- Email: [email protected]
Physical properties of a composite film containing sunflower seed meal protein and its application in packaging smoked duck meat
Journal of Food Engineering 116 (2013) 789–795
Contents lists available at SciVerse ScienceDirect
Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Physical properties of a composite film containing sunflower seed meal protein and its application in packaging smoked duck meat Nak-Bum Song, Hye-Yeon Song, Wan-Shin Jo, Kyung Bin Song ⇑ Department of Food Science & Technology, Chungnam National University, Daejeon 305-764, Republic of Korea
a r t i c l e
i n f o
Article history: Received 12 December 2012 Received in revised form 30 January 2013 Accepted 2 February 2013 Available online 10 February 2013 Keywords: Sunflower seed Cloisite Na+ Red algae Physical property
a b s t r a c t Sunflower seed meal protein (SP) films were prepared using various plasticizers, cross-linking agents, Cloisite Na+ or red algae, and their physical properties, such as tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) were determined. The TS, E, and WVP of the SP film containing sucrose and fructose (2:1) as a plasticizer and cinnamaldehyde as a cross-linking agent were 3.05 MPa, 34.42%, and 2.25 109 g m/m2 s Pa, respectively. The incorporation of Cloisite Na+ improved the physical properties of the SP film. The TS of the SP/Cloisite Na+ composite film containing 3% Cloisite Na+ increased by 2.19 MPa, and the WVP of the composite film decreased by 0.52 109 g m/m2 s Pa compared to the SP film. The incorporation of red algae also improved the TS of the SP film. The TS of the SP composite film containing 1.2% red algae increased by 3.82 MPa compared to the SP film. In addition, an SP/red algae composite film containing grapefruit seed extract (GSE) was prepared and used in food packaging. After 12 days of storage, the population of Listeria monocytogenes inoculated on smoked duck meats packed with the SP/red algae composite film containing 1.2% GSE decreased by 1.31 log CFU/g compared to the control packaging. Therefore, these results suggest that SP composite films can be prepared by the addition of red algae to the SP film–forming solution and that the SP/red algae composite film containing GSE can be used as an antimicrobial food packaging material. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Recently, biodegradable packaging materials have received attention because non-biodegradable plastic packaging can cause serious environmental problems. In particular, studies on edible packaging films have increased (Abdorreza et al., 2011). Various edible film materials, such as protein- and polysaccharide-based films, have been studied as environmentally friendly packaging (Jagannath et al., 2003). However, edible films have some disadvantages: for example, low thermal resistance, low water barrier function, inferior physical properties, and high cost (Cao et al., 2007). Therefore, a less-expensive edible film material and improvements in the physical property of the film are needed. Sunflower is cultivated worldwide for the extraction of sunflower seed oil, and sunflower seed meal is generated as a by-product of oil extraction. Sunflower seed meal consists of 28% protein (Parrado et al., 1991), and like sunflower seed meal, the proteins present in the by-product generated during food processing can be utilized as a raw material for edible films (Gnanasambandam et al., 2006; Brandenburg et al., 2006; Parris and Coffin, 1997).
⇑ Corresponding author. Tel.: +82 42 821 6723; fax: +82 42 825 2664. E-mail address: [email protected] (K.B. Song). 0260-8774/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.02.002
Thus, sunflower seed meal protein (SP) can be used as an edible film source. Protein-based edible films are usually brittle and require the addition of a plasticizer. The use of a plasticizer makes the film flexible and not easily broken (Yamauchi et al., 1996). In general, polyols such as glycerol, sorbitol, and sucrose are used as plasticizers (Cuq et al., 1997; Zhang and Han, 2008). In particular, the use of a plasticizer is necessary for improving the mechanical properties of a brittle film such as SP film. Nano-clays have been used to enhance the physical properties of edible films (Xu et al., 2006; Sothornvit et al., 2009). The polymer/nano-clay matrix is a nanocomposite formed by continuously dispersed clay layers inside the polymer matrix (Kim et al., 2001), which results in improved mechanical properties of the films (Arora et al., 2011; Voon et al., 2012). Red algae such as Gelidium corneum can also be used to enhance the physical properties of edible films. Grapefruit seed extract (GSE) is derived from the seeds and pulp of grapefruit. GSE is a natural antimicrobial agent that contains polyphenolic compounds, and it inhibits the microbial growth of various Gram-positive and Gram-negative bacteria (Heggers et al., 2002; Xu et al., 2007). The antimicrobial effect of GSE has been shown to inhibit the activity of bacterial enzymes and to weaken the bacterial cell wall and cell membrane (Cho et al., 2004; Park and Kim, 2006).
790
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
There have been several studies on the edible films using the proteins extracted from plant seed oil residues (Gnanasambandam et al., 2006; Jang et al., 2011b; Shin et al., 2011; Song et al., 2012). However, SP films have never been prepared and studied before. Therefore, the objectives of this study were to prepare SP composite films with improved mechanical properties and to prepare SP composite films containing GSE and use the films in the packaging of smoked duck meats. 2. Materials and methods 2.1. Materials Sunflower (Helianthus annuus) seed was purchased from Xuanda Food Company (Inner Mongolia, China). The variety of sunflower was Black oil O33, which was cultivated in Inner Mongolia, China, and the protein content of sunflower seed was 28%. Red algae (G. corneum) were harvested on Jeju Island, Korea. Sucrose, fructose, and cinnamaldehyde were purchased from Sigma Chemical Co. (St. Louis, MO, USA). Commercial montmorillonite nano-clay (Cloisite Na+) was purchased from Southern Clay Co. (Gonzales, TX, USA). GSE were obtained from ABC Techno Inc. (Tokyo, Japan). 2.2. Preparation of sunflower seed meal The sunflower seeds were cleaned with water and dried at room temperature for 24 h. The cleaned sunflower seed was ground using a blender at 30,000 rpm (Osaka Chemical Co., Ltd., Osaka, Japan). To remove the sunflower seed oil, the ground sunflower seeds were extracted with 5 volumes of n-hexane for 3 h, and the defatted sunflower seed meal was obtained. 2.3. Extraction of SP The SP was extracted according to the method of Hagenmaier (1974) with a modification. The sunflower seed meal was mixed with 10 volumes of distilled water. The mixture was adjusted to pH 9.5 by the addition of 3 N NaOH and stirred at 40 °C for 1 h. During the extraction, the pH of the suspension was kept constant by adjusting the solution with 0.5 N HCl or 0.5 N NaOH. The solution was then centrifuged at 10,000g for 30 min to remove insoluble materials, and the supernatant was adjusted to pH 4.5 by the addition of 2 N HCl. After 30 min, the solution was centrifuged at 10,000g for 30 min, and the precipitated proteins were washed with distilled water. The protein solutions were subsequently neutralized and freeze-dried. 2.4. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS– PAGE) SDS–PAGE was performed according to the method of Laemmli (1970). Equal amounts of the protein samples were loaded onto each lane for comparison, resolved on a 10% separation gel, and stained with Coomassie brilliant blue. The following molecular weight markers were used: myosin (211 kDa), b-galactosidase (118 kDa), bovine serum albumin (78.9 kDa), ovalbumin (53 kDa), carbonic anhydrase (36.8 kDa), soybean trypsin inhibitor (28.6 kDa), lysozyme (17.8 kDa), and aprotinin (6.4 kDa).
1:1, 1:2, and 0:1. Cinnamaldehyde (0.01 g) was also added to the film-forming solution. For the preparation of the SP/Cloisite Na+ composite films, Cloisite Na+ was first prepared by dispersing various amounts of nano-clay (1%, 3%, 5%, and 7% of the SP) into 100 mL of distilled water; the solution was then stirred for 24 h. SP was dissolved in the nano-clay solution, mixed with plasticizers (sucrose:fructose, 2:1) and a cross-linking agent (cinnamaldehyde, 0.01%), and then stirred for 1 h. The harvested red algae were washed to remove foreign substances and dried under the sunlight. The dried whole red algae were cut, ground, and filtered using an 80-mesh sieve. For the preparation of the SP/red algae composite films, red algae were added to the SP film-forming solution at SP:red algae ratios of 3:0, 2.5:0.5, 2.3:0.7, 2.1:0.9, and 1.8:1.2 and then stirred for 1 h. The film-forming solution was heated in a water bath at 85 °C for 30 min and then cooled to 40 °C for 30 min. 2.6. Film casting and drying The film-forming solutions were strained through cheese cloths and cast onto flat, Teflon-coated glass plates (24 30 cm). A uniform film thickness was maintained by casting a constant quantity of the film-forming solution (80 mL) onto each plate. The plates were then dried at 25 °C for 24 h, and the dried films were peeled intact from the casting surfaces. The film specimens were conditioned in an environmental chamber at 25 °C and 50% relative humidity (RH) for 24 h, and the specimens were partitioned for subsequent water vapor permeability (2 2 cm) and tensile strength (2.54 10 cm) testing. 2.7. Measurement of optical properties The color of the SP composite film was analyzed using a colorimeter (Minolta, CR-400, Tokyo, Japan). Samples were placed on a white standard plate, and Hunter values (L, a, and b) were measured. The Hunter values for the standard plate were L = 94.01, a = 0.11, and b = 2.47. For each sample, 3 measurements were performed. The total color difference (DE), hue angle (h), and chroma (C) were calculated as follows:
DE ¼ ½ðDL Þ2 þ ðDa Þ2 þ ðDb Þ2 1=2
h ¼ 180 þ tan1 ðb =a Þ
C ¼ ½ða Þ2 þ ðb Þ2 1=2 where DL, Da, and Db are differences in the color values between the SP control film and the SP composite film. In addition, the transparency of the films having uniform thickness (61 ± 1 lm) was compared among the composite films by measuring the transmittance (%) at 660 nm using a spectrophotometer (UV-2450, Shimadzu Corporation, Kyoto, Japan). 2.8. Scanning electron microscopy (SEM) Micrographs of the SP samples were obtained using a LEO 1455VP scanning electron microscope (Angstrom Scientific Inc., Cambridge, England). Prior to SEM observation, the SP films were fixed and then coated with a fine gold layer. All the samples were examined using an accelerating voltage of 15 kV. 2.9. Measurement of tensile strength and elongation
2.5. Preparation of the SP film For the preparation of the SP film, 3 g of SP was dissolved in 100 mL of distilled water. The plasticizers (3 g) were then added to the film-forming solution at sucrose:fructose ratios of 1:0, 2:1,
The films’ tensile strength (TS) and elongation at break (E) were determined using an Instron Universal Testing Machine (Model 4484, Instron Co., Canton, MA, USA) according to ASTM method D638 M. An initial grip distance of 5 cm and a cross-head speed
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
of 50 cm/min were used. TS was calculated by dividing the maximum load of a specimen by the initial cross-sectional area, and E was expressed as the percent change from the initial gauge length of a specimen to the point of sample failure. Five replicates from three different films for each treatment were tested for measurement.
