Food Bioscience

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Contents lists available atScienceDirect

Food Bioscience

journal homepage:www.elsevier.com/locate/fbio

Preparation and characterization of chicken skin gelatin/CMC composite ﬁ lm as compared to bovine gelatin ﬁ lm

N.N. Nazmi

^a

, M.I.N. Isa

^b

, N.M. Sarbon

^a,⁎

aSchool of Food Science and Technology, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia

bSchool of Fundamental Science, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia

A R T I C L E I N F O

Keywords:

Chicken skin gelatin Gelatinﬁlm Blendedﬁlm

Carboxymethyl cellulose (CMC) Mechanical properties Physical properties

A B S T R A C T

This study aimed to prepare and characterize the mechanical and physical properties of chicken skin gelatin/

CMC compositefilm. The influence of CMC on the mechanical (tensile strength (TS), elongation at break (EAB), puncture test), physical (water vapour permeability (WVP), FTIR, X-ray diffraction (XRD), light transmission and transparency), and thermal properties (melting point, T_mand glass transition, T_g) of chicken skin gelatinfilm were studied and compared to bovine gelatinfilm. Results shows that chicken skin gelatin/CMC compositefilms was higher in TS, puncture force, WVP, and Tgvalue. However, there were no significance different (p > 0.05) between chicken skin gelatin as compared to bovine gelatinfilm in TS and WVP value. This study demonstrates that a CMC addition to gelatinfilms gives significantly effects on properties offilm produced. The enhancement offilm properties shows potential for using this blendedfilm in packaging materials or coatings in agriculture and food products.

1. Introduction

In the past 20 years, the production and use of plastics worldwide has enormously increased. However, these materials have certain dis- advantages as they are synthesized from a non-renewable source and are not biodegradable, proving a major source of generation and ac- cumulation of residues (Avella et al., 2005; Bucci, Tavares, & Sell, 2005). The growth of environmental concerns over non-biodegradable petrochemical-based plastics has raised interest in the use of biodegradable alternatives in ﬁlm production originating from renewable sources such as proteins and polysaccharides extracted from agri- cultural, marine, animal, or microbial sources. These materials can be degraded by the environment (exposed to soil optimum moisture, mi- croorganisms, and oxygen) into simple substances (water and carbon dioxide) and biomass (Ghanbarzadeh, Almasi, & Entezami, 2010;

González & Igarzabal, 2013).

Various type of biopolymers have been discovered as possible raw resources to produce biodegradable film and coating (Moradi, Tajik, Rohani, & Mahmoudian, 2016). It is as divers for food as well as it has potential to prolong shelf life of food and reduce plastic food packaging (Saberi et al., 2016). Among all biodegradable edible films, protein basedfilms are the most attractive properties as they offer impressive gas barrier properties compared with those prepared from lipids and polysaccharides (Bourtoom, 2009; Wittaya, 2012). Proteins are suitable

as aﬁlm and coating and may be derived from whey, soybeans, gluten and gelatin.

Studies have shown that one protein source material attracting interest nowadays in order to formfilm packaging is gelatin. This is due to its abundance and biodegradability properties. The use of gelatin in the preparation of edible films or coating was very well studied (Nor, Nazmi, & Sarbon, 2016; Nur Hazirah, Isa, & Sarbon, 2016). However several safety concerns and religious issues on commercial gelatin be- come the main reasons for exploring different types of gelatin from different animal sources such as chicken bone, chicken skin, andfish skin as alternatives or substitutes for raw materials in the production of gelatin (Cheow, Norizah, Kyaw, & Howell, 2007; Rosli & Sarbon, 2015;

Sarbon, Badii, & Howell, 2013). Because of that, there is an urgent need tofind alternative source that can replace the current available gelatins as an additional option to meet customer needs. Waste by-products from fisheries industry such as fish skin, bone, fins and scale and poultry industries such as chicken skin may be potential sources to replace mammalian sources of gelatin (Cheow et al., 2007; Jeya Shakila, Jeevithan, Varatharajakumar, Jeyasekaran, & Sukumar, 2012;

Sarbon et al., 2013).

Studies on the production and characterization offish gelatinfilms are very recent, andfindings have shown thatfish gelatin exhibits ex- cellentfilm forming properties (Núñez-Flores et al., 2013; Wu et al., 2014). Studies have also shown that edible films produced by

http://dx.doi.org/10.1016/j.fbio.2017.07.002

Received 21 March 2017; Received in revised form 21 June 2017; Accepted 3 July 2017

⁎Corresponding author.

