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nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus
Accepted Manuscript Optimization of konjac glucomannan/carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus
Rongfei Zhang, Xiangyou Wang, Ling Li, Meng Cheng, Liming Zhang PII: DOI: Reference:
S0141-8130(18)34532-X https://doi.org/10.1016/j.ijbiomac.2018.10.165 BIOMAC 10816
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
28 August 2018 11 October 2018 24 October 2018
Please cite this article as: Rongfei Zhang, Xiangyou Wang, Ling Li, Meng Cheng, Liming Zhang , Optimization of konjac glucomannan/carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus. Biomac (2018), https://doi.org/10.1016/ j.ijbiomac.2018.10.165
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ACCEPTED MANUSCRIPT
Optimization of konjac glucomannan/carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus Rongfei Zhang, Xiangyou Wang*, Ling Li, Meng Cheng, Liming Zhang
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School of Agricultural Engineering and Food Science, Shandong University of Technology, Zibo 255000, China
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Tel.:+86-533-2780897 Fax: +86-533-2780897
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*Corresponding author: Prof. Xiangyou Wang, E-mail address: [email protected] (X.
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Wang)
Abstract: Nano-SiO2 was inserted into konjac glucomannan (KGM)/carrageenan
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(KC) coatings to improve the properties of the coating. The optimization of the concentrations of the nano-SiO2, KGM, and KC of the coatings was investigated
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using a response surface method. The coatings were characterized by scanning
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electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. The effect of the
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nano-SiO2/KGM/KC coatings on the postharvest quality of the white mushrooms
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stored at 4 ± 1 °C was determined. The results showed that the nano-SiO2/KGM/KC coatings exhibited the optimal properties at a nano-SiO2 concentration of 0.3%, a KC concentration of 0.6%, and a KGM concentration of 0.48%. The water vapor transmission rate, transparency, tensile strength, oxygen transmission rate, and carbon dioxide transmission rate were 62.31 g/(m2·d), 83.41%, 323.16N, 0.015 g/(m2·d), 0.18 g/(m2·d) respectively. The nano-SiO2 decreased the gas permeability of the coatings. It demonstrated that the incorporation of the nano-SiO2 delayed the effect of the UV 1
ACCEPTED MANUSCRIPT light on the food quality because it increased the absorbance of the UV light (300 nm) by the KGM/KC three fold. The application of the nano-SiO2/KGM/KC coatings represents a feasible and effective technique for extending the storage time of white mushrooms.
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Keywords: Nano-SiO2; coatings; Agaricus bisporus
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1 Introduction
The quality of white mushrooms (Agaricus bisporus) deteriorates rapidly after
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harvest, which affects the postharvest storage and transportation time. The high
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metabolic activity, respiration rate, and dehydration are responsible for the rapid decay of mushrooms [1-2]. Mushrooms have a relatively short shelf life compared to
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other fresh vegetables and this has been ascribed to the lack of cuticles in white
microbial attack [3].
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mushrooms that act as a physical barrier against mechanical damage, water loss, or
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The recent development in coating products has provided new opportunities to
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extend the freshness of food products. Coatings change the environmental storage conditions to maintain the sensory properties and ensure the product quality [4]. Many research studies have been published on the properties of edible coatings for the preservation of fruits and vegetables. Fakhouri et al. [5] found that red crimson grapes coated with starch/gelatin edible coatings had a lower weight loss than the control group after 21 d of cold storage. Poly-ε-lysine/alginate-based edible coatings preserved the quality of fresh-cut kiwifruit [6]. Fruits and vegetables require different 2
ACCEPTED MANUSCRIPT coatings to maintain their quality because the ingredients in the coatings may affect the color, flavor, and taste of the product. Konjac glucomannan (KGM) and carrageenan (KC) are excellent natural macromolecular materials used for transparent and flavorless coatings. A strong synergistic gelation effect exists between
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KGM and KC [7]. KGM/KC edible coatings possess several desirable properties that
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are not present in the individual monomer glue. However, when combined, they form
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coatings with low friability, high elasticity, and low water release.
It has been demonstrated that nano-based materials with excellent properties
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represent a novel packaging technology in the postharvest industry [8].
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Nanotechnology has been increasingly used recently in many products and in food-contact polymers because the nanoparticles improve certain properties of the
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neat polymers or provide new functions [9]. Nano-SiO2 is one of the most widely
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used inorganic nano-materials in organic material modification. It can be compounded with many macromolecule polymers to prepare nanocomposite coatings to improve
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the coating properties [10]. The European Center for Ecotoxicology and Toxicology
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of Chemicals and the Organization for Economic Cooperation and Development found no acute toxicity of amorphous SiO2 after conducting a toxicity study on rats through oral and dermal exposure, with the highest exposure concentration of 20 g SiO2/kg body weight [11-12].The addition of nano-SiO2 to alginate coatings decreased the water vapor permeability by 10.26-16.57% [13]. Song et al. [14] demonstrated that chitosan/nano-silica greatly improved the postharvest quality and antioxidant capacity of loquat fruit during cold storage. However, studies have been 3
ACCEPTED MANUSCRIPT rarely conducted on the effect of KC/KGM /nano-SiO2 coatings on perishable white mushrooms. The properties, microstructure, preservation mechanism, and optimum content of the nano-SiO2 in the composite coatings also have not been fully elucidated. Hence, this study focuses on the optimum content, the morphology, and the properties
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of the nano-SiO2 composite coatings to evaluate the advantages of the coating for
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food preservation.
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The objective of this study is to determine the optimum ratio of the components in the KC/KGM/ nano-SiO2 coatings to extend the storage time of postharvest white
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mushrooms. The water vapor transmission rate (WVTR) is an important characteristic
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of the coatings to achieve the preservation of white mushrooms. The nano-SiO2 was incorporated into the KC/KGM coatings to enhance the coating’s properties. The
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effects of the concentrations of the nano-SiO2, KGM, and KC on the water
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permeability of the KC/KGM coatings were investigated using a response surface methodology (RSM). The coatings were characterized by scanning electron
and
Ultraviolet-visible (UV-vis) spectroscopy. The
effect
of the
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(XRD),
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microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction
nano-SiO2/KGM/KC coatings on the postharvest quality and shelf life of the white mushrooms stored at 4 ± 1 °C was determined.
2 Materials and methods
2.1 Materials The KGM powder and KC powder are considered food-grade. The nano-SiO2 4
ACCEPTED MANUSCRIPT (HTSi-01, size 20 nm, white fluffy powder, specific surface area ≥ 600 m2/g, high adsorption, many surface hydroxyl groups, good hydrophilicity) was purchased from Haitai Nanotechnical Co., Ltd. (Nanjing, China). The white mushrooms were harvested in Dezhou, Shandong, China. Prior to the package test, mushrooms with
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uniform characteristics (size, shape, and color) were selected as the experimental
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material. The mushrooms were then precooled at 2 °C for 12 h for the subsequent test.
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2.2 Experimental methods
The different concentrations of the nano-SiO2, KC, and KGM were optimized by
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using a response surface regression (RSREG). The test was repeated three times. The
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levels and codes of the test factors are shown in Table 1. Insert Table 1
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2.3 Preparation of coatings
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The different concentrations of the nano-SiO2, KC, and KGM (as shown in Table 2) were added to 300 mL of distilled water. All the concentrations (%) of the materials
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were calculated according to the volume of water (w/v). The mixture was dissolved at
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60 °C for 20 min and sonicated with a VCX 750 ultrasonic processor for 20 min. The solution was subsequently cooled to 35 °C and spread on a glass surface surrounded by frames of equal size (250 mm 250 mm). The coatings on the glass surfaces were dried in an oven at 50 °C. Finally, they were removed for the subsequent experiments. The KC/KGM coatings without the nano-SiO2 were prepared according to the steps described earlier. All coatings were pretreated at 23 °C and 50% relative humidity (RH) in a humidity chamber for 24 h for the following test. 5
ACCEPTED MANUSCRIPT 2.4 WVTR The WVTR of the coatings was determined gravimetrically according to ASTM method E96-95 and the Chinese Standard GB/T 16928 -1997. Briefly, 3 g of anhydrous CaCl2 was weighed and placed in a glass cup. The cup mouth was tightly
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covered with the composite coatings and then fixed with a rubber band and placed in
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a constant temperature and humidity chamber (23 °C, RH 90%) for 24 h. The weight
follows: mf -mi D×S
(1)
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WVTR=
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increase was measured until it remained constant. The WVTR was calculated as
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where mf is the weight of the final bottle and mi is the weight of the initial bottle; D is the time, d; S is the effective area of the coatings, m2.
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2.5 Coating thickness
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The thickness of the coatings was measured using a micrometer with precision of 0.01 mm; each coating was measured in 10 random locations and the average was
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calculated [15].
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2.6 Water resistance and tensile strength (TS) To determine the water solubility (WS) of the coatings, 3 random samples (30 mm 50 mm) were cut from each type of coating. The initial dry matter content were measured after drying at 50 °C for 24 h. The coatings were immersed in 30 mL of distilled water, which was occasionally stirred and maintained at 25 °C for 6 h. The undissolved dry samples were measured by gently rinsing them with distilled water and then drying them in the oven at 50 °C for 24 h to constant weights. The WS of the 6
ACCEPTED MANUSCRIPT coatings was the percentage of soluble matter to initial dry matter in the coating samples [16]. The WS was calculated as follows: WS(%) =
m1 -m2 m1
(2)
where m1 is the weight of the initial dry matter and m2 is the undissolved dry matter.
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The moisture absorption (MA) of the coatings was determined gravimetrically [7].
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The pre-weighted coatings (30 mm 50 mm) were conditioned at 0% RH (prepared
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by dried calcium sulfate) for 24 h. They were then placed in desiccators containing a saturated calcium-nitrite solution at 25 ◦C to ensure an RH of 60%. The coatings were
mt -m0 m0
(3)
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MA(%) =
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weighted (mt) after 6 h. The MA was calculated as follows:
where mo and mt are the weights of the coatings before and after water absorption,
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respectively.
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The tensile properties of coatings were determined using a texture analyzer (TA-XT, Stable Micro Systems UK). The coatings were cut into rectangular strips (50
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mm × 15 mm). An accurate magnetic thickness gauge (AMTG) probe was used. The
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initial distance of separation and the velocity were adjusted to 30 mm and 10 mm/s respectively.
2.7 Transparency
The coating samples (10 mm 40 mm) were cut and placed in a quartz cell. The transparency
of
the
coatings
was
measured
using
an
ultraviolet
(UV)
spectrophotometer (UV-2550, Shimadzu International Trading (Shanghai) Co., Ltd., Shanghai, China) at a wavelength of 600 nm by using the following equation [17]: 7
ACCEPTED MANUSCRIPT T
LogT600 thickness
(4)
2.8 Oxygen transmission rate (OTR) and carbon dioxide transmission rate (CDTR) of coatings The OTR was measured using the deoxidizer absorption method [18]. Three
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grams of the deoxidizer were placed in a glass cup. The cup was covered with the
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different coatings and fixed with a rubber band. Subsequently, they were placed in a
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constant temperature and humidity chamber (23 °C, RH 90%) for 48 h. O2 was absorbed by the deoxidizer through the coatings. The weight increase was measured.
∆m D×S
(5)
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OTR=
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The OTR of the coatings was calculated using the equation:
where ∆m is the amount of O2 absorbed by the deoxidizer; D is the time, d; S is the
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D
effective area of the coatings, m2.
The CDTR was measured using the KOH absorption method [19]. Five grams of KOH were placed in a glass cup that was dried beforehand to a constant mass. The
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cup was covered by coatings and fixed with a rubber band. They were then placed in a
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constant temperature and humidity cabinet chamber (23 °C, RH 90%). After 48 hours, the increase in the mass Δm' (the amount of CO2 absorbed by the KOH) was measured. CO2 is absorbed by the KOH through the coatings. The CDTR was calculated using the following equation: ∆m' CDTR= D×S
(6)
where Δm' is the amount of CO2 absorbed by the KOH; D is the time, d; S is the effective area of the coatings, m2. 8
ACCEPTED MANUSCRIPT 2.9 SEM The morphology of the nano-composite coatings was examined using SEM (FEI Sirion 200, FEI, USA). The samples were placed on a cylindrical stub covered with a carbon strip. They were then covered with using a cathodic sputter [20].