791
on selective agar plates. Aliquots of L. monocytogenes were plated onto Oxford Medium Base Agar (Difco). For determination of L. monocytogenes populations, the plates were incubated at 37 °C for 48 h. The microbial counts were the mean of three determinations and were expressed as log CFU/g. 2.15. Statistical analysis
2.10. Determination of film thickness The film thickness was measured at five random positions using a micrometer (Mitutoyo, Model No. 2046-08, Tokyo, Japan), and the mean value was determined. 2.11. Measurement of water vapor permeability The water vapor permeability (WVP) of the films was determined at 25 °C and 50% RH using the method of Hong et al. (2009). A polymethylacrylate cup (20 mL) was filled up to 1 cm of the top with distilled water and was covered with a film specimen that was previously conditioned in an environmental chamber at 25 °C and 50% RH. The weight loss of the cup was measured over time, and the slope was calculated using linear regression analysis. The WVP (109 g m/m2 s Pa) was then calculated using the following formula:
WVP ¼ ðWVTR LÞ=Dp where the water vapor transmission rate (WVTR) is calculated by dividing the slope by the open area of the cup, L is the mean film thickness, and 4p is the corrected partial vapor pressure difference across the film specimen. 2.12. Diffusion test for antimicrobial activity Listeria monocytogenes (ATTC 19111) was cultured at 37 °C for 24 h in 50 mL conical tubes containing 25 mL Listeria enrichment broth (Oxoid Ltd., Basingstoke, UK). L. monocytogenes (0.1 mL) was plated onto Oxford medium base (Difco, Detroit, MI, USA). Discs (10 mm in diameter) were cut from the films and placed onto the inoculated plates. After 3 h at 4 °C to allow the GSE to diffuse, L. monocytogenes plates were incubated at 37 °C for 48 h. Each microbial count was determined as the mean of three replicates, and the inhibition zone was measured in millimeters using a Digimatic caliper (Model 500-181-20, Mitutoyo Corp., Kawasaki, Japan). 2.13. Inoculation of pathogens on smoked duck meat L. monocytogenes (ATTC 19111) was cultured at 37 °C for 24 h in 50 mL conical tubes containing 25 mL Listeria enrichment broth (Oxoid) until they reached 106 CFU/mL. Aliquots of L. monocytogenes (0.25 mL) were spread evenly on the smoked duck meat surface with a sterile glass rod. The cut smoked duck meat samples (5 g, 3 6 cm) were classified into three groups: the control without the SP film, samples packed with the SP composite film containing GSE, and samples packed with the SP composite film without GSE. Each sample was then sealed in a sterile polyethylene bag (Twirl’Em Sampling Bags, Lab Plas, Quebec, Canada) and kept at 4 ± 1 °C for 10 days, and taken out for measuring microbial counts every 3 days.
Analysis of variance and Duncan’s multiple range tests were performed to analyze the data using the SAS program version 8.1 (SAS Institute, Inc., Cary, NC, USA). All experiments were performed in three replicates, except for measurements of the mechanical properties of the film (n = 5). Significant differences between treatments were determined at a 95% confidence level. All results are expressed as mean ± standard deviation herein. 3. Results and discussion 3.1. SDS–PAGE profile of the extracted SP The extracted SP was analyzed by SDS–PAGE (data not shown). The SDS–PAGE profile showed major bands of 40.8, 31.2, 26, and 13 kDa, with additional minor bands. González-Pérez et al. (2008) reported that the molecular masses of sunflower proteins are approximately 40, 30, and 24 kDa. In our study, there was an extra band at 13 kDa, and this difference might be attributed to different extraction conditions. 3.2. Physical properties of SP film The effects of the plasticizers on the mechanical properties of the SP films are shown in Table 1 In a preliminary study, glycerol, fructose, and sucrose were used as a plasticizer, but the SP film containing glycerol was too sticky to measure its mechanical property. In addition, the SP film plasticized with sucrose alone was too brittle to handle, while the film with fructose alone had a low TS of 1.22 MPa. Conversely, the addition of the combined fructose-sucrose (1:1 and 1:2, w/w) increased the TS of the SP film to 1.78 and 1.82 MPa, values higher than those of the other films. According to a study by Sothornvit and Krochta (2000), small-sized plasticizers can be easily dispersed in the protein polymer matrix and have an efficient plasticizing effect. Because fructose (MW 180.16) is smaller than sucrose (MW 342.3), fructose has a better plasticizing effect. Thus, the addition of sucrose decreased the E value from 31.72% to 24.10%. Jang et al. (2011a) also reported that a red algae film containing fructose had a higher E value than a film containing sucrose. To further improve the mechanical properties of the SP film, various amounts of cinnamaldehyde were incorporated into the film-forming solution. However, there was no significant difference in terms of TS according to the amount of cinnamaldehyde added, although TS increased with the addition of cinnamaldehyde (Table 2). As a result, the SP film with 0.01% cinnamaldehyde had the following values: TS (3.05 MPa), E (34.42%), and WVP (2.25 109 g m/m2 s Pa). Based on the results, the SP composite films were prepared using a combined fructose-sucrose (1:2, w/ w) as a plasticizer and 0.01% cinnamaldehyde as a cross-linking agent.
2.14. Measurement of microbial count 3.3. Optical properties of SP composite film Smoked duck meat samples (5 g) during storage were taken and homogenized for 3 min using a Stomacher (MIX 2, AES Laboratoire, Combourg, France), filtered through sterile cheesecloth, and diluted with 0.1 g peptone water/100 g water for the measurement of microbial counts. Serial dilutions were performed in triplicate
The optical properties of the SP composite films are shown in Table 3. The addition of Cloisite Na+ and red algae affected the optical properties of the SP film, depending on the amount of Cloisite Na+ and red algae. In particular, the addition of Cloisite Na+ in-
792
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
Table 1 Physical properties of the SP films containing various plasticizers. Fructose : sucrose ratio
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
3:0 2:1 1:1 1:2 0:3
1.22c ± 0.21 1.30c ± 0.16 1.78b ± 0.22 1.82b ± 0.19 3.44a ± 0.36
31.72a ± 3.59 29.83ab ± 4.61 27.69ab ± 2.88 24.10b ± 1.14 16.50c ± 1.45
2.32a ± 0.01 2.34a ± 0.35 2.46a ± 0.10 2.46a ± 0.14 2.41a ± 0.07
a–c
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
Table 2 Physical properties of the SP films containing various amounts of cinnamaldehyde. Cinnamaldehyde (%)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
0 0.01 0.02 0.03 0.04
1.82a ± 0.19 3.05b ± 0.19 2.96b ± 0.20 2.72b ± 0.30 2.55b ± 0.22
24.10a ± 2.26 34.42b ± 6.18 36.92b ± 0.46 37.50b ± 7.12 43.17b ± 3.53
2.46a ± 0.35 2.25a ± 0.15 2.25a ± 0.12 2.42a ± 0.19 2.52a ± 0.09
a,b
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
creased lightness (L), redness (a), yellowness (b), chroma (C), and DE value of the SP film, but decreased the hue angle (h). Sothornvit et al. (2009) also reported an increase in b value and DE value for whey protein isolate (WPI)/organo-clay composite films. This effect might be attributed to the high surface hydrophilicity of Cloisite Na+ molecules well-dispersed into a hydrophilic SP polymer matrix, resulting in a color change. The addition of red algae also increased the L, a, and DE values of the film but decreased b, C, and h values. This change might be attributed to the miscibility between the SP polymer and the red algae molecules. Similarly, Tian et al. (2011) reported that both agar and soy protein isolate (SPI) molecules have available hydroxyl functional groups, resulting in good miscibility due to hydrogen bonds between agar and SPI molecules. As a result, the miscibility between red algae and SP molecules affected the color of the films. The transparency of the composite film decreased after incorporation of the Cloisite Na+ and red algae. The composite films of 7% Cloisite Na+ and 1.2% red algae decreased the transmittance from 47.75% to 40.37 and 23.61%, respectively. This observation could be explained by the interaction of the SP with Cloisite Na+ and red algae, which hinders light passage through the film. Our results are in good agreement with the results of Sothornvit et al. (2009), who found that the transparency of WPI-based nano-composite films decreased from 14.38% to 10.00% with increased Cloisite Na+ concentration.