E-mail address:[email protected](N.M. Sarbon).

Available online 05 July 2017

MARK

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combining selected biopolymers have better properties thanfilms made of just one component. Carboxymethul cellulose (CMC) is an alternative polymer used for blending with gelatin due to its excellent viscosity, biocompatibility, and availability. Moreover, the addition of glycerol as plasticizer agents is necessary to improve the film flexibility. Pre- viously, extraction and characterization of chicken skin gelatin have been successfully conducted. However, still have less study on developing ediblefilm from chicken skin gelatin/CMC blends has been reported.

Characterization of chicken skin gelatin was successfully studied by Sarbon et al. (2013)with yield of extracted gelatin obtained was 16%

(based on dry weight basis). The gel strength of extracted chicken gelatin (6.67%, w/v) was significantly higher (355 ± 1.48 g) in terms of bloom value compared to bovine gelatin (229 ± 0.71 g), showing that chicken skin gelatin has better properties when compared to commercial bovine gelatin. Furthermore, amino acid composition, which con- tributes to the chicken gelatin properties such as proline, hyrdrox- yproline, and glycine were reported to be 13.42%, 12.13% and 33.7%, respectively. In addition, the imino acid (proline & hydroxyproline) value of chicken skin gelatin were reported higher than bovine gelatin (12.66% and 10.67%, respectively) (Sarbon et al., 2013). These properties show that chicken skin gelatin has potential on developing the good quality offilm. The study on single chicken skin gelatinfilm affected by concentration of glycerol have been conducted byNor et al.

(2016). However, there has not yet been a study on blendedﬁlm based on chicken skin gelatinﬁlm.

Therefore, the main purpose of this present work was to improve the characteristics of chicken skin gelatinﬁlms by adding polysaccharide of carboxymethyl cellulose. The mechanical, physical, and thermal properties of blended gelatinﬁlms were also investigated.

2. Material and methods

2.1. Materials

The chicken skin gelatin used in the present experiment was extracted from chicken skin obtained from the poultry processing industry at TD Poultry Sdn Bhd. Bovine gelatin powder, Glycerol (LR grade), carboxymethyl cellulose, sodium hydroxide, sulphuric acid and citric acid were purchased from Sigma-Aldrich Company Ltd., United Kingdom and were of analytical grade.

2.2. Methods

2.2.1. Sample preparation

The chicken skins were kept in ice during transport to the labora- tory. The visible fat on the skin was removed and rinsed in water in order to remove impurities. The skin then was dried and grinded before being defatted using the Soxhlet method (AOAC, 2006).

2.2.2. Gelatin extraction

Chicken skin gelatin was prepared following method by Sarbon et al. (2013) with acid–alkaline pretreatment. The defatted grinded chicken skin was soaked in sodium hydroxide (0.15%, w/v), sulphuric acid (0.15%, w/v) and citric acid (0.7%, w/v) solution serially. Each soaking treatment was repeated three times for a total time of 2 h for each treatment. The skins were then subjected to a ﬁnal wash with distilled water in order to remove any residual matter. The solution mixture was extracted in distilled water at controlled temperature (45 °C) for overnight. The clear extract was ﬁltered, concentrated by evaporation under low pressure, and freeze-dried. The dry matter obtained was referred to as‘gelatin powder’.

2.2.3. Preparation ofﬁlms

Gelatinﬁlm was prepared using the casting technique as described byJahit, Nazmi, Isa, and Sarbon (2016)with slight modiﬁcations. In

general, the filmogenic solution was prepared according to the opti- mized formulation generated by response surface methodology software. The design employed for optimization process was Central Composite Design (CCD) with the help of Design Expert Software Ver- sion 6 (Statease Inc). Forfilms preparation, 3 g gelatin was dispersed in 50 ml distilled water, while 3 g CMC was separately dispersed in 50 ml distilled water according formulation inTable 1. Both solutions were mixed together followed by the addition of glycerol as plasticizer (26%). The solutions were heated on heating mantle with continuous stirring at 45 ± 5 °C for 60 ± 5 min and kept at room conditions for 5 min to allow bubbling to dissipate prior to pouring. All of the solutions in the beakers were poured onto plastic containers with dimension of 24 cm × 7 cm. To controlfilm thickness, the quantity of eachfilm forming solutions poured onto these containers was always 50 g and dried at oven at 45 °C until completely dry. Driedfilms were then removed from the container in order to investigate their physical, mechanical and thermal properties. Before characterization of thefilm properties, allfilms were conditioned in desiccators containing silica gel for at least 24 h and stored in plastic container with lid at room temperature (25 °C).

