Development of biodegradable films based on seaweed polysaccharides and Gac pulp (Momordica cochinchinensis), the waste generated from Gac oil production

Food Hydrocolloids 99 (2020) 105322

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Development of biodegradable films based on seaweed polysaccharides and Gac pulp (Momordica cochinchinensis), the waste generated from Gac oil production

T

Thuy T.B. Trana,b,∗, Paul Roacha, Minh H. Nguyena,c, Penta Pristijonoa, Quan V. Vuonga,∗∗ a

School of Environmental and Life Sciences, The University of Newcastle, Ourimbah, NSW, 2258, Australia Faculty of Food Technology, Nha Trang University, Khanh Hoa, Viet Nam c School of Science and Health, Western Sydney University, Penrith, NSW, 2751, Australia b

A R T I C LE I N FO

A B S T R A C T

Keywords: Gac pulp Sodium alginate Carrageenan Glycerol Edible film Optimisation

Gac (Momordica cochinchinensis) is a tropical fruit. It belongs to the Cucurbitaceae family. Gac pulp (or mesocarp) that accounts for 40–50% of fruit weight is commonly discarded during the processing of Gac fruit. However, this by-product is a rich source of nutrients and bioactive compounds, which are potential to produce edible films. This study aimed to determine the effect of sodium alginate, kappa-carrageenan, Gac pulp and glycerol on film properties and optimise the formula of this composite film for further applications using a response surface methodology (RSM). The results showed that sodium alginate, kappa-carrageenan, Gac pulp, and glycerol affected physical and barrier properties, colour parameters, and mechanical properties of the films. The optimal formulation to generate a composite film from Gac pulp include sodium alginate 1.03%, kappa-carrageenan 0.65%, Gac pulp 0.4%, and glycerol 0.85% (w/v), where this film produces high mechanical properties, low water vapour permeability and acceptable physical properties. This optimised film formulation demonstrates a potential for food application.

1. Introduction Edible films are an innovative packaging solution in the food industry. They are commonly produced from major materials including polysaccharides, proteins and lipids or their composite. Polysaccharides that are obtained from animal, plant and algal sources can be used to prepare edible films and coatings (Han, 2014). Polysaccharide based films often have poor water vapour barrier properties, but they are efficient oxygen blockers due to their well-order hydrogen bonding (Bourtoom, 2008), and allow selective permeability for carbon dioxide and resist lipid migration (Hassan, Chatha, Hussain, Zia, & Akhtar, 2018). Protein based materials, such as corn zein, wheat gluten, soy protein or casein, collagen, gelatine and egg albumin have been applied to produce films, which have an excellent barrier for oxygen and carbon dioxide but poor for moisture barrier (Baldwin, 2007; Dursun & Erkan, 2014; Umaraw & Verma, 2017). Unlike polysaccharides and proteins, lipids are not biopolymers and have limited film-forming ability (Elsabee & Abdou, 2013). Lipid based films have excellent barriers

against moisture transmission (Embuscado & Huber, 2009). Recent studies have developed edible films based on composite materials to improve the film properties, while minimising the negative impact of individual materials (Cazón, Velazquez, Ramírez, & Vázquez, 2017). Gac (Momordica cochinchinensis), a tropical fruit, belongs to the Cucurbitaceae family which includes cucumbers, squash, luffa and bitter melon (Parks, Nguyen, Gale, & Murray, 2013). Peel, pulp (or mesocarp) and skin are discarded during Gac oil processing as well as current utilization of Gac fruit. Gac pulp accounts for 40–50% of fruit weight (Parks et al., 2013). This by-product is a rich source of pectin, essential oil, and carotenoids (Kubola & Siriamornpun, 2011), thus this material could be potential for development of edible films. However, none of previous studies have developed composite films from Gac pulp. Therefore, this study aimed to determine the effect of sodium alginate, kappa-carrageenan, Gac pulp and glycerol on film properties and then optimise the film formulation for further applications using a response surface methodology (RSM).

∗

Corresponding author. School of Environmental and Life Sciences, University of Newcastle, 10 Chittaway Road, Ourimbah, NSW, 2258, Australia. Corresponding author. E-mail addresses: [email protected] (T.T.B. Tran), [email protected] (P. Roach), [email protected] (M.H. Nguyen), [email protected] (P. Pristijono), [email protected] (Q.V. Vuong). ∗∗

https://doi.org/10.1016/j.foodhyd.2019.105322 Received 12 June 2019; Received in revised form 16 August 2019; Accepted 19 August 2019 Available online 22 August 2019 0268-005X/ © 2019 Elsevier Ltd. All rights reserved.

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2.3.1.2. Colour. Colour values of edible films were assessed using a colorimeter (Minolta, Model CR-300, Japan). A white colour plate was used as a background for measurement of edible films. The lightness (L), chromaticity parameters ‘a' (redness) and ‘b' (yellowness) were also recorded (Saberi et al., 2016a,b). Numerical value of ‘L', ‘a' and ‘b' parameters were employed to calculate the total colour difference (ΔE) (Eq. (1)), Chroma (Eq. (2)) and Hue angle (Eq. (3)) were calculated from value of ‘L', ‘a', and ‘b' and used to assess the colour changes due to different film formulations (Oliveira, Ramos, Brandão, & Silva, 2015)

2. Materials and methods 2.1. Materials Sodium alginate (E410, NaC6H7O6) and kappa-carrageenan (E407, extracted from Chondrus crispus) were purchased from the Melbourne Food Ingredient Depot, Brunswick East, Melbourne, Australia. Glycerol was purchased from Ajax Finechem Pty Ltd. Australia. Mature Gac fruit was purchased from local market in Nha Trang, Vietnam. The Gac pulp was then separated from the fruit, sliced and dried using a freeze-dryer (LyoBeta 35 Telstar Technologies, S.L, Spain) for 24 h. The freeze-dried Gac pulp was then ground and sieved to obtain particle size of 0.25–0.5 mm and well mixed into one uniform lot.

Δ E=

(L∗ − L)2 + (a∗ − a)2 + (b∗ − b)2 a2 + b2

Chroma =

(2)

Hue angle = Degrees (Atan (b/a))

2.2. Preparation of Gac pulp edible film

(1)

(3)

Where L∗, a∗, b∗ are the standard colour parameter values and L , a , b are the colour parameter values of the film samples (Saberi et al., 2016a,b). A white standard colour plate (L∗ = 94.08, a∗ = −0.4, b∗ = 9.83) for the instrument calibration was used as a control for colour measurement of the films.