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2.10 FTIR spectroscopy
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To investigate the chemical interactions and microstructure of the coatings, the
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FTIR spectra were recorded in the wavelength range of 400-4000 cm−1 using a FTIR spectrometer (Nicolet 5700, Thermo Electron, USA) [21].
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2.11 XRD
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The XRD patterns of the films were obtained using an XRD instrument (XRD, D8 Advance, Bruker, Karlsruhe, Germany). The samples were irradiated by Cu K
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2.12 UV-Vis spectral analysis
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radiation (λ = 0.154 nm).
The coating samples (10 mm 40 mm) were cut and placed in a quartz cell. The
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transmittance of the composite coatings was measured from 200 nm to 800 nm using
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a Shimadzu UV-2550 spectrophotometer. 2.13 Coating treatment of the white mushrooms (Agaricus bisporus) A master solution (nano-SiO2/KGM/KC coatings) was prepared based on the results of the RSREG, which are described in detail in the Supplementary materials (Fig. S1). The KC/KGM coatings without the nano-SiO2 represented another treatment. The white mushrooms without any coatings represented the control. The mushrooms were dipped in the coating solutions for 2 min and were then placed at 9
ACCEPTED MANUSCRIPT room temperature for 2 h on grid trays to allow the excess solution to drip off and the coating to form. The white mushrooms were taken initially and at 3d intervals during storage. Weight loss was determined by weighing the mushrooms before and during the storage period. The color (surface ∆E and flesh ∆E ) was measured with a
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colorimeter (SC-80C, Kangguang Instrument Co., Ltd., Beijing, China). The cell
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membrane permeability was expressed by tissue electrolyte leakage. Electrolyte
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leakage was measured following a procedure from Liu et al. (2010) [22]. The total soluble solids (TSS) were determined at 25 °C using a digital refractometer
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(Atago-PLA1, Tokyo, Japan). The hardness was measured with a GY-1 penetrometer
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(Mudanjiang Machinery Research Institute, Mudanjiang, China). 2.14 Statistical analysis
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All experiments were run in triplicate. The SEM, XRD, FTIR, and UV-Vis test
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were conducted without replication. All statistical analyses were performed using SAS 6.1. The mean values were compared using Duncan’s test with a significance
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level of P< 0.05.
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3 Results and discussion
3.1 Model development and inspection The results of the nano-SiO2/KGM/KC coatings under various conditions and the estimated parameters of the model are shown in Table 2. Table S1 (Supplementary materials) shows the F and p values of the regression equation parameters. The significance test of the regression equation reached a significant (P0.05) or 10
ACCEPTED MANUSCRIPT extremely significant level (P0.01) and the F-test of the missing item (Lack of Fit) was not significant (P0.05). This demonstrated that the implementation of the experiment was correct, the quadratic regression equation fitted well with the actual situation, and the regression relationship was appropriate. Therefore, it was concluded
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that it was appropriate to use the regression equation to predict the films’ permeability
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rate. In addition, the results showed that the obtained model was significant with a
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coefficient of determination R2 = 0.83 (R2>0.8) and the F-value of the quadratic regression model was 18.09, P<0.01. This indicated that the model fit was highly
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significant. The F-value of the missing item was 0.01, P=0.99 (P>0.05), indicating
the analysis of this response trait.
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that the loss-of-profiling test was not significant; the regression model was adapted to
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For the first item, P=0.30 (P>0.05), the quadratic term P<0.01, and the interaction
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term P= 0.41 (P>0.05); this indicated that the quadratic term had a significant effect on the WVTR and the first term and the interaction term exhibited a significant
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difference. The supplementary material Table S2 shows that the nano-SiO2 (X1) and
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KGM (X3) have a significant effect (P0.05) on the water permeability and KC (X2) had a less significant effect (P0.05). The components’ ranking from large to small was KGM (X3) > nano-SiO2 (X1) > KC (X2). The equation for the regression model was: Y=65.38-2.46X1-1.61X2-0.47X3+4.80X1·X1+1.83X2·X1-0.54X2·X2-2.16X3·X1+1.84 X3·X2+8.84 X3·X3. Insert Table 2 11
ACCEPTED MANUSCRIPT 3.2 Two-factor analysis of the WVTR The mutual effects of two factors on the WVTR were obtained by a response surface analysis (Fig. 1). It was evident that the WVTR decreased at first and then increased as the amount of nano-SiO2 (X1) and KGM (X3) increased. Similarly, as the
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amount of nano-SiO2 (X1) and KC (X2) increased, the WVTR decreased at first and
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then increased (Fig. 1 a, b). Figure 1 c shows the same variation. This indicated that
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the addition of the nano-SiO2, KC, and KGM only improved the efficiency of the coating formation to a certain degree and a large addition reduced the performance of
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the composite coatings. Dehnad et al. [23] reported similar observations in an
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optimization study of the physical and mechanical properties of chitosan– nanocellulose biocomposites.
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The response surface analysis results showed that the optimal condition was 0.03%
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nano-SiO2 concentration, 0.6% KC concentration, and 0.48% KGM concentration. Insert Fig. 1
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3.3 Coating thickness
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The KC and KGM exhibited good properties of castability and coating formation. The coatings were uniform after the KC and KGM were combined with the nano-SiO2. The thicknesses of the coatings ranged from 26.1 μm to 25.8 μm (Table 5); the difference in thickness was not significant (P>0.05). The coating thickness depends on the property and composition of the material. A uniform thickness facilitates the investigation of the performance of the coatings. 3.4 Properties of coatings 12
ACCEPTED MANUSCRIPT The optimal nano-SiO2/KC/KGM coatings were prepared based on the results of the RSREG. The WVTR, WS, MA, CDTR, OTR, TS and transparency of the coatings were measured (Table 3). The composite coatings are coated on the surface of fruits and vegetables for preservation. The fruits and vegetables must be cleaned before use.
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Therefore, the WS and MA of the coatings are important indicators for evaluating
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their practicability [24]. As shown in Table 3, the WS and MA were 2.42% and 5.54%
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respectively higher for the nano-SiO2/KC/KGM coatings than for the KC/KGM coatings. In addition, the KC/KGM/nano-SiO2 coatings had a lower WVTR than the
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KC/KGM coatings. This difference might be attributed to the presence of the
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nano-SiO2, which contained large amounts of -OH and formed hydrogen bonds with the water.
0.180
g·m-2·d-1
lower
than
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and
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The OTR and CDTR of the nano-SiO2/KC/KGM coatings were 0.015 g·m-2·d-1 those
of
the
KC/KGM
coatings.
The
nano-SiO2/KC/KGM coatings affected the permeability of O2 and CO2, which
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inhibited the respiratory rate of the vegetables and the lipid peroxidation of the food.
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The transparency of the composite coatings decreased after adding the nano-SiO2. The nano-SiO2 might have certain optical effects because of the small size of the nano-SiO2 particles. A lower transparency indicates a high opacity [25]. It is important to note that highly transparent coatings are preferred for packaging foods that are susceptible to light-induced lipid oxidation [26]. The TS of the coatings was positively affected by the addition of the nano-SiO2 and reached 323.16 N. The composite coatings form a three-dimensional bond matrix 13
ACCEPTED MANUSCRIPT composed of the nano-SiO2, KC, and the KGM chains. This bond matrix was strengthened by electrostatic attraction, hydrogen bonding, or Si-O bonding as a result of adding the nano-SiO2 [27]. Recent research showed that the increased TS of the nano-composite coatings was due to the interfacial interactions between the
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nano-SiO2 and the biopolymer [28].
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Insert Table 3
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3.5 SEM analysis
As shown in Fig. 2(a), the KC and KGM had good compatibility and the coatings
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exhibited no phase separation. The nano-SiO2 particles were uniformly dispersed in
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the composite coatings. This might be attributed to the interaction of the hydrogen bonds among the molecules of the nano-SiO2 and the KC/KGM molecules. Yao et al.
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[29] prepared biodegradable hybrid films consisting of starch/polyvinyl alcohol
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(PVA)/nano-SiO2 and found that the nano-SiO2 particles were well dispersed in the polymers and exhibited good compatibility.
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Insert Fig. 2
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3.6 FTIR analysis
In FTIR spectroscopy, the chemical components and interactions are evaluated by streaming infrared light across the coatings [30]. The infrared spectra of the nano-SiO2/KC/KGM coatings and KC/KGM coatings are shown in Fig. 3. In addition, the microstructure of the nano-composite coatings and the interactions of the nanoparticles with the coatings matrix were investigated using FTIR. Significant peaks were observed at 3380 cm−1 and 3349 cm−1 and were related to the O-H 14
ACCEPTED MANUSCRIPT stretching in the hydrogen bonds between KC and KGM. The hydroxyl stretching peaks of the nano-SiO2/KC/KGM coatings shifted towards a lower wave number. This indicated that the nano-SiO2 interacted with the KC/KGM molecules through hydrogen bonds with the O-H groups of both molecules. The nano-SiO2/KC/KGM
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coatings have better gelation than the KC/KGM coatings, which improves the
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formation of the coating. Therefore, the presence of the hydrogen bonds played a very
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critical role in increasing the compatibility. The result was in good agreement with the results obtained by Thakur et al. [31] and Li et al. [32]. Sun et al. [33] indicated that
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the peaks at the 1000-500 cm-1 region are attributed to the nano-SiO2. The peaks at
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900-800 cm−1 and 700-675 cm-1 were caused by the stretching vibration of the Si-C and Si-O band of the tetrahedral silica layers and the Si-OH stretching vibrations of
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the nano-SiO2 [34-37]. The FTIR results were in agreement with the results of the
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coating property analysis, which indicated that the -OH on the surface of the nano-SiO2 forms hydrogen bond with the active group of KC/KGM, thereby
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Insert Fig. 3
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enhancing the properties of the nano-SiO2/KC/KGM coatings.
3.7 XRD analysis
Figure 4 shows the XRD patterns of the KC/KGM and the nanocomposite coatings. The broad peak located at 2θ = 22° confirmed the amorphous structure of the nano-SiO2 [38]. The XRD patterns of the KC/KGM coatings exhibited a weak peak at 2θ = 29.1°. After the addition of the nano-SiO2 to the KC/KGM coatings, the intensity of the diffraction peak increased, indicating that the crystallinity was higher 15
ACCEPTED MANUSCRIPT for the KC/KGM/nano-SiO2 coatings than the KC/KGM coatings. The increase in the crystallinity of the KC/KGM/nano-SiO2 coatings can be presumably ascribed to the hydrogen bonds between the nano-SiO2 and the KC/KGM blended matrix; the results were in agreement with the FTIR results. The XRD results indicated that the
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nano-SiO2 possibly interacted with the KC/KGM through hydrogen bonding between
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the -OH in the nano-SiO2 and the -COO- or -OH groups in the KC and KGM [39].
