Functional properties of soy protein isolate edible films as affected by rapeseed oil concentration

Accepted Manuscript Functional properties of soy protein isolate edible films as affected by rapeseed oil concentration

Sabina Galus PII:

S0268-005X(18)30192-9

DOI:

10.1016/j.foodhyd.2018.07.026

Reference:

FOOHYD 4555

To appear in:

Food Hydrocolloids

Received Date:

01 February 2018

Accepted Date:

17 July 2018

Please cite this article as: Sabina Galus, Functional properties of soy protein isolate edible films as affected by rapeseed oil concentration, Food Hydrocolloids (2018), doi: 10.1016/j.foodhyd. 2018.07.026

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ACCEPTED MANUSCRIPT Graphical abstract

9

1 % RO 2 % RO 3 % RO

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SPI + GLY + Rapeseed oil (RO)

Volume (%)

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Emulsion films with

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improved

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barrier and

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sorption properties

2 1 0 0.01

0.1

1 10 Particle size (µm)

100

1000

ACCEPTED MANUSCRIPT 1

Physical and structural characterization of soy protein emulsion films

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Optical, mechanical, barrier, sorption, and surface properties of soy protein

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isolate edible films as affected by rapeseed oil concentration

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Functional properties of soy protein isolate edible films as affected by

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rapeseed oil concentration

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Sabina Galus*

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Department of Food Engineering and Process Management, Faculty of Food Sciences,

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Warsaw University of Life Sciences-SGGW (WULS-SGGW),

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159c Nowoursynowska St., 02-776 Warsaw, Poland

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*Corresponding author. Tel.: +48 22 59 37 579; fax: +48 22 59 37 576.

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E-mail address: [email protected] (S. Galus).

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Abstract

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The effect of the rapeseed oil concentration at 0, 1, 2, and 3 % (w/w) on the optical,

17

mechanical, barrier, sorption, and surface properties of soy protein isolate films was

18

evaluated. Bimodal distribution of the oil droplets in film-forming emulsions and decreased

19

volume-surface diameter (D3,2) as a result of oil concentration were observed. The opacity and

20

total colour differences were significantly increased by incorporating oil. A noticeable

21

decrease of water vapour permeability of films with increasing oil content was observed for

22

all relative humidity differentials used (0-50 %, 50-75 %, and 50-100 %). Tensile properties

23

and contact angle analysis showed that oil-containing films exhibited weakened properties.

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The significant improvement of film hydrophobicity due to the addition of oil was observed

25

during the first 24 h hours in the water vapour sorption analysis. The microstructure of the

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films changed after the addition of oil from homogeneous, and smooth to heterogeneous and

27

rough.

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Keywords: edible films; soy protein; rapeseed oil; color, contact angle

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1.

Introduction

31

Biopolymer-based edible films and coatings have been developed as an

32

environmentally friendly packaging which can be obtained from renewable or biodegradable

33

materials (Debeaufort, Quezada-Gallo, & Voilley, 1998). Such edible materials have found

34

many applications in the food industry in order to prevent mass transfer (e.g. moisture, gases,

35

or flavour) between the product and surrounding medium as well as between the phases of

36

composite products. Therefore, many studies have focused on the protective role of these

37

barriers since edible films and coatings help to maintain or to improve food quality and in

38

consequence to prolong the product shelf life (Falguera, Quintero, Jiménez, Muñoz, & Ibarz,

39

2011). Proteins, polysaccharides, and lipids are the components of edible materials. Previous

40

research has shown that soy protein isolate has good film-forming capacity, creating a

41

homogeneous film with good barrier and mechanical properties (Galus, Mathieu, Lenart, &

42

Debeaufort, 2012). Recent reports have described the use of soy proteins to develop edible

43

and biodegradable films. Soy protein isolate is an abundant, inexpensive, biodegradable, and

44

nutritional raw material which is a mixture of proteins with different molecular properties.

45

Among them, the 7 and 11 S fractions, that which make up about 37 % and 31 % of the total

46

extractable protein, provide the capability of polymerization. Sulfhydryl groups of 11 S

47

protein were reported to be responsible for the formation of disulfide linkages that results in

48

the formation of a three dimensional network (Cho & Rhee, 2004; Cao, Fu, & He, 2007).

49

Protein films are characterized by good mechanical resistance and high permeability to

50

water vapour. These materials are very sensitive to environmental conditions, especially to

51

relative humidity, due to the hygroscopic character of proteins. The production of edible films

52

requires the use of a plasticizer in order to increase its flexibility and handling (Rahman &

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Brazel, 2004; Vieira, da Silva, dos Santos, & Beppu,. 2011). Therefore, biopolymer films

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offer several advantages over synthetic polymers, however but their application is still limited

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due to their high affinity to water, consequently leading to textural changes having a strong

56

impact on their mechanical and barrier properties. Numerous studies have concentrated on

57

improving mechanical and barrier properties of protein films through a blending process by

58

incorporation of different lipids (Galus, 2017). Composite protein–lipid films, both laminated

59

and emulsion forms, have been prepared to combine the barrier properties of protein films

60

with the good moisture-barrier characteristics of lipids. Waxes provide the best water vapour

61

barrier properties, but produce fragile/brittle films. The problem of incorporating lipids into a

62

hydrocolloid in a homogeneous way has still to be solved (Galus & Kadzińska, 2015).

63

Previous studies on modification of the soy protein film structure by addition of sorghum wax

64

(Kim, Hwang, Weller, & Hanna, 2002), beeswax (Chao, Yue, Xiaoyan, & Dan, 2010) or fatty

65

acids (Rhim, Wu, Weller, & Schnepf, 1999; Nayak et al. 2008) showed improved water

66

vapour permeability. Similar results were obtained by Monedero, Fabra, Talens, & Chiralt,

67

(2009) for soy protein isolate films prepared with the addition of a mixture containing oleic

68

acid and beeswax. The authors also noted that the values of mechanical parameters (tensile

69

strength, elongation at break and elastic modulus) decreased when lipid content increased,

70

thus increasing the film flexibility. However, little information is available on incorporation

71

of vegetable oils into protein films which is related also with different positive health benefits

72

when those emulsion films are eaten as an edible coating on food product. However, little

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information is available on incorporation of vegetable oils into protein films. My latest study

74

has reported that films Films prepared from whey protein isolate with the addition of almond

75

and walnut oils showed have been reported to show modified physicochemical properties

76

(Galus & Kadziska, 2016b). Hopkins, Chang, Lam, & Nickerson (2015) incorporated flaxseed

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oil into soy protein isolate films to reduce the moisture penetration and water vapour

78

permeability of the films, as well as to increase the nutritional value of the films.

79

Nevertheless, a reduction of water vapour permeability was observed only at the highest

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flaxseed oil concentration (10 %). Additionally, the results showed that flaxseed oil

81

concentration from 1 to 10 % significantly increased both tensile strength and elongation at

82

break of films. Carpiné, Andreotti Dagostin, Canhadas Bertan, & Mafra (2015) obtained soy

83

protein emulsified films with the addition of virgin coconut oil intended for olive oil

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packaging. The authors noted the improved flexibility of films, whereas the water vapour

85

permeability and mechanical properties were weakened. Additionally, the reduction of

86

moisture content and increased opacity were also observed for the obtained films, but such

87

effects may be considered either positive or negative according due to depending on the

88

destination of the packages and the characteristics of the food product to be packaged. Those

89

results showed that vegetable oils have a potential in modifying to modify the physical

90

properties of soy protein films. No information is available in the literature on incorporation

91

of rapeseed oil into soy protein film-forming matrix. Rapeseed oil is produced nowadays

92

Nowadays, rapeseed oil is produced from very low erucic acid rapeseed plants and is

93

characterized by a remarkable fatty acid profile. The oil contains a high amount of

94

monounsaturated fatty acid oleic acid and is high in both linoleic and linolenic acids, whereas

95

it contains very low amounts of saturated fatty acids. Rapeseed oil is suitable for human

96

consumption due to the being very nutritious its nutritional value (having a relatively high

97

level of tocopherols) (Eskin, 2015). Previous A previous work showed that rapeseed oil

98

incorporated into whey protein films resulted in increased film hydrophobicity and improved

99

gas barrier properties (Galus & Kadzińska, 2016a).