The film-forming solution was prepared by a casting process. Suspension solutions were prepared by dissolving sodium alginate (0.5–1.5% w/v), kappa-carrageenan (0.5–1% w/v), Gac pulp (0.2–0.8 w/v) in 100 mL deionized water under control heating (65 °C) and continuous stirring. The range of film-forming materials was selected based on previous studies (Benavides, Villalobos-Carvajal, & Reyes, 2012; Heydari, Bavandi, & Javadian, 2015) and a series of trial experiments. The film forming solution was cooled to 50 °C and glycerol (0.5–1.5% w/v) was then added as plasticizers. The suspension solution was stirred for further 5 min to allow completion of mixing and removal of air bubbles. All films were prepared by casting 20 g of the suspension solution in a Petri dish (10 cm in diameter) and then dried in an oven at 30 °C for 24 h. Dried films were peeled off from the petri dishes and conditioned at 30 °C, relative humidity (RH) 75% for 72 h for further analysis (Thakur et al., 2017). The film was formed with seaweed hydrocolloids, including sodium alginate, kappa-carrageenan; Gac pulp and glycerol (Fig. 1). As can be visually seen, the films obtained were colourless, smoothly and flexible with glossy surfaces.

2.3.1.3. Opacity. Films opacity was examined according to Thakur et al. (2016), with minor modification. Rectangular film samples (10 × 50 mm) was placed individually in a quartz cuvette loaded to a Cary 50 Bio UV–vis Spectrophotometer (Varian Australia Pty. Ltd., Melbourne, VIC Australia). A blank cuvette was measured as a reference. Measurements were conducted by absorbance at 560 nm. The value of opacity was inversely proportional to level of transparency. Opacity if the film samples was calculated using Eq. (4).

O= Abs560 x

(4)

Where. O = Film opacity Abs560 = Absorbance of the film at 560 nm x = thickness of the film in mm

2.3. Characteristics of Gac pulp edible film

2.3.1.4. Moisture content. Moisture content was determined using a method mentioned in a previous report as described by Alves et al. (2018). Specifically, film samples were cut into 15 × 40 mm strips, and then dried at 105 °C for 24 h using a hot-air oven (Labec Laboratory Equipment, Marrickville, NSW, Australia). Moisture content (MC) was calculated using the following equation (Eq. (5)):

2.3.1. Physical properties 2.3.1.1. Thickness. The thickness of Gac pulp edible films was measured according to Thakur et al. (2017) using a digital micrometer (Mitutoyo, Co., Model ID-F125, Japan). Precision of the instrument was 0.001 mm. Film samples were measured individually and at least ten different measurements were randomly taken for each film, including a central point and nine around the perimeter. The film thickness was a mean value from ten measurements. The film thickness was also used for further calculation of water vapour permeability of the film samples.

Moisture content (%) =

Mi − Mf Mi

× 100

(5)

Where Mi and Mf were the masses of initial and final dried samples, respectively. Three replicates were conducted for each sample. 2.3.1.5. Solubility. Solubility of film was measured according to Farahnaky, Saberi, and Majzoobi (2013). Initial dry weight of the film specimen (15 × 40 mm) was separately recorded. Then each film was immersed in a beaker containing 50 mL of distilled water with a periodical mild agitation for 24 h. Undissolved parts were collected and dried at 110 °C for 24 h to obtain the final dry weight of the film. The percentage of the total soluble matter (FS) was determined using the following equation (Eq. (6)):

FS (%) =

(initial dry wt − final dry wt ) × 100 initial dry wt

(6)

2.3.2. Barrier properties 2.3.2.1. Water vapour permeability (WVP). Water vapour permeability was determined using ASTM procedure (ASTM, 2013) according to

Fig. 1. Actual image of the Gac edible film. 2

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the second-order polynomial model was assessed by the lack of fit and the coefficient of determination (R square). The Student's T-test using SPSS software (version 20, IBM, Armonk, NY, USA) was applied to compare the sample means. The differences between the sample means were chosen at the significance level at p < 0.05.

Thakur et al. (2016), with slight modifications. Permeation cells (cup containing anhydrous CaCl2 granules with 0% RH) were sealed tightly by the sample film and placed under controlled RH conditions (NaCl saturated solution; 75% RH) at 25 °C. Water vapour transport was determined using the weight gain of the cell at a steady state of transfer. Changes in weight of individual permeation cells were reported every 2 h. Measurements were made for 24 h and plotted as a function of time. The slope of individual line was estimated by linear regression (r2 > 0.99). The water vapour transmission rate was calculated through the slope of each straight line (g/s) divided by area of the tested film surface (m2). The WVP was calculated as following equation (Eq. (7)):

WVP (gPa −1s−1m−1) =

Δm T A Δt ΔP

3. Results and discussion 3.1. Fitting of the models Based on the Box-Behnken experimental design, experiments were conducted to produce the films. After analysis of the film properties, the data were placed in the table accordingly (Table 1). It is important to check reliability of the models for analysing the interactive effects of the variables on the responses, and for prediction of the optimal film formulation. ANOVA analysis was applied to check the adequacy of the quadratic models and the results are shown in Fig. 2 and Table 2. The results showed that the values of the coefficient of determination (R square) were in range of 0.71–0.96, signifying that all the experimental data can be predictably matched with the actual values (Fig. 2 and Table 2). Especially, the R square for mechanical properties (Elastic modulus (EM), Elongation at break (EAB) and Tensile strength (TS)) closed to 1.0, indicating that the high proportion of fitting between the predicted values and the actual values. Furthermore, the predicted residual sum of square (PRESS) for the models showed the predicted models matched well in the design for all the mechanical properties, thickness, and solubility and certain colour parameters. In terms of lack of fit test, the results also demonstrated that the models fit for all the physical (thickness, moisture content, opacity, solubility and colour parameters) and mechanical (EM, EAB, and TS) properties because p-values of lack of fit were non-significant (p > 0.05) for all tested physical and mechanical properties, confirming that predicted models were reliable. In addition, the values of F for all mechanical properties including EM, EAB, and TS were significantly different, further confirming reliability of the models for prediction and optimisation.