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Insert Fig. 4 3.8 UV-Vis analysis
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The UV-Vis spectra of the nano-SiO2/KC/KGM coatings and the KC/KGM
MA
coatings are shown in Fig. 5. The UV transparency markedly affects the food quality because the lipids, flavors, vitamins, and pigments undergo degradation reactions
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when exposed to light [8]. It was evident that the composition of the composite
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coatings was not changed after the addition of the nano-SiO2. The absorption values of some groups in the molecules were changed. The absorption wavelengths of the
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groups in the composite coating obviously exhibited a redshift (moved to longer
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wavelengths) after the addition of the nanoparticles and their peak values also increased. This indicated that the hydrogen bonding with the nano-composite coatings became stronger and the number of hydrogen bonds was also larger. This further illustrated that the addition of the nano-SiO2 to the KC/KGM coatings may improve the UV-barrier properties of the hosting matrix due to the filled valence band and an empty conduction band of the nano-SiO2 [40]. Insert Fig. 5 16
ACCEPTED MANUSCRIPT 3.9 Coating treatment of the white mushrooms The effects of the coatings on the weight loss (a), surface color variation ∆E (b), flesh color ∆E (c), cell membrane permeability (d), hardness (f), total soluble solids (TSS) (e), and hardness (f) of white mushroom during storage at 4±1°C are shown in
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Fig. 6. The weight loss is an indicator of the mushroom quality during postharvest
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storage. All sample experienced weight loss during storage (Fig. 6a). The control
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samples showed the highest weight loss of 5.4%. Weight losses of 1.3% and 2.5% were recorded for the nano-SiO2/KC/KGM-coated and the KC/KGM-coated
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mushrooms, respectively. The higher weight loss of the control was attributed to the
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unprotected thin epidermal structure. The lower weight loss of the coated mushrooms may be due to the characteristics of the nano-SiO2/KC/KGM coatings acting as a
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semi-permeable barrier against the transfer of water, O2, and CO2 [41-42]. This result
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was in accord with the WVTR analysis of a natural coating conducted by Nasiri et al. [43].
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Changes in color and browning are the primary postharvest problems for
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commercial mushrooms because these parameters mostly affect the consumers’ acceptance [44-45]. The total color variation (ΔE) of the mushrooms was measured (Fig. 6 b, c). Compared to the control, the rates of decrease in the surface color ∆E (b) and flesh color ∆E (c) were lower for the white mushrooms coated with the nano-SiO2/KC/KGM
material
and
the
KC/KGM
material.
The
nano-SiO2/KC/KGM-coated mushrooms inhibited the decrease in the ∆E to maintain a better appearance. These results showed that the nano-SiO2/KC/KGM coatings had 17
ACCEPTED MANUSCRIPT the ability to maintain the color of the white mushrooms, which can be likely attributed to the appropriate OTR and CDTR of the nano-SiO2/KC/KGM coating. It is possible that the lower respiration rate delayed the deterioration of the mushroom quality and the senescence so that the color was maintained for a longer time [44].
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The cell membrane relative leakage rate characterizes the integrity of the
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membranes [46]. The high cell membrane relative leakage rate indicated that the
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mushrooms rapidly aged. The changes in the cell membrane relative leakage rate of the white mushrooms are shown in Fig. 6d. It increased during the storage time,
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which was in agreement with the properties of the different coatings. Specifically, the
and
50.8%,
respectively,
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relative leakage rates in the control and the KC/KGM-coated mushrooms were 55.4% whereas
the
value
was
only
47.8%
for
the
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nano-SiO2/KC/KGM-coated mushrooms at 12 d. This indicated that the
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nano-SiO2/KC/KGM coating had better OTR and CDTR, which inhibited the increase in the respiration rate and delayed the aging of the mushrooms. Therefore, the results
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demonstrated that the loss of the membrane integrity was related to the OTR and
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CDTR of the coatings, which adjusted the atmospheric conditions in the package. The changes in the TSS in the mushrooms are shown in Fig. 6e. The parameters decreased slightly for all coating materials, which is similar to the results reported by Jiang [2]. The TSS of the white mushrooms coated with the KC/KGM and the nano-SiO2/KC/KGM began to decrease at 6 d and 9 d, respectively. Previous studies have shown that the respiration rates decreased to slow down the synthesis and use of metabolites. Thus, decreased respiration rates slow the hydrolysis of carbohydrates to 18
ACCEPTED MANUSCRIPT sugars and result in lower TSS [2]. This indicated that the senescence process was delayed by the nano-SiO2/KC/KGM and the KC/KGM coatings. It showed that the nano-SiO2/KC/KGM coatings provided an excellent semi-permeable coating to control the respiration rates by reducing O2 and increasing CO2.
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The senescence of Agaricus bisporus results in a soft and spongy texture
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characterized by softening of the mushroom tissue [47]. The general trend in hardness
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of Agaricus bisporus for the nano-SiO2/KC/KGM coating and the KC/KGM coating during storage is shown in Fig.6f. It was observed that the hardness decreased for all
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treatments during the storage time, which is similar to the results reported by Qin et al.
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[48]. The control mushrooms had the fastest softening rate, losing about 40.7% of their hardness in 12 d. To a lesser extent, the hardness of the mushrooms treated with
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the KC/KGM coating (37.0%) and the nano-SiO2/KC/KGM coating (21.6%) also
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decreased, respectively. It appears that the nano-SiO2/KC/KGM coating slowed down the degradation of the proteins and polysaccharides, the shrinkage of the hyphae, and
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Insert Fig. 6
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the disruption of the central vacuoles [49].
4 Conclusions
Nano-SiO2 was added to the KC/KGM coating to decrease the WVTR. The concentrations of the nano-SiO2, KC, and KGM affected the coating formation performance to a certain degree as demonstrated by the RSREG results. At a nano-SiO2 concentration of 0.03%, a KC concentration of 0.6%, and a KGM 19
ACCEPTED MANUSCRIPT concentration of 0.48%, the nano-SiO2/KGM/KC coatings exhibited the optimal properties and the WVTR, transparency, TS, OTR, and CDTR were 62.31 g/(m2·d), 83.41%, 323.16N, 0.015 g/(m2·d), and 0.21 g/(m2·d) respectively. The nano-SiO2 interacted with the KC/KGM molecules through hydrogen bonds among the O-H
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groups of both molecules as demonstrated by the results obtained from the SEM,
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XRD, FTIR spectroscopy, and UV-Vis spectroscopy. In addition, the incorporation of
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the nano-SiO2 delayed the effect of the UV light on the food quality because it increased the absorbance of the UV light (300 nm) by the bio-coatings up to threefold.
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The KC/KGM/nano-SiO2 coating extended the storage time of the fresh white
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mushrooms by 5 to 12 d and maintained the whiteness, visual appearance, and hardness. The nano-SiO2/KC/KGM coatings reduced the moisture and gas transfered
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and decreased the respiration of the white mushrooms. Consequently, the coatings
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delayed the deterioration of the mushroom quality and their senescence. Further in-depth examinations should be conducted regarding other influencing factors and
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the development of a good edible package coating.
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Acknowledgments
This research was supported by the National Natural Science Foundation of China under Grant Nos. 31301570 and 30871757. The authors thank the Analysis and Testing Center, Shandong University of Technology for providing the experimental equipment.
References 20
ACCEPTED MANUSCRIPT [1] L. Li,H. Kitazawa, X.Y. Wang, H. Sun, Regulation of respiratory pathway and electron transport chain in relation to senescence of postharvest white mushroom (Agaricus Bisporus) under high O2/CO2 controlled atmospheres, J. Agr. Food Chem. 65 (2017) 3351-3359.
PT
[2] T.J. Jiang, Effect of alginate coating on physicochemical and sensory qualities of
RI
button mushrooms (Agaricus bisporus) under a high oxygen modified
SC
atmosphere, Postharvest Biol. Tec. 76 (2013) 91-97.
[3] R. Gholami, E. Ahmadi, S. Farris, Shelf life extension of white mushrooms
NU
(Agaricus bisporus) by low temperatures conditioning, modified atmosphere, and
MA
nanocomposite packaging material, Food Pack. Shelf Life 14 (2017) 88-95. [4] M. Wrona, K. Bentayeb, C. Nerín, A novel active packaging for extending the
D
shelf-life of fresh mushrooms (Agaricus bisporus), Food Control. 54 (2015)
PT E
200-207.
[5] F. M. Fakhouri, S. M. Martelli, T. Caon, J. I. Velasco, L. H. I. Mei, Edible films
CE
and coatings based on starch/gelatin: film properties and effect of coatings on
AC
quality of refrigerated red crimson grapes, Postharvest Biol. Tec. 109 (2015) 57-64.
[6] S.F. Li, L.H. Zhang, M.P. Liu, X.Y. Wang, G.Y. Zhao, W. Zong, Effect of poly-ε-lysine incorporated into alginate-based edible coatings on microbial and physicochemical properties of fresh-cut kiwifruit, Postharvest Biol. Tec. 134 (2017) 114-121. [7] H. Almasi, B. Ghanbarzadeh, A.A. Entezami, Physicochemical properties of 21
ACCEPTED MANUSCRIPT starch–CMC–nanoclay biodegradable films, Int. J. Biol. Macromol. 46 (2010) 1-5. [8] C. Silvestre, D. Duraccio, S. Cimmino, Food packaging based on polymer nanomaterials, Prog. Polym. Sci. 36 (2011) 1766-1782.
PT
[9] A. Störmer, J. Bott, D. Kemmer, R. Franz, Critical review of the migration
RI
potential of nanoparticles in food contact plastics, Trends Food Sci. Tech. 63
SC
(2017) 39-50.
[10] M.L. Yang, J.S. Shi, Y.Z. Xia, Effect of SiO2, PVA and glycerol concentrations
MA
Macromol. 107 (2018) 2686-2694.
NU
on chemical and mechanical properties of alginate-based films, Int. J. Biol.
[11]ECETOC, 2006. Synthetic Amorphous Silica (CAS No. 7631-86-9). European
D
Centre for Ecotoxicology and Toxicology of Chemicals, Brussels, Belgium
PT E
[12]OECD, S., 2004. Synthetic Amorphous Silica and Silicates, Screening Information Data Set Organization For Economic Cooperation and Development
CE
(OECD). Germany, Berlin.
AC
[13] M.L. Yang, Y.Z. Xia, Preparation and characterization of nano-SiO2 reinforced alginate‐based nanocomposite films (ii), J. Appl. Polym. Sci. 134 (2017) 45286.
[14] H.W. Song, W.M Yuan, P.J Jin, W. Wang, X.F Wang, L.M Yang, Y.F. Zhang, Effects of chitosan/nano-silica on postharvest quality and antioxidant capacity of loquat fruit during cold storage, Postharvest Biol. Tec. 119 (2016) 41-48. [15] G.L. Zhu, L. Sheng, Q.Y. Tong, Preparation and characterization of 22
ACCEPTED MANUSCRIPT carboxymethyl-gellan and pullulan blend films, Food Hydrocoll. 35 (2014) 341-347. [16] J. W. Rhim, Physical-mechanical properties of agar/κ-carrageenan blend film and derived clay nanocomposite film, J. Food Sci. 77 (2012) N66-N73.
PT
[17] J. W. Rhim, S. I. Hong, H. M. Park, P. K. Ng, Preparation and characterization of
RI
chitosan-based nanocomposite films with antimicrobial activity, J. Agr. Food
SC
Chem. 54 (2006) 5814-5822.
[18] Y. X. Lei, Y. L. Yin, J. M. Wang, G. F. Jin, J. H. Zhang, Effect of PVA-based
NU
coating material modified by nano-SiO2 on properties of film-forming package.
MA
Food Science, 33 (6) (2012), 232-237.
[19] L. Wang, M. Xiao, S.H. Dai, J. Song, X.Y. Ni, Y.T. Fang, Interactions between
D
carboxymethyl konjac glucomannan and soy protein isolate in blended films,
PT E
Carbohyd. Polym. 101 (2014) 136-145. [20] B. C. Maniglia, L. Tessaro, A.A. Lucas, D.R. Tapia-Blácido, Bioactive films
AC
383-391.
CE
based on babassu mesocarp flour and starch, Food Hydrocoll. 70 (2017)
[21] S. Shankar, X.N. Teng, G.B Li, J.W. Rhim, Preparation, characterization, and antimicrobial activity of gelatin/zno nanocomposite films, Food Hydrocoll. 45 (2015) 264-271. [22] Z.L. Liu , X.Y. Wang, J.Y. Zhu, J. Wang. Effect of high oxygen modified atmosphere on post-harvest physiology and sensorial qualities of mushroom. Int. J. Food Sci. Tec. 45(6) (2010) 1097-1103. 23
ACCEPTED MANUSCRIPT [23] D. Dehnad, Z. Emamdjomeh, H. Mirzaei, S.M. Jafari, S. Dadashi, Optimization of physical and mechanical properties for chitosan-nanocellulose biocomposites, Carbohyd. Polym.105 (2014) 222-228. [24] F. Ortega, L. Giannuzzi, V.B. Arce, M.A.García, Active composite starch films
PT
containing green synthetized silver nanoparticles, Food Hydrocoll. 70 (2017)
RI
152-162.
