Acros Organics, Geel, Belgium). 2.2. Film production The films were processed in a pilot single screw extruder (BGM, model EL-25, Brazil) equipped with a screw diameter (D) of 25 mm and a screw length of 28 D, four heating zones, and die with two 3 mm diameter holes for the production of pellets. For the production of tubular films, the same extruder was used, with five heating zones, 50 mm film-blowing die with internal air for the formation of the film ‘‘bubble’’. The components of the formulations (starch, chitosan and glycerol) were mixed with a mixer (model Ciranda Classic, Arno, Brazil) at the lowest speed (approximately 780 rpm) for 5 min. In the first stage of the extrusion process, the mixtures were extruded and pelletized twice to obtain good homogenization with a temperature profile of 120/120/120/110 °C and a screw speed of 35 rpm (Fig. 1a). Next, the reprocessed pellets were used to manufacture the film by blown extrusion with a temperature profile of 120/120/120/120/130 °C and 35 rpm screw speed (Fig. 1b). 2.3. Thickness The thickness of the films was measured using a manual micrometer (Mitutoyo, São Paulo, Brazil) with an accuracy of 0.0001 mm.
2.4. Mechanical properties The tensile properties were determined with a texture analyzer (Stable MicroSystems, model TATX2i, England) according to the standard method D882-02 (ASTM, 2002), taking an average of five determinations in each case. The samples were cut parallel to the film flow into 25.4 mm wide and 100 mm long strips using a scalpel, and fit to the tensile grips. The initial grip separation was set at 50 mm and the crosshead speed at 8.3 mm/s. The parameters determined were the following: tensile strength (MPa), elongation at break (%), and Young’s modulus (MPa). For analysis, the samples were conditioned for 48 h in glass desiccators with a relative humidity of 64% and a temperature of 25 °C.
WVPR ¼
m 1 t A
ð1Þ
where: m/t is the angular coefficient of the curve (g water/s), and A is the sample permeation area (m2). Water vapor permeability (WVP) was determined with the following equation:
WVP ¼
WVPR t spðRH1 RH2 Þ
ð2Þ
where: t is the mean sample thickness (m), sp is the water vapor saturation pressure at the assay temperature (Pa), RH1 is the relative humidity of the chamber, and RH2 is the relative humidity inside the capsule.
Fig. 1. Film production by extrusion: (a) acquisition of pellets and (b) formation of tubular film.
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2.6. Opacity The opacity was assessed according to the HunterLab method (1997) by means of a BYK Gardner colorimeter (model Spectroguide 45/0 gloss, Geretsried, Germany) at a 10° angle and illuminant D65 (daylight). The film opacity (Y) was calculated as the ratio between the opacity of a sample placed under a black pattern (Yb) and the opacity of a sample placed under a white pattern (Yw) (Eq. (3)) on an arbitrary scale (between 0% and 100%). Measurements were made in triplicate and the results were presented as mean values:
Y¼
good handling characteristics, and the thicknesses varied between 190 and 230 lm. The proportions of the components in each test and the results of the film properties are presented in Table 2. According to the analysis of variance (Table 3), the models generated for the different properties were significant (p 6 0.05) and yielded values of R2 P 0.84. The significant lack of fit of the model to the Young’s modulus (p 6 0.05) was due to the low value of the pure error (data not shown), which does not affect the predictive ability of this model. 3.1. Mechanical properties
Yb 100 Yw
ð3Þ
