Tunable d-Limonene Permeability in Starch-Based Nanocomposite

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Tunable d-limonene permeability in starch-based nanocomposite films reinforced by cellulose nanocrystals Siyuan Liu, Xiaoxi Li, Ling Chen, Lin Li, Bing Li, and Jie Zhu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b05457 • Publication Date (Web): 05 Jan 2018 Downloaded from http://pubs.acs.org on January 5, 2018

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Journal of Agricultural and Food Chemistry

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Tunable d-limonene permeability in starch-based nanocomposite films reinforced by

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cellulose nanocrystals

3 Siyuan Liu1, Xiaoxi Li1∗∗, Ling Chen1, Lin Li1,2∗∗, Bing Li1, Jie Zhu2

4 5 6

1. Ministry of Education Engineering Research Center of Starch & Protein Processing,

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Guangdong Province Key Laboratory for Green Processing of Natural Products and Product

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Safety, School of Food Sciences and Engineering, South China University of Technology,

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Guangzhou 510640, China

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2. School of Chemical Engineering and Energy Technology, Dongguan University of

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Technology, Dongguan 523808, China

12 13 14 15 16 17 18 19 20 ∗

Corresponding authors. Tel.: +86 20 8711 3252; fax: +86 20 8711 3252. College of Food

Sciences and Engineering, South China University of Technology, Guangzhou 510640, China. Email address: [email protected] (X. Li); [email protected] (L. Li). 1 ACS Paragon Plus Environment


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ABSTRACT

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In order to control d-limonene permeability, the cellulose nanocrystals (CNC) were used to

23

regulate starch-based film multi-scale structures. The effect of sphere-like cellulose nanocrystal

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(CS) and rod-like cellulose nanocrystal (CR) on starch molecular interaction, short-range

25

molecular conformation, crystalline structure and micro-ordered aggregated region structure

26

were systematically discussed. CNC aspect ratio and content were proved to be independent

27

variables to control d-limonene permeability via film structures regulation. New hydrogen

28

bonding formation and increased hydroxypropyl starch (HPS) relative crystallinity could be the

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reason for the lower d-limonene permeability compared with tortuous path model approximation.

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More hydrogen bonding formation, higher HPS relative crystallinity and larger size of micro-

31

ordered aggregated region in CS0.5 and CR2 could explain the lower d-limonene permeability

32

than CS2 and CR0.5, respectively. This study provided a new sight for the control of the flavor

33

release from starch-based films which favored its application in biodegradable food packaging

34

and flavor encapsulation.

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KEYWORDS：：Starch-based nanocomposite; Cellulose nanocrystals; Multi-scale structures;

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d-limonene permeability

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2 ACS Paragon Plus Environment

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INTRODUCTION

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Flavors play important roles in food deterioration and consumer satisfaction1. The loss of

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flavors during food processing and storage was detrimental to food organoleptic quality and

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shelf-life. Starch was chosen as biodegradable food packaging materials for its wide botanical

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source, economic price and totally biodegradable ability

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inherent permeability for starch-based materials leads to the loss of flavors

49

a flavor additive for food applications, is the major component of citrus oils found in orange,

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lemon, mandarin, and grapefruit 6. D-limonene was used as a hydrophobic flavor model to

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present permeability through food packaging 7. In order to guarantee food quality and prolong

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shelf life, starch-based films with enhanced barrier property against highly volatile flavors

53

protected them from volatilization, which would largely promote its application in food

54

packaging. Also, the starch-based films with tunable flavor release rate were beneficial to its

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application in flavor encapsulation.

2, 3

. Despite the many advantages, the 2, 4, 5

. D-limonene, as

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The essence of d-limonene permeation in starch-based materials was the small volatile

57

molecules mass transfer caused by starch chains movement8, 9. The permeability of d-limonene

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was closely related to molecular dynamics or segmental motions of starch chains10,

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changes in starch-based film multi-scale structures including molecular interaction, short range

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molecular conformation, crystalline structure and micro-ordered aggregated region structure

61

were relevant to starch chains mobility, which would finally affect d-limonene permeability.