SC
[25] M. Abdollahi, M. Alboofetileh, M. Rezaei, R. Behrooz, Comparing physico-mechanical and thermal properties of alginate nanocomposite films
NU
reinforced with organic and/or inorganic nanofillers, Food Hydrocoll. 32 (2013)
MA
416-424.
[26] A. R. Mukurumbira, J.J. Mellem, and E.O. Amonsou, Effects of amadumbe
D
starch nanocrystals on the physicochemical properties of starch biocomposite
PT E
films, Carbohyd. Polym. 165 (2017) 142-148. [27] Y.X. Li, Y.F. Jiang, F. Liu, F.Z. Ren, G.H. Zhao, X.J. Leng, Fabrication and
CE
characterization of TiO2/whey protein isolate nanocomposite film, Food
AC
Hydrocoll. 25 (2011) 1098-1104. [28] M. Hassannia-Kolaee, F. Khodaiyan, R. Pourahmad, I. Shahabi-Ghahfarrokhi, Development of ecofriendly bionanocomposite: whey protein isolate/pullulan films with nano-SiO2, Int. J. Biol. Macromol. 86 (2016) 139-144. [29] K.H. Yao, J. Cai, M. Liu, Y. Yu, H.G Xiong, S.W. Tang, S.Y. Ding, Structure and properties of starch/PVA/nano- SiO2, hybrid films, Carbohyd. Polym. 86 (2011) 1784-1789. 24
ACCEPTED MANUSCRIPT [30] S. Sahraee, J.M. Milani, B. Ghanbarzadeh, H. Hamishehkar, H.S. Kafil, Physicochemical and antifungal properties of bio-nanocomposite film based on gelatin-chitin nanoparticles, Int. J. Biol. Macromol. 97 (2016) 373-381. [31] R. Thakur, B. Saberi, P. Pristijono, J. Golding, C. Stathopoulos, C. Scarlett,
PT
Characterization of rice starch- κ-carrageenan biodegradable edible film. effect
RI
of stearic acid on the film properties, Int. J. Biol. Macromol. 93 (2016) 952-960.
SC
[32] J.W. Li, J.W. Ma, S.H. Chen, J.W. He, Y.D. Huang, Characterization of calcium alginate/deacetylated konjac glucomannan blend films prepared by Ca2+
NU
crosslinking and deacetylation, Food Hydrocoll. 82 (2018) 363-369.
MA
[33] T. Sun, C.L. Wu, H. Hao, Y. Dai, J.R. Li, Preparation and preservation properties of the chitosan coatings modified with the in situ, synthesized nano-SiOx, Food
D
Hydrocoll. 54 (2016) 130-138.
PT E
[34] P. Kanmani, J. W. Rhim, Physicochemical properties of gelatin/silver nanoparticle antimicrobial composite films, Food Chem. 148 (2014) 162-169.
CE
[35] K.C. Kavya, R. Jayakumar, S. Nair, K.P. Chennazhi, Fabrication and
AC
characterization of chitosan/gelatin/nano-SiO2 composite scaffold for bone tissue engineering, Int. J. Biol. Macromol. 59 (2013) 255-263. [36] P. Pietras, R. Przekop, H. Maciejewski, New approach to preparation of gelatine/SiO2 hybrid systems by the sol-gel process, Ceramics-Silikáty 57 (2013) 58-65. [37] R. Venkatesan, N. Rajeswari, Mechanical and antimicrobial properties of κ-carrageenan/SiO2 nanocomposite films for active food packaging, J. Polym. 25
ACCEPTED MANUSCRIPT Mater. 32 (2015) 457-466. [38] H. Chen, F. Wang, C.Y. Zhang, Y.C. Shi, G.Y. Jin, S.L. Yuan, Preparation of nanosilica materials: the concept from wheat straw, J. Non-Cryst. Solid 365 (50) (2010) 2781–2785.
PT
[39] M.L. Yang, J.S. Shi, Y.Z. Xia, Effect of SiO2, PVA and glycerol concentrations
RI
on chemical and mechanical properties of alginate-based films, Int. J. Biol.
SC
Macromol. 107 (2018) 2686–2694.
[40] E. Lizundia, J.L. Vilas, A. Sangroniz, A. Etxeberria, Light and gas barrier
NU
properties of plla/metallic nanoparticles composite films, Eur.Polym.J. 91 (2017)
MA
10-20.
[41] A. Fathi, M.A. Sahari, M. Barzegar, H.N. Badi, Antioxidant activity of satureja
PT E
(2013) 51-67.
D
hortensis l. essential oil and its application in safflower oil, J. Med. Plants 12
[42] A. Ali, M. Maqbool, S. Ramachandran, P.G. Alderson, Gum arabic as a novel
CE
edible coating for enhancing shelf-life and improving postharvest quality of
AC
tomato ( solanum lycopersicum, l.) fruit, Postharvest Biol. Tec. 58 (2010) 42-47. [43] M. Nasiri, M. Barzegar, M.A. Sahari, M. Niakousari, Application of tragacanth gum impregnated with satureja khuzistanica essential oil as a natural coating for enhancement of postharvest quality and shelf life of button mushroom (Agaricus bisporus), Int. J. Biol. Macromol. 106 (2017) 218-226. [44] Z. U. Khan, G. Aisikaer, R.U. Khan, J. Bu, Z. Jiang, Z. Ni, Effects of composite chemical pretreatment on maintaining quality in button mushrooms (Agaricus 26
ACCEPTED MANUSCRIPT bisporus) during postharvest storage, Postharvest Biol. Tec. 95 (2014) 36-41. [45] Z.L. Liu, X.Y. Wang, Changes in color, antioxidant, and free radical scavenging enzyme activity of mushrooms under high oxygen modified atmospheres. Postharvest Biol. Tec. 69 (2012) 1-6.
PT
[46] Y.H. Hu, C.M. Chen, L. Xu, Y. Cui, X.Y. Yu, H.J. Gao, Postharvest application of
SC
bisporus), Postharvest Biol. Tec.104 (2015) 33-41.
RI
4-methoxy cinnamic acid for extending the shelf life of mushroom (Agaricus
[47] C. Guillaume, I. Schwab, E. Gastaldi, N. Gontard, Biobased packaging for
NU
improving preservation of fresh common mushrooms (Agaricus bisporus), Innov.
MA
Food Sci. Emerg. Tec. 11 (2010) 690-696.
[48] Y.Y. Qin, D. Liu, Y. Wu, M.L. Yuan, L.L. Li, J.Y. Yang, Effect of
D
PLA/PCL/cinnamaldehyde antimicrobial packaging on physicochemical and
PT E
microbial quality of button mushroom (Agaricus bisporus), Postharvest Biol. Tec. 99 (2015) 73-79.
CE
[49] G. Antmann, G. Ares, P. Lema, C. Lareo, Influence of modified atmosphere
AC
packaging on sensory quality of shiitake mushrooms, Postharvest Biol. Tec. 49 (2008) 164-170.
27
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Figure captions
Fig. 1. Double-factors mutual effect on the water permeability rate (a: Nano-SiO2 (X1) and KGM
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(X3); b: Nano-SiO2 (X1) and KC (X2); c: KGM (X3) and KC(X2)).
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Fig. 2. SEM images and the appearance of the composite coatings (a: the appearance of the
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KC/KGM coatings; b: the SEM image of the KC/KGM coatings; c: the appearance of the nano-SiO2/KC/KGM coatings; d: the SEM image of the nano-SiO2/KC/KGM coatings).
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Fig. 3. FTIR results of the KC/KGM/nano-SiO2 films and KC/KGM coatings.
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Fig. 4. X-ray diffraction patterns of the KC/KGM/nano-SiO2 films and KC/KGM coatings. Fig. 5. The UV-Vis spectroscopy results of the KC/KGM/nano-SiO2 films and KC/KGM coatings.
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Fig. 6. Effect of the coating on the weight loss (a), surface ∆E (b), flesh ∆E (c), relative leakage
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Table captions
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rate (d), total soluble solids (e), and hardness (f) of Agaricus bisporus during storage at 4 ± 1 °C.
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Table 1 Factors and levels of experiments. Table 2 Experimental structural matrix and results of all factors. Table 3 Performances of the nanocomposite coatings.
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ACCEPTED MANUSCRIPT Optimization of konjac glucomannan /carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus
Rongfei Zhang, Xiangyou Wang*, Ling Li, Meng Cheng, Liming Zhang School of Agricultural Engineering and Food Science, Shandong University of
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Technology, Zibo 255000, China
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Tel.:+86-533-2780897;
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Fax: +86-533-2780897;
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*Corresponding author: Professor Xiangyou Wang, E-mail address: [email protected]
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ACCEPTED MANUSCRIPT
Table 1 Factors and levels of experiments. Factors
X1 Nano-SiO2/%
X2 KC/%
X3 KGM/%
0.50 0.40 0.30 0.20 0.10
0.60 0.52 0.40 0.28 0.20
0.70 0.62 0.50 0.38 0.30
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γ 1 0 -1 -γ
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Levels
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All concentrations (%) of materials were according to the volume of water (w/v).
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Table 2 Experimental structural matrix and results of all factors. X3 KGM/ %
WVP /g·(m2·d)-1
1
1
1
1
75.33
2
1
1
-1
77.51
3
1
-1
1
71.65
4
1
-1
-1
5
-1
1
1
6
-1
1
7
-1
-1
8
-1
-1
9
γ
10
-γ
11
0
12
0
13
0
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80.66 81.35 74.34
1
84.42
-1
85.35
0
0
74.56
0
0
82.43
γ
0
60.86
-γ
0
65.89
0
γ
89.50
0
0
-γ
90.29
0
0
0
66.74
0
0
0
71.09
0
0
0
73.25
0
0
0
72.23
19
0
0
0
69.41
20
0
0
0
55.56
21
0
0
0
60.80
22
0
0
0
64.29
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0
0
0
55.25
15
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18
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16 17
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-1
14
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X2 KC/%
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Experimental Group
X1 Nano-SiO2/%
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No.
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Table 3 Performances of nano-composite coatings Nano-SiO2/KC/KGM
KC/KGM
coatings
coatings
WVP/(g·m ·d )
62.31±3.39a
71.34±4.53b
Transparency/%
83.41±0.02b
84.24±0.06a
WS/%
51.78±0.002a
49.36±0.115b
-2
-1
71.36±0.015b
CDTR/( g·m ·d )
0.180±0.002a
0.210 ±0.024b
OTR/( g·m-2·d-1)
0.015±0.001a
0.025±0.004b
TS / N
323.16±0.20a
Thickness/(μm )
26.11±0.21a
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76.90±0.023a -1
-2
189.37±0.60b 25.80±0.18a
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Means within each column with same letters are not significantly different (P < 0.05).
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Data are means ± SD.
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ACCEPTED MANUSCRIPT Highlights •The packaging and fresh-keeping properties of the KGM/KC coatings is improved by nano-SiO2. • Incorporation of nano-SiO2 was a good way to delay UV light affecting the food qualities. •The KC/KGM structure in hydrogen-bonds are slightly affected by nano-SiO2.
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•The preservation properties on Agaricus bisporus are improved.