100

This study was designed to prepare soy protein emulsion films and evaluate the effect

101

of the rapeseed oil concentration on the opacity and colour, mechanical properties, water

102

vapour permeability and sorption kinetics, and surface properties of soy protein films. The

103

particle size and distribution of emulsions and film microstructure were also characterized.

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2.

Materials and Methods

106

2.1.

Materials

107

Soy protein isolate (SUPRO 670, ~90 g protein) was purchased from The Solae

108

Company (Solae LLC. St. Louis., MO, USA). Rapeseed oil was produced by ZP Kruszwica

109

S.A. (Kruszwica, Poland). Anhydrous glycerol and sodium chloride were purchased from

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Avantor Performance Materials Poland S.A. (Gliwice, Poland).

111 112

2.2.

Preparation of film-forming emulsions

113

Plasticized blend films of soy protein isolate and rapeseed oil were prepared by the

114

solution casting method. Film-forming solutions were prepared by dissolving soy protein

115

isolate powder in distilled water at 10 % (w/w) under 250 rpm constant magnetic stirring

116

model RTC basic IKAMAG (Staufen, Germany). pH was adjusted to 10  0.1 with 1 M

117

sodium hydroxide using a LAB 850 pH Meter (SHOTT, Germany). The solutions were heated

118

at 70 ± 1 °C for 20 min, then were cooled down to 23 ± 1 °C and glycerol (plasticizer) at 50

119

% (w/w) was added. Rapeseed oil at 0, 1, 2, and 3 % was homogenized with soy protein

120

isolate solution at 13 500 rpm using an Ultra Turrax homogenizer model IKA Yellowline

121

DI25 basic (Staufen, Germany) for 5 min to produce the film-forming emulsions.

122 123

2.3.

Particle size and disribution

124

Laser light scattering granulometry using a Malvern Mastersizer Hydro 2000 SM

125

instrument (Malvern Instruments Ltd., Worcestershire, UK) at temperature of 22 ± 1 °C and at

126

least in three repetitions was used to determine the structure of film-forming emulsions. The

127

measurement area was from 0.1 to 3000 m at the wavelength of 630 nm. The D3,2 diameter

128

(volume-surface) was measured according to the equation presented by Kokoszka,

129

Debeaufort, Lenart, & Voilley, (2010): 6

ACCEPTED MANUSCRIPT ∑𝑛 𝑑3 i i

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𝐷3,2 = ∑

(Eq. 1)

131

where ni is the number of droplets in each size class and di is the droplet diameter.

2

𝑛i𝑑 i

132 133

2.4.

Film preparation

134

The emulsions were poured on the dishes in the same quantity and were dried at 25  1

135

°C and 50  1 % relative humidity (RH) for 24 h hours in a ventilated chamber model KBF

136

720 Binder (Tuttlingen, Germany). A final film thickness was 70 ± 5 µm. After peeling off

137

the films were stored at 25 ± 1 °C and 50 ± 1 % RH for 48 h prior to testing.

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2.5.

An electronic gauge (Metrison, Poland) having a precision of 1 m was used to

140 141

Film thickness

measure the film thickness.

142 143

2.6.

Film opacity

144

The film opacity index was calculated according to the method described by Han &

145

Floros (1997). The measurement was done by dividing the value of absorbance at 600 nm by

146

film thickness in at least in five repetitions. A UV/VIS Helios Gamma spectrophotometer test

147

cell (Thermo Fisher Scientific, Waltham, MA, USA) was used to measure the absorbance. An

148

empty test cell was used as the reference.

149 150

2.7.

Colour

151

The CIELAB colour parameters were used to express the colour of films with a

152

colorimeter model CR-300 (Minolta, Japan). The measurement was done in ten repetitions.

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L*, a*, and b* values were obtained and the total colour difference (∆E) was calculated

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according to method described by Sobral, dos Santos & Garcia, (2005). The hue angle (h) and

155

chroma (C) of the samples were calculated according to equations presented by Atarés, De

156

Jesús, Talens, & Chiralt (2010).

157 158

2.8.

Mechanical properties

159

A Texture Analyzer TA-XT2i (Stable Microsystems, Haslemere, UK) was used to

160

determine tensile strength (TS), Young’s modulus (YM) and elongation at break (E) of the

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films according to the ASTM standard method D882 (ASTM, 2002) described by Galus &

162

Kadzińska (2016a). The films with the size of 25 mm x 100 mm were stretched at the rate of 1

163

mm s-1 until breaking with a 50 mm initial distance of separation. The analysis was done in at

164

least ten replicates of each film formulation at 22 ± 1 °C and 50 ± 5 % RH.

165 166

2.9.

Water vapour permeability (WVP)

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The modified ASTM E96-80 standard method (Debeaufort, Martin-Polo, & Voilley,

168

1993) was used to determine the water vapour permeability of films. Three RH differentials

169

(0-50, 50-75, and 50-100 %) were used at the temperature of 25 ± 1 °C. WVP was calculated

170

at the steady state and from the change in the cell weight versus time. At least three replicates

171

for each film type and RH gradient were made using the film area exposed to the moisture

172

transfer of 8.04∙10-4 m2.

173 174

2.10. Water vapour sorption kinetics

175

The measurement of water vapour sorption kinetics was conducted in at least three

176

repetitions for each type of film in conditions of constant temperature and relative humidity

177

for 7 days. A saturated sodium chloride solution was used to obtain constant relative humidity

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ACCEPTED MANUSCRIPT 178

of the environment (75.3 %). The measurement was carried out at the temperature of 25 ± 1

179

°C.

180 181

2.11. Contact angle measurement

182

The sessile drop method in which a droplet of the tested liquid was placed on a

183

horizontal film surface was used to measure the contact angle (θ) of films with an Easy Drop

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goniometer, model FM40 (Krüss GmbH, Hamburg, Germany), equipped with image analysis

185

software. 2.0 µL of deionized water droplets were deposited on the air side or support side of

186

film surfaces with a precision syringe. The measurements were carried out in at least six

187

replicates per film.

188 189

2.12. Scanning electron microscopy

190

A scanning electron microscope model Quanta 200 (FEI, Brno, Czech Republic) was

191

used to analyse the film microstructure at an intensity of 25 kV. Film surfaces were observed

192

at magnification of ×500 (surfaces) and film cross-sections at magnification of ×1500.

193 194

2.13. Statistical analysis

195

The analysis of variance (ANOVA) at a significance level of 0.05 was performed with

196

Tukey’s post-hoc test to detect significant differences in film properties using Statistica 10.0

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(StatSoft Inc., Tulsa, OK, USA).

198 199

3.

Results and discussion

200

3.1.