(7)

Where; Δm/Δt = weight of moisture gain per time unit (gs−1) and can be determined by the slope of the straight line A = area of tested film surface (m2) T = thickness of the tested film (mm) ΔP = represents the water vapour pressure difference between inside and outside of the film (Pa) (Thakur et al., 2016). 2.3.3. Mechanical properties Tensile strength (TS), elongation at break (EAB) and elastic modulus (EM) of the films were determined using a Texture Analyser (LLOYD Instrument LTD, Fareham, UK) according to Saberi et al. (2016a,b), with some modifications. Preconditioned film specimens (15 × 40 mm) were griped between two jaws to measure the maximum load (N) and extension (mm) curves at break point of the test samples. The measurement was conducted at crosshead speed of 1 mm/s and initial grip distance 40 mm. For each sample, seven replicates were performed. 2.4. Experimental design and statistical analysis 2.4.1. Response surface methodology (RSM) Response Surface Methodology (RSM) was used to determine the optimum formulation of Gac pulp edible film. A Box-Behnken design with three central points replicates was employed. Twenty-seven edible film formulations consisting of sodium alginate (X1: 0.5%–1.5%), kappa-carrageenan (X2: 0.5%–1.0%), Gac pulp (X3: 0.2%–0.8%) and glycerol (X4: 0.5%–1.5%) were chosen as independent variables. The optimum levels were selected from preliminary single factor tests. The design is shown in Table 1. Effect of Gac pulp and seaweed polysaccharides with plasticizer (independent variables) on properties of the film (responses) was employed through the model equations, to graph 2D contour plots of the responses. The optimum conditions of the independent variables were estimated using the JMP software. The experimental data for relation between responses and independent variables was fitted to the following second order polynomial equation (Eq. (8)) (Saberi et al., 2016a): k

Y = β0 +

k−1

k

i=1 j=2

A second order polynomial mathematical equation (Eq. (8)) was used to express the experimental data obtained from Box-Behnken design through applying multiple regression analysis. The relationship between variables and the responses on the physical and mechanical properties of edible films with Gac pulp was demonstrated in twelve following empirical models with coded factors.

Ythickness = 16.84 + 33.53X1 − 36.97X2 + 71.04X3 + 28.44X2 − 1.4X1 X2 − 0.2X1 X3 − 16X1 X 4 + 28X2 X3 + 40.6X2 X 4 − 47X3 X 4 − 0.24X12 − 0.02X22 − 0.21X32 + 0.64X42

i=1

(9)

YMC = 0.057 − 0.116X1 − 0.075X2 − 0.007X3 + 0.671X 4 + 0.174X1 X2 − 0.025X1 X3 + 0.323X2 X3 − 0.006X1 X 4 + 0.02X2 X 4 − 0.283X3 X 4

k

∑ βi Xi + ∑ ∑ βij Xi Xj + ∑ βii Xi2 i=1

3.2. Development of second order polynomial mathematical models

− 0.015X12 − 0.269X22 + 0.019X32 − 0.142X42

(8)

(10)

Where, Xi are independent variables affecting the responses Y ; and β0 , βi , βii , βij are the regression coefficients for intercept, linear, quadratic and interaction terms, respectively. k represents the number of variables.

Yopacity = 4.628 − 4.351X1 − 0.647X2 + 2.876X3 + 0.073X 4 + 1.964X1 X2

2.4.2. Statistical analysis Experimental design was performed using JMP software (Version 11, SAS, Cary, NC, USA). The program was used to establish the model equations, to graph the 2D contour plots of the responses and to predict the optimum values for the four independent variables. The validity of

Ysolubility = 109.049 − 55.428X1 − 159.129X2 − 35.269X3 + 25.929X 4

− 0.442X1 X3 − 1.258X2 X3 + 0.076X1 X 4 − 0.88X2 X 4 + 1.733X3 X 4 + 1.099X12 − 0.481X22 − 1.465X32 − 0.41X42

(11)

+ 35.147X1 X2 + 3.519X1 X3 + 24.235X2 X3 − 6.69X1 X 4 + 10.746X2 X 4 + 11.241X3 X 4 + 11.743X12 + 55.254X22 + 0.726X32 − 5.634X42 3

(12)

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Table 1 Box-Behnken experimental design for formulation of Gac pulp edible film. Run

Independent variables

Dependent variables Responses

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

X1 (%)

X2 (%)

X3 (%)

X4 (%)

T

MC

O

S

WVP x 10−10

L

E

C

Hue angle

EM

EAB

TS

1.5 1.5 1.5 1.5 1.5 1.5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0.5 0.5 0.5 0.5 0.5 0.5

0.75 0.75 0.5 0.75 1 0.75 0.75 1 0.5 0.75 0.75 0.75 1 1 0.75 0.5 0.5 0.5 0.75 0.75 1 0.75 1 0.75 0.5 0.75 0.75

0.8 0.5 0.5 0.5 0.5 0.2 0.8 0.8 0.8 0.8 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.2 0.2 0.2 0.2 0.8 0.5 0.5 0.5 0.5 0.2

1 1.5 1 0.5 1 1 0.5 1 1 1.5 1 1 0.5 1.5 1 1.5 0.5 1 1.5 0.5 1 1 1 0.5 1 1.5 1

100.9 103.3 91.8 85 106.1 76.9 104 101.3 91.4 103.3 88.5 87 73.5 105.9 85.6 91.9 79.8 67.6 91.7 64.2 69.1 90.3 87.2 61.8 72.2 96.1 61

32.42 40.81 34.38 19.75 28.1 34.87 21.85 29.81 33.3 38.59 35.67 36.1 17.11 44.46 34.62 43.51 17.14 43.39 49.79 16.04 30.24 37.01 27.01 19.83 41.98 46.79 37.98

2.91 2.05 2.33 2.65 1.75 1.47 2.41 2.48 3.09 2.32 2.43 2.58 2.61 2.25 2.25 2.35 2.27 1.81 1.29 2.43 1.58 3.95 2.36 3.14 3.93 2.47 2.25

22.19 30.35 25.08 12.02 26.94 25.3 13.72 24.43 29.45 36.17 25.22 22.98 11.83 38.68 27.46 43.26 21.78 37.03 27.59 11.88 24.74 33.07 26.53 19.9 42.24 44.92 38.29

1.82 1.92 2.79 2.67 3.39 1.41 1.23 2.02 1.99 1.99 1.32 1.44 0.93 2.14 1.31 1.96 0.83 1.28 1.77 1.1 1.2 1.98 1.72 0.99 1.46 2.33 1.28

95.43 96.57 96 95.52 95.38 96.46 94.34 94.44 95.54 95.2 96.22 95.91 95.86 95.97 96.11 95.8 96.03 96.12 96.67 96.55 96.54 96.01 95.73 96.01 96.12 96.27 96.65

8.06 3.24 5.37 9.94 10.45 1.32 14.25 15.19 8.92 7.86 4.94 5.75 6.79 4.71 5.44 7.1 7.14 5.16 1.81 2.47 2.07 8.75 7.5 7.4 7.72 4.53 2.02