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Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Rongfei Zhang, Xiangyou Wang, Ling Li, Meng Cheng, Liming Zhang PII: DOI: Reference:
S0141-8130(18)34532-X https://doi.org/10.1016/j.ijbiomac.2018.10.165 BIOMAC 10816
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
28 August 2018 11 October 2018 24 October 2018
Please cite this article as: Rongfei Zhang, Xiangyou Wang, Ling Li, Meng Cheng, Liming Zhang , Optimization of konjac glucomannan/carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus. Biomac (2018), https://doi.org/10.1016/ j.ijbiomac.2018.10.165
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ACCEPTED MANUSCRIPT
Optimization of konjac glucomannan/carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus Rongfei Zhang, Xiangyou Wang*, Ling Li, Meng Cheng, Liming Zhang
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School of Agricultural Engineering and Food Science, Shandong University of Technology, Zibo 255000, China
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Tel.:+86-533-2780897 Fax: +86-533-2780897
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*Corresponding author: Prof. Xiangyou Wang, E-mail address: [email protected] (X.
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Wang)
Abstract: Nano-SiO2 was inserted into konjac glucomannan (KGM)/carrageenan
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(KC) coatings to improve the properties of the coating. The optimization of the concentrations of the nano-SiO2, KGM, and KC of the coatings was investigated
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using a response surface method. The coatings were characterized by scanning
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electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. The effect of the
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nano-SiO2/KGM/KC coatings on the postharvest quality of the white mushrooms
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stored at 4 ± 1 °C was determined. The results showed that the nano-SiO2/KGM/KC coatings exhibited the optimal properties at a nano-SiO2 concentration of 0.3%, a KC concentration of 0.6%, and a KGM concentration of 0.48%. The water vapor transmission rate, transparency, tensile strength, oxygen transmission rate, and carbon dioxide transmission rate were 62.31 g/(m2·d), 83.41%, 323.16N, 0.015 g/(m2·d), 0.18 g/(m2·d) respectively. The nano-SiO2 decreased the gas permeability of the coatings. It demonstrated that the incorporation of the nano-SiO2 delayed the effect of the UV 1
ACCEPTED MANUSCRIPT light on the food quality because it increased the absorbance of the UV light (300 nm) by the KGM/KC three fold. The application of the nano-SiO2/KGM/KC coatings represents a feasible and effective technique for extending the storage time of white mushrooms.
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Keywords: Nano-SiO2; coatings; Agaricus bisporus
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1 Introduction
The quality of white mushrooms (Agaricus bisporus) deteriorates rapidly after
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harvest, which affects the postharvest storage and transportation time. The high
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metabolic activity, respiration rate, and dehydration are responsible for the rapid decay of mushrooms [1-2]. Mushrooms have a relatively short shelf life compared to
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other fresh vegetables and this has been ascribed to the lack of cuticles in white
microbial attack [3].
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mushrooms that act as a physical barrier against mechanical damage, water loss, or
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The recent development in coating products has provided new opportunities to
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extend the freshness of food products. Coatings change the environmental storage conditions to maintain the sensory properties and ensure the product quality [4]. Many research studies have been published on the properties of edible coatings for the preservation of fruits and vegetables. Fakhouri et al. [5] found that red crimson grapes coated with starch/gelatin edible coatings had a lower weight loss than the control group after 21 d of cold storage. Poly-ε-lysine/alginate-based edible coatings preserved the quality of fresh-cut kiwifruit [6]. Fruits and vegetables require different 2
ACCEPTED MANUSCRIPT coatings to maintain their quality because the ingredients in the coatings may affect the color, flavor, and taste of the product. Konjac glucomannan (KGM) and carrageenan (KC) are excellent natural macromolecular materials used for transparent and flavorless coatings. A strong synergistic gelation effect exists between
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KGM and KC [7]. KGM/KC edible coatings possess several desirable properties that
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are not present in the individual monomer glue. However, when combined, they form
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coatings with low friability, high elasticity, and low water release.
It has been demonstrated that nano-based materials with excellent properties
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represent a novel packaging technology in the postharvest industry [8].
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Nanotechnology has been increasingly used recently in many products and in food-contact polymers because the nanoparticles improve certain properties of the
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neat polymers or provide new functions [9]. Nano-SiO2 is one of the most widely
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used inorganic nano-materials in organic material modification. It can be compounded with many macromolecule polymers to prepare nanocomposite coatings to improve
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the coating properties [10]. The European Center for Ecotoxicology and Toxicology
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of Chemicals and the Organization for Economic Cooperation and Development found no acute toxicity of amorphous SiO2 after conducting a toxicity study on rats through oral and dermal exposure, with the highest exposure concentration of 20 g SiO2/kg body weight [11-12].The addition of nano-SiO2 to alginate coatings decreased the water vapor permeability by 10.26-16.57% [13]. Song et al. [14] demonstrated that chitosan/nano-silica greatly improved the postharvest quality and antioxidant capacity of loquat fruit during cold storage. However, studies have been 3
ACCEPTED MANUSCRIPT rarely conducted on the effect of KC/KGM /nano-SiO2 coatings on perishable white mushrooms. The properties, microstructure, preservation mechanism, and optimum content of the nano-SiO2 in the composite coatings also have not been fully elucidated. Hence, this study focuses on the optimum content, the morphology, and the properties
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of the nano-SiO2 composite coatings to evaluate the advantages of the coating for
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food preservation.
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The objective of this study is to determine the optimum ratio of the components in the KC/KGM/ nano-SiO2 coatings to extend the storage time of postharvest white
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mushrooms. The water vapor transmission rate (WVTR) is an important characteristic
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of the coatings to achieve the preservation of white mushrooms. The nano-SiO2 was incorporated into the KC/KGM coatings to enhance the coating’s properties. The
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effects of the concentrations of the nano-SiO2, KGM, and KC on the water
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permeability of the KC/KGM coatings were investigated using a response surface methodology (RSM). The coatings were characterized by scanning electron
and
Ultraviolet-visible (UV-vis) spectroscopy. The
effect
of the
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(XRD),
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microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction
nano-SiO2/KGM/KC coatings on the postharvest quality and shelf life of the white mushrooms stored at 4 ± 1 °C was determined.
2 Materials and methods
2.1 Materials The KGM powder and KC powder are considered food-grade. The nano-SiO2 4
ACCEPTED MANUSCRIPT (HTSi-01, size 20 nm, white fluffy powder, specific surface area ≥ 600 m2/g, high adsorption, many surface hydroxyl groups, good hydrophilicity) was purchased from Haitai Nanotechnical Co., Ltd. (Nanjing, China). The white mushrooms were harvested in Dezhou, Shandong, China. Prior to the package test, mushrooms with
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uniform characteristics (size, shape, and color) were selected as the experimental
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material. The mushrooms were then precooled at 2 °C for 12 h for the subsequent test.
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2.2 Experimental methods
The different concentrations of the nano-SiO2, KC, and KGM were optimized by
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using a response surface regression (RSREG). The test was repeated three times. The
MA
levels and codes of the test factors are shown in Table 1. Insert Table 1
D
2.3 Preparation of coatings
PT E
The different concentrations of the nano-SiO2, KC, and KGM (as shown in Table 2) were added to 300 mL of distilled water. All the concentrations (%) of the materials
CE
were calculated according to the volume of water (w/v). The mixture was dissolved at
AC
60 °C for 20 min and sonicated with a VCX 750 ultrasonic processor for 20 min. The solution was subsequently cooled to 35 °C and spread on a glass surface surrounded by frames of equal size (250 mm 250 mm). The coatings on the glass surfaces were dried in an oven at 50 °C. Finally, they were removed for the subsequent experiments. The KC/KGM coatings without the nano-SiO2 were prepared according to the steps described earlier. All coatings were pretreated at 23 °C and 50% relative humidity (RH) in a humidity chamber for 24 h for the following test. 5
ACCEPTED MANUSCRIPT 2.4 WVTR The WVTR of the coatings was determined gravimetrically according to ASTM method E96-95 and the Chinese Standard GB/T 16928 -1997. Briefly, 3 g of anhydrous CaCl2 was weighed and placed in a glass cup. The cup mouth was tightly
PT
covered with the composite coatings and then fixed with a rubber band and placed in
RI
a constant temperature and humidity chamber (23 °C, RH 90%) for 24 h. The weight
follows: mf -mi D×S
(1)
NU
WVTR=
SC
increase was measured until it remained constant. The WVTR was calculated as
MA
where mf is the weight of the final bottle and mi is the weight of the initial bottle; D is the time, d; S is the effective area of the coatings, m2.
D
2.5 Coating thickness
PT E
The thickness of the coatings was measured using a micrometer with precision of 0.01 mm; each coating was measured in 10 random locations and the average was
CE
calculated [15].
AC
2.6 Water resistance and tensile strength (TS) To determine the water solubility (WS) of the coatings, 3 random samples (30 mm 50 mm) were cut from each type of coating. The initial dry matter content were measured after drying at 50 °C for 24 h. The coatings were immersed in 30 mL of distilled water, which was occasionally stirred and maintained at 25 °C for 6 h. The undissolved dry samples were measured by gently rinsing them with distilled water and then drying them in the oven at 50 °C for 24 h to constant weights. The WS of the 6
ACCEPTED MANUSCRIPT coatings was the percentage of soluble matter to initial dry matter in the coating samples [16]. The WS was calculated as follows: WS(%) =
m1 -m2 m1
(2)
where m1 is the weight of the initial dry matter and m2 is the undissolved dry matter.
PT
The moisture absorption (MA) of the coatings was determined gravimetrically [7].
RI
The pre-weighted coatings (30 mm 50 mm) were conditioned at 0% RH (prepared
SC
by dried calcium sulfate) for 24 h. They were then placed in desiccators containing a saturated calcium-nitrite solution at 25 ◦C to ensure an RH of 60%. The coatings were
mt -m0 m0
(3)
MA
MA(%) =
NU
weighted (mt) after 6 h. The MA was calculated as follows:
where mo and mt are the weights of the coatings before and after water absorption,
D
respectively.
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The tensile properties of coatings were determined using a texture analyzer (TA-XT, Stable Micro Systems UK). The coatings were cut into rectangular strips (50
CE
mm × 15 mm). An accurate magnetic thickness gauge (AMTG) probe was used. The
AC
initial distance of separation and the velocity were adjusted to 30 mm and 10 mm/s respectively.
2.7 Transparency
The coating samples (10 mm 40 mm) were cut and placed in a quartz cell. The transparency
of
the
coatings
was
measured
using
an
ultraviolet
(UV)
spectrophotometer (UV-2550, Shimadzu International Trading (Shanghai) Co., Ltd., Shanghai, China) at a wavelength of 600 nm by using the following equation [17]: 7
ACCEPTED MANUSCRIPT T
LogT600 thickness
(4)
2.8 Oxygen transmission rate (OTR) and carbon dioxide transmission rate (CDTR) of coatings The OTR was measured using the deoxidizer absorption method [18]. Three
PT
grams of the deoxidizer were placed in a glass cup. The cup was covered with the
RI
different coatings and fixed with a rubber band. Subsequently, they were placed in a
SC
constant temperature and humidity chamber (23 °C, RH 90%) for 48 h. O2 was absorbed by the deoxidizer through the coatings. The weight increase was measured.
∆m D×S
(5)
MA
OTR=
NU
The OTR of the coatings was calculated using the equation:
where ∆m is the amount of O2 absorbed by the deoxidizer; D is the time, d; S is the
PT E
D
effective area of the coatings, m2.
The CDTR was measured using the KOH absorption method [19]. Five grams of KOH were placed in a glass cup that was dried beforehand to a constant mass. The
CE
cup was covered by coatings and fixed with a rubber band. They were then placed in a
AC
constant temperature and humidity cabinet chamber (23 °C, RH 90%). After 48 hours, the increase in the mass Δm' (the amount of CO2 absorbed by the KOH) was measured. CO2 is absorbed by the KOH through the coatings. The CDTR was calculated using the following equation: ∆m' CDTR= D×S
(6)
where Δm' is the amount of CO2 absorbed by the KOH; D is the time, d; S is the effective area of the coatings, m2. 8
ACCEPTED MANUSCRIPT 2.9 SEM The morphology of the nano-composite coatings was examined using SEM (FEI Sirion 200, FEI, USA). The samples were placed on a cylindrical stub covered with a carbon strip. They were then covered with using a cathodic sputter [20].