Particle size and distribution

201

A bimodal distribution of the rapeseed oil droplets in film-forming emulsions was

202

observed (Fig. 1). The two peaks showed show that the majority of oil droplets were present

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in the highest amount in the size of were 1.9 and 8.7 µm. It can be noted that as the oil

204

concentration increased from 1 to 3 % in the film-forming solutions, a decrease in the number

205

of larger droplets and consequently an increase in the number of smaller droplets were

206

observed. It can be noted that as the oil concentration increased from 1 to 3 % in the film-

207

forming solutions an increase in the number of smaller droplets was observed. This is

208

attributed to the molecular interactions between protein matrix and oil. Regarding the second

209

peak, an increase in oil content from 1 to 2 % resulted in an increase in larger droplets.

210

However, when oil content was raised to 3 % a smaller amount of larger droplets was

211

observed. It can be explained by the mechanism occurring during homogenization, including

212

interactions between molecules and protein aggregation which may be greater in the solution

213

at a lower concentration of oil. Additionally, when regarding the first peak close to 1.9 µm an

214

increase in the volume of droplets is noticeable as a result of increasing oil content in film-

215

forming solutions. Generally, the lipid droplet distribution in aqueous solutions depends on

216

the homogenization conditions, including homogenizer type and time of the process. Hopkins

217

et al. (2015) also observed a bimodal distribution of flaxseed oil in soy protein isolate film-

218

forming solutions with smaller droplets less than 10 µm in diameter and larger ones close to

219

100 µm. The authors noted a third, smaller peak for oil droplets with a size less than 1 µm,

220

but they presumed that this peak represented protein aggregates and not protein-coated oil

221

droplets. Similar oil droplet distribution was also observed for almond and walnut oil

222

dispersed in whey protein isolate film-forming solutions (Galus & Kadzińska, 2016b) as well

223

as for gelatin-based film-forming solutions containing olive oil (Ma et al. 2012). The lipid

224

droplets in the emulsions obtained with using a rotor-stator homogenizer, as in this research

225

study, tend to are prone to self-aggregation or coalescence, which might be related to the

226

bimodal or multimodal lipid distribution. These mechanisms are strongly attributed to the

227

lipid type and concentration. The particle size distribution measured directly after their

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preparation may differ than be different from the distribution in final films. During the

229

solution drying water evaporates with different intensity, creating a film structure which

230

depends directly on film properties.

231

Regardless of the film-forming composition, significant changes (p < 0.05) of the

232

volume-surface diameter (D3,2) of oil in film-forming emulsions have been observed due to

233

the lipid concentration (Table 1). The values decreased from 3.61 µm at 1 % oil to 2.55 µm at

234

3 % oil and are close to the values obtained for other hydrocolloid-based film-forming

235

solutions containing oils (Zúñiga, Skurtys, Osorio, Aguilera, & Pedreschi, 2012). This

236

behaviour is attributed to the homogenization process and oil concentrations. Nevertheless,

237

considering the two observed picks peaks (Fig. 1), among the oil droplets it could be expected

238

that the different film structures would result in a more pronounced effect on the film

239

properties. The underlying mechanism for this phenomenon is unclear, but it may be

240

associated with the coalescence, flocculation, or aggregation process that occurred during the

241

emulsion formation. Ma et al. (2012) also observed a tendency to a reduction in the D3,2

242

parameter for gelatin films as a result of olive oil incorporation, indicating that this

243

phenomenon may be partially related to the different balance of interaction forces between

244

water and protein molecules, and between water and oil components.

245 246

3.2.

Film opacity

247

Opacity is a desired parameter in the food packaging field, in the case of packages for

248

products containing photosensitive compounds, since it can reduce the light transition

249

(Carpiné et al. 2015). The average values of opacity of soy protein isolate films with different

250

content of rapeseed oil are shown in Table 2. The values ranged from 2.77 A∙mm-1 for control

251

films to 7.41 A∙mm-1 for films containing 3 % oil and are not much different than the value of

252

4.26 A∙mm-1 obtained for low-density polyethylene film (Guerrero, Nur Hanani, Kerry, & de

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la Caba, 2011). Significant differences between the opacity values of films with different

254

contents of oil were obtained. In general, as oil concentration in the film formulation

255

increased, films became more opaque. Thus, the control films exhibited higher transparency

256

values than those that contain rapeseed oil. This behaviour is attributed to the presence of an

257

oil phase dispersed in the protein matrix, which promotes to light dispersion, and the light

258

scattering effect of oil. Additionally, the light scattering effect is higher when oil droplets are

259

smaller and better distributed in the films, because they more strongly limit light

260

transmittance and consequently reduce the transparency of the emulsion films. Different

261

transparency of the films is related to their internal structure developed during drying. This

262

structure is greatly affected by the initial structure of the emulsions including volume fraction

263

of the dispersed lipids and the size of lipid aggregates. It can be explained by the processes

264

occur throughout the drying process as flocculation, coalescence, and creaming (Fabra,

265

Talens, & Chiralt, 2009). Increased opacity due to the addition of vegetable oils was also

266

observed in our previous studies on whey protein isolate films (Galus & Kadzińska, 2016a,

267

2016b) as well as by other authors for soy protein (Guerrero et al. 2011), gelatin (Ma et al.

268

2012) and chitosan films (Pereda et al. 2012; Binsi, Ravishankar, & Srinivasa Gopa, 2013).

269

However, Carpiné et al. (2015) noted no significant difference in the opacity of soy protein

270

isolate films when virgin coconut oil was added. Among the analysed films, the authors

271

observed only a linear trend of increasing opacity, as the proportion of oil to soy protein

272

isolate increased.

273 274

3.3.

Colour

275

Colour attributes of films are crucial because they directly influence consumer

276

acceptability of coated products. All obtained films were visually yellow, and the yellowish

277

coloration of films which was expected since the commercial soy protein isolate powder used

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ACCEPTED MANUSCRIPT 278

was yellow. Control films were homogeneous and transparent, whereas oil-containing films

279

were more opaque. The colour attributes obtained for each film sample are presented in Table

280

2. The results show that lightness (parameter L*) decreased from 88.7 for control film to 82.8

281

for film at the highest rapeseed oil concentration (3 %), indicating that the films became

282

darker as the oil concentration increased. Moreover, a* values showed a decreasing trend

283

decrease from 0.16 to -0.26 as a result of the increasing content of oil, and the films became

284

more green, except for the 0.53 value obtained for films containing 2 % oil. This can be

285

explained by the lipid distribution in film-forming emulsion. The sample containing 2 % of oil

286

had the highest number of larger oil droplets which may suggest that aggregation mechanism

287

occurred, resulting in an irregular surface of the final film. On the other hand, the b*

288

parameter showed an increase in value with the increasing amount of oil, from 7.9 for control

289

films to 15.5 for films with 3 % oil, which means that the films became more yellow. These

290

results suggest that at higher rapeseed oil concentration soy protein isolate films became more

291

yellowish and the differences in colour parameters depend strongly on film composition. This

292

is due to the nature of rapeseed oil which, is light yellow in colour. The hue angle values

293

ranged from 85.4 ° for control film to 88.5 ° for film containing 3 % of oil. All values were

294

within the green area in the colour scale. Hue angle was affected by oil addition. An increase

295

in values was observed due to the increasing amount of oil. However, the values were

296

statistically significant (p < 0.05) only when observing films containing oil at the

297

concentration of 2 and 3 %. A similar tendency was observed for chroma. The values

298

increased from 7.9 for control film to 15.5 for films with 3 % of oil, indicating that the colour

299

of the films containing oil was more saturated. A significant difference (p < 0.05) was found

300

only for films with the highest oil content (3 %). Additionally, the incorporation of rapeseed

301

oil resulted in an increase in the total colour differences (ΔE) of soy protein isolate films from

302

12.6 to 21.8 with respect to the control films (Table 2). In general, this behaviour is parallel to

13

ACCEPTED MANUSCRIPT 303

that described for opacity and is related to the heterogeneous surfaces developed on the films

304

during drying. Oil droplets made a dispersed phase with a non-homogeneous distribution, but

305

this was observed to be more concentrated on the film surface and with different particle sizes

306

(Fig. 3). The obtained results showed that the real change in soy protein films by

307

incorporation of rapeseed oil was the darkness. This may be attributed to heterogeneity and

308

surface roughness as well as the hydrophobic character of oil. Darker soy protein isolate films

309

as a result of flaxseed oil addition were reported by Hopkins et al. (2015). The authors noted a

310

decrease in lightness and an increase of both a* and b* parameters, which is due to the colour

311

of flaxseed oil. Generally, the incorporation of vegetable oils into hydrocolloid films led to

312

the reduction of film transparency, as a result of which the films were darker, as was

313

previously reported (Zúñiga et al. 2012; Valenzuela, Abugoch, & Tapia, 2013;

314

Tongnuanchan, Benjakul, Prodpran, & Nilsuwan, 2015).