2.7. Experimental design A design for constrained surfaces and mixtures (Statsoft, 2004) was used because it is not possible to produce films with, for example, 100% glycerol. When these experimental limitations occur, it is necessary to adjust the mixture design for conditions in which it can perform the measurements, reducing the original scale, but ensuring that the correct distribution of the experiments is obeyed. This can be done through the pseudo-components, which are combinations of the original components, used to reset the coordinates of mixtures in relation to the experimental space to be effectively studied (Barros Neto et al., 2007). The restrictions for each component were determined in preliminary experiments (data not shown): starch (70–82%), chitosan (0–5%) and glycerol (18–25%). Chitosan concentrations greater than 5% were not used due to its high cost. The following responses were evaluated: tensile strength, elongation at rupture, Young’s modulus, WVP and opacity. The design is presented in Table 1. The coefficients of the models adjusted for each response were estimated by the Scheffé canonical models. The models were subjected to analysis of variance (ANOVA) to assess the level of significance, the coefficient of determination (R2) and the lack of fit of the model. The program Statistica 7.0 (StatSoft, 2004) was used to generate the experimental design and mathematical models, as well as for construction of the graphs. 3. Results and discussion All the films produced in accordance with the mixture design presented a homogeneous surface with no bubbles or cracks and
The concentrations of starch and chitosan had a positive linear effect on the tensile strength of the films (Table 3), i.e., proportionately higher concentrations of both chitosan and starch increased the tensile strength of the films. The interaction between these two components and between chitosan and glycerol, although not significant, contributed to the model fit, with coefficients of the same order of magnitude than the linear effect of chitosan. These interactions were antagonistic (negative), which contributed to the decrease in film resistance. The response surface presented in Fig. 2a shows that the highest concentrations of starch and chitosan (with consequent reduction of crude glycerol) induce the formation of more resistant films. An increase in the values of tensile strength of the biodegradable films with increasing concentrations of starch and chitosan is attributed to the formation of intermolecular hydrogen bonding between –NH2 groups present in the structure of chitosan and the –OH groups of cassava starch (Xu et al., 2005). The ordered crystalline structure of the starch molecules is disorganized by the gelatinization process that occurs during extrusion, resulting in the exposure of –OH groups that quickly form hydrogen bonds with the –NH2 group of chitosan (Bourtoom and Chinnan, 2008). As the chitosan concentration in the films increases, the number of –NH2 groups also increases. Bourtoom and Chinnan (2008) and Shen et al. (2010), working with films from rice starch and sweet potato starch, respectively, found that the tensile strength of the films also increased with increases in the concentrations of chitosan. According to the authors, these films, produced by casting, presented tensile strength values ranging from 27.5 to 38.1 MPa for the rice starch–chitosan film and from 32 to 44 MPa for the sweet potato starch–chitosan film, while that of cassava starch–chitosan produced by extrusion in this study presented values between 0.85 and 2.71 MPa. The difference between the results is due to a greater concentration of
Table 1 Experimental design for the study of the properties of films composed of cassava starch, chitosan and glycerol, in real proportions of the components in the mixture and in pseudo-components. Experimental
Proportion of the components in the ternary mixture In pseudo-componentsa
In real concentrations
1 2 3 4 5 6 7 8 9b 10b 11b a b
Starch (%)
Chitosan (%)
Glycerol (%)
Starch (x1)
Chitosan (x2)
Glycerol (x3)
82.0 70.0 77.0 75.0 78.5 73.5 79.5 72.5 76.0 76.0 76.0
0.0 5.0 5.0 0.0 0.0 5.0 2.5 2.5 2.5 2.5 2.5
18.0 25.0 18.0 25.0 21.5 21.5 18.0 25.0 21.5 21.5 21.5
1.000 0.000 0.583 0.417 0.708 0.291 0.792 0.209 0.500 0.500 0.500
0.000 0.417 0.417 0.000 0.000 0.417 0.208 0.208 0.208 0.208 0.208
0.000 0.583 0.000 0.583 0.292 0.292 0.000 0.583 0.292 0.292 0.292
Calculated based on the following equations: x1 = (Cstarch 0.70)/0.12, x2 = (Cchitosan 0.00)/0.12, x3 = (Cglycerol 0.18)/0.12. Replicates of the central point.