PT
2.10 FTIR spectroscopy
RI
To investigate the chemical interactions and microstructure of the coatings, the
SC
FTIR spectra were recorded in the wavelength range of 400-4000 cm−1 using a FTIR spectrometer (Nicolet 5700, Thermo Electron, USA) [21].
NU
2.11 XRD
MA
The XRD patterns of the films were obtained using an XRD instrument (XRD, D8 Advance, Bruker, Karlsruhe, Germany). The samples were irradiated by Cu K
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2.12 UV-Vis spectral analysis
D
radiation (λ = 0.154 nm).
The coating samples (10 mm 40 mm) were cut and placed in a quartz cell. The
CE
transmittance of the composite coatings was measured from 200 nm to 800 nm using
AC
a Shimadzu UV-2550 spectrophotometer. 2.13 Coating treatment of the white mushrooms (Agaricus bisporus) A master solution (nano-SiO2/KGM/KC coatings) was prepared based on the results of the RSREG, which are described in detail in the Supplementary materials (Fig. S1). The KC/KGM coatings without the nano-SiO2 represented another treatment. The white mushrooms without any coatings represented the control. The mushrooms were dipped in the coating solutions for 2 min and were then placed at 9
ACCEPTED MANUSCRIPT room temperature for 2 h on grid trays to allow the excess solution to drip off and the coating to form. The white mushrooms were taken initially and at 3d intervals during storage. Weight loss was determined by weighing the mushrooms before and during the storage period. The color (surface ∆E and flesh ∆E ) was measured with a
PT
colorimeter (SC-80C, Kangguang Instrument Co., Ltd., Beijing, China). The cell
RI
membrane permeability was expressed by tissue electrolyte leakage. Electrolyte
SC
leakage was measured following a procedure from Liu et al. (2010) [22]. The total soluble solids (TSS) were determined at 25 °C using a digital refractometer
NU
(Atago-PLA1, Tokyo, Japan). The hardness was measured with a GY-1 penetrometer
MA
(Mudanjiang Machinery Research Institute, Mudanjiang, China). 2.14 Statistical analysis
D
All experiments were run in triplicate. The SEM, XRD, FTIR, and UV-Vis test
PT E
were conducted without replication. All statistical analyses were performed using SAS 6.1. The mean values were compared using Duncan’s test with a significance
CE
level of P< 0.05.
AC
3 Results and discussion
3.1 Model development and inspection The results of the nano-SiO2/KGM/KC coatings under various conditions and the estimated parameters of the model are shown in Table 2. Table S1 (Supplementary materials) shows the F and p values of the regression equation parameters. The significance test of the regression equation reached a significant (P0.05) or 10
ACCEPTED MANUSCRIPT extremely significant level (P0.01) and the F-test of the missing item (Lack of Fit) was not significant (P0.05). This demonstrated that the implementation of the experiment was correct, the quadratic regression equation fitted well with the actual situation, and the regression relationship was appropriate. Therefore, it was concluded
PT
that it was appropriate to use the regression equation to predict the films’ permeability
RI
rate. In addition, the results showed that the obtained model was significant with a
SC
coefficient of determination R2 = 0.83 (R2>0.8) and the F-value of the quadratic regression model was 18.09, P<0.01. This indicated that the model fit was highly
NU
significant. The F-value of the missing item was 0.01, P=0.99 (P>0.05), indicating
the analysis of this response trait.
MA
that the loss-of-profiling test was not significant; the regression model was adapted to
D
For the first item, P=0.30 (P>0.05), the quadratic term P<0.01, and the interaction
PT E
term P= 0.41 (P>0.05); this indicated that the quadratic term had a significant effect on the WVTR and the first term and the interaction term exhibited a significant
CE
difference. The supplementary material Table S2 shows that the nano-SiO2 (X1) and
AC
KGM (X3) have a significant effect (P0.05) on the water permeability and KC (X2) had a less significant effect (P0.05). The components’ ranking from large to small was KGM (X3) > nano-SiO2 (X1) > KC (X2). The equation for the regression model was: Y=65.38-2.46X1-1.61X2-0.47X3+4.80X1·X1+1.83X2·X1-0.54X2·X2-2.16X3·X1+1.84 X3·X2+8.84 X3·X3. Insert Table 2 11
ACCEPTED MANUSCRIPT 3.2 Two-factor analysis of the WVTR The mutual effects of two factors on the WVTR were obtained by a response surface analysis (Fig. 1). It was evident that the WVTR decreased at first and then increased as the amount of nano-SiO2 (X1) and KGM (X3) increased. Similarly, as the
PT
amount of nano-SiO2 (X1) and KC (X2) increased, the WVTR decreased at first and
RI
then increased (Fig. 1 a, b). Figure 1 c shows the same variation. This indicated that
SC
the addition of the nano-SiO2, KC, and KGM only improved the efficiency of the coating formation to a certain degree and a large addition reduced the performance of
NU
the composite coatings. Dehnad et al. [23] reported similar observations in an
MA
optimization study of the physical and mechanical properties of chitosan– nanocellulose biocomposites.
D
The response surface analysis results showed that the optimal condition was 0.03%
PT E
nano-SiO2 concentration, 0.6% KC concentration, and 0.48% KGM concentration. Insert Fig. 1
CE
3.3 Coating thickness
AC
The KC and KGM exhibited good properties of castability and coating formation. The coatings were uniform after the KC and KGM were combined with the nano-SiO2. The thicknesses of the coatings ranged from 26.1 μm to 25.8 μm (Table 5); the difference in thickness was not significant (P>0.05). The coating thickness depends on the property and composition of the material. A uniform thickness facilitates the investigation of the performance of the coatings. 3.4 Properties of coatings 12
ACCEPTED MANUSCRIPT The optimal nano-SiO2/KC/KGM coatings were prepared based on the results of the RSREG. The WVTR, WS, MA, CDTR, OTR, TS and transparency of the coatings were measured (Table 3). The composite coatings are coated on the surface of fruits and vegetables for preservation. The fruits and vegetables must be cleaned before use.
PT
Therefore, the WS and MA of the coatings are important indicators for evaluating
RI
their practicability [24]. As shown in Table 3, the WS and MA were 2.42% and 5.54%
SC
respectively higher for the nano-SiO2/KC/KGM coatings than for the KC/KGM coatings. In addition, the KC/KGM/nano-SiO2 coatings had a lower WVTR than the
NU
KC/KGM coatings. This difference might be attributed to the presence of the
MA
nano-SiO2, which contained large amounts of -OH and formed hydrogen bonds with the water.
0.180
g·m-2·d-1
lower
than
PT E
and
D
The OTR and CDTR of the nano-SiO2/KC/KGM coatings were 0.015 g·m-2·d-1 those
of
the
KC/KGM
coatings.
The
nano-SiO2/KC/KGM coatings affected the permeability of O2 and CO2, which
CE
inhibited the respiratory rate of the vegetables and the lipid peroxidation of the food.
AC
The transparency of the composite coatings decreased after adding the nano-SiO2. The nano-SiO2 might have certain optical effects because of the small size of the nano-SiO2 particles. A lower transparency indicates a high opacity [25]. It is important to note that highly transparent coatings are preferred for packaging foods that are susceptible to light-induced lipid oxidation [26]. The TS of the coatings was positively affected by the addition of the nano-SiO2 and reached 323.16 N. The composite coatings form a three-dimensional bond matrix 13
ACCEPTED MANUSCRIPT composed of the nano-SiO2, KC, and the KGM chains. This bond matrix was strengthened by electrostatic attraction, hydrogen bonding, or Si-O bonding as a result of adding the nano-SiO2 [27]. Recent research showed that the increased TS of the nano-composite coatings was due to the interfacial interactions between the
PT
nano-SiO2 and the biopolymer [28].
RI
Insert Table 3
SC
3.5 SEM analysis
As shown in Fig. 2(a), the KC and KGM had good compatibility and the coatings
NU
exhibited no phase separation. The nano-SiO2 particles were uniformly dispersed in
MA
the composite coatings. This might be attributed to the interaction of the hydrogen bonds among the molecules of the nano-SiO2 and the KC/KGM molecules. Yao et al.
D
[29] prepared biodegradable hybrid films consisting of starch/polyvinyl alcohol
PT E
(PVA)/nano-SiO2 and found that the nano-SiO2 particles were well dispersed in the polymers and exhibited good compatibility.
CE
Insert Fig. 2
AC
3.6 FTIR analysis
In FTIR spectroscopy, the chemical components and interactions are evaluated by streaming infrared light across the coatings [30]. The infrared spectra of the nano-SiO2/KC/KGM coatings and KC/KGM coatings are shown in Fig. 3. In addition, the microstructure of the nano-composite coatings and the interactions of the nanoparticles with the coatings matrix were investigated using FTIR. Significant peaks were observed at 3380 cm−1 and 3349 cm−1 and were related to the O-H 14
ACCEPTED MANUSCRIPT stretching in the hydrogen bonds between KC and KGM. The hydroxyl stretching peaks of the nano-SiO2/KC/KGM coatings shifted towards a lower wave number. This indicated that the nano-SiO2 interacted with the KC/KGM molecules through hydrogen bonds with the O-H groups of both molecules. The nano-SiO2/KC/KGM
PT
coatings have better gelation than the KC/KGM coatings, which improves the
RI
formation of the coating. Therefore, the presence of the hydrogen bonds played a very
SC
critical role in increasing the compatibility. The result was in good agreement with the results obtained by Thakur et al. [31] and Li et al. [32]. Sun et al. [33] indicated that
NU
the peaks at the 1000-500 cm-1 region are attributed to the nano-SiO2. The peaks at
MA
900-800 cm−1 and 700-675 cm-1 were caused by the stretching vibration of the Si-C and Si-O band of the tetrahedral silica layers and the Si-OH stretching vibrations of
D
the nano-SiO2 [34-37]. The FTIR results were in agreement with the results of the
PT E
coating property analysis, which indicated that the -OH on the surface of the nano-SiO2 forms hydrogen bond with the active group of KC/KGM, thereby
AC
Insert Fig. 3
CE
enhancing the properties of the nano-SiO2/KC/KGM coatings.
3.7 XRD analysis
Figure 4 shows the XRD patterns of the KC/KGM and the nanocomposite coatings. The broad peak located at 2θ = 22° confirmed the amorphous structure of the nano-SiO2 [38]. The XRD patterns of the KC/KGM coatings exhibited a weak peak at 2θ = 29.1°. After the addition of the nano-SiO2 to the KC/KGM coatings, the intensity of the diffraction peak increased, indicating that the crystallinity was higher 15
ACCEPTED MANUSCRIPT for the KC/KGM/nano-SiO2 coatings than the KC/KGM coatings. The increase in the crystallinity of the KC/KGM/nano-SiO2 coatings can be presumably ascribed to the hydrogen bonds between the nano-SiO2 and the KC/KGM blended matrix; the results were in agreement with the FTIR results. The XRD results indicated that the
PT
nano-SiO2 possibly interacted with the KC/KGM through hydrogen bonding between
RI
the -OH in the nano-SiO2 and the -COO- or -OH groups in the KC and KGM [39].