2.2.4. Functional properties ofﬁlms

2.2.4.1. Microstructure Using Scanning Electron Microscopy (SEM). The morphology of theﬁlm was examined by scanning electron microscopy (Nova Nano SEM 230, FEI, USA). Film specimens (2 mm × 2 mm) were fractured by immersion in liquid nitrogen for 2 min and mounted on copper stubs perpendicularly to their surface. Samples were gold coated using an accelerating voltage of 30 kV and observed using magniﬁcation from 500 to 1500.

2.2.4.2. Fourier Transforms Infrared Spectroscopy (FTIR). Infrared spectra of theﬁlms were measured using FTIR spectrometer (Nicolet, Thermo Electron). The sample scanning frequencies were in range of 4000 to 650cm⁻¹with spectra resolution of 4 cm⁻¹. The interactions among gelatin, glycerol and CMC were determined through spectra obtained. Measurements were performed at room temperature and data were collected in triplicate. The peaks of amide A, amide I, amide II and amide III were identiﬁed by software and assigned according to the literature values.

2.2.4.3. X-Ray Diﬀraction (XRD). X ray pattern of chicken skin gelatin/

CMC blended film was analysed using Rigaku X-Ray Diffractometer following a method according toNur Hazirah et al. (2016)with some modifications. The sample was mounted on 2 × 2 in. glass slide and secured on the X-ray platform using tape. This analysis was run with Cu Ka radiation at current of 30 mA and voltage of 40 kV. The sample then was scanned between 2Ө= 3 to 80° with a scanning time 30 min per running. Allfilms were tested in triplicate.

2.2.4.4. Tensile Strength (TS) and elongation at break (EAB). Tensile strength (TS) and elongation at break (EAB) of the ﬁlm were determined using a texture analyzer (TA.TX Plus, STable Micro System, UK) following ASTM method D882-97 (ASTM, 1997). A 20 mm × 100 mmﬁlm strip was prepared by using a cutting blade Table 1

Film formulation for chicken skin gelatin/ CMC blendedfilm, bovine gelatin/CMC blendedfilm, and chicken skin gelatinfilm.

Film Gelatin (g) CMC (g) Glycerol (ml)

CSG 3 0 0.78

CCG/CMC 3 3 0.78

BV/CMC 3 3 0.78

Chicken skin gelatin (CSG), Chicken skin gelatin/CMC blendedﬁlm (CSG/CMC), bovine gelatin/CMC blendedﬁlm (BV/CMC).

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and was placed onto grip pairs of AT/G probe which was attached to the texture analyzer with 10 kg load cell. The initial gap between the up and down parts of the grip was set to 60 mm. The ﬁlm strip was stretched moving the headspace of 100 mm/min until broken. The measurement was done withﬁve replications. TS (MPa) was calculated using the following equation:

= Tensile strength(MPa) F (N)

A(m )

max

2 (1)

Where Fmaxis max load (N) needed to pull the sample apart, A is cross sectional area (mm²) ofﬁlm sample.

Meanwhile, the percentage of elongation at break (EAB) was calculated as:

=l EAB(%) l x

max 100

o (2)

Wherel_max is theﬁlm elongation (mm) at the moment of rupture andl₀ is the initial grip length (mm) of the sample.

2.2.4.5. Puncture strength. A puncture test was performed following method described by Nur Hazirah et al. (2016), to determine the strength and deformation of theﬁlms at the breaking point. Theﬁlms were placed in a cell 5.6 cm in diameter and perforated to the breaking point using an Instron model 4501 Universal Testing Machine (Instron Co., Canton, MA, USA) with a round-ended stainless-steel plunger 2 mm in diameter at a crosshead speed of 1 mm/s and a 50 N load cell.

Breaking strength was expressed in N and breaking deformation in percent as previously described (Nur Hazirah et al., 2016). All determinations were the means of at leastﬁve measurements.