315 316

3.4.

Mechanical properties

317

Due to the direct influence on the functional character of edible films or coatings, the

318

mechanical properties are among the most important and extensive properties of biomaterial

319

films. Generally, to play a role as a protective layer, a film or coating should provide a

320

continuous structure during the whole time of storage when used as a package or integral

321

edible layer of the product. All obtained soy protein isolate films modified with the addition

322

of rapeseed oil were plasticized with glycerol, and thus were easy to handle. The tensile

323

strength, Young modulus, and elongation at break values are given in Table 3. When

324

comparing all mechanical parameters, significant differences were observed between the

325

control and emulsified films. Tensile strength values decreased from 1.93 to 0.91 MPa,

326

whereas Young modulus values decreased from 1.19 to 0.68 MPa. It was observed that films

327

containing oil showed lower mechanical resistance than control films. This phenomenon can

14

ACCEPTED MANUSCRIPT 328

be explained by the film composition of emulsion films. In those structure structures the lipid

329

molecules filled the protein matrix and interactions between lipid and polar molecules

330

occurred, which seemed to be weaker than those between only polar molecules of control

331

films. Additionally, all films also showed very good swelling capacity in contact with water.

332

There was no possibility to measure the film solubility in water and swelling index. When the

333

films were immersed in water the structure became smooth and film dissolution started, which

334

prevented any possibility to take out the films in one, integral or undamaged form. This could

335

be explained also by the greater degree of discontinuity and deformability of the soy protein

336

films when the oil concentration increased. The liquid state of rapeseed oil could be mainly

337

responsible for this phenomenon. This behaviour is also attributed to the plasticization of

338

protein structure by the presence of liquid oil. Probably, the The addition of a lower content of

339

plasticizer to those films would likely limit this negative effect, however, a minimal amount

340

of plasticizer is necessary to prepare continuous soy protein isolate films (Kokoszka,

341

Debeaufort, Hambleton, Lenart, & Voilley, 2010). Similar results to those obtained in this

342

study were also reported for soy protein isolate films containing coconut oil (Carpiné et al.

343

2015), quinoa protein-chitosan films containing sunflower oil (Valenzuela et al. 2013),

344

hydroxypropyl methylcellulose films containing sunflower oil (Zúñiga et al. 2012), and

345

chitosan films containing virgin coconut oil (Binsi et al. 2013). The same tendency, when the

346

tensile strength decreased as the hydrophobic substance increased, was also noted by Liu &

347

Yu (2016) for soy flour films prepared with the addition of paraffin. The authors explained

348

this behaviour by the association between the decreased tensile strength of analysed films and

349

the weak structure of formed protein, which was caused by the breakages of the crystal

350

structure and hydrogen bonds. The paraffin emulsion added to soy flour film-forming

351

solutions also carried anions, which would further increase the negative charges among

352

protein chains. However, an increase in tensile strength was obtained for chitosan films as a

15

ACCEPTED MANUSCRIPT 353

result of olive oil incorporation (Pereda et al. 2012) and for soy protein isolate films as a

354

result of epoxidized soybean oil (Xia et al. 2015). On the other hand, while the inclusion of oil

355

in biopolymer films caused a linear trend in mechanical parameter values, it depends strongly

356

on lipid type and concentration. Thus, Ma et al. (2012) noted an increase in tensile strength

357

and elastic modulus for gelatin films when lower olive oil concentrations were used (5-15 %).

358

Thus, Ma et al. (2012) noted an increase in tensile strength and elastic modulus for gelatin

359

films at the olive oil concentration from 5 to 15 %. The authors observed a decrease in

360

mechanical parameters for films at the highest content of olive oil (20 %). Those results

361

indicate that the mechanical resistance of emulsion-based films depends strongly on film

362

composition.

363

The elongation at break increased slightly from 3.95 % for control film to 4.19 % for

364

film containing the highest content of oil (Table 3). An increase in the elongation at break

365

results in better flexibility of films, which is an important parameter when such material is

366

used as a package. However, this effect may be considered either positive or negative and

367

depends depending on the destination or function of the packages. The addition of vegetable

368

oils to the hydrocolloid-based films usually provides an increase in elongation at break. This

369

phenomenon occurs since oils play a role as a plasticizer or a lubricant in hydrocolloid matrix,

370

which improves the stretchability of films and has been widely described in literature

371

(Carpiné et al. 2015; Pereda et al. 2012; Binsi et al. 2013; Galus & Kadzińska, 2016a, 2016b).

372

On the other hand, Zúñiga et al. (2012) noted a decrease in elongation at break of

373

hydroxypropyl methylcellulose films as a result of sunflower oil addition indicating that the

374

oil presence in the films leads to weakening of their structure.

375 376

3.5.

Water vapour permeability

16

ACCEPTED MANUSCRIPT 377

Generally, protein films provide limited resistance to moisture transmission due to the

378

substantial inherent hydrophilicity of proteins and to the considerable amounts of hydrophilic

379

plasticizers incorporated into protein films to impart adequate flexibility. Those materials are

380

hydrophilic with polar groups in their molecular structures, and the interactions of polar

381

groups with permeating water molecules caused the water vapour permeability to behave

382

atypically. This is attributed to the variation of film structure and can be connected with free

383

volume theory. Water increases the polymer free volume, allowing the polymeric chain

384

segments to increase their mobility which results in higher water vapour permeability (Su et

385

al. 2010). The addition of rapeseed oil to soy protein isolate films caused a decrease in the

386

water vapour permeability which was expected due to the increase in their hydrophobicity

387

(Table 4). The values ranged from 2.84 to 5.12 ∙ 10-10 g m-1 Pa-1 s-1 for control films and from

388

2.23 to 3.62 ∙ 10-10 g m-1 Pa-1 s-1 for films containing 3 % oil at 0-50 % and 50-100 % relative

389

humidity differentials, respectively. Regardless of the concentration of rapeseed oil used, by

390

increasing the oil content from 1 to 3 % there was also a decrease in water vapour

391

permeability values. This tendency was observed for all relative humidity differential used

392

differentials (0-50 %, 50-75 %, and 50-100 %). An increase in water vapour barrier efficiency

393

of soy protein isolate films is attributed to the increasing amount of oil added as well as the

394

size of the oil droplets distributed in the film-forming solutions, which was decreased as a

395

result of increased oil content (Table 1). The highest values for water vapour permeability of

396

analysed films were obtained at higher relative humidity used. It is attributed to the significant

397

hydrogen bonding interactions between film components and water, and subsequently to the

398

film plasticization and swelling by the absorbed water vapour.