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Therefore the d-limonene permeability could be controlled by means of starch structure

63

regulation. However, the former study about flavor barrier property in nanocomposite films just

64

focused on the tortuous path contributed by impermeable nanoparticles to explain the barrier


11

. The


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property improvement

. It was neglected that the influence of starch-based film multi-scale

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structures change after nanoparticles addition on flavor barrier property.

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Cellulose nanocrystals (CNC) had a good compatibility with starch as structure similarity15.

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The homogeneous dispersion of CNC in starch matrix favored the hydrogen bonding formation

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between the two components. Notably, the change of CNC aspect ratio and content led to the

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variation of contact surface area with starch, as well as the steric hindrance for starch chains

71

rearrangement in film forming process. Therefore the CNC aspect ratio and content were

72

potential independent variables to regulate starch-based film multi-scale structures. Recently,

73

related study has found the starch crystallinity was changed after nanoparticles addition 16-19. But

74

there was still no consistent result of how the nanoparticle addition affected starch crystallinity.

75

More importantly, the starch-based films multi-scale structures were very closely connected 20, 21.

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For example, the starch double helices were the main component of starch crystalline structure.

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The change of starch crystallinity indicated the variation of helical structure portion. Moreover,

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the starch crystallinity change would lead to the variation of film micro-ordered aggregated

79

region, which was the aggregation structure at larger scale

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nanoparticles addition on film multi-scale structures change needs to be stated in details.

20, 21

. Therefore, the effect of

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In order to control d-limonene permeability, how the change of film multi-scale structures

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would influence d-limonene permeability was urgently needed to be clarified. Accordingly, the

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rod-like CNC (CR) and sphere-like CNC (CS) were used to regulate starch-based nanocomposite

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films multi-scale structures. The changes in molecular interactions, short range molecular

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conformation, crystalline structure and micro-ordered aggregated region structure in the films

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were characterized in details by attenuated total reflectance - fourier transform infrared

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spectroscopy (ATR-FTIR), 13C CP/MAS Nuclear Magnetic Resonance (13C CP/MAS NMR), X-


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ray diffraction (XRD) and small angle X-ray scattering (SAXS). The functional-structure

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relationship between film multi-scale structures and d-limonene permeability would support the

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rational design of biodegradable starch-based films for food packaging and flavor encapsulation.

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MATERIALS AND MATHODS

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Materials. Hydroxypropyl starch (HPS) was prepared with molar substitution (MS) 0.11 by 22

23

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the method in the previous study

94

purchased from blue goose Biorefineries Inc. (Canada). Glycerol as plasticizer was purchased

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from Aladdin Chemistry Co. Ltd. (Shanghai, China). Distilled water prepared with a Milli-Q

96

filter system (Millipore, Bedford, MA) was used as solvent for HPS gelatinization.

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. CS was prepared by previous method

and CR was

Film preparation. HPS-based CNC nanocomposite films were prepared according to the 24

98

method of previous study with proper modification

99

g/g of HPS) were first dissolving in distilled water. The solutions were heated to gelatinization

100

temperature (90 °C) and continuously stirred for 1 h. CR or CS suspension was prepared by the

101

addition of CNC in distilled water and stirred at 75 °C for 3 h. The starch solution and CR or CS

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suspension were mixed with high speed homogenizer (14,000 r/min) for 5 min and then treated

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in ultrasound for 30 min to obtain the final nanocomposites with CNC content of 0.5% and 2%

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(g/g, CNC in HPS). The resulting solutions were poured into polystyrene petri dishes and water

105

evaporation was carried out at 35 °C for 48 h. The obtained nanocomposite films were named as

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CR0.5, CR2, CS0.5 and CS2 based on the CNC aspect ratio and content. The thickness of the

107

nanocomposite films were 60±5 µm (L&W 250, ADEV, Sweden). In all cases, the

108

nanocomposite films were conditioned at the temperature of 23±2°C and relative humidity of

109

50±5% for three weeks before d-limonene permeability testing and structure characterization.