2.2.4.6. Water vapour permeability (WVP). Water vapour permeability (WVP) was measured by using the modified ASTM E96 (ASTM, 1993) method as described byJahit et al. (2016). Thefilms were sealed onto a cup containing silica gel (0% RH) with silicone vacuum grease and a rubber band to hold thefilms in place. The cups withfilms were then weighted to record the initial weight. The cups then placed in desiccators containing distilled water at 30 °C. The cups were weighted at 1 h intervals over 7 h of period. Three films were used for WVP determination and the measurement was conducted in triplicate. WVP of thefilm was calculated as follows (McHugh et al., 1993):

= ⁻ t ΔPa⁻ −

WVP wxA 1¹ ¹ ¹ (3)

Where:

w is the weight gain of the cup (g), x is theﬁlm thickness (m), A is the exposed area ofﬁlm (m²), t is the time of gain (s),

ΔPa is the vapour pressure diﬀerence across theﬁlm (Pa)

2.2.4.7. Differential Scanning Calorimetry (DSC). The measurement of thermal stability offilm was conducted following the method described by Alipoormazandarani, Ghazihoseini, and Nafchi (2015)with some modification, using a DSC (DSC Q2000 Modulated, TA Instrument, USA) equipped with a cooling device (Intercooler II) and supported by Pyris Thermal Analysing System. Temperature calibration has performed using the Indium thermogram for about 1 h. About 5 mg of film were weighted using the Metler Toledo precision balance (AL 204, Mettler-Toledo Ltd., Beaumont Leys Leicester, UK) into aluminium pans, sealed and scanned at a heating rate of 10 °C/min with temperature range from 25 to 150 °C. The reference was an empty pan sealed with a lid to give a suitable heat capacity. Glass transition and melting point were measured. The temperature at which one-half of the gelatin film denatured was taken as the top of the peak. The endothermic peak was selected as the melting temperature for gelatin

ﬁlm and an average reading was taken from three replications.

2.2.4.8. Film light transmission. The ultraviolet (UV) and visible light barrier properties of the ﬁlms were measured according to the procedure reported by Ma et al. (2012). 1 × 2 cm ﬁlm size was prepared and placed directly into the test cell, with empty test cell was used as a reference. The absorbances (%) against UV and visible light at selected wavelength (200, 280, 350, 400, 600, 800 nm) were measured.

Absorbances were recorded using an UV-160A UV–vis spectrophotometer (Shimadzu, Japan). The transparency (T) of ﬁlms was calculated according to the following equation:

=

Opacity O, A₆₀₀/x(Maetal.,2012) (4)

where A600 is the absorbance at 600 nm and x is theﬁlm thickness (mm). According to this equation, a higher value ofOwould indicate a higher degree of opacity and lower degree of transparency. Allﬁlms were tested in triplicate.

2.2.5. Statistical analysis

For statistical analysis, one-way ANOVA variance analysis was performed by Minitab 14.0 software and comparisons of means utilized Tukey's test at a conﬁdence level of p < 0.05. The design of experiment was using completely randomized design. The mechanical analysis was calculated in ﬁve replication while others analysis was calculated in triplicate.

3. Results and discussion

3.1. Functional properties

3.1.1. Scanning electron microscopy (SEM) analysis

Table 2presents the surface and cross section of chicken skin gelatin film, chicken skin gelatin/CMC blendedfilm and bovine gelatin/CMC blendedfilm. It is clear from the images that distinctivefilm structures were formed and were dependent on the type and ratio of ingredients employed. For chicken skin gelatinfilm, the morphology offilm surface was relatively smooth and homogenous. However, the surface of the chicken skin gelatinfilm added with CMC showed rough and bumpier surface with a crater-like pitch. The greater formation of crater-like pits revealed a weak interaction between gelatin and CMC, at the surface of film (Cheng, Abd Karim, & Seow, 2008). In contrast with surface microstructure, the observation for cross section of controlfilm showed more long-lined structured crack as compared to chicken skin gelatin/

CMC blendedfilm and bovine gelatin/CMC blendedfilm which have short, scattered crack that indicated homogeneous structure. This may be because of hydrogen bonding and between gelatin and CMC as well as inter and intramolecular bonding betweenfilm components. This is clearly evident and supported by X-ray diffractometry, in which the X- ray diffraction pattern of the chicken skin gelatin–CMCfilm showed a much lower and broader peak as compared to the controlled one. This suggests that the matrix of blendedfilm is highly amorphous.

