Food Technology
Maryam Zamanian; Hassan Sadrnia; Mehdi Khojastehpour; Fereshteh Hosseini; Jules Thibault
Abstract
Introduction: Among the different types of polymers used for packaging and coating, polyvinyl alcohol (PVA), given its very enviable properties, has been used in various industrial applications. It is used for instance as controlled release in pharmaceutical elements, paper, textile and food supplement ...
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Introduction: Among the different types of polymers used for packaging and coating, polyvinyl alcohol (PVA), given its very enviable properties, has been used in various industrial applications. It is used for instance as controlled release in pharmaceutical elements, paper, textile and food supplement coating due to its good physical properties, chemical resistance, thermostability, film-forming capability, efficiency and biodegradability. The aim of this work was to examine the combined effect of montmorillonite (MMT) platelets and titanium oxide (TiO2) spherical nanoparticles on the physical and mechanical properties of PVA/ TiO2/MMT nanocomposites, and to determine the optimal combination to provide good properties, using response surface methodology (RSM). Materials & methods: PVA, PVA/TiO2, PVA/MMT and PVA/ TiO2/MMT nanocomposite films were prepared by the solution casting method. For each sample, 1.8 g of PVA was dissolved in 50 mL deionized water and maintained for 24 h at room temperature. The mixture was then heated to 90˚C and stirred using a magnetic stirrer up to 3 h to ensure the complete dissolution of PVA, followed by cooling down the solution to room temperature. Various amounts of TiO2 nanoparticles (1 and 2 w% on a dry basis) were added to deionized water and agitated with a stirrer for 12 h at 500 rpm. This method was also used for MMT (2 and 4 w% on a dry basis). The nanoparticle suspension was subjected to ultrasonic homogenization for 20 min to ensure a good dispersion. The 50 mL nanoparticle suspension was added to the PVA solution drop by drop during a period of 5 min while maintaining intense stirring (1000 rpm). Mixing was continued and glycerol (30 w% based on the polymer) was added. Vacuum with a rotary vacuum pump was applied to remove air bubbles from the solution. The solution was poured into a 15-cm internal diameter Petri dish with a perfectly flat bottom and carefully aligned horizontally. Homogeneous films were peeled off after drying in an air oven at 40˚C for 72 h. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were performed for characterizing the morphology of nanocomposite films. The effect of these two nanoparticles on physical and mechanical properties, was evaluated by response surface methodology (RSM). A three-level factorial design was used to define the test points for the series of experiments. Among the various design alternatives suggested by theoretical algorithm, the selected design consisted of 13 experiments including five replicate central points used for variance calculation. Furthermore, PVA film data were analyzed using the Design-Expert program (Version 7.0, Stat-Ease Inc., Minneapolis, Minnesota) to find the optimum combination of constituents for the best properties. Results and discusions: X-ray diffraction patterns showed that the nanoparticles were well dispersed in the polymer matrix of PVA/ TiO2 and PVA / MMT films with layered microstructure. In addition, the linear effect of MMT nanoparticles and the interaction of TiO2 and MMT on tensile strength were significant. The linear, quadratic and interaction effects of both nanoparticles on Young's modulus were also significant. In general, the optimum values of TiO2 and MMT were 1% and 4% respectively for mechanical properties. The presence of both nanoparticles had a significant effect on transparency and ΔE. Results of nanocomposite films indicated that the film with 2% TiO2 and 4% MMT has higher WI and actually is darker than other samples. By analyzing different results with response surface method, the nanocomposite film with 0.5% TiO2 and 4% MMT was proposed as optimum combination for mechanical and physical properties
Seyed Mahdi Ojagh; Akbar Vejdan Taleshmikaeil; Mehdi Abdollahi
Abstract
Introduction: Natural polymers have gained increasing attention for the development of packaging to reduce ecologically-related problems caused by plastic packaging (environmental pollution). Among these natural polymers, proteins such as gelatin is considered a good candidate for food packaging. However, ...
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Introduction: Natural polymers have gained increasing attention for the development of packaging to reduce ecologically-related problems caused by plastic packaging (environmental pollution). Among these natural polymers, proteins such as gelatin is considered a good candidate for food packaging. However, several studies have shown that gelatin films are brittle, and their hydrophilic nature connotes high water vapor permeability and water solubility. Different solutions have been suggested to overcome these weaknesses, including adding crosslinking agents and chemical modification, adding nanoparticles and developing bio-film blends and bilayers with polysaccharides. Agar is a polysaccharide extracted from marine red algae, which is biocompatible, has good mechanical properties and possesses good film-forming properties. Preventing food spoilage from light and oxygen-induced oxidation is one of the greatest concerns in the food industry. Despite having good mechanical and relatively good water vapor permeability properties, protein- or polysaccharide-based films don't have sufficient barrier properties against oxygen and UV light that can't properly prevent the oxidation of food products. Among nanoparticles, metal oxides like TiO2 (such as antiradiation and antimicrobial activities) and Montmorillonite (such as improved mechanical and barrier properties against moisture, WVP and gases) have evidenced good potential to improve functional properties of bio-films. Thus, the present study aimed to develop a new biodegradable bilayer agar/gelatin film incorporating nanoclay and TiO2 for food packaging, with maximum water sensitivity and maximum UV light and oxygen barrier properties.