SC
Insert Fig. 4 3.8 UV-Vis analysis
NU
The UV-Vis spectra of the nano-SiO2/KC/KGM coatings and the KC/KGM
MA
coatings are shown in Fig. 5. The UV transparency markedly affects the food quality because the lipids, flavors, vitamins, and pigments undergo degradation reactions
D
when exposed to light [8]. It was evident that the composition of the composite
PT E
coatings was not changed after the addition of the nano-SiO2. The absorption values of some groups in the molecules were changed. The absorption wavelengths of the
CE
groups in the composite coating obviously exhibited a redshift (moved to longer
AC
wavelengths) after the addition of the nanoparticles and their peak values also increased. This indicated that the hydrogen bonding with the nano-composite coatings became stronger and the number of hydrogen bonds was also larger. This further illustrated that the addition of the nano-SiO2 to the KC/KGM coatings may improve the UV-barrier properties of the hosting matrix due to the filled valence band and an empty conduction band of the nano-SiO2 [40]. Insert Fig. 5 16
ACCEPTED MANUSCRIPT 3.9 Coating treatment of the white mushrooms The effects of the coatings on the weight loss (a), surface color variation ∆E (b), flesh color ∆E (c), cell membrane permeability (d), hardness (f), total soluble solids (TSS) (e), and hardness (f) of white mushroom during storage at 4±1°C are shown in
PT
Fig. 6. The weight loss is an indicator of the mushroom quality during postharvest
RI
storage. All sample experienced weight loss during storage (Fig. 6a). The control
SC
samples showed the highest weight loss of 5.4%. Weight losses of 1.3% and 2.5% were recorded for the nano-SiO2/KC/KGM-coated and the KC/KGM-coated
NU
mushrooms, respectively. The higher weight loss of the control was attributed to the
MA
unprotected thin epidermal structure. The lower weight loss of the coated mushrooms may be due to the characteristics of the nano-SiO2/KC/KGM coatings acting as a
D
semi-permeable barrier against the transfer of water, O2, and CO2 [41-42]. This result
PT E
was in accord with the WVTR analysis of a natural coating conducted by Nasiri et al. [43].
CE
Changes in color and browning are the primary postharvest problems for
AC
commercial mushrooms because these parameters mostly affect the consumers’ acceptance [44-45]. The total color variation (ΔE) of the mushrooms was measured (Fig. 6 b, c). Compared to the control, the rates of decrease in the surface color ∆E (b) and flesh color ∆E (c) were lower for the white mushrooms coated with the nano-SiO2/KC/KGM
material
and
the
KC/KGM
material.
The
nano-SiO2/KC/KGM-coated mushrooms inhibited the decrease in the ∆E to maintain a better appearance. These results showed that the nano-SiO2/KC/KGM coatings had 17
ACCEPTED MANUSCRIPT the ability to maintain the color of the white mushrooms, which can be likely attributed to the appropriate OTR and CDTR of the nano-SiO2/KC/KGM coating. It is possible that the lower respiration rate delayed the deterioration of the mushroom quality and the senescence so that the color was maintained for a longer time [44].
PT
The cell membrane relative leakage rate characterizes the integrity of the
RI
membranes [46]. The high cell membrane relative leakage rate indicated that the
SC
mushrooms rapidly aged. The changes in the cell membrane relative leakage rate of the white mushrooms are shown in Fig. 6d. It increased during the storage time,
NU
which was in agreement with the properties of the different coatings. Specifically, the
and
50.8%,
respectively,
MA
relative leakage rates in the control and the KC/KGM-coated mushrooms were 55.4% whereas
the
value
was
only
47.8%
for
the
D
nano-SiO2/KC/KGM-coated mushrooms at 12 d. This indicated that the
PT E
nano-SiO2/KC/KGM coating had better OTR and CDTR, which inhibited the increase in the respiration rate and delayed the aging of the mushrooms. Therefore, the results
CE
demonstrated that the loss of the membrane integrity was related to the OTR and
AC
CDTR of the coatings, which adjusted the atmospheric conditions in the package. The changes in the TSS in the mushrooms are shown in Fig. 6e. The parameters decreased slightly for all coating materials, which is similar to the results reported by Jiang [2]. The TSS of the white mushrooms coated with the KC/KGM and the nano-SiO2/KC/KGM began to decrease at 6 d and 9 d, respectively. Previous studies have shown that the respiration rates decreased to slow down the synthesis and use of metabolites. Thus, decreased respiration rates slow the hydrolysis of carbohydrates to 18
ACCEPTED MANUSCRIPT sugars and result in lower TSS [2]. This indicated that the senescence process was delayed by the nano-SiO2/KC/KGM and the KC/KGM coatings. It showed that the nano-SiO2/KC/KGM coatings provided an excellent semi-permeable coating to control the respiration rates by reducing O2 and increasing CO2.
PT
The senescence of Agaricus bisporus results in a soft and spongy texture
RI
characterized by softening of the mushroom tissue [47]. The general trend in hardness
SC
of Agaricus bisporus for the nano-SiO2/KC/KGM coating and the KC/KGM coating during storage is shown in Fig.6f. It was observed that the hardness decreased for all
NU
treatments during the storage time, which is similar to the results reported by Qin et al.
MA
[48]. The control mushrooms had the fastest softening rate, losing about 40.7% of their hardness in 12 d. To a lesser extent, the hardness of the mushrooms treated with
D
the KC/KGM coating (37.0%) and the nano-SiO2/KC/KGM coating (21.6%) also
PT E
decreased, respectively. It appears that the nano-SiO2/KC/KGM coating slowed down the degradation of the proteins and polysaccharides, the shrinkage of the hyphae, and
AC
Insert Fig. 6
CE
the disruption of the central vacuoles [49].
4 Conclusions
Nano-SiO2 was added to the KC/KGM coating to decrease the WVTR. The concentrations of the nano-SiO2, KC, and KGM affected the coating formation performance to a certain degree as demonstrated by the RSREG results. At a nano-SiO2 concentration of 0.03%, a KC concentration of 0.6%, and a KGM 19
ACCEPTED MANUSCRIPT concentration of 0.48%, the nano-SiO2/KGM/KC coatings exhibited the optimal properties and the WVTR, transparency, TS, OTR, and CDTR were 62.31 g/(m2·d), 83.41%, 323.16N, 0.015 g/(m2·d), and 0.21 g/(m2·d) respectively. The nano-SiO2 interacted with the KC/KGM molecules through hydrogen bonds among the O-H
PT
groups of both molecules as demonstrated by the results obtained from the SEM,
RI
XRD, FTIR spectroscopy, and UV-Vis spectroscopy. In addition, the incorporation of
SC
the nano-SiO2 delayed the effect of the UV light on the food quality because it increased the absorbance of the UV light (300 nm) by the bio-coatings up to threefold.
NU
The KC/KGM/nano-SiO2 coating extended the storage time of the fresh white
MA
mushrooms by 5 to 12 d and maintained the whiteness, visual appearance, and hardness. The nano-SiO2/KC/KGM coatings reduced the moisture and gas transfered
D
and decreased the respiration of the white mushrooms. Consequently, the coatings
PT E
delayed the deterioration of the mushroom quality and their senescence. Further in-depth examinations should be conducted regarding other influencing factors and
CE
the development of a good edible package coating.
AC
Acknowledgments
This research was supported by the National Natural Science Foundation of China under Grant Nos. 31301570 and 30871757. The authors thank the Analysis and Testing Center, Shandong University of Technology for providing the experimental equipment.
References 20
ACCEPTED MANUSCRIPT [1] L. Li,H. Kitazawa, X.Y. Wang, H. Sun, Regulation of respiratory pathway and electron transport chain in relation to senescence of postharvest white mushroom (Agaricus Bisporus) under high O2/CO2 controlled atmospheres, J. Agr. Food Chem. 65 (2017) 3351-3359.
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[2] T.J. Jiang, Effect of alginate coating on physicochemical and sensory qualities of
RI
button mushrooms (Agaricus bisporus) under a high oxygen modified
SC
atmosphere, Postharvest Biol. Tec. 76 (2013) 91-97.
[3] R. Gholami, E. Ahmadi, S. Farris, Shelf life extension of white mushrooms
NU
(Agaricus bisporus) by low temperatures conditioning, modified atmosphere, and
MA
nanocomposite packaging material, Food Pack. Shelf Life 14 (2017) 88-95. [4] M. Wrona, K. Bentayeb, C. Nerín, A novel active packaging for extending the
D
shelf-life of fresh mushrooms (Agaricus bisporus), Food Control. 54 (2015)
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200-207.
[5] F. M. Fakhouri, S. M. Martelli, T. Caon, J. I. Velasco, L. H. I. Mei, Edible films
CE
and coatings based on starch/gelatin: film properties and effect of coatings on
AC
quality of refrigerated red crimson grapes, Postharvest Biol. Tec. 109 (2015) 57-64.
[6] S.F. Li, L.H. Zhang, M.P. Liu, X.Y. Wang, G.Y. Zhao, W. Zong, Effect of poly-ε-lysine incorporated into alginate-based edible coatings on microbial and physicochemical properties of fresh-cut kiwifruit, Postharvest Biol. Tec. 134 (2017) 114-121. [7] H. Almasi, B. Ghanbarzadeh, A.A. Entezami, Physicochemical properties of 21
ACCEPTED MANUSCRIPT starch–CMC–nanoclay biodegradable films, Int. J. Biol. Macromol. 46 (2010) 1-5. [8] C. Silvestre, D. Duraccio, S. Cimmino, Food packaging based on polymer nanomaterials, Prog. Polym. Sci. 36 (2011) 1766-1782.
PT
[9] A. Störmer, J. Bott, D. Kemmer, R. Franz, Critical review of the migration
RI
potential of nanoparticles in food contact plastics, Trends Food Sci. Tech. 63
SC
(2017) 39-50.
[10] M.L. Yang, J.S. Shi, Y.Z. Xia, Effect of SiO2, PVA and glycerol concentrations
MA
Macromol. 107 (2018) 2686-2694.
NU
on chemical and mechanical properties of alginate-based films, Int. J. Biol.
[11]ECETOC, 2006. Synthetic Amorphous Silica (CAS No. 7631-86-9). European
D
Centre for Ecotoxicology and Toxicology of Chemicals, Brussels, Belgium
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[12]OECD, S., 2004. Synthetic Amorphous Silica and Silicates, Screening Information Data Set Organization For Economic Cooperation and Development
CE
(OECD). Germany, Berlin.
AC
[13] M.L. Yang, Y.Z. Xia, Preparation and characterization of nano-SiO2 reinforced alginate‐based nanocomposite films (ii), J. Appl. Polym. Sci. 134 (2017) 45286.
[14] H.W. Song, W.M Yuan, P.J Jin, W. Wang, X.F Wang, L.M Yang, Y.F. Zhang, Effects of chitosan/nano-silica on postharvest quality and antioxidant capacity of loquat fruit during cold storage, Postharvest Biol. Tec. 119 (2016) 41-48. [15] G.L. Zhu, L. Sheng, Q.Y. Tong, Preparation and characterization of 22
ACCEPTED MANUSCRIPT carboxymethyl-gellan and pullulan blend films, Food Hydrocoll. 35 (2014) 341-347. [16] J. W. Rhim, Physical-mechanical properties of agar/κ-carrageenan blend film and derived clay nanocomposite film, J. Food Sci. 77 (2012) N66-N73.
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[17] J. W. Rhim, S. I. Hong, H. M. Park, P. K. Ng, Preparation and characterization of
RI
chitosan-based nanocomposite films with antimicrobial activity, J. Agr. Food
SC
Chem. 54 (2006) 5814-5822.
[18] Y. X. Lei, Y. L. Yin, J. M. Wang, G. F. Jin, J. H. Zhang, Effect of PVA-based
NU
coating material modified by nano-SiO2 on properties of film-forming package.
MA
Food Science, 33 (6) (2012), 232-237.
[19] L. Wang, M. Xiao, S.H. Dai, J. Song, X.Y. Ni, Y.T. Fang, Interactions between
D
carboxymethyl konjac glucomannan and soy protein isolate in blended films,
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Carbohyd. Polym. 101 (2014) 136-145. [20] B. C. Maniglia, L. Tessaro, A.A. Lucas, D.R. Tapia-Blácido, Bioactive films
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383-391.