3.1.2. Fourier transform infrared spectroscopy (FTIR) analysis

Fourier transform infrared spectroscopy (FTIR) technique was used in order to identify the structure of thefilm produce as the effect of interactions of different molecules between chicken skin gelatin and CMC. Table 3 presents FTIR spectra of chicken skin gelatin/CMC blendedfilm, bovine gelatin/CMC blendedfilm and chicken skin gelatin film which Amide A, Amide I, Amide II and Amide III band were observed.

Amide A represent N–H stretching vibration (Wu et al., 2013;

Bitencourt et al., 2014). The FTIR spectra pattern for chicken skin gelatin film shows a broad peak located around 3296 cm⁻¹. This was assigned to O-H stretching which was affected by the inter-molecular or intra-molecular hydrogen bonds. With an addition of CMC into chicken skin gelatin basedfilm, the peak of O-H stretching shifted toward lower

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wavelength from 3295.71 to 3293.78 cm⁻¹. While for bovine gelatin/

CMC blendedfilm, the O-H band also significantly at lower wavelength as compared to chicken skin gelatin film. This shifted into a lower wavelength, indicating that the hydrogen bonds acting on the –OH groups for the blends were weaker compared to the pure gelatinfilms (Tong, Xiao, & Lim, 2008). This is due to the intermolecular interaction between hydroxyl group from gelatin and carboxyl group from CMC, thus reducing the amount of hydrogen bonds that can act on free hydroxyl group.

Amide I represents C=O stretching vibration coupled with CN stretch, CCN deformation and in plane NH bending modes. The amide-I band is the most sensitive spectral region to the protein secondary structural. Each peak was in the same wavelength position for both temperature but with difference in their intensity (Hanani, Roos, & Kerry, 2011). The peak increased for amide I in blendedfilm from 1633.71 to 1635.64 cm⁻¹ as shown inTable 3 shows that the addition of CMC proportion infilm caused conformational changes in gelatin polypeptide chains, resulting in a decrease in the presence of single-helices, random coils and disordered structures (Fakhreddin, Rezaei, Zandi, & Farahmand, 2013). This also provides evidence that the antisymmetric and symmetric vibrations of C=O and C–O bonds were enhanced, probably due to the disruption of intermolecular hydrogen bonds present originally between the carboxylic groups caused by added of CMC (Tong et al., 2008).

Amide II arises from bending vibration of N–H groups and stretching vibrations of C–N groups. From the result, the Amide II band in chicken skin gelatin/CMC blendedfilm (Table 3) was shifted from 1544.98 cm⁻¹ to 1550.77 cm⁻¹ as compared to single chicken skin gelatinfilm. The differences observed may be due to the alteration of the secondary structure of gelatin polypeptide chains caused by the addition of CMC.

Amide III represents in-plane vibrations of C—N and N—H groups of bound amide or vibrations of CH2groups of glycine (Benbettaïeb et al., 2014). From the result, Amide III band in chicken skin gelatin

film (Table 3) shifted to a higher wavelength, from 1238.30 cm⁻¹to 1242.16 cm⁻¹when CMC was added to the gelatin basedfilm. These results show that the–OH group in CMC and amino groups in gelatin were consumed during the blending process. Thisfinding was similar to that ofSu, Huang, Yuan, Wang, and Li (2010).

3.1.3. X-Ray Diﬀraction (XRD) analysis

X-ray diffraction (XRD) analysis was used in order to investigate the crystal structure and assess the compatibility of each material in blendedfilm production (Su et al., 2012).Fig. 1shows the diffractogram pattern of chicken skin gelatinfilm, chicken skin gelatin/CMC blendedfilm and bovine gelatin/CMC blendedfilm. The diffractogram pattern showed peaks at 2θ= 20–21° for allfilms. The diffractogram pattern of chicken skin gelatinfilm, chicken skin gelatin/CMC blended film and bovine skin /CMC blendedfilm have showed similar stronger reflections at 20°. Most of the gelatinfilm will show a stronger reflec- tion on at 2θ = 20–21° (Bergo & Sobral, 2007; Pereda, Ponce, Marcovich, Ruseckaite, & Martucci, 2011). The result shows that, there is no effect when added CMC on the crystallinity of thefilm. The addition of CMC doesn’t reduce the crystallinity of the chicken skin gelatin film.