399

The effect of incorporation of vegetable oils on the water barrier properties of the

400

edible films has been analysed in previous studies, and different results have been presented.

401

Carpiné et al. (2015) noted significant reduction of water vapour permeability of soy protein

17

ACCEPTED MANUSCRIPT 402

isolate films prepared with the presence of soy lecithin due to the addition of virgin coconut

403

oil. The reduction of water vapour permeability as a result of the presence of vegetable oils

404

was also found for other hydrocolloid films (Bravin, Peressini, & Sensidoni, 2004; Zúñiga et

405

al. 2012; Binsi et al. 2013; Valenzuela et al. 2013; Galus & Kadzińska, 2016b). The

406

incorporation of hydrophobic substances into hydrophilic biopolymer matrix tends usually

407

usually tends to reduce the water vapour permeability due to the character of the lipid phase.

408

Nevertheless, the concentration and type of lipid are strongly dependent factors of emulsion-

409

based films. Hopkins et al. (2015) observed firstly an initial increase of water vapour

410

permeability of soy protein isolate films when flaxseed oil was at 1 %, to a plateau of the

411

concentration of oil in the ranged of 3 to 7.5 %, and finally a decrease for films containing 10

412

% oil. The authors explained this trend by the factors of oil concentration and apparent

413

viscosity of the film solutions. Film-forming solutions with the addition of 10 % flaxseed oil

414

showed the highest viscosity, indicating that a thicker film-forming solution leads to a greater

415

reduction of water vapour mobility through the film. A significant decrease in water vapour

416

permeability was demonstrated for corn starch and methylcellulose films modified by the

417

incorporation of soybean oil (Bravin et al. 2004). However, the authors noted the negative

418

effect of water vapour permeability of the same films when cocoa butter was added. Thus, the

419

differences in water vapour transmission through emulsified films is due firstly to the lipid

420

nature, and secondly to the lipid phase distribution in films.

421 422

3.6.

Water vapour sorption kinetics

423

Understanding the relative importance of different mechanisms controlling moisture

424

transfer through hygroscopic films is also important for designing new films with improved

425

and selective barrier properties. Consequently, both equilibrium properties and kinetics of

426

water transport through the packaging material are of great importance (Müller, Laurindo, &

18

ACCEPTED MANUSCRIPT 427

Yamashita, 2009). The effect of rapeseed oil content on water vapour sorption kinetics is

428

shown in Fig. 2. The highest intensity of the water vapour adsorption was observed during the

429

first 24 hours of measurement. This behaviour is attributed to the mechanisms occurring

430

during the adsorption process. In the beginning, water vapour is adsorbed to the monolayer

431

and afterwards to deeper areas of films, which is reduced with time due to the higher water

432

content of adsorbed material. After 24 h hours the water content remains constant, indicating

433

that thermodynamic equilibrium was reached. These results might be also attributed to

434

saturation by water reducing the interstitial spaces in the film protein matrix, and

435

consequently decreasing the rate of diffusion of water molecules through the films (Su et al.

436

2010). A similar phenomenon was previously observed for soy protein films (Galus et al.

437

2012) as well as for many other hydrocolloid films (Binsi et al. 2013) and food products

438

(Ciurzyńska, Lenart, & Kawka, 2013).

439

The reduction of water vapour adsorption was observed for analysed soy protein films

440

due to the presence of rapeseed oil, which is understandable expected since oil is hydrophobic

441

in nature. It was noted that with increasing oil concentration from 1 to 3 %, the lower water

442

vapour adsorption was observed. This result suggests that rapeseed oil filled the space

443

between the soy protein molecules of the heterogeneous structure, causing greater water

444

vapour resistance of films. This result suggests that rapeseed oil particles filled the space

445

between the soy protein molecules of the heterogeneous structure, causing greater water

446

vapour resistance of films. Oil particles were dispersed in the film matrix and caused a

447

reduction of water migration through the film. When oil molecules are smaller and well

448

dispersed in the film matrix, water vapour molecules are not able to pass through the film.

449

Particle size distribution showed that analysed film-forming solutions had a higher amount of

450

smaller oil droplets as a result of increasing oil concentration. Those observations are in

451

accordance with mechanical properties (Table 3) and water vapour permeability (Table 4) of

19

ACCEPTED MANUSCRIPT 452

films. The increasing concentration of oil caused a decrease in mechanical resistance and in

453

water vapour permeability of soy protein films.

454

reduction of water absorption of soy protein isolate films by the addition of epoxidized

455

soybean oil. A similar tendency was also reported by Liu & Yu (2016) for soy flour films

456

prepared with the addition of paraffin emulsion. Binsi et al. (2013) observed a linear reduction

457

of moisture sorption of chitosan films as a result of virgin coconut oil addition. The authors

458

also remarked that when the oil content increased the water content of films decreased, which

459

is logical since the lipid droplets are dispersed in the film matrix. It is also attributed to the

460

lower ability of water vapour absorption process into the film structure, resulting in a lower

461

amount of water vapour being absorbed by the films.

Xia et al. (2015) obtained significant

462 463

3.7.

Contact angle

464 465

Effect of oil addition

466

Generally, the surface hydrophobicity increases with the addition of hydrophobic

467

compounds, and the water contact angle of films containing those substances is higher in

468

comparison to the control ones which was previously reported (Kokoszka et al. 2010; Pereda,

469

Amica, Marcovich, 2012; Wang et al. 2014). However, an opposite effect is observed in this

470

research (Table 5). The value of the initial contact angle for control soy protein isolate films

471

was 20.5 ° while for films containing rapeseed oil at 1-3 % it ranged from 10.3 to 10.9 °. This

472

means that the addition of oil to soy protein isolate films caused the reduction of contact angle

473

in comparison to the control film by approximately 50 %. This behaviour is attributed to weak

474

film structure, resulting also in low mechanical resistance, which is due to the nature of soy

475

proteins as a plant source of protein. All films showed to be very sensitive in contact with

476

water and the moisture sensitivity of these films was increased by oil content. This is also

20

ACCEPTED MANUSCRIPT 477

connected with high water solubility of films since this analysis did not show the results. All

478

films immersed in water had lost the integrated structure. Nevertheless, an increasing trend in

479

contact angle values of analysed films was observed as a result of the concentration of

480

rapeseed oil. It is attributed to the higher number of hydrophobic interactions in the films.

481

These results are in accordance with the analysis of the water vapour sorption kinetics (Fig.

482

2). However, the values obtained for both air and support film sides were not significantly

483

different (p < 0.05). However, the values of contact angle obtained on an air side for films

484

containing oil at 1, 2, and 3 % were not significantly different (p < 0.05). The value of contact

485

angle obtained for control film is lower than those obtained for soy protein isolate films from

486

the range of 26.8-32.3 ° reported by Kokoszka et al. (2010) and those of 40.2 ° (for films

487

dried on a glass plate) or 82.2 ° (for films dried on a plastic plate) noted by Zhong, Cavender,

488

& Zhao (2014). A higher contact angle (58 °) was also noted by Wang et al. (2014). The

489

differences are probably due to the film preparation method and the volume of water droplet

490

used in the measurement. The value of contact angle obtained for control film is lower than

491

those obtained for soy protein isolate films from the range of 26.8-32.3 ° reported by

492

Kokoszka et al. (2010). The differences are probably due to the film preparation method and

493

the volume of water droplets used in the measurements. The authors analysed films with

494

similar thickness (52.6 – 83.6 μm), but moisture content was probably lower as they were

495

obtained at a lower temperature (20 ºC) and relative humidity (30 %). The water droplets used

496

in the contact measurement were ∼1 μL. A higher contact angle (58 °) was also noted by

497

Wang et al. (2014) for soy films dried and conditioned at the same conditions as this study.

