Microstructures, physical and sustained antioxidant properties of hydroxypropyl methylcellulose based microporous photophobic films

Journal Pre-proofs Microstructures, physical and sustained antioxidant properties of hydroxypropyl methylcellulose based microporous photophobic films Liang Zhang, Yu-Qi Lu, Jian-Ya Qian, Li-Na Yue, Qian Li, Li-Xia Xiao, Xiang-Li Ding, Cheng-Ran Guan PII: DOI: Reference:

S0141-8130(19)34621-5 https://doi.org/10.1016/j.ijbiomac.2019.10.187 BIOMAC 13688

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International Journal of Biological Macromolecules

Received Date: Revised Date: Accepted Date:

20 June 2019 10 October 2019 21 October 2019

Please cite this article as: L. Zhang, Y-Q. Lu, J-Y. Qian, L-N. Yue, Q. Li, L-X. Xiao, X-L. Ding, C-R. Guan, Microstructures, physical and sustained antioxidant properties of hydroxypropyl methylcellulose based microporous photophobic films, International Journal of Biological Macromolecules (2019), doi: https://doi.org/ 10.1016/j.ijbiomac.2019.10.187

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Microstructures, physical and sustained antioxidant properties of hydroxypropyl methylcellulose based microporous photophobic films Liang Zhang1, Yu-Qi Lu1, Jian-Ya Qian1, 2*, Li-Na Yue1, Qian Li1, Li-Xia Xiao1, 2*, Xiang-Li Ding Cheng-Ran Guan1, 2 School of Food Science and Engineering, Yangzhou University, Huayang Xilu 196, Yangzhou, Jiangsu 225127, People’s Republic of China 2

Jiangsu Key Laboratory of Dairy Biotechnology and Safety Control, Yangzhou University, Huayang Xilu 196,

Yangzhou, Jiangsu, 225127, People’s Republic of China

* Corresponding author. Tel: +86 189 0527 6343, +86 136 6524 8752. Fax: +86 514 8797 8096. E-mail address: [email protected] (Jian-Ya Qian); [email protected] (Li-Xia Xiao)

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Abstract: Hydroxypropyl methylcellulose (HPMC) / sodium citrate (SC) / lipid tea polyphenol (LTP) photophobic films with different pore sizes from micron scale to nanometer scale were prepared by regulating the SC content (1%-7%). The microstructures, physical and sustained antioxidant properties of these films were studied by using wide angel X-ray diffraction, small angle X-ray scattering (SAXS), scanning electron microscope, whiteness meter, ultraviolet spectrophotometer, texture analyzer and peroxide value test. Composite films with higher SC content showed larger pore size and whiteness. With the increasing SC content, crystallinity first increased then decreased. The addition of SC decreased the Ds (surface fractal dimension) value, smoothness of the cross-section structure, tensile strength, elongation and modulus of composite films. HPMC/SC/LTP microporous films possessed control-release property in oil system, reflected by the lowest peroxide value of peanut oil enclosed in film with 3% SC during three weeks, meaning this film showed the best sustained antioxidant property.

Keywords: Hydroxypropyl methylcellulose; microporous film; antioxidant properties

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1. Introduction Porous materials have been widely used to protect and control-release functional ingredients. The most used inorganic porous materials are carbon nanotubes [1], porous silicon [2], titanium dioxide [3]. However, the safety of these inorganic porous materials is to be discussed and their application in the food industry has been limited. Organic degradable polymers are also used to prepare porous wall materials to achieve control-release property [4, 5]. Commonly used organic degradable porous materials are chitosan [6, 7], HPMC/chitosan [8], cellulose [9], etc. The common methods for the preparation of these biodegradable porous polymer materials are freeze drying, heat-induced phase separation and supercritical fluids [10, 11]. Compared with freeze drying and supercritical fluids methods, heat-induced phase separation is less dependent on the expensive machine and of low-cost, which can promote their usage in the food industry. Previously, an EC-ethanol (a solvent)–water (a non-solvent) ternary system was used to form microporous ethylcellulose (EC) films based on the thermally induced micro-phase separation process [12]. Similarly, on the basis of the phase inversion technique, a polymer mixture (PLLA-methylene chloride-ethylacetate) were used to prepare porous poly (Llactide) films [13]. Hydroxypropyl methylcellulose (HPMC) is a kind of cellulose derivative which is widely used in edible films [14,15]. Sodium citrate (SC) is a safety salt, which is widely used as food additives. In our previous research, different kinds of salts were blended with HPMC to produce microporous photophobic films [16]. SC was found to endow HPMC film microporous structure and photophobic property without showing large influence on its mechanical properties [16]. In this case, the microporous films may be formed through the thermally induced solid-liquid phase separation of polymer solution [17]. Specifically, SC can cause the salting-out effect [18], which 3