3.1.4. Tensile strength (TS) and elongation at break (EAB)

The tensile strength (TS) and elongation at break (EAB) of chicken skin gelatinfilm, chicken skin gelatin/CMC blendedfilm, and bovine gelatin/CMC blendedfilm were shown inTable 4. Film prepared from bovine gelatin/CMC blended film (11.80 MPa) resulted the highest tensile strength compared to chicken skin gelatin/CMC blendedfilm (5.53 MPa) and single chicken skin gelatinfilm (0.98 MPa). The higher tensile strength of the bovine gelatin/CMC blendedfilm and chicken skin gelatin/CMC blended films may be attributed to the increased stiffness of thefilms by the addition of CMC. The enhanced mechanical properties of blendedfilms may be attributed to the long-chain CMC molecules, which contain many–OH groups that participate in strong Table 2

Scanning electron microscopy of chicken skin gelatin/CMC blendedfilm, bovine gelatin/CMC blendedfilm and chicken skin gelatinfilm.

Table 3

FTIR band of chicken skin gelatin/CMC blendedfilm, bovine gelatin/CMC blendedfilm and chicken skin gelatinfilm.

Film Formulations Amide A Amide I Amide II Amide III

(cm−¹) (cm−¹) (cm-¹) (cm-¹)

O–H stretching vibration C=O stretching Bending vibration N-H group, stretching vibration of C-N group.

Stretching vibration of C-N bands and N-H groups of bound amide, vibration of C-H groups of glycine

CSG 3295.71 ± 1.11^a 1633.71 ± 0.00^b 1545.62 ± 1.11^b 1238.30 ± 0.00^c

CSG/CMC 3293.78 ± 1.11^b 1635.64 ± 0.00^a 1552.70 ± 1.11^a 1242.16 ± 0.00^b

BV/CMC 3292.49 ± 0.00^b 1634.35 ± 1.11^b 1549.48 ± 1.11^ab 1244.09 ± 0.00^a

a–cmean within a column with different letters are significant difference (p< 0.05).

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intermolecular bonding and electrostatic interaction between chicken skin gelatin and CMC. These interactions may include hydrogen bonding, dipole–dipole, and charge eﬀect. Most of blended ﬁlms showed improvements in their tensile strength because of the same reason (Ghanbarzadeh, Almasi, & Entezami, 2011; Su et al., 2010;

Tongdeesoontorn, Mauer, Wongruong, Sriburi, & Rachtanapun, 2011).

The higher value of tensile strength of bovine/CMC blended than chicken skin gelatin/CMCfilm may be because of different sources of gelatin, which contained different percent on its amino acid. This may contribute to the crosslinking between gelatin and CMC, thus effecting the tensile strength offilm. Elongation at break of bovine gelatin/CMC blendedfilm (257%) is lower than chicken skin gelatin/CMC blended film (310%) and chicken skin gelatinfilm (561%). Generally, the increased TS precedes a decrease in EAB (Tong et al., 2008). An intermolecular interaction had formed between carboxyl group of CMC and hydroxyl group of gelatin with the addition of CMC gelatin basedfilm (Tongdeesoontorn et al., 2011). This strong interaction reduced the flexibility of chicken skin gelatin/CMC blendedfilm, thus reducing the elongation at break offilm.

3.1.5. Puncture force

The results of puncture force tests for the chicken skin gelatinfilm, chicken skin and bovine gelatinfilm blended with CMC are shown on Table 4. A puncture test is a measure of the resistance of thefilm to be perforated. The force at the breaking point of thefilm were determined in puncture test. Comparing the values of the puncture force of chicken skin gelatinfilm (0.1 N) with chicken skin gelatin/CMC blendedfilm (6.18 N) and bovine gelatin/CMC blendedfilm (6.31 N), blendedfilms show a significantly higher value than singlefilm (p < 0.05). The addition of CMC considerably higher the puncture force both gelatinfilms as well as tensile strength properties. CMC appears to have increased the reinforcement of thefilm's matrix via crosslinking reactions. Sup- porting thesefindings,Nur Hazirah et al. (2016)found that the addition of xanthan gum significantly increased the gelatin/CMC blendedfilm puncture crosslinking betweenfilms.