3.4. SEM analysis of SP composite film SEM image analysis was undertaken to examine the microstructure of the composite films. SEM images of the cross-sections of the SP film, SP/Cloisite Na+ composite film, and SP/red algae composite film are shown in Fig. 1. The composite film containing Cloisite Na+ had a more compact structure than the SP film. Kumar et al. (2010) reported that the cross-sectional SEM images of nanocomposite films represent the compatibility between the Cloisite Na+ molecules and the polymer matrix. In addition, the SP composite film containing Cloisite Na+ had a homogeneous structure, while the SP composite film containing red algae had a less homogeneous structure than the SP/Cloisite Na+ composite film, probably due to less compatibility between the SP and red algae molecules as the amount of red algae increases. However, it should be noted that the SP composite film containing red algae was smoother and more porous than the SP/Cloisite Na+ composite film. 3.5. Physical properties of SP/Cloisite Na+ composite film Incorporation of nano-clay into the SP film improved the mechanical properties of the film (Table 4). Cloisite Na+, a typical nano-clay, was used in the preparation of SP composite films. The TS of SP/Cloisite Na+ composite film was highest with the addition of 3% Cloisite Na+. The SP film containing 3% Cloisite Na+ had a TS of 5.24 MPa, while the SP film without Cloisite Na+ had a TS of 3.05 MPa. However, above 5% Cloisite Na+, the TS of the composite film decreased. The increase in TS by the addition of Cloisite Na+ up to 3% can be explained by the uniform dispersion of Cloisite Na+ molecules in the protein matrix (Bhattacharya et al., 2008). Lim et al. (2010) also reported that the TS of a G. corneum/nano-clay composite film increased with the addition of Cloisite Na+ compared to the film without Cloisite Na+, but the TS decreased with the addition of 5% or more Cloisite Na+. These results are in good agreement with our results. The decrease in the TS of SP composite films containing 5% or more Cloisite Na+ may be due to the aggregation of nanoparticles with high surface energies in the polymer matrix (Xu et al., 2006). The WVP is one of the most important functional properties of the films. The WVP of the SP/Cloisite Na+ composite film decreased with the addition of Cloisite Na+ (Table 4). The WVP of the SP film without Cloisite Na+ was 2.25 109 g m/m2 s Pa, whereas the SP/ Cloisite Na+ composite film with 7% Cloisite Na+ had a WVP of 1.69 109 g m/m2 s Pa. The decrease in the WVP of the SP composite film containing nano-clays could be due to the presence of a layered structure of nano-clays, which interferes with the transmission of water vapor through the film matrix (Park et al., 2003). Lim et al. (2010) also reported that the WVP of a G. corneum/nanoclay composite film decreased with the addition of Cloisite Na+ compared to the film without Cloisite Na+.
Table 3 Optical properties of SP composite films. Film
L
a
b
SP film
66.85g ± 0.77
4.36h ± 0.03
13.96e ± 0.16
14.62c ± 0.15
107.33a ± 0.28
69.53f ± 0.58 70.09f ± 1.29 71.20e ± 0.21 71.57e ± 0.28
4.21g ± 0.04 4.17f ± 0.05 4.14f ± 0.01 3.94e ± 0.03
14.18ef ± 0.13 14.38f ± 0.18 14.73g ± 0.29 14.99h ± 0.27
14.79bc ± 0.14 14.96b ± 0.22 15.30a ± 0.28 15.50a ± 0.24
106.54b ± 0.13 106.16c ± 0.30 105.69d ± 0.29 104.72e ± 0.21
2.55g ± 0.51 3.48f ± 0.70 4.43e ± 0.23 4.90e ± 0.19
46.27b ± 0.27 45.36b ± 0.16 42.50c ± 0.34 40.37d ± 0.28
76.61d ± 0.29 77.39c ± 0.46 80.46b ± 0.42 83.27a ± 0.46
3.59d ± 0.02 3.47c ± 0.04 3.10b ± 0.03 2.64a ± 0.02
12.31d ± 0.08 11.71c ± 0.22 10.46b ± 0.13 9.10a ± 0.13
12.81d ± 0.09 12.25e ± 0.21 10.91f ± 0.13 9.47g ± 0.11
106.26bc ± 0.12 106.44bc ± 0.37 106.53b ± 0.06 106.18c ± 0.21
9.82d ± 0.15 10.76c ± 0.53 14.11b ± 0.42 17.19a ± 0.41
45.86b ± 0.98 40.90d ± 0.86 33.14e ± 1.49 23.61f ± 0.80
Cloisite Na 1% 3% 5% 7% Red algae 0.5% 0.7% 0.9% 1.2% a–h
Chorma (C)
Hue angle (h)
DE
T660 (%)
–
47.75a ± 0.33
+
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
793
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
Fig. 1. Cross-sectional SEM images of SP composite films. (a) SP film. (b) SP/Cloisite Na + composite film. (c) SP/red algae composite film.
Table 4 Physical properties of the SP/Cloisite Na+ composite films.
Table 6 Physical properties of the 1.8% SP/1.2% red algae composite film containing GSE.
Cloisite Na+ (%)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
0 1 3 5 7
3.05bc ± 0.19 3.49b ± 0.52 5.24a ± 0.55 2.97bc ± 0.07 2.65c ± 2.00
34.42b ± 6.18 42.37a ± 6.74 21.10c ± 5.28 17.98c ± 0.77 17.15c ± 4.95
2.25a ± 0.15 1.74b ± 0.11 1.73b ± 0.02 1.70b ± 0.07 1.69b ± 0.01
GSE (%)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/m2 s Pa)
0 0.7 0.9 1.2
6.87a ± 0.36 4.84b ± 0.44 3.75c ± 0.34 3.18c ± 0.10
31.66b ± 8.03 55.93a ± 10.26 55.50a ± 7.56 55.92a ± 6.82
1.98b ± 0.11 2.31a ± 0.02 2.32a ± 0.09 2.33a ± 0.03
a–c
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
a–c
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
Table 5 Physical properties of the SP/red algae composite films. SP (g)
Red algae (g)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
3 2.5 2.3 2.1 1.8
0 0.5 0.7 0.9 1.2
3.05a ± 0.19 3.63cd ± 0.10 4.01c ± 0.04 4.70b ± 0.33 6.87a ± 0.36
34.42ab ± 6.18 41.24a ± 6.27 39.32a ± 7.53 37.47a ± 5.89 31.66ab ± 8.03
2.25a ± 0.15 2.21a ± 0.23 2.09a ± 0.18 1.99a ± 0.41 1.98a ± 0.11
a–e
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
3.6. Physical properties of SP/red algae composite film Red algae were incorporated into the film-forming solution to improve the mechanical properties of the SP film (Table 5). The TS of the SP/red algae composite film increased as the amount of red algae increased, with a maximum at the 1.8:1.2 ratio of SP and red algae. The SP film without red algae had a TS of 3.05 MPa, while the SP composite film containing 1.2% red algae had a TS of 6.87 MPa. Shin et al. (2011) reported that the TS of rice bran protein composite film increased with the addition of 1 to 3% red algae. It has been reported that red algae film including the insoluble pulp fraction has good physical properties (Jang et al., 2011a). The reason for the increase in TS with increasing amounts of red algae could be due to the increase in molecular interactions between SP and red algae molecules. In contrast, the E of the SP/red
algae composite film decreased with the addition of red algae (Table 5). The SP composite film with 0.5% red algae had the highest E (41.24%), while the SP composite film with 1.2% red algae had the lowest E (31.66%). Shin et al. (2011) also reported similar results for the rice bran protein composite films containing red algae. On the contrary, the WVP of the SP/red algae composite film was not affected by the addition of red algae. 3.7. Physical properties of SP/red algae composite film containing GSE In general, the addition of GSE to the film-forming solution as an antimicrobial agent decreases the TS of the films (Jang et al., 2011b). Therefore, the SP composite film containing red algae was used for antimicrobial film containing GSE because the SP/ red algae composite film had higher TS than the SP/Cloisite Na+ composite film. The incorporation of GSE into the SP/red algae
Table 7 Antimicrobial activity of SP/red algae composite films containing GSE against L. monocytogenes.