498

This result can be explained by the following: a lower concentration of soy protein isolate (3

499

g), an addition of carboxymethyl cellulose (0.3 g), the conditions used during film preparation

500

(80 ºC, 35 min), significantly higher film thickness (209 µm), and volume of water liquid

501

droplets used in the measurement (3 µL). Ortiz, Salgado, Dufresne, & Mauri (2018) also

21

ACCEPTED MANUSCRIPT 502

noted higher value of contact angle (68.4 º) for soy protein films. The differences can be

503

explained by a lower temperature of denaturation (60 ºC during 3 h) and a higher volume of

504

water droplets used for analysis (5 µL).

505 506

Effect of film side

507

Regardless of the film side, significant differences in water contact angle values were

508

found (Table 5). The value for control film on the support side (15.5 °) was lower in

509

comparison to the value obtained on the air side (20.5 °). This behaviour is attributed to the

510

film formation during the drying process, since the water evaporates from support and middle

511

areas to the upper film surface. However, an opposite film side effect can be observed for oil-

512

containing films. Higher values of contact angle were obtained for all films at the support side

513

than the air side. This phenomenon is strongly dependent on film microstructure, especially

514

on the presence of oil particles in the film matrix. It seems that the oil, which might migrate to

515

the air side of soy protein isolate films caused a more heterogeneous film surface, whereas the

516

film support surface was found to be more compact.

517

The soy proteins present a great structural versatility depending of its surrounding

518

environment. Generally, the molecular structure of proteins is formed by different amino

519

acids. This composition confers amphiphilic character in the most proteins, and consequently

520

the present surface activity at both, an air-water side and an oil-water interfaces at both air-

521

water and oil-water interfaces (Gálvez-Ruiz, 2017). Additionally, an amphiphilic feature of

522

soy proteins protein allows it to interact with oil, leading to modify its function. However,

523

such results are strongly related to the film composition and character of compounds used.

524

Our previous study showed the same tendency for whey protein isolate films with walnut oil

525

but the opposite effect on films containing almond oil (Galus & Kadzińska, 2016b).

526

22

ACCEPTED MANUSCRIPT 527

3.8.

Film microstructure

528

Scanning electron microscopy micrographs of surfaces and cross-sections of the

529

analysed films are presented in Fig. 3. Control films showed a smooth and regular surface,

530

while films containing rapeseed oil are characterized by a heterogeneous structure with a

531

rough, discontinuous, and irregular surface. Higher lipid droplets are observed on the

532

micrograph of film with the addition of oil at 1 % than on those for films with 2 or 3 % oil.

533

This phenomenon is due to the oil droplet size and concentration which was also observed in

534

the lipid distribution analysis. Generally, the addition of rapeseed oil to soy protein film-

535

forming solutions promoted irregularities on the film surface which are connected with the

536

low miscibility of oil in the protein matrix. Light scattering granulometry (Fig. 1) showed that

537

the oil droplets were dispersed in the soy protein film-forming solutions in different sizes,

538

indicating that during the drying process of the poured mixtures when the viscosity increases

539

some mechanisms such as flocculation, aggregation or coalescence may occur, affecting the

540

film microstructure. The intensity of such phenomena depends also on the properties of the

541

interfacial surface of the oil droplets. In addition, the gravitational phase separation occurs

542

during drying, which can be more intensive when the aqueous phase is of low viscosity and

543

oil aggregates are large. This can be explained by the greater oil droplet sizes, which make

544

them more unstable and provoke the progress of destabilization phenomena during drying and

545

consequently the great accumulation of lipid aggregates on its surface. The migration of oil

546

droplets from the support and middle areas to the air film surface during water evaporation

547

might change the film heterogeneity and finally impact on their functional properties. In these

548

films, a small quantity of oil was observed on the air film surface (oily upper surface), which

549

is generally attributed to the migration oil droplets to the upper surface during the drying time

550

and was also reported for other films (Yang & Paulson, 2000). The appearance of obtained

551

emulsified films was similar to those previously described for hydrocolloid-based materials

23

ACCEPTED MANUSCRIPT 552

with different vegetable oils incorporated (Ma et al. 2012; Pereda et al. 2012; Zúñiga et al.

553

2012; Binsi et al. 2013; Valenzuela et al. 2013). Differences in the distribution of oil droplets

554

in the polymer matrix depend strongly on the lipid used, homogenization and drying process

555

conditions. It must be kept in mind that thermal treatment (70 ± 1 °C, 20 min) was performed

556

on the casting film-forming solutions before drying, which had also influence on greater

557

dense structure of films. Additionally, a different film surface character was noted. The film

558

surface in contact with the support Petri dishes was more smoother and shinier when the

559

upper film surface was less regular. This is strongly attributed to the film structure formation

560

during the drying process and was also observed for whey protein isolate films modified with

561

soya oil (Shaw, Monahan, O’Riordan, & O’Sullivan, 2002).

562 563

4.

Conclusions

564

Rapeseed oil was found to be effective in improving water vapour barrier and sorption

565

properties of soy protein isolate films, thus increasing their functionality. The few changes

566

obtained in the optical, mechanical, and barrier properties of soy films as a result of the

567

incorporation of rapeseed oil show that the concentrations used are suitable for reducing the

568

transparency and tensile strength of the films while providing other positive effects such as

569

improvement of the water vapour barrier or adsorption efficiency. In conclusion, the present

570

study demonstrated the potential to produce blend soy protein isolate films incorporated with

571

rapeseed oil at low concentrations which may have useful applications in those food systems

572

where the edible films should dissolve during cooking or eating. In addition, the blended films

573

would be appropriate as protective coatings for products naturally containing lipids, such as

574

nuts, cheeses or meat, a subject that needs further studies.

575 576

24

ACCEPTED MANUSCRIPT 577 578

Acknowledgments

579

This work was supported by the Ministry of Science and Higher Education (grant

580

number IP2011 013371). The work was also co-financed by a statutory activity subsidy from

581

the Polish Ministry of Science and Higher Education for the Faculty of Food Sciences of

582

Warsaw University of Life Sciences. The author acknowledges MSc Grzegorz Dmochowski

583

for his help in the preparation and analysis of films.

584 585

References

586

ASTM (2002). Standard test methods for tensile properties of plastics. Method ASTM D882-

587

02. Philadelphia, PA: American Society for Testing and Materials.

588

Atarés, L., De Jesús, C., Talens, P., & Chiralt, A. (2010). Characterization of SPI-based edible

589

films incorporated with cinnamon or ginger essential oils. Journal of Food

590

Engineering, 99, 384-391.

591

Binsi, P. K., Ravishankar, C. N., & Srinivasa Gopa, T. K. (2013). Development and

592

Characterization of an edible composite film based on chitosan and virgin coconut oil

593

with improved moisture sorption properties. Journal of Food Science, 78 (4), 526-534.

594

Bravin, B., Peressini, D., & Sensidoni, A. (2004). Influence of emulsifier type and content on

595

functional properties of polysaccharide lipid-based edible films. Journal of

596

Agricultural and Food Chemistry, 52 (21), 6448-6455.

597 598

Cao N., Fu, Y., & He, J. (2007). Preparation and physical properties of soy protein isolate and gelatin composite films. Food Hydrocolloids, 21, 1153-1162.

599

Carpiné, D., Andreotti Dagostin, J. L., Canhadas Bertan, L., & Mafra, R. M. (2015).