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a b
Experimental
Proportions of the components (%)a
Dependent variablesb
x1
x2
x3
Y1
Y2
Y3
Y4
Y5
1 2 3 4 5 6 7 8 9 10 11
82.0 70.0 77.0 75.0 78.5 73.5 79.5 72.5 76.0 76.0 76.0
0.0 5.0 5.0 0.0 0.0 5.0 2.5 2.5 2.5 2.5 2.5
18.0 25.0 18.0 25.0 21.5 21.5 18.0 25.0 21.5 21.5 21.5
2.45 ± 0.20 0.85 ± 0.08 2.54 ± 0.01 1.08 ± 0.03 1.97 ± 0.10 2.06 ± 0.21 2.71 ± 0.25 0.99 ± 0.05 1.33 ± 0.05 1.38 ± 0.03 1.53 ± 0.05
21.95 ± 1.98 25.81 ± 2.01 23.07 ± 1.67 34.74 ± 1.20 34.50 ± 0.92 35.44 ± 3.74 22.56 ± 4.29 51.26 ± 1.27 57.40 ± 2.18 62.15 ± 2.83 74.04 ± 2.67
140.36 ± 5.30 14.76 ± 2.75 72.34 ± 5.17 30.76 ± 2.89 63.34 ± 4.65 36.44 ± 3.61 106.64 ± 5.76 22.98 ± 2.41 51.58 ± 3.95 51.50 ± 4.63 51.08 ± 4.58
1.39 ± 0.16 1.99 ± 0.23 1.00 ± 0.01 2.22 ± 0.06 2.11 ± 0.09 1.72 ± 0.08 1.36 ± 0.30 2.14 ± 0.16 1.84 ± 0.05 1.80 ± 0.00 1.79 ± 0.06
44.10 ± 2.14 36.01 ± 0.51 51.25 ± 1.13 28.68 ± 2.04 31.82 ± 2.07 43.71 ± 0.14 46.38 ± 2.35 31.83 ± 0.73 32.98 ± 1.69 33.97 ± 0.79 33.87 ± 0.62
x1 = Starch, x2 = chitosan, x3 = glycerol. Y1 = Tensile strength (MPa), Y2 = elongation at rupture (%), Y3 = Young’s modulus (MPa), Y4 = WVP 1010 (g/Pa m s), Y5 = opacity (%), ±standard deviation.
Table 3 Regression coefficients of the response variables and analysis of variance of the polynomial models.a Coefficients
Linear b1 b2 b3 Quadratic b12 b13 b23
Response variablesb Y1
Y2
Y3
Y4
Y5
2.55*** 6.08* 0.09
14.65 241.38* 37.66
137.01*** 5.61 32.16**
1.46*** 0.46 1.98***
44.69*** 112.24** 44.29**
5.46
184.74***
6.78
450.15* 206.86* 615.66*
1.98* 2.64*
84.73* 64.77* 148.76*
0.92 0.11
0.84 0.39
0.99 0.00
0.97 0.08
Cubic b123 R2c Lack of fit
97.28 0.98 0.07
a Y = b1x1 + b2x2 + b3x3 + b12x1x2 + b13x1x3 + b23x2x3 + b123x1x2x3, x1 = starch, x2 = chitosan, x3 = glycerol. b Y1 = Tensile strength (MPa), Y2 = elongation at rupture (%), Y3 = Young’s modulus (MPa), Y4 = WVP 1010 (g/Pa m s), Y5 = opacity (%). c Coefficient of determination. * p 6 0.05. ** p 6 0.01. *** p 6 0.001.