may facilitate the thermally induced solid-liquid phase separation of HPMC solution, resulting into the formation of HPMC based microporous films after water evaporated. This film possesses both porous structure and photophobic property, which is not only of potential to be used as control-release material, but also can overcome the light-induced negative effect of functional food ingredients, such as oxidation of light-sensitive moieties (carotenoids and vitamins, etc.), variations of color, disappearance of aroma, and formation of off-flavors [19-23]. This kind of edible film possesses great application prospect in control-releasing and protecting light sensitive food ingredients. Lipid-soluble tea polyphenols (LTP), an antioxidant, is prominent in the oil system, almost as effective as tert-butylhydroquinone (TBHQ) in some oil. It can retard lipid oxidation, improve oil quality and prolong oil shelf life. However, direct addition of LTP into fatty foods induces some problems: 1) the bitter taste of LTP affects the taste of food; 2) LTP contains multiple phenolic hydroxyl groups, which have poor stability and are easily affected by light and other factors, resulting in the occurrence of free radical oxidation reactions and decreased antioxidant property. Therefore, proper photophobic embedding materials should be put forward to protect the antioxidant, and the embedding material is also expected to possess control-release property, which can assist in extending the shelf life of oil products. In this research, HPMC/SC microporous photophobic film was selected as the embedding material for LTP. HPMC/SC/LTP films with different pore sizes were prepared by regulating the SC content to achieve sustained antioxidant property. The microstructure (crystalline, fractal and morphological structure), physical properties (whiteness, transmittance and mechanical properties) and sustained antioxidant effects of those composite films of the HPMC/SC/LTP

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composite films were investigated. The relationship between the multiscale structures and properties were established.

2. Materials and Methods 2.1 Materials HPMC (ZW-E6) (methoxy content: 29%; hydroxypropoxy content: 8.4%; the viscosity of 2% (w/w) HPMC: 6 mPa.s; weight-average molecular weight (Mw): 2.441 × 104 g/mol) was purchased from Hopetop Pharmaceutical Company (China). Tween 20 (chemical purity), sodium citrate (ı 99.0%, analytical grade), glacial acetic acid (ı 99.5%, analytical grade), chloroform mixture (analytical grade), potassium iodide (ı 99.0%, analytical grade) and sodium thiosulfate (analytical grade) were purchased from Sinopharm Chemical Reagent Co., Ltd (China). Peanut oil (fat content ı 99.9%) was purchased from Shandong Luhua Group Co., Ltd (China). Lipid tea polyphenol (ZC01, tea polyphenol content ı 90.0%) was obtained from Hangzhou Puremedie Biological Technology Co., Ltd (China).

2.2 Film preparation HPMC powder (5% mass concentration) and different contents of SC (0, 1, 2, 3, 5 and 7% based on HPMC weight) were added to 100 mL beakers, respectively, followed by the addition of an emulsion (1.6% based on HPMC weight) which constituted a mixture of LTP and Tween 20 (emulsifier) with a mass ratio of 1:1. Then, hot water of 85°C was added to the beaker to disperse HPMC to maintain HPMC mass concentration of 5%. The mixed solutions were 5

maintained at 70°C and slowly stirred for 20 min with a magnetic stirrer to obtain homogeneous dispersion. The dispersion was cooled to room temperature naturally compared by mild stirring and stirred for another 30 min at room temperature until HPMC was dissolved completely. Before casting film, all samples were defoamed in a vacuum environment. 40 g of the solution was casted onto a square polymethyl methacrylate (PMMA) plate with bottom size of 18×18 cm and dried at room temperature for 12 h. The films were peeled off from the plate and kept at 59% RH (controlled with saturated NaBr solution at room temperature) for further characterization.

2.3 X-ray diffraction (XRD) measurement XRD pattern of the film samples were identified by using a Bruker AXS D8 Advance X-ray diffractometer (Bruker Inc., Germany) with Ni-filtered Cu Kα radiation at a voltage of 40 kV and a current of 40 mA (λ = 0.154 nm). The scanning scope of 2θ was 3-60° at a scanning rate of 3° min-1. The crystallinity of the film was calculated as the percentage ratio of diffraction peak area (crystalline area: ac) to total diffraction area (at) [24]. The diffraction peak was separated with the smooth curve connecting each point of the peak valley in the range of 30° and 4°, and the area between the diffraction curve and the smooth curve was regarded as ac. The area between the diffraction curve and the straight line joining the two points of intensity at 30° and 4° was regarded as at.