. The HPS (5%, w/v) and glycerol (20%,



110

Scanning electron microscope (SEM). Films were frozen by liquid nitrogen then they were

111

fractured, subsequently fixed on sample stages. CNC suspension (1 mg/mL, CNC in water) were

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homogenized with high speed homogenizer (14,000 r/min) for 5 min and then treated in

113

ultrasound for 30 min. About 50 µL of the suspension was dripped on the glass plate and water

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evaporated at 23±2°C. All the samples were coated with a thin gold film then observed with an

115

EVO 18 scanning electron microscope (Carl Zeiss Microscopy, Oberkochen, Germany)

116

operating at 20 kV voltages.

117

Fourier transform infrared (FTIR). The Fourier transform infrared (FTIR) spectra of the

118

films were measured in a Bruker (Germany) Tensor 37 spectrometer attached to the ATR

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(Attenuated Total Reflectance) accessory in the wavelength range of 600-4000 cm-1. The number

120

of accumulated scans was 32 at a resolution of 4 cm-1 and air was used as background. The –OH

121

peak position was found with PeakFit version 4.12.

122

13

C CP/MAS Nuclear Magnetic Resonance (13C CP/MAS NMR) Spectroscopy. The solid-

123

state

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Germany) equipped with a 4 mm broad band double-resonance CP/MAS probe. Each of the film

125

samples (about 500 mg) was sealed in the rotor and inserted into the center of magic field. The

126

13

127

than 6000 scans were accumulated for a spectrum with a cycle delay of 2s. In order to find out

128

the changes in the short-range molecular conformation of the samples, all the spectra were then

129

decomposed into several peaks using PeakFit version 4.12.

13

C CP/MAS NMR was performed on a Bruker Avance HD 400 spectrometer (Bruker,

C NMR spectrum with CP and MAS was recorded at a temperature of 23±2°C. A total of more

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X-ray diffraction (XRD). XRD patterns were operated with an X-ray diffractometer

131

(X’PertProx, PANalytical, Eindhoven, Netherlands) operating at 40 kV and 40 mA with Cu Kα

132

radiation (λ=0.1542 nm). Samples were scanned in the range of the diffraction angle 2θ from 5°


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to 45° with a step of 0.02° and the scanning speed is 0.1 degree per second.

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Small angle X-ray scattering (SAXS). SAXS was performed using the SAXSess camera

135

(Anton-Paar, Graz, Austria). The PW3830 X-ray generator with a long fine focus sealed glass X-

136

ray tube (PANalytical, Eindhoven, Netherlands) was operated at 40 kV and 50 mA. A focusing

137

multi-layer optics and a block collimator provided an intense monochromatic primary beam (Cu-

138

Kα, λ=0.1542 nm). A semi-transparent beam stop enabled measurement of attenuated primary

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beam at zero scattering vectors. The nanocomposite films strip was fixed on the sample holder

140

and placed in TCS 120 temperature-controlled unit in the evacuated camera housing. The

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sample-to-detector distance was 261.2 mm, and the temperature was kept at 26°C. The 2D

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scattered intensity distribution recorded by an imaging-plate (IP) detector was read out by

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Cyclone storage phosphor system (PerkinElmer, Waltham, USA). The 2D data were integrated

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into the one-dimensional scattering function I(q) as a function of the magnitude of the scattering

145

vector q defined as: q = 4πsinθ/λ, where λ (nm) is the wavelength of the X-ray source, 2θ (°) is

146

the scattering angle and q (nm−1) is the scalar of scattering vector.

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PEN3 electronic nose for d-limonene permeability testing. The PEN3 (Airsense Analytics,

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Schwerin, Germany), a portable electronic nose provided with ten metal oxide semiconductor

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(MOS) sensors, was used to detect the short-term permeability of d-limonene. 2g d-limonene

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was put in 50 mL centrifuge tube. The sample film was sealed on the top of the centrifuge tube

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by the O-ring. Then the centrifuge tube was put in 500 mL beaker which was sealed by double

152

layers of aluminum foil at 25 °C for 1 h. The air in the beaker was tested by the PEN3 electronic

153

nose. The testing temperature was 25°C, controlled by thermostatic bath, and atmospheric air at a

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flow rate of 400 mL/min was used as the carrier gas.