CE
based on babassu mesocarp flour and starch, Food Hydrocoll. 70 (2017)
[21] S. Shankar, X.N. Teng, G.B Li, J.W. Rhim, Preparation, characterization, and antimicrobial activity of gelatin/zno nanocomposite films, Food Hydrocoll. 45 (2015) 264-271. [22] Z.L. Liu , X.Y. Wang, J.Y. Zhu, J. Wang. Effect of high oxygen modified atmosphere on post-harvest physiology and sensorial qualities of mushroom. Int. J. Food Sci. Tec. 45(6) (2010) 1097-1103. 23
ACCEPTED MANUSCRIPT [23] D. Dehnad, Z. Emamdjomeh, H. Mirzaei, S.M. Jafari, S. Dadashi, Optimization of physical and mechanical properties for chitosan-nanocellulose biocomposites, Carbohyd. Polym.105 (2014) 222-228. [24] F. Ortega, L. Giannuzzi, V.B. Arce, M.A.García, Active composite starch films
PT
containing green synthetized silver nanoparticles, Food Hydrocoll. 70 (2017)
RI
152-162.
SC
[25] M. Abdollahi, M. Alboofetileh, M. Rezaei, R. Behrooz, Comparing physico-mechanical and thermal properties of alginate nanocomposite films
NU
reinforced with organic and/or inorganic nanofillers, Food Hydrocoll. 32 (2013)
MA
416-424.
[26] A. R. Mukurumbira, J.J. Mellem, and E.O. Amonsou, Effects of amadumbe
D
starch nanocrystals on the physicochemical properties of starch biocomposite
PT E
films, Carbohyd. Polym. 165 (2017) 142-148. [27] Y.X. Li, Y.F. Jiang, F. Liu, F.Z. Ren, G.H. Zhao, X.J. Leng, Fabrication and
CE
characterization of TiO2/whey protein isolate nanocomposite film, Food
AC
Hydrocoll. 25 (2011) 1098-1104. [28] M. Hassannia-Kolaee, F. Khodaiyan, R. Pourahmad, I. Shahabi-Ghahfarrokhi, Development of ecofriendly bionanocomposite: whey protein isolate/pullulan films with nano-SiO2, Int. J. Biol. Macromol. 86 (2016) 139-144. [29] K.H. Yao, J. Cai, M. Liu, Y. Yu, H.G Xiong, S.W. Tang, S.Y. Ding, Structure and properties of starch/PVA/nano- SiO2, hybrid films, Carbohyd. Polym. 86 (2011) 1784-1789. 24
ACCEPTED MANUSCRIPT [30] S. Sahraee, J.M. Milani, B. Ghanbarzadeh, H. Hamishehkar, H.S. Kafil, Physicochemical and antifungal properties of bio-nanocomposite film based on gelatin-chitin nanoparticles, Int. J. Biol. Macromol. 97 (2016) 373-381. [31] R. Thakur, B. Saberi, P. Pristijono, J. Golding, C. Stathopoulos, C. Scarlett,
PT
Characterization of rice starch- κ-carrageenan biodegradable edible film. effect
RI
of stearic acid on the film properties, Int. J. Biol. Macromol. 93 (2016) 952-960.
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[32] J.W. Li, J.W. Ma, S.H. Chen, J.W. He, Y.D. Huang, Characterization of calcium alginate/deacetylated konjac glucomannan blend films prepared by Ca2+
NU
crosslinking and deacetylation, Food Hydrocoll. 82 (2018) 363-369.
MA
[33] T. Sun, C.L. Wu, H. Hao, Y. Dai, J.R. Li, Preparation and preservation properties of the chitosan coatings modified with the in situ, synthesized nano-SiOx, Food
D
Hydrocoll. 54 (2016) 130-138.
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[34] P. Kanmani, J. W. Rhim, Physicochemical properties of gelatin/silver nanoparticle antimicrobial composite films, Food Chem. 148 (2014) 162-169.
CE
[35] K.C. Kavya, R. Jayakumar, S. Nair, K.P. Chennazhi, Fabrication and
AC
characterization of chitosan/gelatin/nano-SiO2 composite scaffold for bone tissue engineering, Int. J. Biol. Macromol. 59 (2013) 255-263. [36] P. Pietras, R. Przekop, H. Maciejewski, New approach to preparation of gelatine/SiO2 hybrid systems by the sol-gel process, Ceramics-Silikáty 57 (2013) 58-65. [37] R. Venkatesan, N. Rajeswari, Mechanical and antimicrobial properties of κ-carrageenan/SiO2 nanocomposite films for active food packaging, J. Polym. 25
ACCEPTED MANUSCRIPT Mater. 32 (2015) 457-466. [38] H. Chen, F. Wang, C.Y. Zhang, Y.C. Shi, G.Y. Jin, S.L. Yuan, Preparation of nanosilica materials: the concept from wheat straw, J. Non-Cryst. Solid 365 (50) (2010) 2781–2785.
PT
[39] M.L. Yang, J.S. Shi, Y.Z. Xia, Effect of SiO2, PVA and glycerol concentrations
RI
on chemical and mechanical properties of alginate-based films, Int. J. Biol.
SC
Macromol. 107 (2018) 2686–2694.
[40] E. Lizundia, J.L. Vilas, A. Sangroniz, A. Etxeberria, Light and gas barrier
NU
properties of plla/metallic nanoparticles composite films, Eur.Polym.J. 91 (2017)
MA
10-20.
[41] A. Fathi, M.A. Sahari, M. Barzegar, H.N. Badi, Antioxidant activity of satureja
PT E
(2013) 51-67.
D
hortensis l. essential oil and its application in safflower oil, J. Med. Plants 12
[42] A. Ali, M. Maqbool, S. Ramachandran, P.G. Alderson, Gum arabic as a novel
CE
edible coating for enhancing shelf-life and improving postharvest quality of
AC
tomato ( solanum lycopersicum, l.) fruit, Postharvest Biol. Tec. 58 (2010) 42-47. [43] M. Nasiri, M. Barzegar, M.A. Sahari, M. Niakousari, Application of tragacanth gum impregnated with satureja khuzistanica essential oil as a natural coating for enhancement of postharvest quality and shelf life of button mushroom (Agaricus bisporus), Int. J. Biol. Macromol. 106 (2017) 218-226. [44] Z. U. Khan, G. Aisikaer, R.U. Khan, J. Bu, Z. Jiang, Z. Ni, Effects of composite chemical pretreatment on maintaining quality in button mushrooms (Agaricus 26
ACCEPTED MANUSCRIPT bisporus) during postharvest storage, Postharvest Biol. Tec. 95 (2014) 36-41. [45] Z.L. Liu, X.Y. Wang, Changes in color, antioxidant, and free radical scavenging enzyme activity of mushrooms under high oxygen modified atmospheres. Postharvest Biol. Tec. 69 (2012) 1-6.
PT
[46] Y.H. Hu, C.M. Chen, L. Xu, Y. Cui, X.Y. Yu, H.J. Gao, Postharvest application of
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bisporus), Postharvest Biol. Tec.104 (2015) 33-41.
RI
4-methoxy cinnamic acid for extending the shelf life of mushroom (Agaricus
[47] C. Guillaume, I. Schwab, E. Gastaldi, N. Gontard, Biobased packaging for
NU
improving preservation of fresh common mushrooms (Agaricus bisporus), Innov.
MA
Food Sci. Emerg. Tec. 11 (2010) 690-696.
[48] Y.Y. Qin, D. Liu, Y. Wu, M.L. Yuan, L.L. Li, J.Y. Yang, Effect of
D
PLA/PCL/cinnamaldehyde antimicrobial packaging on physicochemical and
PT E
microbial quality of button mushroom (Agaricus bisporus), Postharvest Biol. Tec. 99 (2015) 73-79.
CE
[49] G. Antmann, G. Ares, P. Lema, C. Lareo, Influence of modified atmosphere
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packaging on sensory quality of shiitake mushrooms, Postharvest Biol. Tec. 49 (2008) 164-170.
27
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Figure captions
Fig. 1. Double-factors mutual effect on the water permeability rate (a: Nano-SiO2 (X1) and KGM
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(X3); b: Nano-SiO2 (X1) and KC (X2); c: KGM (X3) and KC(X2)).
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Fig. 2. SEM images and the appearance of the composite coatings (a: the appearance of the
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KC/KGM coatings; b: the SEM image of the KC/KGM coatings; c: the appearance of the nano-SiO2/KC/KGM coatings; d: the SEM image of the nano-SiO2/KC/KGM coatings).
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Fig. 3. FTIR results of the KC/KGM/nano-SiO2 films and KC/KGM coatings.
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Fig. 4. X-ray diffraction patterns of the KC/KGM/nano-SiO2 films and KC/KGM coatings. Fig. 5. The UV-Vis spectroscopy results of the KC/KGM/nano-SiO2 films and KC/KGM coatings.
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Fig. 6. Effect of the coating on the weight loss (a), surface ∆E (b), flesh ∆E (c), relative leakage
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Table captions
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rate (d), total soluble solids (e), and hardness (f) of Agaricus bisporus during storage at 4 ± 1 °C.
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Table 1 Factors and levels of experiments. Table 2 Experimental structural matrix and results of all factors. Table 3 Performances of the nanocomposite coatings.
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ACCEPTED MANUSCRIPT Optimization of konjac glucomannan /carrageenan/nano-SiO2 coatings for extending the shelf-life of Agaricus bisporus
Rongfei Zhang, Xiangyou Wang*, Ling Li, Meng Cheng, Liming Zhang School of Agricultural Engineering and Food Science, Shandong University of
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Technology, Zibo 255000, China
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Tel.:+86-533-2780897;
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Fax: +86-533-2780897;
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*Corresponding author: Professor Xiangyou Wang, E-mail address: [email protected]
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Table 1 Factors and levels of experiments. Factors
X1 Nano-SiO2/%
X2 KC/%
X3 KGM/%
0.50 0.40 0.30 0.20 0.10
0.60 0.52 0.40 0.28 0.20
0.70 0.62 0.50 0.38 0.30
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γ 1 0 -1 -γ
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Levels
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All concentrations (%) of materials were according to the volume of water (w/v).
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Table 2 Experimental structural matrix and results of all factors. X3 KGM/ %
WVP /g·(m2·d)-1
1
1
1
1
75.33
2
1
1
-1
77.51
3
1
-1
1
71.65
4
1
-1
-1
5
-1
1
1
6
-1
1
7
-1
-1
8
-1
-1
9
γ
10
-γ
11
0
12
0
13
0
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80.66 81.35 74.34
1
84.42
-1
85.35
0
0
74.56
0
0
82.43
γ
0
60.86
-γ
0
65.89
0
γ
89.50
0
0
-γ
90.29
0
0
0
66.74
0
0
0
71.09
0
0
0
73.25
0
0
0
72.23
19
0
0
0
69.41
20
0
0
0
55.56
21
0
0
0
60.80
22
0
0
0
64.29
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0
0
0
55.25
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16 17
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X2 KC/%
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Experimental Group
X1 Nano-SiO2/%
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No.
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Table 3 Performances of nano-composite coatings Nano-SiO2/KC/KGM
KC/KGM
coatings
coatings
WVP/(g·m ·d )
62.31±3.39a
71.34±4.53b
Transparency/%
83.41±0.02b
84.24±0.06a
WS/%
51.78±0.002a
49.36±0.115b
-2
-1
71.36±0.015b
CDTR/( g·m ·d )
0.180±0.002a
0.210 ±0.024b
OTR/( g·m-2·d-1)
0.015±0.001a
0.025±0.004b
TS / N
323.16±0.20a
Thickness/(μm )
26.11±0.21a
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76.90±0.023a -1
-2
189.37±0.60b 25.80±0.18a
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Means within each column with same letters are not significantly different (P < 0.05).
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Data are means ± SD.
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ACCEPTED MANUSCRIPT Highlights •The packaging and fresh-keeping properties of the KGM/KC coatings is improved by nano-SiO2. • Incorporation of nano-SiO2 was a good way to delay UV light affecting the food qualities. •The KC/KGM structure in hydrogen-bonds are slightly affected by nano-SiO2.
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•The preservation properties on Agaricus bisporus are improved.
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Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6