3.1.6. Water vapour permeability (WVP)

The water vapour permeability (WVP) values of thefilms are important measures for the applications of packaging materials. One of the main functions of food packaging is to prevent or minimize moisture transfer between food and the surrounding atmosphere. Low WVP broadens the application of the composite packagingfilm, especially in a highly humid environment (Qi et al., 2015). The data collected for Water Vapour Permeability (WVP) of chicken skin gelatinfilm, chicken skin gelatin/CMC blendedfilm and bovine gelatin/CMC blendedfilm was demonstrated inTable 4. Chicken skin gelatin/CMC blendedfilm were significantly higher WVP value (1.62 × 10⁻⁴g m⁻¹s⁻¹Pa⁻¹) as compared to chicken skin gelatinfilm (1.36 × 10⁻⁴g m⁻¹s⁻¹Pa⁻¹) but not significantly different as compared to bovine gelatin/CMC blendedfilm (1.59 × 10⁻⁴g m⁻¹s⁻¹Pa⁻¹). From the result obtained, WVP of single gelatinfilm was shown increased with the addition of CMC. Thisfinding was in contrast with other researches, which observed with the addition of cross linking agent such as chitosan (Fakhreddin et al., 2013), gellan (Pranoto, Min, & Jin, 2007) carrageenan (Pranoto et al., 2007) into gelatin based film. However, the effect of addition of crosslinking agent on water vapour barrier properties may be due to the chemical properties of material added. The addition of CMC into chicken skin gelatinfilm and bovine gelatin based film results in increasing of WVP value, perhaps due to the increased free-volume of the composite matrix caused by the bulkier anionic side groups of CMC thus lead to higher water absorption through thefilm.

Thisfinding is similar to a study byTong et al. (2008), which found that addition of CMC to pullulan resulted in an increased WVP for the resulting compositefilms. Other study byWeng and Zheng (2015)found that the addition of soy protein isolate (SPI) into gelatinfilms, results in slight increase (p < 0.05) of WVP. However, the WVP value of chicken skin gelatin/CMCfilm has no significant difference with WVP value of bovine gelatin/CMC blendedfilm because there is not much different in functional group of–OH for both gelatin as presented inTable 5.

3.1.7. Thermal properties of blended gelatinﬁlms

Glass transition (Tg) and melting temperature (Tm) values of chicken skin gelatinfilm, chicken skin gelatin/CMC blended film and bovine gelatin/CMC blendedfilm are presented inTable 4. The bovine gelatin/

CMC blendedfilm was significantly higher in Tgthan chicken skin gelatin/CMC blended film and chicken skin gelatin film (control film) (p < 0.05). Meanwhile, the Tgvalues of chicken skin gelatinfilm which incorporate with CMC was significantly higher Tgvalue compared to controlfilm (p < 0.05). For both blended gelatin/CMCfilm, the glass transition values obtained indicated that the crosslinking reaction contributed by addition of CMC have affected the thermal properties of thefilm. Crosslinking of the gelatin macromolecule and CMC increases the thermal stability of gelatinfilms, as shown by the shift of Tgto a higher value. Besides, the hydrogen bonding between–NH3group of gelatin and -COOH group of CMC in this blendedfilm lead to higher enthalpy needed to break the bond. Thisfinding is similar with a study bySu et al. (2010), observed soy protein isolate (SPI)/CMC blended film showed a higher value of glass transition than for SPI and CMC due to the presence of crosslinks in the blends.

Meanwhile, bovine gelatin /CMCfilm showed the highest Tmvalue, Fig. 1.X-Ray Diffractogram of chicken skin gelatin film, chicken skin gelatin/CMC

blendedﬁlm and bovine gelatin/CMC blendedﬁlm.

Table 4

Tensile strength, elongation at break, puncture test, water vapour permeability, melting point and glass transition of chicken skin gelatin/CMC blendedfilm, bovine gelatin/CMC blended film and chicken skin gelatinfilm.