chitosan in the films produced by casting (20–45%). Moreover, in the casting process, the formation of hydrogen bonds between starch and chitosan is increased due to protonation of the amino group ðNHþ 3 Þ resulting from the use of acid to solubilize the chitosan (Xu et al., 2005). Galdeano et al. (2009a) studied the effect of the production process on the properties of oat starch films. Films produced by casting showed a tensile strength of 15 MPa, while those produced by extrusion showed a tensile strength of only 2 MPa. Both used glycerol as a plasticizer. According to the authors, during extrusion, the starch chains may be degraded when exposed to high temperature and shear stress, thus decreasing the mechanical strength of the films. The concentration of chitosan showed a negative linear effect on the elongation at rupture of the films, but the chitosan–starch, starch–glycerol and chitosan–glycerol interactions had a positive effect (Table 3), i.e., there was a synergistic effect between the components, resulting in a maximum elongation in the region near the central point, slightly shifted towards higher levels of glycerol (Fig. 2b). Moving away from this region and moving toward increasing concentrations of chitosan and decreased concentrations of starch or glycerol, it was verified that there was a reduction in elongation. The films with greater glycerol content and without
chitosan presented an elongation of 35%. However, when using maximum and minimum concentrations of chitosan and glycerol, respectively, this value fell to 23%. The reason for this behavior is primarily linked to reducing the plasticizer content but could also be attributed to a potential increase in the crystallinity of starch caused by chitosan. Xu et al. (2005) observed that the crystalline structure of waxy starch (high in amylopectin) in the composition of the films was apparently caused by adding chitosan, while Bourtoom and Chinnan (2008) also observed similar results with rice starch–chitosan films. The concentrations of starch and glycerol had a positive linear effect on the Young’s modulus of the films, but the starch–glycerol interaction presented a negative effect (Table 3). The greatest values of the Young’s modulus were obtained, especially for higher starch concentrations, with a tendency to form more rigid films (Fig. 2c). While films without chitosan and with lower glycerol content showed a Young’s modulus of 140 MPa, this value decreased to 20 MPa when the maximal concentrations of chitosan and glycerol were employed. The conditions employed during the manufacturing process of the films, such as high temperature, pressure and shear force of the extruder, allowed the approximation of the starch chains, favoring the formation of a denser and more rigid matrix. Several studies have reported that increasing the concentration of glycerol in the films decreases the Young’s modulus (Alves et al., 2007; Mali et al., 2004; Sobral et al., 2001). The authors reported that the addition of the plasticizer made the matrix of the films less dense, facilitating the movement of the polymer chains and enhancing the flexibility of the films. 3.2. Water vapor permeability (WVP) The concentrations of starch and glycerol presented a positive linear effect on the WVP of the films. Moreover, the starch–glycerol and chitosan–glycerol interactions also had a positive effect (Table 3). The greatest WVP values (2.22 1010 g/Pa m s) were obtained for high concentrations of starch and glycerol (Fig. 3). The effects of these compounds on WVP are in agreement with results reported by other authors (Alves et al., 2007; Bangyekan et al., 2006; Chillo et al., 2008; Mali et al., 2004). The increased WVP values at high concentrations of glycerol might be related to changes in the network structure of starch, which can become less dense due to the plasticizing effect of glycerol (Arvanitoyannis and Biliaderis, 1998; Mali et al., 2004). The films also exhibited greater WVP values with an increasing concentration of starch, which may be attributed to the greater number of free hydroxyl groups and a consequent increase in hygroscopicity. However, the increased number of interactions between chitosan and starch (hydrogen bonding) along with the increased chitosan
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Fig. 2. Quadratic response surface models of the mechanical properties of the films, in terms of pseudo-components: (a) tensile strength (MPa), (b) elongation of rupture (%) and (c) Young’s modulus (MPa). The area highlighted between the points indicates the experimentally analyzed region.
Fig. 3. Surface response for the quadratic model of the WVP variable (1010 g/Pa m s), in terms of pseudo-components. The area highlighted between the points indicates the experimentally analyzed region.
Fig. 4. Surface response for the special cubic model of the opacity variable (%), in terms of pseudo-components. The area highlighted between the points indicates the experimentally analyzed region.