2.4 Small angle X-ray scattering (SAXS) measurement

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The experiments were carried out using a Nano STAR small-angle X-ray scattering machine (Bruker-AXS, Germany) operated at 50 mA and 40 kV, using Cu Kα radiation with a wavelength of 0.154 nm as X-ray source. Each sample was placed in a paste sample cell and exposed at the incident X-ray monochromatic beam for 10 min. The data, recorded using an image plate, were collected by the IP Reader software. All data were normalized, and the background intensity and smeared intensity were removed using SAXS quant software 3.0 for further analysis. The concept of fractal dimension is produced to describe a random substance with expansion symmetry after a dimensional change [25]. The fractal system can be divided into mass fractal dimension (Dm) and surface fractal dimension (Ds). A double logarithmic SAXS curve was applied to the films, from which the fractal dimension D of the starch can be calculated, according to the Power's law below I‫ן‬q-α

(1)

where I is the scattering intensity, q is the scattering vector, and α is used as an index to measure the surface fractal or mass fractal characteristics of the scatter [26]. -α refers to the slope of lnI-lnq in SAXS graph. The relation between α and D goes as Ds = 6 - α (3 < α < 4) when a surface fractal exists, and Dm = -α (1 < α < 3), which is regarded as a mass fractal. Ds can be used as an indicator of the degree of smoothness, and the value of Ds is equal to 2 when the surface of the scattering objects is smooth. Dm is used to predicate the compactness [14, 26, 27]. The scattering objects of surface fractal are more compact than those of mass fractal.

2.5 Scanning electron microscopy (SEM) observation 7

Specimens were glued on specimen stubs using silver conducting tape and coated with gold-palladium using a sputter coater (BAL-TEC SCD 500, Liechtenstein). The cross section morphology of the cast films were observed using an environmental scanning electron microscope (XL 30 ESEM, Philips, Holland) with the parameters HJ: 20 kV, resolution ratio: 3.4 nm, and spot: 4.

2.6 Whiteness measurement An Automatic Whiteness Meter (ADCI-60, CTK, China) was used to measure the whiteness of the films. Measurement was done before the calibration by using standard white baseboard. The reported values were the average of 3 readings taken randomly on each film sample.

2.7 Transmittance measurement Put rectangle strips (40 mmൈ 8 mm) cut from films into the cuvette vertically with the strips’ surface in the face of the light source. An ultraviolet spectrophotometer (Lambda 35, PerkinElmer, Singapore) was used to measure the transmittance of the different films. The transmittance of wavelength between 200-800 nm was recorded in this work.

2.8 Mechanical property measurement

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The films were cut into rectangle strips (60 mmൈ 6 mm). The thickness of all these films were measured individually and they were in the range of 0.053 ± 0.008 mm. The load cell and original clamp distance is 1000 N and 40 mm, respectively. The tensile properties of specimens were measured using a texture analyzer (TMS-Pro, Food Technology Corporation, USA) in a tensile mode. Each test trial per film consisted of five replicates. Tensile strength, elongation and Young’s modulus were measured at a crosshead speed of 10 mm/min. Where, tensile strength (σt) is the ratio of rupturing force to cross-sectional area of the specimen, and elongation (εt) is the strain value when samples ruptures, Young’s modulus (σs) is the slope of the elastic deformation zone of the stress-strain curve. They were calculated based on equation (2), (3), and (4), respectively. σt = p/(bd)

(2)

where, p is the rupturing force (N)˗b is the sample width (6 mm)˗d is the sample thickness (mm). εt = (L-L0)/L0

(3)

where, L is the clamp distance when sample ruptures (mm)˗L0 is the original clamp distance (40 mm). σs = ᇞf /ᇞε

(4)

where, ᇞf is the variation of stress between two points in the elastic deformation zone of the

stress-strain curve, and ᇞε is the variation of strain between two points in the elastic deformation

zone of the stress-strain curve.