600

Development and characterization of soy protein isolate emulsion-based edible films

25

ACCEPTED MANUSCRIPT 601

with added coconut oil for olive oil packaging: barrier, mechanical, and thermal

602

properties. Food Bioprocess and Technology, 8, 1811-1823.

603

Chao, Z., Yue, M., Xiaoyan, Z., & Dan, M. (2010). Development and soybean protein-isolate

604

edible films incorporated with beeswax, Span 20, and glycerol. Journal of Food

605

Science, 75, 493-497.

606

Cho, S. Y., & Rhee, C. (2004). Mechanical properties and water vapor permeability of edible

607

films made from fractionated soy proteins with ultrafiltration. LWT – Food Science

608

and Technology, 37 (8), 833–839.

609

Ciurzyńska, A., Lenart, A., & Kawka, P. (2013). Influence of chemical composition ad

610

structure on sorption properties of freeze-dried pumpkin. Drying Technology, 32, 655-

611

665.

612 613

Debeaufort, F., Martin-Polo, M., & Voilley, A. (1993). Polarity and structure affect water vapor permeability of model edible films. Journal of Food Science, 58, 428-434.

614

Debeaufort, F., Quezada-Gallo, J. A. & Voilley, A. (1998). Edible films and coatings:

615

tomorrow’s packagings: A review. Critical Review in Food Science and Nutrition, 38,

616

299–313.

617 618

Eskin, N. A. M. (2015). Rapeseed oil/Canola. In B. Caballero, P. M. Finglas, & F. Toldrá (Eds.), Encyclopedia of Food and Health (pp. 581-585). Waltham: Academic Press.

619

Fabra, M. J. Talens, P., & Chiralt, A. (2009). Microstructure and optical properties of sodium

620

caseinate films containing oleic acid–beeswax mixtures. Food Hydrocolloids, 23, 676-

621

783.

622

Falguera, V., Quintero, J. P., Jiménez, A., Muñoz, A., & Ibarz, A. (2011). Edible films and

623

coatings: structures, active functions and trends in their use. Trends Food Science and

624

Technology, 22, 291-303.

26

ACCEPTED MANUSCRIPT 625

Galus S. (2017). Soy protein edible films with improved properties through the blending

626

process. In V. Kumar Thakur, M. Kumari Thakur, & M. R. Kessler (Eds.), Soy-Based

627

Bioplastics (pp. 151-166). Shrewsbury: Smithers Rapra.

628 629

Galus, S., & Kadzińska, J. (2015). Food applications of emulsion-based edible films and coatings. Trends in Food Science & Technology, 45 (2), 273-283.

630

Galus, S., & Kadzińska, J. (2016a). Moisture sensitivity, optical, mechanical and structural

631

properties of whey protein-based edible films incorporated with rapeseed oil. Food

632

Technology and Biotechnology, 54 (1), 78-89.

633 634

Galus, S., & Kadzińska, J. (2016b). Whey protein edible films modified with almond and walnut oils. Food Hydrocolloids, 52, 78-86.

635

Galus, S., Mathieu, H., Lenart, A., & Debeaufort, F. (2012). Effect of modified starch or

636

maltodextrines incorporation on the barrier and mechanical properties, moisture

637

sensitivity and appearance of soy protein isolate-based edible films. Innovative Food

638

Science and Emerging Technologies, 16, 148-154.

639 640

Gálvez-Ruiz, M. J. (2017). Different approaches to study protein films at air/water interface. Advances in Colloid and Interface Science, 247, 533-542.

641

Guerrero, P., Nur Hanani, Z. A., Kerry, J. P., & de la Caba K. (2011). Characterization of soy

642

protein-based films prepared with acids and oils by compression. Journal of Food

643

Science, 107, 41-49.

644

Han J. H., & Floros J. D. (1997). Casting antimicrobial packaging films and measuring their

645

physical properties and antimicrobial activity. Journal of Plastic Film and Sheets, 13,

646

287-298.

647

Hopkins, E. J., Chang, Ch., Lam, R. S. H., & Nickerson, M. T. (2015). Effects of flaxseed oil

648

concentration on the performance of a soy protein isolate-based emulsion-type film.

649

Food Research International, 67, 418-425.

27

ACCEPTED MANUSCRIPT 650

Kim, K. M., Hwang, K. T., Weller, C. L., & Hanna, M. A. (2002). Preparation and

651

characterization of soy protein isolate films modified with sorghum wax. Journal of

652

the American Oil Chemists’ Society, 79 (6), 615-619.

653

Kokoszka, S., Debeaufort, F., Hambleton, A., Lenart, A., & Voilley, A. (2010). Protein and

654

glycerol contents affect physico-chemical properties of soy protein isolate-based

655

edible films. Innovative Food Science and Emerging Technologies, 11 (3), 503-510.

656

Kokoszka, S., Debeaufort, F., Lenart, A., & Voilley, A. (2010). Liquid and vapour water

657

transfer through whey protein/lipid emulsion films. Journal of the Science of Food and

658

Agriculture, 90 (10), 1673-1680.

659

Liu, X., & Yu, M. (2016). Effects of paraffin emulsion on the structure and properties of soy

660

protein films. Journal of Dispersion Science and Technology, 37 (9), 1252-1258.

661

Ma, W., Tang, Ch-H., Yin, S-W., Yang, X-Q., Wang, Q., Liu, F., & Wei, Z-H. (2012).

662

Characterization of gelatin-based edible films incorporated with olive oil. Food

663

Research International, 49, 572-579.

664

Monedero, F. M., Fabra, M. J., Talens, P., & Chiralt, A. (2009). Effect of oleic acid-beeswax

665

mixtures on mechanical, optical and water barrier properties of soy protein isolate

666

based films. Journal of Food Engineering, 91, 509-515.

667

Müller, C. M. O., Laurindo, J. B., & Yamashita, F. (2009). Effect of cellulose fibers on the

668

crystallinity and mechanical properties of starch-based films at different relative

669

humidity values. Carbohydrate Polymers, 77, 293-299.

670

Nayak, P., Sasmal, A., Nanda, P. K., Nayak, P. L., Kim, J., & Chang, Y-W. (2008).

671

Preparation and characterization of edible films based on soy protein isolate-fatty acid

672

blends. Polymer – Plastics Technology and Engineering, 47 (5), 466-472.

28

ACCEPTED MANUSCRIPT 673

Ortiz, C. M., Salgado, P. R., Dufresne, A., & Mauri, A. M. (2018). Microfibrillated cellulose

674

addition improved the physicochemical and bioactive properties of biodegradable films

675

based on soy protein and clove essential oil. Food Hydrocolloids, 79, 416-427.

676 677

Pereda, M., Amica, G., & Marcovich, N. E. (2012). Development and characterization of edible chitosan/olive oil eülsion films. Carbohydrate Polymers, 87, 1318-1325.

678

Rahman, M., & Brazel, C. S. (2004). The plasticizer market: An assessment of traditional

679

plasticizers and research trends to meet new challenges. Progress in Polymer Science,

680

29, 1223–1248.

681 682

Rhim, J., Wu, Y., Weller, C. L., & Schnepf, M. (1999). Physical characteristics of emulsified soy protein-fatty acid composite films. Sciences des Aliments, 19 (1), 57-71.

683

Shaw, N. B., Monahan F. J., O’Riordan, E. D., O’Sullivan, M. (2002). Effect of soya oil and

684

glycerol on physical properties of composite WPI films. Journal of Food Engineering,

685

51 (4), 299-304.