concentration reduces the availability of hydrophilic groups, thereby decreasing the rate of water vapor permeation (Chillo et al., 2008; Xu et al., 2005). Thus, with the maximum content of chitosan and minimum content of glycerol, the WVP was reduced to 1.00 1010 g/Pa m s. Similar results were found by Vásconez et al. (2009) and Shen et al. (2010) in films of cassava starch and sweet potato starch, respectively. The cassava starch–chitosan films plasticized with glycerol had higher WVP values than films of low-density polyethylene (LDPE) (0.0036 1010 g/Pa m s) (Shellhammer and Krochta, 1997) and of oat starch plasticized with glycerol and produced by casting (0.042 1010 g/Pa m s) and extrusion (0.22 1010 g/Pa m s) (Galdeano et al., 2009a). However, these values were lower when compared with the WVP of other biodegradable films, for example,
wheat gluten plasticized with glycerol (7.00 1010 g/Pa m s) and amylose (3.80 1010 g/Pa m s) (Gennadios et al., 1994) and also similar to the WVP films of cellophane (0.84 1010 g/Pa m s) (Shellhammer and Krochta, 1997) and methylcellulose films (0.50 1010 g/Pa m s) (Turhan and Sahbaz, 2004). 3.3. Opacity The concentrations of starch, glycerol and chitosan showed a positive linear effect on the opacity of the films, though all the binary interactions were negative (Table 3). Fig. 4 indicates that the highest opacity values were principally obtained at high chitosan concentrations. These results suggest that the presence of chitosan might result in more opaque and darker films, possibly because of
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the yellowish color of chitosan. Similar results, based on the assessment of color, were found by Bourtoom and Chinnan (2008) and Chillo et al. (2008). 4. Conclusions The design of constrained surfaces and mixtures proved to be a useful tool in studying the development of biodegradable films due to the complexity of the linear effects, such as the interactions between components of the mixture. The concentrations of starch, chitosan and glycerol and their interactions influenced the mechanical and optical properties, as well as the water vapor barrier properties of the films. The addition of relatively small amounts of chitosan increases the mechanical resistance and decreases the WVP of starch films, which are promising results for the use of such films in food packaging. The models generated by the experimental design allow for the production of films with the desired characteristics within the limits studied and might also indicate a more promising direction for new formulations. Acknowledgements The authors thanks the financial support provided by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Secretaria de Estado da Ciência, Tecnologia e Ensino Superior do Paraná (SETI-PR). References Aider, M., 2010. Chitosan application for active bio-based films production and potential in the food industry: review. LWT-Food Science and Technology 43, 837–842. Alves, V.D., Mali, S., Beléia, A., Grossmann, M.V.E., 2007. Effect of glycerol and amylose enrichment on cassava starch film properties. Journal of Food Engineering 78, 941–946. Arvanitoyannis, I., Biliaderis, C.G., 1998. Physical properties of polyol-plasticized edible films made from sodium caseinate and soluble starch blends. Food Chemistry 62 (3), 333–342. ASTM, 2000. Standard test methods for water vapor transmission of material (E9600). In: Annual Book of ASTM Standards. American Society for Testing and Materials, Philadelphia, PA. ASTM, 2002. Standard test method for tensile properties of thin plastic sheeting (D882-02). In: Annual Book of ASTM Standards. American Society for Testing and Materials, Philadelphia, PA. Bangyekan, C., Aht-Ong, D., Srikulkit, K., 2006. Preparation and properties evaluation of chitosan-coated cassava starch films. Carbohydrate Polymers 63, 61–67. Barros Neto, B., Scarmínio, I.S., Bruns, R.E., 2007. Planejamento e otimização de experimentos. Unicamp, Campinas, pp. 390–392. Bourtoom, T., Chinnan, M.S., 2008. Preparation and properties of rice starch– chitosan blend biodegradable film. Food Science and Technology 41, 1633– 1641.