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2.9 Peroxide value (POV) Analysis The films were made into a 4 cm × 9 cm bag through four sides heat sealing by using a Deli 16499 hand-pressed plastic sealing machine in four gear. 4.5 g of oil was enclosed into different bags and stored at room temperature (25 ± 2Ԩ), the POV was measured every other week. The oil stored into a sealed polyethylene terephthalate (PET) bottle was set as a control sample and marked as “oil” in Fig. 6. POV was determined according to the China National standard method GB 5009.227üü2016. The oil sample was dissolved in 30 mL of acetic acid/chloroform mixture (3/2, v/v) solution within a 250 mL Erlenmeyer flask. Then saturated potassium iodide solution (0.5 mL) was added into the flask and the flask was agitated for 1 min. After addition of distilled water (50 mL), the mixture was titrated against sodium thiosulfate (0.002 M) with starch as an indicator. A blank titration without oil was treated the same way. POV (mequiv of oxygen kg-1) was calculated using the formula below: ܱܸܲ ൌ ͳʹǤ͸ͻ ൈ ܸ ൈ ܿȀ݉

(5)

where, V is the volume of sodium thiosulfate solution (blank corrected) in mL, c is the

normality of the sodium thiosulfate solution, and m is the weight of the oil sample in g. Each test trial per sample consisted of three replicates.

2.10 Statistical analysis Data were analyzed by using SPSS Statistics 19 (IBM Software Inc., NY, USA) and presented as means ± standard deviations (SD). Means were compared using one-or two-way analysis of variance (ANOVA) followed by Tukey's multiple comparison tests. Numbers bearing 10

different letters mean significant (P < 0.05), numbers bearing same letter mean not significant (P > 0.05).

3. Results and discussion 3.1 Microstructures of HPMC/SC/LTP film 3.1.1Porous morphology of HPMC/SC/LTP film As shown in

1, the cross-section of HPMC film is smooth. Compared with the HPMC

film, some embossment appeared in HPMC/LTP film, which may be because of the incompatibility induced by the formation of emulsion, similar embossment was also observed in HPMC/rosemary oil system in a previous research [25]. While, after the addition of SC, some holes with different sizes were observed for HPMC/LTP/SC films. During the drying process, when water content is decreased to some extent, the increasing concentration of SC can induce the salting-out effect of HPMC and solidliquid phase transition, thus, the HPMC macromolecules aggregated and formed clusters. Further water evaporation induced the formation of HPMC coagulation phase which enclosed the remaining water phase. Ultimately, the enclosed water evaporated and micro-pores formed. After the addition of 1% SC, small round pores were observed. With the increasing content of SC, the holes became large with relative rough fracture surface and the hole number increased. Most of the holes were not round, but with oval structures, so it is much more accurate to choose average pore area instead of diameter to describe hole size. The average pore area (APA) and pore distribution proportions (PDP) of HPMC/SC/LTP films calculated by using

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Image J was shown in Table 1. APA of 0.324, 0.691, 0.723, 1.945 and 2.557 μm2 were observed for HPMC/SC/LTP film samples with 1%, 2%, 3%, 5% and 7% SC, respectively. And from PDP data, it can be seen that with the increase of SC content, proportions of pores with smaller areas is decreased, and proportions of pores with larger areas is increased, which contributed to larger APA values with increasing SC content. This is because when the SC concentration is higher, salting-out effect is intensified, the HPMC macromolecules may aggregated and formed larger clusters which contains much more water. Therefore, after evaporation, larger pores formed. It can be concluded that the hole size can be well regulated from micron scale to nanometer scale by simply changing SC content.

3.1.2 Crystalline structures of HPMC/SC/LTP films The cast films prepared from HPMC solutions exhibited two relative broad diffraction peaks at 7.8͘and 20͘(

2), which were the typical semi-crystalline peaks of native HPMC

[29]. After the addition of LTP, the widths of these two peaks did not change, meaning similar crystalline integrity. While, lower crystallinity was observed in Table 2, which may be due to the appearance of the emulsifier and LTP which inhibit HPMC chains to combine. Compared with HPMC/LTP, the addition of lower content of SC (1%-3%) did not show much influence on the width of HPMC/LTP films, meaning similar crystal integrity. And, increased crystallinity was observed for these films (Table 2), which may be because that fewer SC can promote the movement of HPMC chains as plasticizers, thus increasing the collision and recombination of HPMC molecular chains, and resulting in increased crystallinity. However,

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with the further increasing of SC content (5% and 7%), the crystalline peak at 7.8͘ became wider (as circled in Fig. 2), meaning lower crystalline integrity. Decreased crystallinity was observed with the further increasing of SC content to 5% and 7% (Table 2), which was similar with that of HPMC/LTP film, which might be because that the interrupting (as a new obstructive ingredients) and promoting effects (similar as plasticizers) of SC to HPMC molecular chains balanced at higher SC content.