11.14 6.47 8.52 13.07 13.09 4.38 17.24 18.22 12.05 12.74 8.12 9.42 9.93 7.84 8.61 10.25 10.01 8.33 5 5.66 5.25 10.49 10.64 10.58 10.9 7.73 5.23

94.26 94.01 95.14 95.75 94.96 92.92 91.75 93.58 94.13 94.66 95.07 94.85 94.31 93.52 94.62 94.98 95.31 92.75 93.07 94.9 94.44 94.04 95.17 95.81 94.28 93.69 93.34

17947.8 7893.46 8366.96 23168.56 14745.25 9097.49 26520.29 23890.12 11247.45 18105.59 15100.36 16525.79 33736.69 12614.54 13674.92 6375.555 18638.49 3938.49 8046.54 25067.35 18922.58 19771.09 56612.51 33254.17 10813.18 11633.2 27761.29

21.14 25.37 21.08 17.34 19.33 20.6 15.78 18.58 16.4 14.88 17.13 18.69 13.46 19.35 15.57 18.53 14.46 19.61 20.82 12.58 18.77 11.94 11.35 10.27 15.17 12.42 8.72

1599.92 1346.16 1245.14 2503.86 1590.03 1233.13 1625.06 1688.35 943.55 836.03 1225.84 1379.86 1667.49 1164.66 1071.81 664.16 1176.59 530.08 860.07 1169.66 1521.09 819.38 1259.45 997.49 603.72 628.51 555.07

Independent variables: X1, Sodium alginate (0.5–1.5%); X2, Kappa-carrageenan (0.5–1.0%); X3, Gac pulp powder (0.2–0.8%); X4, glycerol (0.5–1.5%) Responses (Y): T, thickness (μm); MC, moisture content (%); S, solubility (%); O, Opacity (%); WVP, water vapour permeability (gs−1 m−1 pa−1); L, brightness; ΔE, total colour difference; C, Chroma; Hue angle; EM, Elastic modulus (N/m); EAB, Elongation at break (mm); TS, tensile strength (N/m).

YWVP = 2.974 − 1.991X1 − 8.071X2 + 1.125X3 + 2.002X 4 + 0.68X1 X2

YE = 26.535 − 5.589X1 − 112.56X2 − 4.814X3 + 6.061X 4 + 10.6X1 X2

− 0.483X1 X3 + 0.367X2 X3 − 2.09X1 X 4 + 0.16X2 X 4 + 0.15X3 X 4 + 2.26X12 + 4.94X22 − 0.236X32 + 0.31X42

+ 0.017X1 X3 + 31.2X2 X3 − 3.83X1 X 4 − 4.08X2 X 4 − 9.55X3 X 4 + 0.768X12 + 26.72X22 + 4.33X22 + 1.24X42

(13)

YL = 94.327 − 1.118X1 + 7.33X2 + 2.987X3 − 0.955X 4 − 0.46X1 X2

YEM = 2314.398 − 5634.371X1 + 103844.218X2 − 30439.995X3

− 0.65X1 X3 − 5.067X2 X3 + 0.79X1 X 4 + 0.68X2 X 4 + 1.233X3 X 4

− 31445.049X 4 − 78842.093X1 X2 + 28067.527X1 X3 − 7804.741X2 X3 + 6345.866X1 X 4 − 17718.42X2 X 4 + 14343.506X3 X 4 + +

20221.682X22

+

729.31X32

+

+ 0.38X12 − 3.72X22 − 2X32 − 0.3X42

15636.997X12

7631.734X42

3.3. Effects of independent variables on film properties

− 4.457X1 X3 + 10.071X2 X3 + 5.882X1 X 4 + 3.634X2 X 4

3.3.1. Effect of independent variables on thickness The results showed that all the four film-forming materials, including sodium alginate, kappa-carrageenan, Gac pulp and glycerol had significant effects on the thickness of the edible film (p < 0.05) (Table 3). The effects of materials were in the decreasing order glycerol > Gac pulp > sodium alginate > kappa-carrageenan. The results revealed that thickness of the films increased when increasing concentration of sodium alginate, kappa-carrageenan, Gac pulp and glycerol (Fig. 3). These can be explained by the films, which were casted with the same volume of film-forming solution with various dry matters, with their thickness depending on quantity of the adding materials. The results also showed that only interaction between Gac pulp and glycerol had a negative and significant effect on film thickness (p < 0.05) (Table 3). Therefore, it can be concluded that all four filmforming materials directly affected film thickness, and Gac pulp and glycerol had major influence on the film thickness. The thickness results were reported to affect the structural properties, including water vapour permeability and film opacity (Maran, Sivakumar, Sridhar, and Thirugnanasambandham (2013).

(15)

YTS = −2362.525 + 1856.382X1 + 3031.179X2 + 2994.011X3 + 240.24X 4 − 621.687X1 X2 + 170.792X1 X3 − 820.713X2 X3 − 788.725X1 X 4 + 19.22X2 X 4 − 799.07X3 X 4 + 34.491X12 − 517.16X22 − 1293.758X32 + 163.423X42

(16)

Ychroma = 28.58 − 3.684X1 − 54.58X2 − 9.525X3 + 4.271X 4 + 9.664X1 X2 + 2.5X1 X3 + 30.84X2 X3 − 3.75X1 X 4 − 4.66X2 X 4 − 6.4X3 X 4 − 0.44X12 + 23.82X22 + 3.625X32 + 1.7X42

(17)

YHue angle = 91.121 + 0.417X1 + 7.814X2 + 9.599X3 − 3.074X 4 − 2.14X1 X2 + 1.067X1 X3 − 7.467X2 X3 + 0.38X1 X 4 − 0.92X2 X 4 + 7.9X3 X 4 + 0.196X12 − 0.816X22 − 12.689X32 − 0.608X42

(20)

(14)

YEAB = 9.37 + 8.848X1 − 29.899X2 + 13.344X3 + 9.488X 4 + 4.142X1 X2 − 15.236X3 X 4 − 3.222X12 + 9.849X22 − 1.868X32 − 2.95X42

(19)

(18) 4

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Fig. 2. Correlation between predicted and experimental values for thickness (a), moisture content (b), opacity (c), solubility (d), water vapour permeability (e), L (f), E (g), chroma (h), Hue angle (i), elastic modulus (k), elongation at break (l), and tensile strength (m).