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Gravimetric method for d-limonene permeability testing. 2g d-limonene was put in 50 mL

156

centrifuge tube. The sample film was sealed on the top of the centrifuge tubes by the O-ring.

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Then the samples were stored at 25 °C and relative humidity (RH) of 75%. The weight loss of

158

the samples were recorded every 24 h for 10 days. The average weight loss of the sample was

159

used to calculate long-term d-limonene permeability.

160

Statistical analysis. The data was analyzed using SPSS 22.0 Statistics software (IBM, New

161

York, USA). Analysis of variance (ANOVA) was followed by Tukey HSD test to compare the

162

data. The significance level was set as P < 0.05.

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RESULTS AND DISCUSSION

164

The permeability of d-limonene. As its high sensitivity, the electronic nose can be used to

165

detect short-term d-limonene permeation. G/G0 is the ratio of the sensors conductivity response

166

of the sample gas (G) relative to the carrier gas (G0) over time. After 1 h storage with control

167

film, senor-7 was more sensitive to d-limonene than other sensors thus it was chosen to detect d-

168

limonene permeation (Fig.1b). As shown in Fig.1c, the G/G0 value of sensor-7 obviously rose

169

over time. The CNC intensified films had lower signal intensity than the control film, which

170

indicated CNC addition was an effective method to decrease d-limonene permeability (Fig.1c).

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Histograms of normalized intensity responses of sensor-7 were presented in Fig.1d. CS0.5

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presented lower signal intensity than CS2 but CR0.5 showed higher signal intensity than CR2.

173

The tortuous path was the most widely accepted theory to explain the improvement of barrier 12, 14, 25

174

property against flavor transfer in nanocomposite films

175

model assumed all the nanoparticles were paralleled oriented in the starch matrix 26. The relative

176

permeability can be approximated according to equation 1.

177

nanocomposite films，P0 was the permeability of unfilled control film; φ was the volume


. As shown in Fig.2, Nielsen

Peff was the permeability of

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fraction of nanoparticles, τ was the tortuous facor, L/W was the aspect ratio of nanoparticles. 1 − 1− = = (1)

1 + (2 )

179

Bharadwaj thought the rod-like and platelet-like nanoparticles were random oriented in the

180

polymer matrix. The order parameter S was offered to further develop the model 27. As shown in

181

Fig.2, θ was the angle between preferred orientation (n) and filler sheet normals (p). S equaled 0

182

(θ=45°) for the random oriented nanoparticles in the polymer matrix. 1− = (2) 2 1 1 + 3( ) ( + ) 2 2 =

1 (2 − 1) (3) 2

183

Gravimetric method was suitable to detect long-term permeation of d-limonene. The results of

184

d-limonene permeability measured by gravimetric method were consistent with the results of

185

electronic nose. As shown in Fig.3a, the d-limonene permeability of nanocomposite films was

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lower than control film. CS0.5 presented lower relative permeability than CS2 but CR0.5 showed

187

higher relative permeability than CR2. The relative permeability variation among nanocomposite

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films were more obvious than the result tested by electric nose as the storage time was much

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longer. The aspect ratio and content of CNC were proved to be independent variables to control

190

d-limonene permeability. However, the relative d-limonene permeability of the nanocomposite

191

films obviously deviated from the Nielson and Bharadwaj model approximation, respectively. It

192

suggested that the only tortuous path contributed by CNC could not accurately explain the

193

improvement of barrier property. = − (4)



194

Moreover, the ΔP is the deviation value of the relative permeability tested in this study from

195

tortuous path model approximation. From Fig.3b, ΔP for the nanocomposite films were positive,

196

which suggested the change of film multi-scale structures comprehensively improved d-limonene

197

barrier property. But ΔP for CS and CR intensified films at the same nanoparticles content were

198

not the same, which indicated the structure difference caused by the various aspect ratio and

199

content of CNC addition in the nanocomposite films. In order to better interpret the relative

200

permeability change, it is necessary to find out how the aspect ratio and content of CNC affect

201

the film multi-structures change.