3.1.3 Fractal structures of HPMC/SC/LTP films From

3a, it can be seen that the scattering intensity increased after the introduction of

LTP and SC. And, with the increasing SC content, the scattering intensity of the films increased, which could be attributed to the increased difference value between the electron density in crystalline region and amorphous region. Loose amorphous region which can increase the difference value was also observed in HPMC/CaCl2 [30] and HPMC/sodium dihydrogen phosphate film [31], proved by decreased Tg of HPMC based system after introduction of CaCl2 or sodium dihydrogen phosphate. The slope of the straight portion (-α) in the graph can be calculated from

3b, and the

fractal dimensions calculated from α are shown in Table 3. It is seen that all the samples showed surface fractal, the addition of LTP increased the Ds, meaning that fractal structure of HPMC/LTP was less smooth and compact. The scattering objects in HPMC/SC/LTP film showed lower Ds than that of HPMC/LTP, meaning that these scatters were much more compact and smooth. Fractal structures of HPMC/SC/LTP samples with more than 1% SC showed similar

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Ds values, which were a little smaller than those with 1% SC, meaning fractal structures of HPMC/SC/LTP film with higher SC were more smooth and compact than those with 1% SC.

3.2 Physical properties of HPMC/SC/LTP films 3.2.1 Whiteness of HPMC/SC/LTP films The photos and blue whiteness of HPMC and HPMC/SC films with HPMC, HPMC/LTP, and HPMC/SC/LTP films are shown in Fig. 4A and Fig. 4B, respectively. HPMC and HPMC/LTP films were transparent with blue whiteness of around 3%. With increasing SC content, all the HPMC/SC/LTP films were white with increased blue whiteness. To be specific, blue whiteness were 10.30%, 10.89%, 11.65%, 15.25%, 17.36% for HPMC/SC/LTP films with 1%, 2%, 3%, 5% and 7% SC, respectively, indicating that these films were photophobic. The changes of transmittance of film were due to the changes of supramolecular structures in a previous research related to HPMC/surfactants film [32]. Specifically, increased crystallinity, more compact fractal structure and more porous structures are deemed to decrease the transmittance and contribute to the photophobic property. For HPMC/SC/LTP films with 1%-3% SC, increased crystallinity, more compact fractal structure and more porous structures were observed, which may contribute to these films’ whiteness property. For HPMC/SC/LTP films with 5%-7% SC, similar crystallinity compared with HPMC/LTP film was observed, then the more compact fractal structure and more porous structures may contribute to the whiteness property. The porous morphology is the dominating factors for the formation of the white color of these films since the difference between the refraction index of polymer phase and air phase of

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these porous materials can lead to appearance of white color, which was similar to foamed (porous) white plastic materials.

3.2.2 Transmittance of HPMC/SC/LTP films The transmittance of HPMC and HPMC/SC/LTP films was shown in Fig. 5. With the increasing wavelength, the transmittance first increased then achieved balance. Pure HPMC film showed balanced transmittance of around 90%. After adding LTP, the transmittance of HPMC/LTP film did not change much. After adding SC, the transmittance decreased. With the increasing SC content, the transmittance decreased from around 40% for HPMC/1%SC/LTP film to around 10% for HPMC/7%SC/LTP film, meaning these films were becoming more and more photophobic. Similar reason was for the changes of transmittance with the changes of whiteness.

3.2.3 Mechanical properties of HPMC/SC/LTP films The tensile test records the force applied to the sample and the deformation of the sample to obtain the tensile stress-strain curve during the stretching process. From the tensile stress-strain curve, the mechanical properties of the material, such as tensile strength, elongation and modulus can be calculated. Compared with pure HPMC film, the tensile strength, elongation and modulus of HPMC/LTP decreased after the addition of LTP

6), which may be due to the coarser cross-

section morphology. With increasing SC content, these mechanical parameters of HPMC/SC/LTP films decreased. It may be related to the changes of the crystallinity, fractal and 15

porous morphological structures of the film. From

2 and 3, it can be seen that

HPMC/SC/LTP films with 1 to 3% SC showed increased crystallinity, while HPMC/SC/LTP films with 5 to 7% SC showed similar crystallinity with that of HPMC/LTP films; the compactness and smoothness of fractal dimension first increased and then remained unchanged with the increase of SC. Normally, increased crystallinity and compactness of fractal structure can increase tensile strength and modulus of films similar with the effect of nano-reinforced particles [16]. In this system, HPMC/SC/LTP films which possessed higher or similar crystallinity and higher fractal compactness than HPMC/LTP film did not correspond with the presented smaller tensile strength and modulus. This was because that less smooth and more porous morphological structures of HPMC/SC/LTP films can result in decreased mechanical parameters, thus surpassing the influence of crystalline structure and fractal structure and dominating the decreasing trends of the mechanical parameters.