5

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Table 2 Analysis of variance for determination of model fitting. Parameters 2

R PRESS Lack of fit F ratio of model p of model F

T

MC

O

S

WVP

L

ΔE

Chroma

Hue angle

EM

EAB

TS

0.936 1897.166 0.062 12.592 < 0.001

0.965 489.249 0.067 23.592 < 0.001

0.817 10.279 0.143 3.822 0.013

0.946 689.255 0.34 14.886 < 0.001

0.745 14.031 0.021 2.505 0.06

0.854 7.419 0.174 5.026 0.004

0.906 167.553 0.056 8.273 < 0.001

0.878 211.371 0.111 6.157 0.002

0.711 39.843 0.071 2.111 0.101

0.88 > 210 × 106 0.053 6.306 0.001

0.911 187.708 0.52 8.767 < 0.001

0.905 26 × 106 0.398 8.125 < 0.001

moisture content of the films, whereas, increasing glycerol concentration resulted in lower moisture content of the films. Positive effect of glycerol on film moisture content was in agreement with findings reported by Fundo, Quintas, and Silva (2011). This could be explained based on the hydrophilic nature of glycerol, which assisted in the formation of hydrogen bonding with free OH groups (Cerqueira, Souza, Teixeira, & Vicente, 2012). The results also showed that Gac pulp and glycerol had a negative and interactive influence on the film moisture content (Table 3). This means that moisture content of the films remarkably increased with higher concentration of glycerol together with lower amount of Gac pulp.

Table 3 Analysis of variance for effects of different factors on the responses. P

Thickness

Moisture content

Opacity

Solubility

WVP

L

Prob > |t|

Prob > |t|

Prob > |t|

Prob > |t|

Prob > |t|

Prob > |t|

βo

< .0001

< .0001

< .0001

< .0001

0.0002

< .0001

β1

0.0002

0.048

0.0032

0.0001

0.0191

0.2367

β2

0.0209

0.0017

0.0647

0.0015

0.4946

0.1668

β3

< .0001

0.0571

0.0005

0.6155

0.0814

< .0001

β4

< .0001

< .0001

0.0611

< .0001

0.0164

0.0831

β12

0.9480

0.1281

0.2309

0.0189

0.7118

0.7346

β13

0.6235

0.7829

0.739

0.7501

0.7524

0.5672

β23

0.4401

0.0934

0.6364

0.2837

0.9024

0.0407

β14

0.1541

0.2894

0.9234

0.3221

0.0387

0.2564

β24

0.0776

0.8541

0.5821

0.4232

0.9245

0.6173

β34

0.0200

0.0077

0.2063

0.3183

0.9245

0.2861

β11

0.6826

0.7531

0.1287

0.0582

0.018

0.5205

β22

0.8960

0.1698

0.8613

0.0254

0.1801

0.1312

β33

0.3291

0.8874

0.449

0.9636

0.7991

0.2336

β44

0.2878

0.0096

0.55

0.3351

0.8138

0.6108

P

ΔE Prob > |t|

Chrome Prob > |t|

Hue angle Prob > |t|

EM Prob > |t|

EAB Prob > |t|

TS Prob > |t|

βo

< .0001

< .0001

< .0001

0.0006

< .0001

< .0001

β1

0.9337

0.8599

0.7927

0.0016

< .0001

< .0001

β2

0.3468

0.4366

0.8213

0.0002

0.4747

0.0002

β3

< .0001

< .0001

0.7116

0.2294

0.6957

0.0372

β4

0.0047

0.0194

0.1656

0.0004

0.0006

0.0002

β12

0.1156

0.1954

0.4963

0.0043

0.5586

0.4577

β13

0.9975

0.6778

0.6822

0.1598

0.4522

0.8046

β23

0.0112

0.0221

0.1676

0.8384

0.3973

0.5546

β14

0.2438

0.308

0.8075

0.5827

0.1132

0.0753

β24

0.5262

0.5208

0.7681

0.4458

0.6072

0.9815

β34

0.0916

0.297

0.0091

0.4586

0.021

0.2595

β11

0.7813

0.8877

0.8841

0.1341

0.301

0.9233

β22

0.0296

0.0746

0.8802

0.6129

0.425

0.7189

β33

0.5754

0.6764

0.0047

0.9789

0.8253

0.209

β44

0.6554

0.5876

0.6534

0.4481

0.3419

0.6496

3.3.3. Effect of independent variables on opacity Transparency of the edible films in this study was determined by opacity value. Lowest opacity value corresponds to high transparency. Opacity was relatively crucial property for application of film to coat food as it affects consumer acceptability (Maran et al., 2013). As can be seen from Table 3, while carrageenan and glycerol did not show any significant impact on opacity of the films, sodium alginate and Gac pulp showed significant effects on film opacity (p < 0.05). Gac pulp had the greatest impact, followed by sodium alginate and glycerol, and carrageenan had the least impact on film opacity. This can be explained by existence of the oil in Gac pulp that caused a film transparency reduction. Atarés and Chiralt (2016) reported that existence of the oil caused a decrease of light transmission. This was possibly due to the light scattering caused by the film matrix imbedded with oil. As a result, an increase in opacity of films was obtained together with higher amount of Gac pulp. The results from Fig. 3 indicated that Gac pulp had positive impact on film opacity. There was no significant impact between interaction of the tested variables (p > 0.05). 3.3.4. Effect of independent variables on solubility Water solubility plays an important role in film properties because it reveals the film's water affinity, especially films intend to come in contact with high moisture food products (Bourbon et al., 2011). As can be seen from Table 3 and Fig. 3, sodium alginate, kappa-carrageenan, and glycerol significantly affected film solubility (p < 0.05), whereas Gac pulp did not significantly affect solubility. Sodium alginate, carrageenan and Gac pulp had negative effects, while glycerol had positive effects. The Gac pulp was reported to contain oil (Kubola and Sirimornpun, 2011) that significantly affects the solubility of edible films. These results were in agreement with the studies conducted by Nur Fatin and Nur Hanani (2017) and Cerqueira et al. (2012) related to the concentration of plant oil. The increase of oil concentration or Gac pulp amount leads to a significant decrease in water solubility. This was due to the presence of aliphatic groups in the film when Gac pup containing oil was added. As a result, the hydrophobic property of Gac oil changed the film structure that became less soluble (Nur Fatin and Nur Hanani 2017). Besides, the combination of Gac oil and the seaweed hydrocoloids (sodium alginate and carrageenan) can be seen as an interaction between the hydroxyl groups of polysaccharide chains and the plant oil components. This interaction declined the availability of the polysaccharide-water interactions and caused a decrease in film solubility (Shojaee-Aliabadi et al., 2014). There was also an interactive effect observed between sodium alginate and carrageenan on film solubility (p < 0.05). Solubility of the edible films increased with higher

Significantly different at p < 0.05; P: parameter; βo : intercept; β1, β2 , β3 , and β4 : linear regression coefficients for sodium alginate, carrageenan, Gac pulp and glycerol; β12 , β13 , β23 , β14 , β24 , and β34 : regression coefficients for interaction between sodium alginate × carrageenan, sodium alginate × Gac pulp, carrageenan × Gac pulp, sodium alginate × glycerol, carrageenan × glycerol, and Gac pulp × glycerol; β11, β22 , β33 and β44 : quadratic regression coefficients for sodium alginate × sodium alginate, carrageenan × carrageenan, Gac pulp × Gac pulp, glycerol × glycerol.