a–c
GSE (%)
Inhibition zone (mm)
0 0.7 0.9 1.2
0 23.68a ± 0.55 26.71b ± 0.78 27.84c ± 0.33
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
794
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
Table 8 Change in the populations of L. monocytogenes in smoked duck meat during storage at 4 °C (log CFU/g). Type of packaging
Control SP film SP-GSE film A–C a,b
Storage time (day) 0
3
6
9
12
6.31Ba ± 0.34 6.44Ca ± 0.03 6.24Aa ± 0.30
6.92Aa ± 0.27 6.84ABab ± 0.12 6.43Ab ± 0.21
7.26Aa ± 0.24 7.00Aa ± 0.04 6.60Ab ± 0.11
6.33Ba ± 0.14 6.54BCa ± 0.32 5.25Bb ± 0.26
6.46Ba ± 0.34 6.26Ca ± 0.23 5.15Bb ± 0.13
Mean values with different letters within a raw are significantly different by Duncan’s multiple range test at p < 0.05. Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
composite film decreased TS as GSE concentration increased (Table 6). The SP/red algae composite film had a TS of 6.87 MPa, while the composite film containing 0.7 or 1.2% GSE had a TS of 4.84 or 3.18 MPa, respectively. However, the addition of GSE increased the E value from 32% to 56%. Jang et al. (2011b) reported that the TS of rapeseed protein-gelatin films containing GSE decreased with the addition of GSE. Corrales et al. (2009) also reported that the TS of pea starch films decreased with the addition of GSE. The decrease in TS due to the addition of GSE can be attributed to a reduction in intermolecular interactions among protein molecules caused by GSE molecules. The WVP of the SP/red algae composite films increased with the addition of GSE (Table 6). The WVP of the SP/red algae composite film without GSE was 1.98 109 g m/m2 s Pa, while the SP/red algae composite films with 1.2% GSE had a WVP of 2.34 109 g m/ m2 s Pa. Mastromatteo et al. (2009) reported that the increase in WVP due to the addition of GSE can be attributed to the loss of intermolecular interaction in the protein matrix as well as to the increase in the average pore size of the films. 3.8. Antimicrobial activity of SP/red algae composite film containing GSE The antimicrobial activity of the composite film containing GSE against L. monocytogenes is presented in Table 7. The inhibition zone against L. monocytogenes increased with increasing concentration of GSE up to 1.2%. For the SP/red algae composite film containing 1.2% GSE, the inhibition zone was 27.84 mm. These results indicate that GSE can be used as an antimicrobial agent in an SP composite film. 3.9. Microbiological analysis in smoked duck meats packed with SP film during storage The population of L. monocytogenes inoculated on smoked duck meat packed with the SP/red algae composite film containing 1.2% GSE was determined during storage. The initial population of L. monocytogenes inoculated on the smoked duck meats was 6.30 log CFU/g (Table 8). The population of L. monocytogenes in the smoked duck meats increased during storage for the first 6 days after inoculation and then decreased thereafter through 12 days of storage. Similarly, Neetoo et al. (2010) reported that the population of L. monocytogenes in cold-smoked salmon slices increased for 12 days and then decreased thereafter. The growth pattern of bacteria can be affected by the growth condition of bacteria and the availability of nutrients for microbial growth during storage. After 12 days of storage, the population of L. monocytogenes in the smoked duck meats packed with SP/algae composite film without GSE was 6.26 log CFU/g, whereas the population of L. monocytogenes in the smoked duck meats with the composite film containing 1.2% GSE was 5.15 log CFU/g, resulting in a decrease of 1.11 log CFU/g. Hong et al. (2009) also reported that the population of L. monocytogenes in pork loin with G. corneum–gelatin blend films containing GSE was reduced by 0.98 log CFU/g after 10 days
of storage, compared to the control. These results suggest that GSE can be incorporated as an antimicrobial in packaging films. 4. Conclusions SP can be used as a source of edible film because of its filmforming capacity and low cost. For the preparation of SP film, a plasticizer composed of a combination of fructose and sucrose as well as cinnamaldehyde as a cross-linking agent was used to yield optimal film conditions. The addition of 3% Cloisite Na+ improved the mechanical properties of the SP film, and the addition of 1.2% red algae also increased the TS of the film. The incorporation of 1.2% GSE into the SP composite film reduced the population of L. monocytogenes inoculated on smoked duck meat during storage, suggesting that the SP composite film containing GSE can be used as an antimicrobial packaging film in the food industry. References Abdorreza, M.N., Cheng, L.H., Karim, A., 2011. Effects of plasticizers on thermal properties and heat sealability of sago starch films. Food Hydrocolloids 25 (1), 56–60. Arora, A., Choudhey, V., Sharma, D.K., 2011. Effect of clay content and clay/ surfactant on the mechanical, thermal and barrier properties of polystyrene/ organoclay nanocomposites. Journal of Polymer Research 18 (4), 843–857. Bhattacharya, S.N., Gupta, R.K., Kamal, M.R., 2008. Polymeric Nanocomposites: Theory and Practice. Hanser Gardner, Munich, Germany. Brandenburg, A.H., Weller, C.L., Testin, R.F., 2006. Edible films and coatings from soy protein. Journal of Food Science 58 (5), 1086–1089. Cao, N., Fu, Y., He, J., 2007. Preparation and physical properties of soy protein isolate and gelatin films. Food Hydrocolloids 21 (7), 1153–1162. Cho, S.H., Kim, C.H., Park, W.P., 2004. Antimicrobial activities of botanical antimicrobial agent-grapefruit seed extract mixture for the preparation of antimicrobial packaging paper. Korean Journal of Food Preservation 11 (3), 411– 416. Corrales, M., Han, J.H., Tauscher, B., 2009. Antimicrobial properties of grape seed extracts and their effectiveness after incorporation into pea starch films. International Journal of Food Science and Technology 44 (2), 425–433. Cuq, B., Gontard, N., Cuq, J.L., Guilbert, S., 1997. Selected functional properties of fish myofibrillar protein-based films as affected by hydrophilic plasticizers. Journal of Agricultural and Food Chemistry 45 (3), 622–626. Gnanasambandam, R., Hettiarachchy, N.S., Coleman, M., 2006. Mechanical and barrier properties of rice bran films. Journal of Food Science 62 (2), 395–398. González-Pérez, S., Merck, K.B., Vereijken, J.M., Van Koningsveld, G.A., Gruppen, H., Voragen, A.G.J., 2008. Isolation and characterization of undenatured chlorogenic acid free sunflower (Helianthus annuus) proteins. Journal of Agricultural and Food Chemistry 50 (6), 1713–1719. Hagenmaier, F.D., 1974. Aqueous processing of full-fat sunflower seeds: yields of oil and protein. Journal of the American Oil Chemists Society 51 (10), 470–471. Heggers, J.P., Conttingham, J., Gusman, J., Reagor, L., Mccoy, L., Carino, E., Cox, R., Zhao, J.G., 2002. The effectiveness of processed grapefruit-seed extract as an antibacterial agent: II. Mechanism of action and in vitro toxicity. The Journal of Alternative and Complementary Medicine 8 (3), 333–340. Hong, Y.H., Lim, G.O., Song, K.B., 2009. Physical properties of Gelidium corneum– gelatin blend films containing grapefruit seed extract or green tea extract and its application in the packaging of pork loins. Journal of Food Science 74 (1), C6– C10. Jagannath, J.H., Nanjappa, C., Das Gupta, D.K., Bawa, A.S., 2003. Mechanical and barrier properties of edible starch–protein-based films. Journal of Applied Polymer Science 88 (1), 64–71. Jang, S.A., Shin, Y.J., Seo, Y.B., Song, K.B., 2011a. Effects of various plasticizers and nanoclays on the mechanical properties of red algae film. Journal of Food Science 76 (3), N30–N34. Jang, S.A., Shin, Y.J., Song, K.B., 2011b. Effect of rapeseed protein–gelatin film containing grapefruit seed extract on ‘Maehyang’ strawberry quality. International Journal of Food Science and Technology 46 (3), 620–625.
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795 Kim, G.M., Lee, D.H., Hoffmann, B., Kressler, J., Stoppelmann, G., 2001. Influence of nanofillers on the deformation process in layered silicate/polyamide-12 nanocomposites. Polymer 42 (3), 1095–1100. Kumar, P., Sandeep, K.P., Alavi, S., Truong, V.D., Gorga, R.E., 2010. Preparation and characterization of bio-nanocomposite films based on soy protein isolate and montmorillionite using melt extrusion. Journal of Food Engineering 100 (3), 480–489. Laemmli, U.K., 1970. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature 227, 680–685. Lim, G.O., Jang, S.A., Song, K.B., 2010. Physical and antimicrobial properties of Gelidium corneum/nano-clay composite film containing grapefruit seed extract or thymol. Journal of Food Engineering 98 (4), 415–420. Mastromatteo, M., Barbuzzi, G., Conte, A., Nobile, M.A.D., 2009. Controlled release of thymol from zein based film. Innovative Food Science & Emerging Technologies 10 (2), 222–227. Neetoo, H., Ye, M., Chen, H., 2010. Bioactive alginate coatings to control Listeria monocytogenes on cold-smoked salmon slices and fillets. International Journal of Food Microbiology 136 (3), 326–331. Park, H.K., Kim, S.B., 2006. Antimicrobial activity of grapefruit seed extract. Korean Journal of Food and Nutrition 19 (4), 526–531. Park, H.M., Lee, W.K., Park, C.Y., Cho, W.J., Ha, C.S., 2003. Environmentally friendly polymer hybrids. Part I. Mechanical, thermal, and barrier properties of thermoplastic starch/clay nanocomposites. Journal of Materials Science 38 (5), 909–915. Parrado, J., Bautista, J., Machado, A., 1991. Production of soluble enzymatic protein hydrolysate from industrially defatted nondehulled sunflower meal. Journal of Agricultural and Food Chemistry 39 (3), 447–450. Parris, N., Coffin, D.R., 1997. Composition factors affecting the water vapor permeability and tensile properties of hydrophilic zein films. Journal of Agricultural and Food Chemistry 45 (5), 1596–1599.
795
Shin, Y.J., Jang, S.A., Song, K.B., 2011. Preparation and mechanical properties of rice bran protein composite films containing gelatin or red algae. Food Science and Biotechnology 20 (3), 703–707. Song, H.Y., Shin, Y.J., Song, K.B., 2012. Preparation of a barley bran protein–gelatin composite film containing grapefruit seed extract and its application in salmon packaging. Journal of Food Engineering 113, 541–547. Sothornvit, R., Krochta, J.M., 2000. Plasticizer effect on oxygen permeability of blactoglobulin films. Journal of Agricultural and Food Chemistry 48 (12), 6298– 6302. Sothornvit, R., Rhim, J.W., Hong, S.I., 2009. Effect of nano-clay type on the physical and antimicrobial properties of whey protein isolate/clay composite films. Journal of Food Engineering 91 (3), 468–473. Tian, H., Xu, G., Yang, B., Guo, G., 2011. Microstructure and mechanical properties of soy protein/agar blend films: effect of composition and processing methods. Journal of Food Engineering 107 (1), 21–26. Voon, H.C., Bhat, R., Easa, A.M., Liong, M.T., Karim, A.A., 2012. Effect of addition of halloysite nanoclay and SiO2 nanoparticles on barrier and mechanical properties of bovine gelatin films. Food and Bioprocess Technology 5 (5), 1766–1774. Xu, Y., Ren, X., Hanna, M.A., 2006. Chitosan/clay nanocomposite film preparation and characterization. Journal of Applied Polymer Science 99 (4), 1684–1691. Xu, W., Qu, W., Huang, K., Guo, F., Yang, J., Zhao, H., Luo, Y., 2007. Antibacterial effect of grapefruit seed extract on food-borne pathogens and its application in the preservation of minimally processed vegetables. Postharvest Biology and Technology 45 (1), 126–133. Yamauchi, K., Yamauchi, A., Kusunoki, T., Kohda, A., Konishi, Y., 1996. Preparation of stable aqueous solution of keratins, and physiochemical and biodegradation properties of films. Journal of Biomedical Materials Research 31 (4), 439–444. Zhang, Y., Han, J.H., 2008. Sorption isotherm and plasticization effect of moisture and plasticizers in pea starch film. Journal of Food Science 73 (7), E313–E324.