Film formulation Tensile strength (MPa) Elongation at break (%) Puncture Test (g) WVP × 10⁻⁴ Melting temperature, Tm Glass transition, Tg

(g m⁻¹s⁻¹Pa⁻¹) (°C) (°C)

CSG 0.98 ± 0.14^c 561 ± 2.35^a 0.1 ± 0.00^c 1.36 ± 0.00^b 134.22 ± 3.60^b 47.94 ± 0.00^c

CSG/CMC 5.53 ± 1.40^b 310 ± 0.94^b 6.18 ± 0.00^b 1.62 ± 0.00^a 126.93 ± 3.32^c 66.85 ± 0.00^b

BV/CMC 11.80 ± 5.7â 257 ± 9.90^c 6.31 ± 0.07â 1.59 ± 0.18â 134.53 ± 0.02â 77.26 ± 0.25â

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following by controlfilm and chicken skin gelatin/CMCfilm. Similar as Tgvalue, bovinefilm showed the highest melting point value, as con- tribution of crosslinking reaction of CMC with gelatin macromolecule increased the thermal stability of gelatinfilm, thus affecting the thermal properties of thefilm. In contrast with glass transition value, Tmvalue of chicken skin gelatin showed significantly lowered compared to controlfilm. The addition of CMC to gelatin decreased Tmdue to the evolution of residual water. So, the interaction between two macro- molecules increases and CMC tends to plasticize the gelatin. Finally, crosslinkedfilm shows higher stability. Thisfinding was similar with a study byAsma, Meriem, Mahmoud, and Djaafer (2014).

3.1.8. Light transmission and opacity

Optical properties are essential to define the ability offilms and coatings to be applied over a food surface, since these affect the ap- pearance of the coated product, which is an important quality factor (Pereda, Dufresne, Aranguren, & Marcovich, 2014). Light transmission and opacity of allfilms at selected wavelengths are shown inTable 5. In the UV range (200–280 nm) chicken skin gelatinfilms blended with CMC and also bovine gelatin/CMC blendedfilm exhibited low UV light transmission compared to chicken skin gelatinfilm. The intermolecular bonding formed between gelatin and CMC help to prevent the UV light from penetrate through the film. Films with a lower UV light transmission value possess a good barrier of UV penetration through the film. Thisfinding was similar with study performed byFakhreddin et al.

(2013). Packagingfilm's function is to protect food from the effects of light, especially UV radiation, as it can cause oxidative deterioration of packaged foods, leading to nutrient losses, discoloration and off-flavors (Li, Miao, Wu, Chen, & Zhang, 2014; Martins, Cerqueira, & Vicente, 2012). The lower UV light penetration also may be due to the presence of aromatic amino acids (tyrosine, 1.22%; phenylalanine, 1.77%; and tryptophan, 0.04%) (Sarbon et al., 2013) contributed by the gelatin molecules, which are well known as sensitive chromophores that absorb light at wavelengths below 300 nm (Guerrero, Nur Hanani, Kerry, & De La Caba, 2011). Films containing high aromatic amino acid content play an important role in UV barrier properties.

Generally, opacity (O) offilm is an assistant criterion to judge the miscibility of blendedfilm (Qi et al., 2015). Light transmission offilms is most likely governed by the arrangement or alignment of polymer in film network. In transparent material, non-uniformities in the composition of the material could cause significant changes in optical properties (Ahmad, Benjakul, Prodpran, & Winarni, 2012).O values of all film formulation are presented inTable 5. The results show thatOvalue of both blendedfilm are significantly lower as compared with single chicken skin gelatinfilm (p < 0.05). The lower theOvalue, the lower the opacity offilm, which means blendedfilm (with transparency value of 2.92 ± 0.23 and 2.88 ± 0.00) is less opacity as compare to control film (with transparency value of 47.74 ± 0.61).

4. Conclusion

In conclusion, the addition of CMC into chicken skin gelatin based film greatly affected and the mechanical, physical and thermal properties of chicken skin gelatinfilm. The addition of CMC improved the

mechanical properties offilm as it has increased the tensile strength and puncture test offilm. Furthermore, the addition of CMC also reduced the extensibility, opacity and UV-light penetration of the blendedfilms.

Although the water vapour permeability of single chicken skin gelatin film is lower than blendedfilm, the presence of CMC had increase the thermal stability offilm. Strong interactions between functional groups of chicken skin gelatin and CMC have been verified by FTIR and XRD analysis. The crosslinking and intermolecular bonding formed within gelatin and CMC functional group matrix with addition of CMC into gelatin based film have improved some of mechanical and physical properties offilm.

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Table 5

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200 280 350 400 500 600 700 800

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