3.3.2. Effect of independent variables on moisture content Results for the independent variables on moisture content are presented in Table 3 and show that sodium alginate, Gac pulp and glycerol had significant effects on the moisture content of the edible film (p < 0.05). Gac pulp did not significantly affect moisture content of the film. Effects of independent variables are in decreasing order as follows: glycerol > kappa-carrageenan > sodium alginate > Gac pulp. It can be observed from Fig. 3 that increasing concentration of kappa-carrageenan, sodium alginate and Gac pulp resulted in higher 6

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Fig. 3. Interactive effects of factors on film properties.

7

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findings were in agreement with previous studies, which also found that addition of glycerol reduced the Chroma values of the edible films (Cardoso et al., 2016; Saberi et al., 2016a,b; Veiga-Santos, Suzuki, Cereda, & Scamparini, 2005).

glycerol level applied. Particularly, the solubility increased from 20% to around 40% together with 0.6% and 1.4% respectively in the proportion of glycerol. It was explained by Singh, Chatli, and Sahoo (2015) that three hydrophilic hydroxyl groups that present in glycerol may enhance film solubility in water.

3.3.7. Effect of independent variables on mechanical properties: elastic modulus, elongation at break, and tensile strength Mechanical properties of edible coatings play important roles in packaging that protects food from external stress and maintains its integrity during transportation and display (Rao, Kanatt, Chawla, & Sharma, 2010). Mechanical properties are measured on the basic of tensile strength (TS), elongation at break (EAB), and elastic modulus (EM). As can be seen from Table 3, sodium alginate, carrageenan, Gac pulp and glycerol had a significant influence on TS (p < 0.05), of which, sodium alginate, Gac pulp and carrageenan had positive effect, while glycerol had a negative impact on TS of the films. Only interaction between sodium alginate and Gac pulp had a significant impact on TS of the films. The results indicated that sodium alginate, carrageenan and glycerol had a significant influence on EM (p < 0.05), whereas Gac pulp did not show a significant impact on EM of the films (Table 3). Carrageenan had positive impact while sodium alginate and glycerol had negative impact on EM of the films. Only sodium alginate and carrageenan showed a significant interactive impact on EM of the films. The results also revealed that only sodium alginate and glycerol had significant positive influence on EAB of the films. This study observed that sodium alginate had a significant influence on mechanical properties including TS, EM and EAB. These findings are in agreement with previous study and can be explained due to formation of existing inter-molecular hydrogen bonds that contain NH2 and OH groups in structure of polymer film-forming materials. This would improve stability and integrity of the edible films, leads to increases in TS, EM and EAB (Thakur et al., 2017). This study found that carrageenan majorly contributed to improve TS and EM, but not EAB and these findings are in agreement with data in a previous study (Paula et al., 2015). This study also revealed that glycerol improved TS and EM while decreased EAB of the films and the similar findings also supported by the results reported by Paula et al. (2015).

3.3.5. Effect of independent variables on water vapour permeability Water vapour permeability (WVP) is important to understand the mechanisms of the possible mass transfer through the film surface. According to Ma, Chang, and Yu (2008), this parameter should be low to prevent moisture loss during preservation of fresh food products. The results showed that sodium alginate, glycerol and interaction of sodium alginate × glycerol had significant effects on the water vapour permeability of the edible films (p < 0.05) (Table 3). Observation showed that increasing glycerol concentration resulted in increasing WVP values. According to Maran et al. (2013), addition of glycerol increased the free volume and chain movements as well as the molecular mobility of the films, which contributed to the diffusion of water vapour into films. However, WVP initially reduced with higher sodium alginate level but later on increased after reaching to a certain minimum at 1.62 (gs−1m−1pa−1) (Fig. 3). Interaction between sodium alginate and glycerol was significant due to changes in concentration of these ingredients that caused fluctuations in film density, which resulted in films with pores and cracks in their structure, and this facilitated the water vapour permeability of the films (Wu, Geng, Chang, Yu, & Ma, 2009). 3.3.6. Effect of independent variables on colour Colour of edible films or coatings play a crucial role in film application as it influences food products' appearance and consumer acceptability. Film colour attributes can be determined by instrumental colour parameters, including Lightness (L), total colour difference (ΔE), Chroma, and Hue angle (Ramos et al., 2013). The colour brightness coordinate ‘L' indicated the whiteness value (Oliveira et al., 2015). This value ranges from black at 0 to white at 100. The results in Table 3 indicated that only the Gac pulp had significant impact on L value of the films (< 0.05). In addition, interaction of carrageenan and Gac pulp also had a significant effect on L value, while sodium alginate, carrageenan, and glycerol and their interaction did not show a significant influence. The results from Fig. 3 showed that increasing concentration of Gac pulp powder resulted in lower L value. This can be explained by the yellow in colour of Gac pulp, which was contributed by carotenoids in the pulp (Chuyen, Nguyen, Roach, Golding, & Parks, 2015). Therefore, transparency of edible films can be affected by level of Gac pulp powder. Total colour difference (ΔE) was established based on colour difference between the control and the experimental samples. The results showed that Gac pulp and glycerol significantly affected ΔE of the films (Table 3), where increasing Gac pulp concentration increased ΔE, whereas increasing glycerol concentration decreased ΔE of the films (Fig. 3). In addition, interaction between carrageenan × Gac pulp showed positive significant effect on ΔE. Hue angle is the colour description in language (red, yellow, green, etc.) and Chroma performs the colour intensity (Cardoso et al., 2016). Both parameters provide details spatial distribution of colour than direct value of chromaticity measurements (Oliveira et al., 2015). The results showed that all four independent variables, including sodium alginate, carrageenan, Gac pulp and glycerol had no significant effects on Hue angle. However, interaction between Gac pulp and glycerol had a positively significant effect on Hue angle of the films (p < 0.05) (Table 3). This result could be due to changes in reflection of the light at the film surface in higher solid concentration, leading to film samples with high hue angle value (Martins et al., 2012). For Chroma, Gac pulp and glycerol significantly affected Chroma of the films (p < 0.05) (Table 3). Gac pulp had significant positive effect, whereas glycerol had a negative significant impact on Chroma of the films (Fig. 3). These