Contents lists available at SciVerse ScienceDirect
Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Physical properties of a composite film containing sunflower seed meal protein and its application in packaging smoked duck meat Nak-Bum Song, Hye-Yeon Song, Wan-Shin Jo, Kyung Bin Song ⇑ Department of Food Science & Technology, Chungnam National University, Daejeon 305-764, Republic of Korea
a r t i c l e
i n f o
Article history: Received 12 December 2012 Received in revised form 30 January 2013 Accepted 2 February 2013 Available online 10 February 2013 Keywords: Sunflower seed Cloisite Na+ Red algae Physical property
a b s t r a c t Sunflower seed meal protein (SP) films were prepared using various plasticizers, cross-linking agents, Cloisite Na+ or red algae, and their physical properties, such as tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) were determined. The TS, E, and WVP of the SP film containing sucrose and fructose (2:1) as a plasticizer and cinnamaldehyde as a cross-linking agent were 3.05 MPa, 34.42%, and 2.25 109 g m/m2 s Pa, respectively. The incorporation of Cloisite Na+ improved the physical properties of the SP film. The TS of the SP/Cloisite Na+ composite film containing 3% Cloisite Na+ increased by 2.19 MPa, and the WVP of the composite film decreased by 0.52 109 g m/m2 s Pa compared to the SP film. The incorporation of red algae also improved the TS of the SP film. The TS of the SP composite film containing 1.2% red algae increased by 3.82 MPa compared to the SP film. In addition, an SP/red algae composite film containing grapefruit seed extract (GSE) was prepared and used in food packaging. After 12 days of storage, the population of Listeria monocytogenes inoculated on smoked duck meats packed with the SP/red algae composite film containing 1.2% GSE decreased by 1.31 log CFU/g compared to the control packaging. Therefore, these results suggest that SP composite films can be prepared by the addition of red algae to the SP film–forming solution and that the SP/red algae composite film containing GSE can be used as an antimicrobial food packaging material. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Recently, biodegradable packaging materials have received attention because non-biodegradable plastic packaging can cause serious environmental problems. In particular, studies on edible packaging films have increased (Abdorreza et al., 2011). Various edible film materials, such as protein- and polysaccharide-based films, have been studied as environmentally friendly packaging (Jagannath et al., 2003). However, edible films have some disadvantages: for example, low thermal resistance, low water barrier function, inferior physical properties, and high cost (Cao et al., 2007). Therefore, a less-expensive edible film material and improvements in the physical property of the film are needed. Sunflower is cultivated worldwide for the extraction of sunflower seed oil, and sunflower seed meal is generated as a by-product of oil extraction. Sunflower seed meal consists of 28% protein (Parrado et al., 1991), and like sunflower seed meal, the proteins present in the by-product generated during food processing can be utilized as a raw material for edible films (Gnanasambandam et al., 2006; Brandenburg et al., 2006; Parris and Coffin, 1997).
⇑ Corresponding author. Tel.: +82 42 821 6723; fax: +82 42 825 2664. E-mail address: [email protected] (K.B. Song). 0260-8774/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.02.002
Thus, sunflower seed meal protein (SP) can be used as an edible film source. Protein-based edible films are usually brittle and require the addition of a plasticizer. The use of a plasticizer makes the film flexible and not easily broken (Yamauchi et al., 1996). In general, polyols such as glycerol, sorbitol, and sucrose are used as plasticizers (Cuq et al., 1997; Zhang and Han, 2008). In particular, the use of a plasticizer is necessary for improving the mechanical properties of a brittle film such as SP film. Nano-clays have been used to enhance the physical properties of edible films (Xu et al., 2006; Sothornvit et al., 2009). The polymer/nano-clay matrix is a nanocomposite formed by continuously dispersed clay layers inside the polymer matrix (Kim et al., 2001), which results in improved mechanical properties of the films (Arora et al., 2011; Voon et al., 2012). Red algae such as Gelidium corneum can also be used to enhance the physical properties of edible films. Grapefruit seed extract (GSE) is derived from the seeds and pulp of grapefruit. GSE is a natural antimicrobial agent that contains polyphenolic compounds, and it inhibits the microbial growth of various Gram-positive and Gram-negative bacteria (Heggers et al., 2002; Xu et al., 2007). The antimicrobial effect of GSE has been shown to inhibit the activity of bacterial enzymes and to weaken the bacterial cell wall and cell membrane (Cho et al., 2004; Park and Kim, 2006).
790
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
There have been several studies on the edible films using the proteins extracted from plant seed oil residues (Gnanasambandam et al., 2006; Jang et al., 2011b; Shin et al., 2011; Song et al., 2012). However, SP films have never been prepared and studied before. Therefore, the objectives of this study were to prepare SP composite films with improved mechanical properties and to prepare SP composite films containing GSE and use the films in the packaging of smoked duck meats. 2. Materials and methods 2.1. Materials Sunflower (Helianthus annuus) seed was purchased from Xuanda Food Company (Inner Mongolia, China). The variety of sunflower was Black oil O33, which was cultivated in Inner Mongolia, China, and the protein content of sunflower seed was 28%. Red algae (G. corneum) were harvested on Jeju Island, Korea. Sucrose, fructose, and cinnamaldehyde were purchased from Sigma Chemical Co. (St. Louis, MO, USA). Commercial montmorillonite nano-clay (Cloisite Na+) was purchased from Southern Clay Co. (Gonzales, TX, USA). GSE were obtained from ABC Techno Inc. (Tokyo, Japan). 2.2. Preparation of sunflower seed meal The sunflower seeds were cleaned with water and dried at room temperature for 24 h. The cleaned sunflower seed was ground using a blender at 30,000 rpm (Osaka Chemical Co., Ltd., Osaka, Japan). To remove the sunflower seed oil, the ground sunflower seeds were extracted with 5 volumes of n-hexane for 3 h, and the defatted sunflower seed meal was obtained. 2.3. Extraction of SP The SP was extracted according to the method of Hagenmaier (1974) with a modification. The sunflower seed meal was mixed with 10 volumes of distilled water. The mixture was adjusted to pH 9.5 by the addition of 3 N NaOH and stirred at 40 °C for 1 h. During the extraction, the pH of the suspension was kept constant by adjusting the solution with 0.5 N HCl or 0.5 N NaOH. The solution was then centrifuged at 10,000g for 30 min to remove insoluble materials, and the supernatant was adjusted to pH 4.5 by the addition of 2 N HCl. After 30 min, the solution was centrifuged at 10,000g for 30 min, and the precipitated proteins were washed with distilled water. The protein solutions were subsequently neutralized and freeze-dried. 2.4. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS– PAGE) SDS–PAGE was performed according to the method of Laemmli (1970). Equal amounts of the protein samples were loaded onto each lane for comparison, resolved on a 10% separation gel, and stained with Coomassie brilliant blue. The following molecular weight markers were used: myosin (211 kDa), b-galactosidase (118 kDa), bovine serum albumin (78.9 kDa), ovalbumin (53 kDa), carbonic anhydrase (36.8 kDa), soybean trypsin inhibitor (28.6 kDa), lysozyme (17.8 kDa), and aprotinin (6.4 kDa).
1:1, 1:2, and 0:1. Cinnamaldehyde (0.01 g) was also added to the film-forming solution. For the preparation of the SP/Cloisite Na+ composite films, Cloisite Na+ was first prepared by dispersing various amounts of nano-clay (1%, 3%, 5%, and 7% of the SP) into 100 mL of distilled water; the solution was then stirred for 24 h. SP was dissolved in the nano-clay solution, mixed with plasticizers (sucrose:fructose, 2:1) and a cross-linking agent (cinnamaldehyde, 0.01%), and then stirred for 1 h. The harvested red algae were washed to remove foreign substances and dried under the sunlight. The dried whole red algae were cut, ground, and filtered using an 80-mesh sieve. For the preparation of the SP/red algae composite films, red algae were added to the SP film-forming solution at SP:red algae ratios of 3:0, 2.5:0.5, 2.3:0.7, 2.1:0.9, and 1.8:1.2 and then stirred for 1 h. The film-forming solution was heated in a water bath at 85 °C for 30 min and then cooled to 40 °C for 30 min. 2.6. Film casting and drying The film-forming solutions were strained through cheese cloths and cast onto flat, Teflon-coated glass plates (24 30 cm). A uniform film thickness was maintained by casting a constant quantity of the film-forming solution (80 mL) onto each plate. The plates were then dried at 25 °C for 24 h, and the dried films were peeled intact from the casting surfaces. The film specimens were conditioned in an environmental chamber at 25 °C and 50% relative humidity (RH) for 24 h, and the specimens were partitioned for subsequent water vapor permeability (2 2 cm) and tensile strength (2.54 10 cm) testing. 2.7. Measurement of optical properties The color of the SP composite film was analyzed using a colorimeter (Minolta, CR-400, Tokyo, Japan). Samples were placed on a white standard plate, and Hunter values (L, a, and b) were measured. The Hunter values for the standard plate were L = 94.01, a = 0.11, and b = 2.47. For each sample, 3 measurements were performed. The total color difference (DE), hue angle (h), and chroma (C) were calculated as follows:
DE ¼ ½ðDL Þ2 þ ðDa Þ2 þ ðDb Þ2 1=2
h ¼ 180 þ tan1 ðb =a Þ
C ¼ ½ða Þ2 þ ðb Þ2 1=2 where DL, Da, and Db are differences in the color values between the SP control film and the SP composite film. In addition, the transparency of the films having uniform thickness (61 ± 1 lm) was compared among the composite films by measuring the transmittance (%) at 660 nm using a spectrophotometer (UV-2450, Shimadzu Corporation, Kyoto, Japan). 2.8. Scanning electron microscopy (SEM) Micrographs of the SP samples were obtained using a LEO 1455VP scanning electron microscope (Angstrom Scientific Inc., Cambridge, England). Prior to SEM observation, the SP films were fixed and then coated with a fine gold layer. All the samples were examined using an accelerating voltage of 15 kV. 2.9. Measurement of tensile strength and elongation
2.5. Preparation of the SP film For the preparation of the SP film, 3 g of SP was dissolved in 100 mL of distilled water. The plasticizers (3 g) were then added to the film-forming solution at sucrose:fructose ratios of 1:0, 2:1,
The films’ tensile strength (TS) and elongation at break (E) were determined using an Instron Universal Testing Machine (Model 4484, Instron Co., Canton, MA, USA) according to ASTM method D638 M. An initial grip distance of 5 cm and a cross-head speed
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
of 50 cm/min were used. TS was calculated by dividing the maximum load of a specimen by the initial cross-sectional area, and E was expressed as the percent change from the initial gauge length of a specimen to the point of sample failure. Five replicates from three different films for each treatment were tested for measurement.