3.3 Sustained antioxidant property of HPMC/SC/LTP films The POV of oil samples enclosed by different HPMC samples stored at different periods were shown in

7. The larger the POV, the larger extent of oil oxidation. The POV of all the

samples increased with the storage time for all the samples except for HPMC/SC/LTP films with 2% and 3% SC, which showed no significant changes between 7 and 14 days, meaning these films showed good antioxidant property during these periods. For samples in the same storage periods, the POV of samples enclosed with different films were different. For samples stored for 7 and 21 days, oil enclosed in the HPMC film showed a little larger POV than the oil sample enclosed in sealed plastic bottle, which was because that HPMC film showed a little larger extent

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of oxygen permeability than PET plastic material. Similar POV of oil samples packaged in HPMC and HPMC/LTP film was observed within the three weeks test (P>0.05), this might be because that lower LTP was released into the oil system from the HPMC/LTP film since its imperforate cross-section morphology. The POV of oils enclosed in HPMC/SC/LTP film first decreased and then increased with the increasing SC content for samples stored for 14 and 21 days, with the lowest point at a SC content of 3%. This might be mainly related to the pore morphology of these films. Pores can induce both an enhanced releasing effect of LTP due to its relative loose structure, and a slowing down releasing effect of LTP due to its maze-like path which may increase the length of dispersion. With the increasing SC content (<3%), decreased POV value was observed, meaning that active LTP content increased in the oil, it was guessed that the enhanced releasing effect due to its relative loose structure may dominate. Films with a 3% SC content showed the lowest POV value, meaning that the largest content of active LTP was in the oil system, which might be due to its moderate pore size and quantity which enhanced the releasing effect of LTP to the largest extent. With the further increase of SC content (5% and 7%), the slow-down effect of much denser maze-like path may dominate, thus, resulting in relative lower LTP in oil. Therefore, higher POV was observed for oil samples sealed in HPMC films with 5% and 7% SC.

4. Conclusion HPMC/SC/LTP microporous films with different pore sizes and microstructures to achieve photophobic and sustained antioxidant properties of oil system were established. The lowest POV was observed for oil samples sealed in HPMC/3%SC/LTP film. The pore number and size

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increased with increasing SC content. Surface fractal dimensions decreased after adding SC, representing more compact and smoother scatters formed. The addition of SC from 1 to 3% content increased the crystallinity of HPMC/LTP film, while films with 5 to 7% SC showed similar crystallinity with that of HPMC/LTP film. With the increase of SC content, increased whiteness, decreased transmittance, tensile strength, elongation and modulus were observed.

The authors would like to acknowledge the research funds Natural Science Foundation of China (31901604), Natural Science Foundation of Jiangsu Province (BK20160467), Science & Technology Innovation Foundation of Yangzhou University (2017CXJ109), Postgraduate Research & Practice Innovation Program of Jiangsu Province (XSJCX18_102) and Qing Lan Project of Yangzhou University.

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[17] D. R. Lloyd, K. E. Kinzer, H. S. Tseng, Microporous membrane formation via thermally induced phase separation I. Solid-liquid phase separation, J. Membrane Sci. 52 (1990) 239-261. [18] R. Sadeghi, F. Jahani, Salting-in and salting-out of water-soluble polymers in aqueous salt solutions, J. Phys. Chem. B 116 (2012) 5234-5241. [19] F. Galgano, M. C. Caruso, N. M. Ventura, C. Magno, F. Favati, Effects of anti-UV film and protective atmosphere on fresh-cut iceberg lettuce preservation, Acta Aliment. 46 (2017) 35-42. [20] C. Olarte, S. Sanz, J.F.E. chavarri, F. Ayala, Effect of plastic permeability and exposure to light during storage on the quality of minimally processed broccoli and cauliflower, Food Sci. Tech. 42 (2009) 402-411. [21] F. Ayala, J. F. Echávarri, C. Olarte, S. Sanz, Quality characteristics of minimally processed leek processed using different films and stored in lighting conditions, Int. J. Food Sci. Tech. 44 (2009) 1333-1343. [22] S. Sanz, C. Olarte, J. F. Echavarri, F. Ayala, Influence of exposure to light on the sensorial quality of minimally processed cauliflower, J. Food Sci. 72 (2007) S12-S18. [23] K. Kakinoki, K. Yamane, R. Teraoka, M. Otsuka, Y. Matsuda, Effect of relative humidity on the photocatalytic activity of titanium dioxide and photostability of famotidine, J. Pharm. Sci. 93 (2004) 582-589. [24] S. Nara, T. Komiya, Studies on the relationship between water saturated state and crystallinity by the diffraction method for moistened potato starch, Starch/Stärke 35 (1983) 407-410. [25] B. B. Mandelbrot, J. A. Wheeler, The fractal geometry of nature, Am. J. Phys. 51 (1998) 468. [26] T. Suzuki, A. Chiba, T. Yano, Interpretation of small angle X-ray scattering from starch on the basis of fractals, Carbohydr. Polym. 34 (1997) 357-363. 21