3.4. Optimisation and validation of the models Good edible films should have high mechanical properties, low water vapour permeability and acceptable physical properties as these enable them to be suitable for coating or using as food packaging materials. Therefore, this study optimised the film formula from sodium alginate, carrageenan, Gac pulp and glycerol in order to obtain film with low water vapour permeability and acceptable physical properties as well as strong mechanical properties. Based on the prediction profilers of the JMP software, the optimal film formula included sodium alginate 1.03%, kappa-carrageenan 0.65%, Gac pulp 0.4%, and glycerol 0.85%. Under these conditions, a film with low thickness, low water vapour permeability, acceptable colour and transparency and good EM, EAB and TS can be prepared for further applications. In comparison with previous studies, thickness of the Gac pulp contained edible films is similar to results reported by Thakur et al. (2017) using pea starch and chitosan, however produced thinner the films than that was made of sodium alginate (Norajit, Kim, & Ryu, 2010). This study observed that the films had lower solubility and permeability values than polysaccharide-based edible coating reported by Norajit et al. (2010) and Thakur et al. (2017). Thus, the observation of Gac pulp films describe the better barrier properties. Gac pulp contained edible films had significantly higher in mechanical properties, tensile strength and elongation at break than the biopolymer films based on pea starch and chitosan Thakur et al. (2017). Low solubility and better mechanical and barrier properties are beneficial values of this study, which meet the important requirements in food applications. 8

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Table 4 Comparison of predicted optimal formulation with actual experiment results. Variables response Thickness (mm) Moisture content (%) Opacity (%) Solubility (%) WVP (gs−1 m−1 pa−1) L ΔE Chroma Hue angle Elastic modulus Elongation at break Tensile strength

Predicted value

Experimental value (n = 3)

a

0.078 ± 0.006 32.66 ± 2.98 a 2.34 ± 0.44 a 24.29 ± 3.64 a 1.21 ± 0.51 a 96.21 ± 0.37 a 4.74 ± 1.76 a 8.07 ± 1.98 a 94.82 ± 0.86 a 13434.47 ± 6326 16.84 ± 1.94 a 1140 ± 228 a

M. A. C., et al. (2011). Physico-chemical characterization of chitosan-based edible films incorporating bioactive compounds of different molecular weight. Journal of Food Engineering, 106(2), 111–118. Bourtoom, T. (2008). Edible films and coatings: Characteristics and properties. International Food Research Journal, 15(3), 237–248. Cardoso, G. P., Dutra, M. P., Fontes, P. R., Ramos, A.d. L. S., Gomide, L. A.d. M., & Ramos, E. M. (2016). Selection of a chitosan gelatin-based edible coating for color preservation of beef in retail display. Meat Science, 114, 85–94. Cazón, P., Velazquez, G., Ramírez, J. A., & Vázquez, M. (2017). Polysaccharide-based films and coatings for food packaging: A review. Food Hydrocolloids, 68, 136–148. Cerqueira, M. A., Souza, B. W. S., Teixeira, J. A., & Vicente, A. A. (2012). Effect of glycerol and corn oil on physicochemical properties of polysaccharide films – a comparative study. Food Hydrocolloids, 27(1), 175–184. Chuyen, H. V., Nguyen, M. H., Roach, P. D., Golding, J. B., & Parks, S. E. (2015). Gac fruit (momordica cochinchinensis spreng.): A rich source of bioactive compounds and its potential health benefits. International Journal of Food Science and Technology, 50(3), 567–577. Dursun, S., & Erkan, N. (2014). The effect of edible coating on the quality of smoked fish. Italian Journal of Food Science, 26(4), 370–382. Elsabee, M. Z., & Abdou, E. S. (2013). Chitosan based edible films and coatings: A review. Materials Science and Engineering: C, 33(4), 1819–1841. Embuscado, M. E., & Huber, K. C. (2009). Edible films and coatings for food applications. Springer. Farahnaky, A., Saberi, B., & Majzoobi, M. (2013). Effect of glycerol on physical and mechanical properties of wheat starch edible films. Journal of Texture Studies, 44(3), 176–186. Fundo, J. F., Quintas, M. A., & Silva, C. L. (2011). Influence of film forming solutions on properties of chitosan/glycerol films. Han, J. H. (2014). Edible films and coatings: A review. Innovations in food packaging (pp. 213–255). (2nd ed.). Elsevier. Hassan, B., Chatha, S. A. S., Hussain, A. I., Zia, K. M., & Akhtar, N. (2018). Recent advances on polysaccharides, lipids and protein based edible films and coatings: A review. International Journal of Biological Macromolecules, 109, 1095–1107. Heydari, R., Bavandi, S., & Javadian, S. R. (2015). Effect of sodium alginate coating enriched with horsemint (Mentha longifolia) essential oil on the quality of bighead carp fillets during storage at 4°C. Food Sciences and Nutrition, 3(3), 188–194. Kubola, J., & Siriamornpun, S. (2011). Phytochemicals and antioxidant activity of different fruit fractions (peel, pulp, aril and seed) of Thai gac (Momordica cochinchinensis Spreng). Food Chemistry, 127(3), 1138–1145. Ma, X., Chang, P. R., & Yu, J. (2008). Properties of biodegradable thermoplastic pea starch/carboxymethyl cellulose and pea starch/microcrystalline cellulose composites. Carbohydrate Polymers, 72(3), 369–375. Maran, J. P., Sivakumar, V., Sridhar, R., & Thirugnanasambandham, K. (2013). Development of model for barrier and optical properties of tapioca starch based edible films. Carbohydrate Polymers, 92(2), 1335–1347. Martins, J. T., Cerqueira, M. A., Bourbon, A. I., Pinheiro, A. C., Souza, B. W. S., & Vicente, A. A. (2012). Synergistic effects between κ-carrageenan and locust bean gum on physicochemical properties of edible films made thereof. Food Hydrocolloids, 29(2), 280–289. Norajit, K., Kim, K. M., & Ryu, G. H. (2010). Comparative studies on the characterization and antioxidant properties of biodegradable alginate films containing ginseng extract. Journal of Food Engineering, 98(3), 377–384. Nur Fatin, N. R., & Nur Hanani, Z. A. (2017). Physicochemical characterization of kappacarrageenan (Euchema cottoni) based films incorporated with various plant oils. Carbohydrate Polymers, 157, 1479–1487. Oliveira, S. M., Ramos, I. N., Brandão, T. R. S., & Silva, C. L. M. (2015). Effect of air-drying temperature on the quality and bioactive characteristics of dried galega kale (Brassica oleraceaL. Var. Acephala). Journal of Food Processing and Preservation, 39(6), 2485–2496. Parks, S. E., Nguyen, M. H., Gale, D., & Murray, C. (2013). Assessing the potential for a gac (Cochinchin gourd) industry in Australia. Paula, G. A., Benevides, N. M. B., Cunha, A. P., de Oliveira, A. V., Pinto, A. M. B., Morais, J. P. S., et al. (2015). Development and characterization of edible films from mixtures of κ-carrageenan, ι-carrageenan, and alginate. Food Hydrocolloids, 47, 140–145. Ramos, Ó. L., Reinas, I., Silva, S. I., Fernandes, J. C., Cerqueira, M. A., Pereira, R. N., et al. (2013). Effect of whey protein purity and glycerol content upon physical properties of edible films manufactured therefrom. Food Hydrocolloids, 30(1), 110–122. Rao, M., Kanatt, S., Chawla, S., & Sharma, A. (2010). Chitosan and guar gum composite films: Preparation, physical, mechanical and antimicrobial properties. Carbohydrate Polymers, 82(4), 1243–1247. Saberi, B., Thakur, R., Vuong, Q. V., Chockchaisawasdee, S., Golding, J. B., Scarlett, C. J., et al. (2016a). Optimization of physical and optical properties of biodegradable edible films based on pea starch and guar gum. Industrial Crops and Products, 86, 342–352. Saberi, B., Vuong, Q. V., Chockchaisawasdee, S., Golding, J. B., Scarlett, C. J., & Stathopoulos, C. E. (2016b). Mechanical and physical properties of pea starch edible films in the presence of glycerol. Journal of Food Processing and Preservation, 40(6), 1339–1351. Shojaee-Aliabadi, S., Mohammadifar, M. A., Hosseini, H., Mohammadi, A., Ghasemlou, M., Hosseini, S. M., et al. (2014). Characterization of nanobiocomposite kappa-carrageenan film with Zataria multiflora essential oil and nanoclay. International Journal of Biological Macromolecules, 69, 282–289. Singh, T. P., Chatli, M. K., & Sahoo, J. (2015). Development of chitosan based edible films: Process optimization using response surface methodology. Journal of Food Science & Technology, 52(5), 2530–2543. Thakur, R., Saberi, B., Pristijono, P., Golding, J., Stathopoulos, C., Scarlett, C., et al.