791
on selective agar plates. Aliquots of L. monocytogenes were plated onto Oxford Medium Base Agar (Difco). For determination of L. monocytogenes populations, the plates were incubated at 37 °C for 48 h. The microbial counts were the mean of three determinations and were expressed as log CFU/g. 2.15. Statistical analysis
2.10. Determination of film thickness The film thickness was measured at five random positions using a micrometer (Mitutoyo, Model No. 2046-08, Tokyo, Japan), and the mean value was determined. 2.11. Measurement of water vapor permeability The water vapor permeability (WVP) of the films was determined at 25 °C and 50% RH using the method of Hong et al. (2009). A polymethylacrylate cup (20 mL) was filled up to 1 cm of the top with distilled water and was covered with a film specimen that was previously conditioned in an environmental chamber at 25 °C and 50% RH. The weight loss of the cup was measured over time, and the slope was calculated using linear regression analysis. The WVP (109 g m/m2 s Pa) was then calculated using the following formula:
WVP ¼ ðWVTR LÞ=Dp where the water vapor transmission rate (WVTR) is calculated by dividing the slope by the open area of the cup, L is the mean film thickness, and 4p is the corrected partial vapor pressure difference across the film specimen. 2.12. Diffusion test for antimicrobial activity Listeria monocytogenes (ATTC 19111) was cultured at 37 °C for 24 h in 50 mL conical tubes containing 25 mL Listeria enrichment broth (Oxoid Ltd., Basingstoke, UK). L. monocytogenes (0.1 mL) was plated onto Oxford medium base (Difco, Detroit, MI, USA). Discs (10 mm in diameter) were cut from the films and placed onto the inoculated plates. After 3 h at 4 °C to allow the GSE to diffuse, L. monocytogenes plates were incubated at 37 °C for 48 h. Each microbial count was determined as the mean of three replicates, and the inhibition zone was measured in millimeters using a Digimatic caliper (Model 500-181-20, Mitutoyo Corp., Kawasaki, Japan). 2.13. Inoculation of pathogens on smoked duck meat L. monocytogenes (ATTC 19111) was cultured at 37 °C for 24 h in 50 mL conical tubes containing 25 mL Listeria enrichment broth (Oxoid) until they reached 106 CFU/mL. Aliquots of L. monocytogenes (0.25 mL) were spread evenly on the smoked duck meat surface with a sterile glass rod. The cut smoked duck meat samples (5 g, 3 6 cm) were classified into three groups: the control without the SP film, samples packed with the SP composite film containing GSE, and samples packed with the SP composite film without GSE. Each sample was then sealed in a sterile polyethylene bag (Twirl’Em Sampling Bags, Lab Plas, Quebec, Canada) and kept at 4 ± 1 °C for 10 days, and taken out for measuring microbial counts every 3 days.
Analysis of variance and Duncan’s multiple range tests were performed to analyze the data using the SAS program version 8.1 (SAS Institute, Inc., Cary, NC, USA). All experiments were performed in three replicates, except for measurements of the mechanical properties of the film (n = 5). Significant differences between treatments were determined at a 95% confidence level. All results are expressed as mean ± standard deviation herein. 3. Results and discussion 3.1. SDS–PAGE profile of the extracted SP The extracted SP was analyzed by SDS–PAGE (data not shown). The SDS–PAGE profile showed major bands of 40.8, 31.2, 26, and 13 kDa, with additional minor bands. González-Pérez et al. (2008) reported that the molecular masses of sunflower proteins are approximately 40, 30, and 24 kDa. In our study, there was an extra band at 13 kDa, and this difference might be attributed to different extraction conditions. 3.2. Physical properties of SP film The effects of the plasticizers on the mechanical properties of the SP films are shown in Table 1 In a preliminary study, glycerol, fructose, and sucrose were used as a plasticizer, but the SP film containing glycerol was too sticky to measure its mechanical property. In addition, the SP film plasticized with sucrose alone was too brittle to handle, while the film with fructose alone had a low TS of 1.22 MPa. Conversely, the addition of the combined fructose-sucrose (1:1 and 1:2, w/w) increased the TS of the SP film to 1.78 and 1.82 MPa, values higher than those of the other films. According to a study by Sothornvit and Krochta (2000), small-sized plasticizers can be easily dispersed in the protein polymer matrix and have an efficient plasticizing effect. Because fructose (MW 180.16) is smaller than sucrose (MW 342.3), fructose has a better plasticizing effect. Thus, the addition of sucrose decreased the E value from 31.72% to 24.10%. Jang et al. (2011a) also reported that a red algae film containing fructose had a higher E value than a film containing sucrose. To further improve the mechanical properties of the SP film, various amounts of cinnamaldehyde were incorporated into the film-forming solution. However, there was no significant difference in terms of TS according to the amount of cinnamaldehyde added, although TS increased with the addition of cinnamaldehyde (Table 2). As a result, the SP film with 0.01% cinnamaldehyde had the following values: TS (3.05 MPa), E (34.42%), and WVP (2.25 109 g m/m2 s Pa). Based on the results, the SP composite films were prepared using a combined fructose-sucrose (1:2, w/ w) as a plasticizer and 0.01% cinnamaldehyde as a cross-linking agent.
2.14. Measurement of microbial count 3.3. Optical properties of SP composite film Smoked duck meat samples (5 g) during storage were taken and homogenized for 3 min using a Stomacher (MIX 2, AES Laboratoire, Combourg, France), filtered through sterile cheesecloth, and diluted with 0.1 g peptone water/100 g water for the measurement of microbial counts. Serial dilutions were performed in triplicate
The optical properties of the SP composite films are shown in Table 3. The addition of Cloisite Na+ and red algae affected the optical properties of the SP film, depending on the amount of Cloisite Na+ and red algae. In particular, the addition of Cloisite Na+ in-
792
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
Table 1 Physical properties of the SP films containing various plasticizers. Fructose : sucrose ratio
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
3:0 2:1 1:1 1:2 0:3
1.22c ± 0.21 1.30c ± 0.16 1.78b ± 0.22 1.82b ± 0.19 3.44a ± 0.36
31.72a ± 3.59 29.83ab ± 4.61 27.69ab ± 2.88 24.10b ± 1.14 16.50c ± 1.45
2.32a ± 0.01 2.34a ± 0.35 2.46a ± 0.10 2.46a ± 0.14 2.41a ± 0.07
a–c
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
Table 2 Physical properties of the SP films containing various amounts of cinnamaldehyde. Cinnamaldehyde (%)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
0 0.01 0.02 0.03 0.04
1.82a ± 0.19 3.05b ± 0.19 2.96b ± 0.20 2.72b ± 0.30 2.55b ± 0.22
24.10a ± 2.26 34.42b ± 6.18 36.92b ± 0.46 37.50b ± 7.12 43.17b ± 3.53
2.46a ± 0.35 2.25a ± 0.15 2.25a ± 0.12 2.42a ± 0.19 2.52a ± 0.09
a,b
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
creased lightness (L), redness (a), yellowness (b), chroma (C), and DE value of the SP film, but decreased the hue angle (h). Sothornvit et al. (2009) also reported an increase in b value and DE value for whey protein isolate (WPI)/organo-clay composite films. This effect might be attributed to the high surface hydrophilicity of Cloisite Na+ molecules well-dispersed into a hydrophilic SP polymer matrix, resulting in a color change. The addition of red algae also increased the L, a, and DE values of the film but decreased b, C, and h values. This change might be attributed to the miscibility between the SP polymer and the red algae molecules. Similarly, Tian et al. (2011) reported that both agar and soy protein isolate (SPI) molecules have available hydroxyl functional groups, resulting in good miscibility due to hydrogen bonds between agar and SPI molecules. As a result, the miscibility between red algae and SP molecules affected the color of the films. The transparency of the composite film decreased after incorporation of the Cloisite Na+ and red algae. The composite films of 7% Cloisite Na+ and 1.2% red algae decreased the transmittance from 47.75% to 40.37 and 23.61%, respectively. This observation could be explained by the interaction of the SP with Cloisite Na+ and red algae, which hinders light passage through the film. Our results are in good agreement with the results of Sothornvit et al. (2009), who found that the transparency of WPI-based nano-composite films decreased from 14.38% to 10.00% with increased Cloisite Na+ concentration.