202

The dispersion of CNC in HPS matrix. As shown in Fig.4a, the main diameter range of CS

203

was 80-120 nm. The length of CR was 200-300 nm and the width was 20-30 nm (Fig.4b). The

204

aspect ratio of CS was 1 and the aspect ratio of CR was about 10. Compared with control

205

(Fig.4c,d), the white dots in Fig.4e were CS and the embossed white dots in Fig.4f were the ends

206

of CR. As the structure similarity, both CS and CR with the content of 2% (g/g, CNC in HPS)

207

were homogeneously dispersed in the HPS matrix. The good dispersion of CS or CR in the HPS

208

matrix led to larger contact surface area between HPS and CNC, which favored the hydrogen

209

bonding formation between HPS and CNC.

210

Change of hydrogen bonding interaction. Multiple hydrogen bonding interaction were the

211

most crucial secondary interaction to construct supermolecular architectures in polymer based

212

nanocomposites

213

wavenumber (blue shift or red shift), indicating that the O-H was enhanced or weakened. The

214

higher wavenumber shifts presented higher energy between O-H bond, while weak molecular

215

interactions among the molecules

216

interaction based on the –OH stretching vibration peak position. As shown in Fig.5, the –OH

28

. The peak position of -OH stretching vibration shifted to a higher or lower

29, 30

. This study discussed the change of hydrogen bonding


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peak in control film was at 3316.2 cm-1, while the –OH peak in CS and CR were at 3327.0 and

218

3323.8 cm-1, respectively. After CNC addition, the –OH peak in nanocomposite films shifted to

219

lower wavenumber compared with control film. The –OH peak position shift to lower

220

wavenumber as the new hydrogen bonding averaged the electron density in O-H bonds. Thus it

221

indicated new hydrogen bonding formed between CNC and HPS in the films. The hydrogen

222

bonding forming sites on the surface of HPS molecules were occupied by CNC thus the inter-

223

and intra- hygrogen bonding in HPS were changed.

224

For the CNC aspect ratio, there was no obvious difference of -OH peak position between

225

CS0.5 and CR0.5. But with further increase of CNC content, -OH peak position of CS2 was

226

higher than that of CR2. As the higher aspect ratio, CR had larger contact surface area with HPS

227

than CS at the same nanoparticle content. The difference between –OH peaks in CS0.5 and

228

CR0.5 were not obvious as the low CNC content. However, at the CNC content of 2%, the larger

229

contact surface area favored the hydrogen bonding formation between CR and HPS, which made

230

–OH peak shifted to lower wavenumber. For the CNC content, the –OH peak wavenumber of

231

CS0.5 was lower than CS2 but CR0.5 had higher wavenumber than CR2. The steric hindrance of

232

CS was more obvious than CR as the larger particle volume. The abundant CS in CS2 prevented

233

HPS molecules from hydrogen bonding as steric hindrance, thus CS2 had a higher wavenumber

234

than CS0.5. But the steric hindrance of CR was weaker than CS as smaller nanoparticles volume.

235

It provided more absoption site for hydrogen bonding formation in CR2, thus CR2 had a lower

236

wavenumber than CR0.5.

237

Change of short-range molecular conformation. 13C CP/MAS -NMR was an effective tool 31-33

238

to characterize the short-range molecular conformation in the starch-based materials

239

shown in Fig.6, six kinds of C atom in the glucose unit showed various chemical shifts as the


. As


240

different chemical environment. The C1 and C4 relative area ratio could be used to calculate the

241

portion of double helices, single helix and random coil of starch chains34. C1 peak at 102.40 ppm

242

was the resonance peak of V-type single helix and double peak at 100.43 and 98.85 ppm were

243

the resonance peak of amylopectin double helices35, 36. On the one hand, the double helices were

244

the major constitutional unit of crystalline structure. On the other hand, part of double helices

245

appeared in the amorphous region with less mobility than the random coils. C4 peak at 81-84

246

ppm was the resonance peak of random coils in the amorphous region which were loosely

247

arranged with high mobility.

248

From table 1, CS and CR showed C1 resonance peak at 104.52 ppm and 104.41 ppm,

249

respectively. But the Area1 of nanocomposite films decreased with the rise of CNC content.