267
Chillo, S., Flores, S., Mastromatteo, M., Conte, A., Gerschenson, L., Del Nobile, M.A., 2008. Influence of glycerol and chitosan on tapioca starch-based edible film properties. Journal of Food Engineering 88, 159–168. Devlieghere, F., Vermeulen, A., Debevere, J., 2004. Chitosan: antimicrobial activity, interactions with food components and applicability as a coating on fruit and vegetables. Food Microbiology 21, 703–714. Dutta, P.K., Tripathi, S., Mehrotra, G.K., Dutta, J., 2009. Perspectives for chitosan based antimicrobial films in food applications. Food Chemistry 114, 1173–1182. Galdeano, M.C., Grossmann, M.V.E., Mali, S., Bello-Perez, L.A., García, M.A., ZamudioFlores, P.B., 2009a. Effects of production process and plasticizers on stability of films and sheets of oat starch. Materials Science and Engineering C 29, 492–498. Galdeano, M.C., Mali, S., Grossmann, M.V.E., Yamashita, F., García, M.A., 2009b. Effects of plasticizers on the properties of oat starch films. Materials Science and Engineering C 29, 532–538. Gennadios, A., Weller, C.L., Gooding, C.H., 1994. Measurements errors in water vapor permeability of highly permeable, hydrofilic edible films. Journal of Food Engineering 21, 395–409. HUNTERLAB, 1997. Universal Software Versions 3.2 and Above. User’s Manual. Hunter Associates Laboratory, Reston, VA. Mali, S., Grossmann, M.V.E., García, M.A., Martino, M.N., Zaritzky, N.E., 2004. Barrier, mechanical an optical properties of plasticized yam starch films. Carbohydrate Polymers 56, 129–135. Müller, C.M.O., Laurindo, J.B., Yamashita, F., 2009. Effect of cellulose fibers addition on the mechanical properties and water vapor barrier of starch-based films. Food Hydrocolloids 23, 1328–1333. Müller, C.M.O., Yamashita, F., Laurindo, J.B., 2008. Evaluation of the effects of glycerol and sorbitol concentration and water activity on the water barrier properties of cassava starch films through a solubility approach. Carbohydrate Polymers 72, 82–87. Pelissari, F.M., Grossmann, M.V.E., Yamashita, F., Pineda, E.A.G., 2009. Antimicrobial, mechanical, and barrier properties of cassava starch–chitosan films incorporated with oregano essential oil. Journal of Agricultural and Food Chemistry 57, 7499–7504. Pelissari, F.M., Yamashita, F., Grossmann, M.V.E., 2011. Extrusion parameters related to starch/chitosan active films properties. International Journal of Food Science and Technology 46, 702–710. Shellhammer, T.H., Krochta, J.M., 1997. Whey protein emulsion film performance as affected by lipid type amount. Journal of Food Science 62 (2), 390–394. Shen, X.L., Wu, J.M., Chen, Y., Zhao, G., 2010. Antimicrobial and physical properties of sweet potato starch films incorporated with potassium sorbate or chitosan. Food Hydrocolloids 24, 285–290. Sobral, P.J.A., Menegalli, F.C., Hubinger, M.D., Roques, M.A., 2001. Mechanical water vapor barrier and thermal properties of gelatin based edible films. Food Hydrocolloids 15 (6), 423–432. Sothornvit, R., Olsen, C.W., McHugh, T.H., Krochta, J.M., 2007. Tensile properties of compression-molded whey protein sheets: determination of molding condition and glycerol-content effects and comparison with solution-cast films. Journal of Food Engineering 78, 855–860. STATSOFT, 2004. STATISTICA for Windows – Computer Program Manual. Statsoft Inc., Tulsa. Thunwall, M., Kuthanova, V., Boldizar, A., Rigdahl, M., 2008. Film blowing of thermoplastic starch. Carbohydrate Polymers 71, 583–590. Turhan, K.N., Sahbaz, F., 2004. Water vapor permeability, tensile properties and solubility of methylcellulose-based edible films. Journal of Food Engineering 61 (3), 459–466. Vásconez, M.B., Flores, S.K., Campos, C.A., Alvarado, J., Gerschenson, L.N., 2009. Antimicrobial activity and physical properties of chitosan–tapioca starch based edible films and coatings. Food Research International 42, 762–769. Xu, Y.X., Kim, K.M., Hanna, M.A., Nag, D., 2005. Chitosan–starch composite film: preparation and characterization. Industrial Crops and Products 21, 185–192.