3.4. SEM analysis of SP composite film SEM image analysis was undertaken to examine the microstructure of the composite films. SEM images of the cross-sections of the SP film, SP/Cloisite Na+ composite film, and SP/red algae composite film are shown in Fig. 1. The composite film containing Cloisite Na+ had a more compact structure than the SP film. Kumar et al. (2010) reported that the cross-sectional SEM images of nanocomposite films represent the compatibility between the Cloisite Na+ molecules and the polymer matrix. In addition, the SP composite film containing Cloisite Na+ had a homogeneous structure, while the SP composite film containing red algae had a less homogeneous structure than the SP/Cloisite Na+ composite film, probably due to less compatibility between the SP and red algae molecules as the amount of red algae increases. However, it should be noted that the SP composite film containing red algae was smoother and more porous than the SP/Cloisite Na+ composite film. 3.5. Physical properties of SP/Cloisite Na+ composite film Incorporation of nano-clay into the SP film improved the mechanical properties of the film (Table 4). Cloisite Na+, a typical nano-clay, was used in the preparation of SP composite films. The TS of SP/Cloisite Na+ composite film was highest with the addition of 3% Cloisite Na+. The SP film containing 3% Cloisite Na+ had a TS of 5.24 MPa, while the SP film without Cloisite Na+ had a TS of 3.05 MPa. However, above 5% Cloisite Na+, the TS of the composite film decreased. The increase in TS by the addition of Cloisite Na+ up to 3% can be explained by the uniform dispersion of Cloisite Na+ molecules in the protein matrix (Bhattacharya et al., 2008). Lim et al. (2010) also reported that the TS of a G. corneum/nano-clay composite film increased with the addition of Cloisite Na+ compared to the film without Cloisite Na+, but the TS decreased with the addition of 5% or more Cloisite Na+. These results are in good agreement with our results. The decrease in the TS of SP composite films containing 5% or more Cloisite Na+ may be due to the aggregation of nanoparticles with high surface energies in the polymer matrix (Xu et al., 2006). The WVP is one of the most important functional properties of the films. The WVP of the SP/Cloisite Na+ composite film decreased with the addition of Cloisite Na+ (Table 4). The WVP of the SP film without Cloisite Na+ was 2.25 109 g m/m2 s Pa, whereas the SP/ Cloisite Na+ composite film with 7% Cloisite Na+ had a WVP of 1.69 109 g m/m2 s Pa. The decrease in the WVP of the SP composite film containing nano-clays could be due to the presence of a layered structure of nano-clays, which interferes with the transmission of water vapor through the film matrix (Park et al., 2003). Lim et al. (2010) also reported that the WVP of a G. corneum/nanoclay composite film decreased with the addition of Cloisite Na+ compared to the film without Cloisite Na+.
Table 3 Optical properties of SP composite films. Film
L
a
b
SP film
66.85g ± 0.77
4.36h ± 0.03
13.96e ± 0.16
14.62c ± 0.15
107.33a ± 0.28
69.53f ± 0.58 70.09f ± 1.29 71.20e ± 0.21 71.57e ± 0.28
4.21g ± 0.04 4.17f ± 0.05 4.14f ± 0.01 3.94e ± 0.03
14.18ef ± 0.13 14.38f ± 0.18 14.73g ± 0.29 14.99h ± 0.27
14.79bc ± 0.14 14.96b ± 0.22 15.30a ± 0.28 15.50a ± 0.24
106.54b ± 0.13 106.16c ± 0.30 105.69d ± 0.29 104.72e ± 0.21
2.55g ± 0.51 3.48f ± 0.70 4.43e ± 0.23 4.90e ± 0.19
46.27b ± 0.27 45.36b ± 0.16 42.50c ± 0.34 40.37d ± 0.28
76.61d ± 0.29 77.39c ± 0.46 80.46b ± 0.42 83.27a ± 0.46
3.59d ± 0.02 3.47c ± 0.04 3.10b ± 0.03 2.64a ± 0.02
12.31d ± 0.08 11.71c ± 0.22 10.46b ± 0.13 9.10a ± 0.13
12.81d ± 0.09 12.25e ± 0.21 10.91f ± 0.13 9.47g ± 0.11
106.26bc ± 0.12 106.44bc ± 0.37 106.53b ± 0.06 106.18c ± 0.21
9.82d ± 0.15 10.76c ± 0.53 14.11b ± 0.42 17.19a ± 0.41
45.86b ± 0.98 40.90d ± 0.86 33.14e ± 1.49 23.61f ± 0.80
Cloisite Na 1% 3% 5% 7% Red algae 0.5% 0.7% 0.9% 1.2% a–h
Chorma (C)
Hue angle (h)
DE
T660 (%)
–
47.75a ± 0.33
+
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
793
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
Fig. 1. Cross-sectional SEM images of SP composite films. (a) SP film. (b) SP/Cloisite Na + composite film. (c) SP/red algae composite film.
Table 4 Physical properties of the SP/Cloisite Na+ composite films.
Table 6 Physical properties of the 1.8% SP/1.2% red algae composite film containing GSE.
Cloisite Na+ (%)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
0 1 3 5 7
3.05bc ± 0.19 3.49b ± 0.52 5.24a ± 0.55 2.97bc ± 0.07 2.65c ± 2.00
34.42b ± 6.18 42.37a ± 6.74 21.10c ± 5.28 17.98c ± 0.77 17.15c ± 4.95
2.25a ± 0.15 1.74b ± 0.11 1.73b ± 0.02 1.70b ± 0.07 1.69b ± 0.01
GSE (%)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/m2 s Pa)
0 0.7 0.9 1.2
6.87a ± 0.36 4.84b ± 0.44 3.75c ± 0.34 3.18c ± 0.10
31.66b ± 8.03 55.93a ± 10.26 55.50a ± 7.56 55.92a ± 6.82
1.98b ± 0.11 2.31a ± 0.02 2.32a ± 0.09 2.33a ± 0.03
a–c
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
a–c
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
Table 5 Physical properties of the SP/red algae composite films. SP (g)
Red algae (g)
Tensile strength (MPa)
Elongation (%)
WVP (109 g m/ m2 s Pa)
3 2.5 2.3 2.1 1.8
0 0.5 0.7 0.9 1.2
3.05a ± 0.19 3.63cd ± 0.10 4.01c ± 0.04 4.70b ± 0.33 6.87a ± 0.36
34.42ab ± 6.18 41.24a ± 6.27 39.32a ± 7.53 37.47a ± 5.89 31.66ab ± 8.03
2.25a ± 0.15 2.21a ± 0.23 2.09a ± 0.18 1.99a ± 0.41 1.98a ± 0.11
a–e
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
3.6. Physical properties of SP/red algae composite film Red algae were incorporated into the film-forming solution to improve the mechanical properties of the SP film (Table 5). The TS of the SP/red algae composite film increased as the amount of red algae increased, with a maximum at the 1.8:1.2 ratio of SP and red algae. The SP film without red algae had a TS of 3.05 MPa, while the SP composite film containing 1.2% red algae had a TS of 6.87 MPa. Shin et al. (2011) reported that the TS of rice bran protein composite film increased with the addition of 1 to 3% red algae. It has been reported that red algae film including the insoluble pulp fraction has good physical properties (Jang et al., 2011a). The reason for the increase in TS with increasing amounts of red algae could be due to the increase in molecular interactions between SP and red algae molecules. In contrast, the E of the SP/red
algae composite film decreased with the addition of red algae (Table 5). The SP composite film with 0.5% red algae had the highest E (41.24%), while the SP composite film with 1.2% red algae had the lowest E (31.66%). Shin et al. (2011) also reported similar results for the rice bran protein composite films containing red algae. On the contrary, the WVP of the SP/red algae composite film was not affected by the addition of red algae. 3.7. Physical properties of SP/red algae composite film containing GSE In general, the addition of GSE to the film-forming solution as an antimicrobial agent decreases the TS of the films (Jang et al., 2011b). Therefore, the SP composite film containing red algae was used for antimicrobial film containing GSE because the SP/ red algae composite film had higher TS than the SP/Cloisite Na+ composite film. The incorporation of GSE into the SP/red algae
Table 7 Antimicrobial activity of SP/red algae composite films containing GSE against L. monocytogenes.
a–c
GSE (%)
Inhibition zone (mm)
0 0.7 0.9 1.2
0 23.68a ± 0.55 26.71b ± 0.78 27.84c ± 0.33
Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
794
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795
Table 8 Change in the populations of L. monocytogenes in smoked duck meat during storage at 4 °C (log CFU/g). Type of packaging
Control SP film SP-GSE film A–C a,b
Storage time (day) 0
3
6
9
12
6.31Ba ± 0.34 6.44Ca ± 0.03 6.24Aa ± 0.30
6.92Aa ± 0.27 6.84ABab ± 0.12 6.43Ab ± 0.21
7.26Aa ± 0.24 7.00Aa ± 0.04 6.60Ab ± 0.11
6.33Ba ± 0.14 6.54BCa ± 0.32 5.25Bb ± 0.26
6.46Ba ± 0.34 6.26Ca ± 0.23 5.15Bb ± 0.13
Mean values with different letters within a raw are significantly different by Duncan’s multiple range test at p < 0.05. Mean values with different letters within a column are significantly different by Duncan’s multiple range test at p < 0.05.