[27] B. Zhang, X. Li, J. Liu, F. Xie, L. Chen, Supramolecular structure of A- and B-type granules of wheat starch, Food Hydrocolloid. 57 (2013) 348-355. [28] N. Perone, E. Torrieri, S. Cavella, P. Masi, Effect of Rosemary oil and HPMC concentrations on film structure and properties, Food Bioprocess Technol., 7 (2014) 605-609. [29] N. S. Rani, J. Sannappa, T. Demappa, Mahadevaiah, Effects of CdCl2 concentration on the structural, thermal and ionic conductivity properties of HPMC polymer electrolyte films, Ionics 21 (2014) 133-140. [30] S. Shiraishi, Y. Sakata, H. Yamaguchi, Practical application to time indicator of a novel white film formed by interaction of calcium salts with hydroxypropyl methylcellulose, Int. J. Pharm., 383 (2009) 255-263. [31] L. Zhang, Y.-Q. Lu, Y.-L. Peng, Y.-X. Yu, Y. Zhao, Y. Ma, Microstructures and properties of photophobic films composed of hydroxypropyl methylcellulose and different salts, Int. J. Biol. Macromol. 120 (2018) 945-951. [32] R. Villalobos, J. Chanona, P. Hernandez, G. Gutierrez, A. Chiralt, Gloss and transparency of hydroxypropyl methylcellulose films containing surfactants as affected by their microstructure, Food Hydrocolloid. 19 (2005) 53-61.

22

Table 1 Average pore area (APA) and pore distribution proportions (PDP) of HPMC, HPMC/LTP, and HPMC/SC/LTP films. HPMC

PDP (%)

HPMC

HPMC

HPMC

HPMC

HPMC

HPMC

/ LTP

/

/

/

/

/

1%SC/

2%SC/

3%SC/

5%SC/

7%SC/

LTP

LTP

LTP

LTP

LTP

APA (μm2)

——

——

0.324

0.691

0.723

1.945

0-0.3 (μm2)

——

——

70%

48%

25%

29%

0.3-0.6 (μm2)

——

——

20%

26%

35%

17%

4%

0.6-1 (μm2)

——

——

10%

7%

5%

13%

16%

1-2 (μm2)

——

——

7%

35%

13%

36%

2-3 (μm2)

——

——

4%

8%

12%

3-4 (μm2)

——

——

7%

8%

12%

4-9 (μm2)

——

——

12%

20%

23

2.557

Table 2 Crystalline degree (CD) of HPMC, HPMC/LTP, and HPMC/SC/LTP films HPMC

HPMC/ LTP

HPMC/

HPMC/

HPMC/

HPMC/

HPMC/

1%SC/

2%SC/

3%SC/

5%SC/

7%SC/

LTP

LTP

LTP

LTP

LTP

46.7±0.8d

34.9±1.4a

35.2±1.8a

44.3±1.3c

CD (%) 42.6±1.4c

34.8±1.3a

40.1±1.2b

d

24

Table 3 Slope (−α) of ln I–ln q curve and surface/mass fractal dimension (Ds/Dm) of HPMC, HPMC/LTP, and HPMC/SC/LTP films HPMC