686

Sobral, P. J., dos Santos J. S., & Garcia, F. T. (2005). Effect of protein and plasticizer

687

concentration in film forming solutions on physical properties of edible films based on

688

muscle proteins of a Thai Tilapia. Journal of Food Engineering, 70, 93-100.

689

Su, J-F., Huang, Z., Zhao, Y-H., Yuan, X-Y., Wang, X-Y, & Li, M. (2010). Moisture sorption

690

and water vapor permeability of soy protein isolate/poly(vinyl alcohol)/glycerol blend

691

films. Industrial Crops and Products, 31, 266-276.

692

Tongnuanchan, P., Benjakul, S., Prodpran, T., & Nilsuwan, K. (2015). Emulsion film based

693

on fish skin gelatin and palm oil: Physical, structural and thermal properties. Food

694

Hydrocolloids, 48, 248-259.

695

Valenzuela, C., Abugoch, L., & Tapia, C. (2013). Quinoa protein–chitosan–sunflower oil

696

edible film: mechanical, barrier and structural properties. LWT - Food Science and

697

Technology, 50, 531–537.

29

ACCEPTED MANUSCRIPT 698 699

Vieira, M. G. A., da Silva, M. A., dos Santos, L. O., & Beppu, M. M. (2011). Natural-based plasticizers and biopolymer films: a review. European Polymer Journal, 47, 254-263.

700

Wang, Z., Zhou, J., Wang, X., Zhang, N., Sun, X. & Ma, Z. (2014). The effects of

701

ultrasonic/microwave assisted treatment on the water vapor barrier properties of

702

soybean protein isolate-based oleic acid/stearic acid blend edible films. Food

703

Hydrocolloids, 35, 51-58.

704

Xia, Ch., Wang, L., Dong, Y., Zhang, S., Shi, S. Q., Cai, L., & Li, J. (2015). Soy protein

705

isolate-based films cross-linked by epoxidized soybean oil. RSC Advances, 5 (101),

706

82765-82771.

707 708

Yang, L., & Paulson A.T. (2000). Mechanical and vapor barrier properties of edible gellan films. Food Research International, 33, 571-578.

709

Zhong, Y., Cavender, G., Zhao, Y. (2014). Investigation of different coating application

710

methods on the performance of edible coatings on Mozzarella cheese. LWT – Food

711

Science and Technology, 56, 1-8.

712

Zúñiga, R. N., Skurtys, O., Osorio, F., Aguilera, J. M., & Pedreschi F. (2012). Physical

713

properties of emulsion-based hydroxypropyl methylcellulose films: effect of their

714

microstructure. Carbohydrate Polymers, 90, 1147-1158.

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ACCEPTED MANUSCRIPT

Fig. 1.

Water absorbed (g water g d.m.-1)

ACCEPTED MANUSCRIPT 0.4

0.3

0.2

0.1 0 % RO

1 % RO

2 % RO

3 % RO

0.0 0 Fig. 2.

30

60

Time (h) 90

120

150

Control

Fig. 3.

1 % RO

2 % RO

3 % RO

ACCEPTED MANUSCRIPT Figure captions

1 2 3

Fig. 1. Particle size distribution in soy protein film-forming solutions with rapeseed oil (RO).

4 5

Fig. 2. Water vapour sorption kinetics of soy protein films with rapeseed oil (RO).

6 7

Fig. 3. Scanning electron micrographs of surfaces (Magnification ×500) and cross-sections

8

(Magnification ×1500) of soy protein films without and with rapeseed oil (RO) at 1, 2, and

9

3.0 %.

ACCEPTED MANUSCRIPT Highlights

1 2



Emulsion SPI-rapeseed oil films were developed and characterized

3



Film opacity and total colour difference increased with the oil addition

4



Rapeseed oil reduced WVP, tensile strength and contact angle of SPI films

5



Oil-containing films showed heterogeneous and rough structure

ACCEPTED MANUSCRIPT 1

Table 1.

2

Rapeseed oil D3,2 (%) (µm) 0 1 3.61 (0.02)c 2 3.16 (0.02)b 3 2.55 (0.02)a Mean values with standard deviations in brackets. Different superscripts letters (a-c) within the

3

same column indicate significant differences between the films (p < 0.05).

1

Table 2. Rapeseed oil (%)

Opacity (A∙mm-1)

L*

a*

b*

h (°)

C

ΔE

0

2.77 (0.41)a

88.7 (1.8)b

0.16 (0.53)ab

7.9 (3.6)a

85.4 (3.9)a

7.9 (3.6)a

12.6 (4.0)a

1

4.73 (0.78)ab

86.6 (1.5)b

0.07 (0.42)ab

9.1 (3.1)a

87.7 (3.0)ab

9.1 (3.0)a

14.5 (3.3)a

2

2 6.20 (2.64)bc 83.5 (3.4)a 0.53 (0.39)b 11.0 (4.3)ab 87.9 (1.4)b 11.1 (4.2)a 17.5 (5.3)ab 3 7.41 (1.71)c 82.8 (2.8)a (-0.26) (0.28)a 15.5 (4.7)c 88.5 (0.9)b 15.5 (4.7)b 21.8 (5.4)b Mean values with standard deviations in brackets. Different superscripts letters (a-c) within the same column indicate significant differences

3

between the films (p < 0.05).

ACCEPTED MANUSCRIPT 1

Table 3. Rapeseed oil (%)

TS (MPa)

YM (MPa)

E (%)

2

0 1.93 (0.63)b 1.19 (0.37)b 3.95 (0.15)a 1 1.21 (0.42)a 0.91 (0.29)ab 4.12 (0.14)ab 2 1.01 (0.36)a 0.78 (0.29)a 4.14 (0.12)b 3 0.91 (0.19)a 0.68 (0.12)a 4.19 (0.16)b Mean values with standard deviations in brackets. Different superscripts letters (a-b) within the

3

same column indicate significant differences between the films (p < 0.05).

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Table 4. WVP (×10-10 g m-1 Pa-1 s-1) Rapeseed oil (%)

RH differentials (%) 0-50

50-75

50-100

2

0 2.84 (0.27)abcd 4.28 (0.34)gh 5.12 (0.31)i 1 2.65 (0.07)abc 3.47 (0.36)def 4.39 (0.19)h 2 2.36 (0.13)ab 3.26 (0.26)cdef 3.87 (0.32)fgh 3 2.23 (0.03)a 2.96 (0.18)bcde 3.62 (0.10)efg Mean values with standard deviations in brackets. Different superscripts letters (a-i) within the

3

same column indicate significant differences between the films (p < 0.05).

ACCEPTED MANUSCRIPT 1

Table 5. Rapeseed oil (%)

Film side

θ (°)

2

air 20.5 (1.3)f support 15.5 (1.1)e air 10.3 (0.6)a 1 support 11.8 (0.9)bc air 10.5 (1.0)a 2 support 12.8 (0.8)cd air 10.9 (0.8)ab 3 support 13.4 (1.0)d Mean values with standard deviations in brackets. Different superscripts letters (a-f) within the

3

same column indicate significant differences between the films (p < 0.05).

0

ACCEPTED MANUSCRIPT Content of Tables

1 2 3

Table 1. Mean diameter (D3,2) of rapeseed oil particles in soy protein film-forming solutions

4 5

Table 2. Film opacity, colour attributes (L*, a*, b*), hue angle (h), chroma (C), and total

6

colour difference (ΔE) of soy protein emulsion films

7 8

Table 3. Tensile strength (TS), Young modulus (YM) and elongation at break (E) of soy

9

protein emulsion films

10 11

Table 4. Water vapour permeability of soy protein emulsion films

12 13

Table 5. Contact angle (θ) of soy protein emulsion films