250

Compared with control film, CS and CR showed smaller C4 resonance peak at 83.41 ppm and

251

83.54 ppm, respectively. But C4 area increased after CNC addition. Thus the CNC did not

252

obviously interfere the change of starch

253

the addition of CNC increased the sum of Area2 and Area3 in C1. It suggested that the starch

254

double helices structure needed to be stabilized by hydrogen bonding thus the new hydrogen

255

bonding formation between CNC and HPS favored double helices formation. But for V-type

256

single helix, it could be stabilized by the complexion with lipid thus its portion did not increase

257

as double helices after CNC addition. Moreover, the C4 peak area obviously increased compared

258

with control because the addition of CNC disrupted the HPS conformation in amorphous region.

259

The Area4 and the sum of Area2 and Area3 in C1 of CS intensified film were both larger than

260

that of CR intensified film at same nanoparticle content.

261

13

C-NMR spectra signal as their low content. Notably,

Total change value = (Area1 + Area2 + Area3)/Area4 (5)


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262

In order to comprehend short range molecular conformation change as a whole, the ratio

263

between helical structure and random coil was used as total change (TC) value (eq.5). The higher

264

the TC value, the more ordered the starch short range molecular conformation. As shown in

265

Fig.7, the addition of CNC decreased the TC value of the nanocomposite films compared with

266

control, which suggested the overall short range molecular conformation was disrupted by CNC.

267

The TC value of CR0.5 and CR2 were higher than CS0.5 and CS2, respectively. Even the double

268

helices portion increased, the decreased single helix portion and largely increased random coil

269

portion after CS addition decreased the lower TC value. More hydrogen bonding formation and

270

weaker steric hindrance could be the reason for the higher TC value of CR intensified film

271

compared with CS intensified films at same CNC content.

272

Change of crystalline structure. The crystalline structure of starch is ascribed into A-, B-, C-

273

and V-type based on the packing of amylopectin side chains double helices and amylose single

274

helix

275

forming crystalline structure. In Fig.8a, for the XRD pattern of control film, the diffraction peaks

276

at 5.8° and 17.3° suggested it was the B-type crystalline pattern of HPS 39. The diffraction peak

277

for CR and CS both appeared at 15.2° and 22.9°. After the addition of CS and CR, the same HPS

278

diffraction peak position for nanocomposite films suggested HPS crystalline type did not change.

279

But the intensity of the HPS diffraction peak at 5.8° and 17.3° obviously increased. The film

280

crystallinity can be calculated according to the diffraction peak area by MDI jade software.

37, 38

. During film forming process, parts of HPS chains arranged perfectly in regularity

281

Cry3 = Cry4 − Cry5 × ω (6)

282

As the crystallinity of CNC were relative high, in order to investigate the starch crystallinity

283

change affected by CNC, the CNC crystallinity was subtracted from film crystallinity based on

284

the equation 6. Crys was the starch crystallinity, Cryf was the film crystallinity, Cryc was the CNC



285

crystallinity, ω was the CNC content (g/g, CNC in HPS). As shown in Fig.8b, the film overall

286

crystallinity obviously increased after CNC addition. Both CS and CR offered hydrogen bonding

287

absorption sites for the plasticized HPS chains thus they worked as nucleating agent for HPS

288

recrystallization. The Crys of CS0.5 was higher than that of CS2, but Crys of CR0.5 was lower

289

than that of CR2. The steric hindrance of CS in CS2 might be the reason for the Crys drop as the

290

redundant CS prevented HPS recrystallization. As the various shape and smaller particle volume,

291

the steric hindrance of CR was weaker than CS. The increased CR content offered more

292

nucleating sites thus the Crys in CR2 was higher than that of CR0.5.

293

The nucleating effect and steric hindrance effect determined the change of HPS crystallinity.

294

Considering the former short-range molecular conformation results, the increased portion of

295

double helices led to the increased order in starch long-range molecular conformation.

296

Additionally, the starch crystallinity increased but the TC value of the nanocomposite films

297

decreased compared with control, which indicated there was a further amorphization in the film

298

amorphous region after CNC addition. This result was in consistent with the increased random

299

coil portion in the amorphous region after CNC addition.