HPMC/

HPMC/

HPMC/

HPMC/

HPMC/

HPMC/

1%SC/

2%SC/

3%SC/

5%SC/

7%SC/

LTP

LTP

LTP

LTP

LTP

-3.35±

-3.47±

-3.46±

LTP

-α

-3.43± 0.024bc

Ds

2.57± 0.024bc

-3.18± 0.010a 2.82± 0.010a

0.029b 2.65± 0.029b

0.021c 2.53±

0.045c 2.54±

0.021c

25

0.045c

-3.43± 0.05bc 2.57± 0.05bc

-3.48± 0.025c 2.52± 0.025c

Figure captions

Fig. 1 Cross-section morphology of HPMC, HPMC/LTP, and HPMC/SC/LTP films. HPMC film (A); HPMC/LTP film (B); HPMC/1%SC/LTP film (C); HPMC/2%SC/LTP film (D); HPMC/3%SC/LTP film (E); HPMC/5%SC/LTP film (F); HPMC/7%SC/LTP film (G). Fig. 2 XRD spectra of HPMC, HPMC/LTP, and HPMC/SC/LTP films. Fig. 3 SAXS spectra of HPMC, HPMC/LTP, and HPMC/SC/LTP films. I-q curve (a); Ln I-Ln q curve (b). Fig. 4 Photos (A) and blue whiteness (B) of HPMC, HPMC/LTP, and HPMC/SC/LTP films. HPMC, 0%SC, 1%SC, 2%SC, 3%SC, 5%SC and 7%SC represent HPMC film (a), HPMC /LTP film (b), HPMC/1%SC/LTP film (c), HPMC/2%SC/LTP film (d), HPMC/3%SC/LTP film (e), HPMC/5%SC/LTP film (f) and HPMC/7%SC/LTP film (g), respectively. Fig. 5 Transmittance of HPMC, HPMC/LTP, and HPMC/SC/LTP films. Fig. 6 Mechanical properties of HPMC, HPMC/LTP, and HPMC/SC/LTP films. Tensile strength (a); Elongation (b); Modulus (c). HPMC, 0%SC, 1%SC, 2%SC, 3%SC, 5%SC and 7%SC represent HPMC film, HPMC/LTP film, HPMC/1%SC/LTP film, HPMC/2%SC/LTP film, HPMC/3%SC/LTP film, HPMC/5%SC/LTP film and HPMC/7%SC/LTP film, respectively. Fig.7 Peroxide values of oils enclosed in HPMC, HPMC/LTP and HPMC/SC/LTP bags. Lowercase letters were annotated for the significance analysis among different samples stored at the same periods; capital letters were annotated for the significance analysis among the same samples stored at different periods.

26

Fig. 1

A

B

C

D

E

F

G

27

Fig. 2

HPMC

Intensity (a.u.)

HPMC/LTP HPMC/1%SC/LTP

HPMC/2%SC/LTP HPMC/3%SC/LTP HPMC/5%SC/LTP HPMC/7%SC/LTP

3

13

23

33

2θ (Degree)

28

43

Fig.3

29

Fig. 4

A

a

B

b

c

d

f

e

g

20 e

Blue whiteness (%)

18 d

16 14 12

b

bc

c

10 8 6 4

a

a

HPMC

0%SC

2 0 1%SC

2%SC

3%SC

5%SC

HPMC and HPMC/SC/LTP film

30

7%SC

Fig. 5 HPMC

100

HPMC/LTP

Transmittance (%)

90

HPMC/1%SC/LTP

80

HPMC/3%SC/LTP

70

HPMC/5%SC/LTP

60

HPMC/7%SC/LTP

50 40

30 20 10 0

200

300

400

500

600

Wavelength (nm)

31

700

800

Fig. 6

a

40 a

a

a

Tensile strength˄MPa˅

35

a

a

30 b

25

b

20 15 10 5 0 HPMC

0%SC

1%SC

2%SC

3%SC

5%SC

7%SC

HPMC and HPMC/SC/LTP film

b

10 a

9

ab

Elongation˄%˅

8

bc

7

cd

cd

6

d

d

5%SC

7%SC

5 4 3 2 1 0

HPMC

0%SC

1%SC

2%SC

3%SC

HPMC and HPMC/SC/LTP film

c

1400

a

ab ab

Modulus˄MPa˅

1200

bc

1000

cd

d d

800 600 400

200 0

HPMC

0%SC

1%SC

2%SC

3%SC

5%SC

HPMC and HPMC/SC/LTP film

32

7%SC

Fig. 7 0.6

D DD DCCDD

Oil

a

POV (g/100g sample)

HPMC

0.5

b

HPMC/LTP

ab

b

bc c

HPMC/1%SC/LTP

0.4 0.3 0.2

HPMC/2%SC/LTP HPMC/3%SC/LTP HPMC/5%SC/LTP

B B BB B BBB

ab ab HPMC/7%SC/LTP b a ab b b ab

C C CC BB CC ab ab

ab

b

ab

c c c

AAA A AAAA

a a a a a a a a

0.1

0 0

b

7

14

Storage time (day)

33

21

ab