composite film decreased TS as GSE concentration increased (Table 6). The SP/red algae composite film had a TS of 6.87 MPa, while the composite film containing 0.7 or 1.2% GSE had a TS of 4.84 or 3.18 MPa, respectively. However, the addition of GSE increased the E value from 32% to 56%. Jang et al. (2011b) reported that the TS of rapeseed protein-gelatin films containing GSE decreased with the addition of GSE. Corrales et al. (2009) also reported that the TS of pea starch films decreased with the addition of GSE. The decrease in TS due to the addition of GSE can be attributed to a reduction in intermolecular interactions among protein molecules caused by GSE molecules. The WVP of the SP/red algae composite films increased with the addition of GSE (Table 6). The WVP of the SP/red algae composite film without GSE was 1.98 109 g m/m2 s Pa, while the SP/red algae composite films with 1.2% GSE had a WVP of 2.34 109 g m/ m2 s Pa. Mastromatteo et al. (2009) reported that the increase in WVP due to the addition of GSE can be attributed to the loss of intermolecular interaction in the protein matrix as well as to the increase in the average pore size of the films. 3.8. Antimicrobial activity of SP/red algae composite film containing GSE The antimicrobial activity of the composite film containing GSE against L. monocytogenes is presented in Table 7. The inhibition zone against L. monocytogenes increased with increasing concentration of GSE up to 1.2%. For the SP/red algae composite film containing 1.2% GSE, the inhibition zone was 27.84 mm. These results indicate that GSE can be used as an antimicrobial agent in an SP composite film. 3.9. Microbiological analysis in smoked duck meats packed with SP film during storage The population of L. monocytogenes inoculated on smoked duck meat packed with the SP/red algae composite film containing 1.2% GSE was determined during storage. The initial population of L. monocytogenes inoculated on the smoked duck meats was 6.30 log CFU/g (Table 8). The population of L. monocytogenes in the smoked duck meats increased during storage for the first 6 days after inoculation and then decreased thereafter through 12 days of storage. Similarly, Neetoo et al. (2010) reported that the population of L. monocytogenes in cold-smoked salmon slices increased for 12 days and then decreased thereafter. The growth pattern of bacteria can be affected by the growth condition of bacteria and the availability of nutrients for microbial growth during storage. After 12 days of storage, the population of L. monocytogenes in the smoked duck meats packed with SP/algae composite film without GSE was 6.26 log CFU/g, whereas the population of L. monocytogenes in the smoked duck meats with the composite film containing 1.2% GSE was 5.15 log CFU/g, resulting in a decrease of 1.11 log CFU/g. Hong et al. (2009) also reported that the population of L. monocytogenes in pork loin with G. corneum–gelatin blend films containing GSE was reduced by 0.98 log CFU/g after 10 days
of storage, compared to the control. These results suggest that GSE can be incorporated as an antimicrobial in packaging films. 4. Conclusions SP can be used as a source of edible film because of its filmforming capacity and low cost. For the preparation of SP film, a plasticizer composed of a combination of fructose and sucrose as well as cinnamaldehyde as a cross-linking agent was used to yield optimal film conditions. The addition of 3% Cloisite Na+ improved the mechanical properties of the SP film, and the addition of 1.2% red algae also increased the TS of the film. The incorporation of 1.2% GSE into the SP composite film reduced the population of L. monocytogenes inoculated on smoked duck meat during storage, suggesting that the SP composite film containing GSE can be used as an antimicrobial packaging film in the food industry. References Abdorreza, M.N., Cheng, L.H., Karim, A., 2011. Effects of plasticizers on thermal properties and heat sealability of sago starch films. Food Hydrocolloids 25 (1), 56–60. Arora, A., Choudhey, V., Sharma, D.K., 2011. Effect of clay content and clay/ surfactant on the mechanical, thermal and barrier properties of polystyrene/ organoclay nanocomposites. Journal of Polymer Research 18 (4), 843–857. Bhattacharya, S.N., Gupta, R.K., Kamal, M.R., 2008. Polymeric Nanocomposites: Theory and Practice. Hanser Gardner, Munich, Germany. Brandenburg, A.H., Weller, C.L., Testin, R.F., 2006. Edible films and coatings from soy protein. Journal of Food Science 58 (5), 1086–1089. Cao, N., Fu, Y., He, J., 2007. Preparation and physical properties of soy protein isolate and gelatin films. Food Hydrocolloids 21 (7), 1153–1162. Cho, S.H., Kim, C.H., Park, W.P., 2004. Antimicrobial activities of botanical antimicrobial agent-grapefruit seed extract mixture for the preparation of antimicrobial packaging paper. Korean Journal of Food Preservation 11 (3), 411– 416. Corrales, M., Han, J.H., Tauscher, B., 2009. Antimicrobial properties of grape seed extracts and their effectiveness after incorporation into pea starch films. International Journal of Food Science and Technology 44 (2), 425–433. Cuq, B., Gontard, N., Cuq, J.L., Guilbert, S., 1997. Selected functional properties of fish myofibrillar protein-based films as affected by hydrophilic plasticizers. Journal of Agricultural and Food Chemistry 45 (3), 622–626. Gnanasambandam, R., Hettiarachchy, N.S., Coleman, M., 2006. Mechanical and barrier properties of rice bran films. Journal of Food Science 62 (2), 395–398. González-Pérez, S., Merck, K.B., Vereijken, J.M., Van Koningsveld, G.A., Gruppen, H., Voragen, A.G.J., 2008. Isolation and characterization of undenatured chlorogenic acid free sunflower (Helianthus annuus) proteins. Journal of Agricultural and Food Chemistry 50 (6), 1713–1719. Hagenmaier, F.D., 1974. Aqueous processing of full-fat sunflower seeds: yields of oil and protein. Journal of the American Oil Chemists Society 51 (10), 470–471. Heggers, J.P., Conttingham, J., Gusman, J., Reagor, L., Mccoy, L., Carino, E., Cox, R., Zhao, J.G., 2002. The effectiveness of processed grapefruit-seed extract as an antibacterial agent: II. Mechanism of action and in vitro toxicity. The Journal of Alternative and Complementary Medicine 8 (3), 333–340. Hong, Y.H., Lim, G.O., Song, K.B., 2009. Physical properties of Gelidium corneum– gelatin blend films containing grapefruit seed extract or green tea extract and its application in the packaging of pork loins. Journal of Food Science 74 (1), C6– C10. Jagannath, J.H., Nanjappa, C., Das Gupta, D.K., Bawa, A.S., 2003. Mechanical and barrier properties of edible starch–protein-based films. Journal of Applied Polymer Science 88 (1), 64–71. Jang, S.A., Shin, Y.J., Seo, Y.B., Song, K.B., 2011a. Effects of various plasticizers and nanoclays on the mechanical properties of red algae film. Journal of Food Science 76 (3), N30–N34. Jang, S.A., Shin, Y.J., Song, K.B., 2011b. Effect of rapeseed protein–gelatin film containing grapefruit seed extract on ‘Maehyang’ strawberry quality. International Journal of Food Science and Technology 46 (3), 620–625.
N.-B. Song et al. / Journal of Food Engineering 116 (2013) 789–795 Kim, G.M., Lee, D.H., Hoffmann, B., Kressler, J., Stoppelmann, G., 2001. Influence of nanofillers on the deformation process in layered silicate/polyamide-12 nanocomposites. Polymer 42 (3), 1095–1100. Kumar, P., Sandeep, K.P., Alavi, S., Truong, V.D., Gorga, R.E., 2010. Preparation and characterization of bio-nanocomposite films based on soy protein isolate and montmorillionite using melt extrusion. Journal of Food Engineering 100 (3), 480–489. Laemmli, U.K., 1970. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature 227, 680–685. Lim, G.O., Jang, S.A., Song, K.B., 2010. Physical and antimicrobial properties of Gelidium corneum/nano-clay composite film containing grapefruit seed extract or thymol. Journal of Food Engineering 98 (4), 415–420. Mastromatteo, M., Barbuzzi, G., Conte, A., Nobile, M.A.D., 2009. Controlled release of thymol from zein based film. Innovative Food Science & Emerging Technologies 10 (2), 222–227. Neetoo, H., Ye, M., Chen, H., 2010. Bioactive alginate coatings to control Listeria monocytogenes on cold-smoked salmon slices and fillets. International Journal of Food Microbiology 136 (3), 326–331. Park, H.K., Kim, S.B., 2006. Antimicrobial activity of grapefruit seed extract. Korean Journal of Food and Nutrition 19 (4), 526–531. Park, H.M., Lee, W.K., Park, C.Y., Cho, W.J., Ha, C.S., 2003. Environmentally friendly polymer hybrids. Part I. Mechanical, thermal, and barrier properties of thermoplastic starch/clay nanocomposites. Journal of Materials Science 38 (5), 909–915. Parrado, J., Bautista, J., Machado, A., 1991. Production of soluble enzymatic protein hydrolysate from industrially defatted nondehulled sunflower meal. Journal of Agricultural and Food Chemistry 39 (3), 447–450. Parris, N., Coffin, D.R., 1997. Composition factors affecting the water vapor permeability and tensile properties of hydrophilic zein films. Journal of Agricultural and Food Chemistry 45 (5), 1596–1599.
795
Shin, Y.J., Jang, S.A., Song, K.B., 2011. Preparation and mechanical properties of rice bran protein composite films containing gelatin or red algae. Food Science and Biotechnology 20 (3), 703–707. Song, H.Y., Shin, Y.J., Song, K.B., 2012. Preparation of a barley bran protein–gelatin composite film containing grapefruit seed extract and its application in salmon packaging. Journal of Food Engineering 113, 541–547. Sothornvit, R., Krochta, J.M., 2000. Plasticizer effect on oxygen permeability of blactoglobulin films. Journal of Agricultural and Food Chemistry 48 (12), 6298– 6302. Sothornvit, R., Rhim, J.W., Hong, S.I., 2009. Effect of nano-clay type on the physical and antimicrobial properties of whey protein isolate/clay composite films. Journal of Food Engineering 91 (3), 468–473. Tian, H., Xu, G., Yang, B., Guo, G., 2011. Microstructure and mechanical properties of soy protein/agar blend films: effect of composition and processing methods. Journal of Food Engineering 107 (1), 21–26. Voon, H.C., Bhat, R., Easa, A.M., Liong, M.T., Karim, A.A., 2012. Effect of addition of halloysite nanoclay and SiO2 nanoparticles on barrier and mechanical properties of bovine gelatin films. Food and Bioprocess Technology 5 (5), 1766–1774. Xu, Y., Ren, X., Hanna, M.A., 2006. Chitosan/clay nanocomposite film preparation and characterization. Journal of Applied Polymer Science 99 (4), 1684–1691. Xu, W., Qu, W., Huang, K., Guo, F., Yang, J., Zhao, H., Luo, Y., 2007. Antibacterial effect of grapefruit seed extract on food-borne pathogens and its application in the preservation of minimally processed vegetables. Postharvest Biology and Technology 45 (1), 126–133. Yamauchi, K., Yamauchi, A., Kusunoki, T., Kohda, A., Konishi, Y., 1996. Preparation of stable aqueous solution of keratins, and physiochemical and biodegradation properties of films. Journal of Biomedical Materials Research 31 (4), 439–444. Zhang, Y., Han, J.H., 2008. Sorption isotherm and plasticization effect of moisture and plasticizers in pea starch film. Journal of Food Science 73 (7), E313–E324.