300

Change of micro-ordered aggregated region. The micro-ordered aggregated region was the

301

characterization of starch ordered aggregation structure at the larger scale than crystalline

302

structure. SAXS is a proper tool to characterize the change of aggregated structure of HPS-based

303

films40,

304

aggregated region and amorphous aggregated region. The micro-ordered aggregated region is

305

mainly formed by the aggregates assembled with the starch crystalline structure. The amorphous

306

aggregated region is formed by the disordered starch chains. Based on the previous study, the

307

starch crystalline structure constituted the micro-ordered aggregated region in the starch-based

41

. The starch aggregated structures in the film could be classified to micro-ordered


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Page 15 of 35


308

films42-44. The electron density discrepancy between the HPS micro-ordered aggregated region

309

and amorphous aggregated region was showed by the signal intensity in I-q figure

310

shown in Fig.9, the SAXS intensity at low q range obviously increased after the CNC addition.

311

The increased starch crystallinity and increased portion of random coil in the amorphous

312

enhanced the electron density discrepancy in the films, which led to the increase of SAXS signal

313

intensity. The lowest Crys and random coil portion in CR0.5 could be the reason for the lowest

314

signal intensity compared with other nanocomposite films.

45, 46

. As

315

Ln:I(q)= = Ln:I(0) − R @ q /3= (7)

316

After Guinier transition (eq.7), the radius of gyration (Rg) can be calculated by the slope of the

317

liner regression (Fig.10a) which reflected the size of the micro-ordered aggregated region47. As

318

shown in Fig.10b, the Rg of CS0.5 was larger than that of CS2 but the Rg of CR0.5 was smaller

319

than that of CR2. The size of micro-ordered aggregated region decreased which was caused by

320

the more compactness of the aggregates which assembled by the perfected HPS crystalline

321

structure.

322

Structure-functional relationship from view of film multi-scale structures. After CNC

323

addition, new hydrogen bonding formed between CNC and HPS. The order of short-range

324

molecular conformation of the nanocomposite films were lower than that of control as random

325

coils portion in amorphous region largely increased. The HPS relative crystallinity was

326

obviously increased. But the sizes of micro-ordered aggregated region were decreased compared

327

with control. New hydrogen bonding formation between starch and CNC favored the starch

328

double helices formation, and the increased portion of double helices contributed to more starch

329

crystalline formation.



330

The d-limonene permeability is closely related to molecular dynamics or segmental motions of

331

HPS chains. At first, the new hydrogen bonding formation between HPS and CNC decreased the

332

mobility of HPS chains. The cohesive energy density increased for more hydrogen bonding

333

formation which favored the inhibition of d-limonene permeation. Secondly, as the amorphous

334

region was the main permeation path for penetrant, the increased portion of random coils in the

335

amorphous region favored the d-limonene permeation. Moreover, the crystalline domains were

336

impermeable for the small molecules. The increased HPS relative crystallinity after CNC

337

addition contributed to more blocks to barrier d-limonene permeation. Additionally, at the larger

338

scale, the HPS mobility in the micro-ordered aggregated region was restricted. The increased

339

size of micro-ordered aggregated region indicated more HPS chains were restricted which

340

favored d-limonene barrier property.

341

Comprehensively, the multi-scale structures changes caused by CNC led to more restrained

342

HPS chains, which contributed to lower d-limonene permeability than tortuous path model

343

approximation. Even the increased random coils portion and decreased size of micro-ordered

344

aggregated region impaired d-limonene barrier property, new hydrogen bonding formation and

345

increased HPS relative crystallinity could be the reason for the lower d-limonene permeability

346

compared with tortuous path model approximation. Moreover, more hydrogen bonding

347

formation, higher HPS relative crystallinity and increased size of micro-ordered aggregated

348

region in CS0.5 and CR2 contributed to the lower d-limonene permeability than CS2 and CR0.5,

349

respectively. As for the films multi-scale structures regulation, the CNC aspect ratio and content

350

were proved to be effective independent variables to control d-limonene permeability. The

351

formulation of starch-based CNC nanocomposite films can be adjusted based on the requirement

352

of different d-limonene permeability. The structure-functional relationship of d-limonene


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353

permeability from the view of films multi-scale structures provided a new sight for flavor barrier

354

property in nanocomposite materials. The starch-based films with tunable flavor permeability

355

favored its application in biodegradable food packaging and flavor encapsulation.