a

0.074 ± 0.002 a 33.06 ± 1.24 a 2.67 ± 0.17 a 26.30 ± 1.67 a 1.67 ± 0.11 a 94.28 ± 0.03 a 6.27 ± 0.28 a 11.13 ± 0.19 a 95.02 ± 0.33 a 14797.94 ± 3040 18.45 ± 2.58 a 1241.45 ± 108 a

a

Data are means ± standard deviations. Data in the same row sharing similar superscript letters are not significantly different at p > 0.05.

The predicted values under these optimal conditions are shown in Table 4. To validate these predicted values, the film was prepared under this optimal formula and then tested in at least triplicates. The results indicated that the experimental values found to be similar to the predicted values (Table 4). Thus, conditions of this optimal formula are reliable and validated, and this optimal formula is recommended to develop edible films from Gac by-products for further applications. 4. Conclusion Response surface methodology using Box-Behnken design was successfully developed for the optimisation of the film formulation from sodium alginate, kappa-carrageenan, Gac pulp and glycerol. All four tested film-forming materials significantly affected film thickness and tensile strength. Sodium alginate and carrageenan significantly affected physical and mechanical properties, whereas Gac pulp showed significant effect on colour parameters and physical properties. Glycerol contributed significant effect on most of the film properties, except for opacity and certain colour values. The optimum formula of edible film contained Gac pulp includes sodium alginate 1.03%, kappa-carrageenan 0.65% w/v, Gac pulp 0.4% w/v, glycerol 0.85% w/v. The film prepared under these optimal conditions potentially suitable for food coating materials and future studies are recommended to apply this film on different types of food to extend their shelf-life and quality. Conflicts of interest The authors declare no conflict of interest. Acknowledgements This work was supported by the Vietnamese Government through the Ministry of Education and Training, Vietnam and The University of Newcastle, Australia. References Alves, V., Rico, B., Cruz, R., Vicente, A., Khmelinskii, I., & Vieira, M. C. (2018). Preparation and characterization of a chitosan film with grape seed extract-carvacrol microcapsules and its effect on the shelf-life of refrigerated Salmon (Salmo salar). Lebensmittel-Wissenschaft und -Technologie, 89, 525–534. ASTM. (2013). Standard test methods for water vapor transmission of materials. ASTM International. Atarés, L., & Chiralt, A. (2016). Essential oils as additives in biodegradable films and coatings for active food packaging. Trends in Food Science & Technology, 48, 51–62. Baldwin, E. A. (2007). Surface treatments and edible coatings in food preservation. Handbook of food preservation. Boca Raton, FL. USA: CRC Press. Benavides, S., Villalobos-Carvajal, R., & Reyes, J. E. (2012). Physical, mechanical and antibacterial properties of alginate film: Effect of the crosslinking degree and oregano essential oil concentration. Journal of Food Engineering, 110(2), 232–239. Bourbon, A. I., Pinheiro, A. C., Cerqueira, M. A., Rocha, C. M. R., Avides, M. C., Quintas,

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T.T.B. Tran, et al. (2016). Characterization of rice starch-ι-carrageenan biodegradable edible film. Effect of stearic acid on the film properties. International Journal of Biological Macromolecules, 93, 952–960. Thakur, R., Saberi, B., Pristijono, P., Stathopoulos, C. E., Golding, J. B., Scarlett, C. J., et al. (2017). Use of response surface methodology (RSM) to optimize pea starch–chitosan novel edible film formulation. Journal of Food Science & Technology, 54(8), 2270–2278. Umaraw, P., & Verma, A. K. (2017). Comprehensive review on application of edible film

on meat and meat products: An eco-friendly approach. Critical Reviews in Food Science and Nutrition, 57(6), 1270–1279. Veiga-Santos, P., Suzuki, C. K., Cereda, M. P., & Scamparini, A. R. P. (2005). Microstructure and color of starch–gum films: Effect of gum deacetylation and additives. Part 2. Food Hydrocolloids, 19(6), 1064–1073. Wu, Y., Geng, F., Chang, P. R., Yu, J., & Ma, X. (2009). Effect of agar on the microstructure and performance of potato starch film. Carbohydrate Polymers, 76(2), 299–304.

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