356

ABBREVIATION USED

357

CNC, cellulose nanocrystal; CR, Rod-like cellulose nanocrystal; CS, Sphere-like nanocrystal;

358

HPS, Hydroxypropyl starch

359

ACKNOLEGEMENT

360

The present study is part of the Ph.D. work of Siyuan Liu and it was financially supported

361

under projects by the National Natural Science Foundation of China (No. 21376095, 31771930,

362

31130042, 31271824, 31401586), the Science and Technology Program of Guangzhou

363

(201607010109),

364

(2015KTSCX006), the Ministry of Education Program for Supporting New Century Excellent

365

Talents (NCET-12-0193) and the Fundamental Research Funds for the Central Universities.

366

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Amylose/Amylopectin Ratio of Esterified Starch-based Films on Inhibition of Plasticizer

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Control 2014, 36, 55-62.

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44. Li, X. X.; He, Y.; Huang, C.; Zhu, J.; Lin, A. H. M.; Chen, L.; Li, L., Inhibition of plasticizer

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migration from packaging to foods during microwave heating by controlling the esterified starch

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film structure. Food Control 2016, 66, 130-136.

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485


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486

FIGURE CAPTIONS

487

Fig.1 Schematic diagram of the diffusion chamber for electric nose testing (a); Detection of d-

488

limonene permeability of control film with electric nose (b); Sensor-7 signals for the

489

nanocomposite films (c); normalized intensity responses of sensor-7 (d)

490

Fig.2 The schematic diagram of tortuous path model

491

Fig.3 Relative permeability of d-limonene tested by gravimetric method and tortuous theory

492

model approximation (a); the relative d-limonene permeability deviation from tortuous theory

493

model approximation of the nanocomposites films (b)

494

Fig.4 Morphology of CS (a); CR (b); fracture surface of control film (c,d); fracture surface of

495

CS2 (e) and CR2 (f).

496

Fig.5 ATR-FTIR spectra of nanocomposite films

497

Fig.6 CP/MAS 13C-NMR spectra of starch-based nanocomposite films

498

Fig.7 Total change value of starch-based CNC nanocomposite films

499

Fig.8 XRD pattern of starch-based nanocomposite films (a) and the starch relative crystallinity in

500

the films (b)

501

Fig.9 SAXS spectra of the starch-based nanocomposite films

502

Fig.10 Guinier plots of the starch-based nanocomposite films (a) and Rg value of the films (b)

503 504 505 506 507



Page 24 of 35

Table 1 Relative area ratios of C1 and C4 peaks after deconvolution of starch-based nanocomposite films 13C-NMR spectra C1

C4

Sample

Center (ppm)

Area1 Center Area2 Center Area3 Are2+Area3 (%) (ppm) (%) (ppm) (%) (%)

Center (ppm)

Area (%)

Control CS0.5 CS2 CR0.5 CR2 CS CR

102.40 102.33 102.37 102.48 102.30 104.52 104.41

6.56 4.97 4.73 7.15 6.49 18.99 19.30

81.12 81.26 81.34 80.86 81.33 83.41 83.54

9.05 12.34 12.26 10.21 11.66 6.83 6.67

100.43 100.11 100.53 100.85 100.15

4.54 10.25 9.24 5.12 8.84

98.85 99.02 98.12 98.82 98.90

4.62 3.70 5.27 4.90 3.36


9.16 13.95 14.51 10.02 12.20

Page 25 of 35


Fig.1



Fig.2


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Fig.3



Fig.4


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Fig.5



Fig.6


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Fig.7



Fig.8


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Fig.9



Fig.10


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GRAPHIC FOR TABLE OF CONTENTS


Tunable d-Limonene Permeability in Starch-Based Nanocomposite

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