Materials and Methods: Agar/gelatin bilayer films were prepared by a two-step casting technique. First, the agar layer was produced by solubilization of 1.5 g of agar powder (agar-agar analytical grade were obtained from Merck Co., Germany) in 100 mL of distilled water. Then, glycerol (obtained from Merck Co., Germany) was added as plasticizer. The agar film-forming solution was casted onto petri-dish. In the next step, the gelatin (obtained from cold water fish skin was purchased from Sigma-Aldrich, St. Louis, MO, USA) solutions were prepared by dissolving 4 g of the fish gelatin in 100 mL of distilled water. Glycerol was also added as plasticizer. The TiO2 dispersions (in ratios of 0 and 2% of the gelatin) and MMT (Na+–montmorillonite (in ratios of 0, 3, 5 and 10% of the gelatin)) were added to the gelatin solution and stirred and sonnicated. Finally, produced solutions were then casted. The agar/gelatin films, with or without TiO2 and MMT, were characterized using SEM analysis. Film transparency, water vapor permeability, water solubility, swelling, surface color and mechanical properties of the bilayer films were also examined.
Results and Discussion: In this study, bilayer films based on agar and gelatin incorporated with TiO2-MMT nanoparticles have been successfully developed. Results demonstrated that some properties of the bilayer films were greatly influenced by TiO2 and MMT nanoparticle content. So that, the addition of TiO2 decreased water vapor permeability of the bilayers more than 15%, upon increasing TiO2 content to 2%. However, swelling ratio and moisture content increased with the increase in the nano-TiO2 content, probably due to the hydrophilic nature of the TiO2 nanoparticles. Also, whiteness index (WI) increased by adding 2% of TiO2 nanoparticles. As shown in the surface photograph of the bilayer films, TiO2 generated more opaque and whiter films, which might be related to the white color of TiO2 nanoparticles in solution form. Also, the addition of MMT (0, 3, 5, and 10%) to bilayer-2% TiO2 significantly decreased water vapor permeability and transmission of UV light of the bilayer films. However, tensile strength (TS) decreased with further increase of the nanoparticle concentration. Increasing the concentration of nanoparticles' MMT to 5%, the tensile TS of the agar/gelatin films increased from 12.86 to 20.54 MPa; it might also be related to the interactions between sulphydryl and carboxylic groups from certain amino acids in the gelatin structure with MMT and TiO2 nanoparticles. However, the TS decreased again with further increase of the filler content up to 10% MMT. Also, the addition of MMT from 3%-10% concentration significantly reduced the elongation at break value (EB) of the bilayer films from 41.77 to 28.90% for the bilayer films (p
Ronak Gholami; Jalal Dehghan nia; Babak Ghanbarzadeh
Abstract
Introduction: In recent years, demand for edible and biodegradable films has increased. One reason for this increase is the pollution caused by synthetic polymers. Edible films are produced from different biopolymers such as lipids, polysaccharides and proteins. Starch is a common polysaccharide in the ...
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Introduction: In recent years, demand for edible and biodegradable films has increased. One reason for this increase is the pollution caused by synthetic polymers. Edible films are produced from different biopolymers such as lipids, polysaccharides and proteins. Starch is a common polysaccharide in the preparation of edible films which is taken into consideration because of its low price and easy access. Structure and composition of starch-based films affects the resulting film properties such as moisture sorption, gas permeability, plasticizer crystallization, glass transition temperature and its mechanical properties. Starch films have usually poor mechanical properties and are permeable to water vapor. The use of nanofillers such as cellulose nanocrystal (CNC) in the structure of starch films and production of nanocomposite films is one way to modify properties of the films. The most important purpose of the application of edible films is to prevent moisture or other compounds such as carbon dioxide or volatile components transfer between the product and the environment or between different layers of the product. Modeling mass transfer and moisture permeability of edible films can be effective in predicting film properties and packaged product during storage. For example, it can be predicted that at a certain temperature, relative humidity and time, how much moisture packaging material will absorb. Therefore, before using edible film as a protective coating for food, calculation of the amount of moisture sorption and permeability to water vapor is essential. The purpose of this study was to investigate mass transfer in starch - CNC nanocomposite films. The effect of adding different percentages of CNC on the water vapor permeability and moisture sorption kinetics of nanocomposite films was studiedMaterials and Methods: First, 100 ml of potato starch solution with a concentration of 4% (w/v) was prepared by dispersion of the starch in distilled water and was gelatinized at 90ºC for 5 min. Different levels of CNC (0, 3, 5, 7 and 9% w/w) were dissolved in distilled water and were added to the gelatinized starch after treatment with ultrasound for 10 min. Then, glycerol, as a plasticizer, with concentrations of 0.2, 0.3 and 0.4% (w/w) were added to the solution. The film solutions were distributed on polystyrene surfaces and the resulting films were dried in an oven at 40°C for 24 hours. The Fickʹs second law and four empirical equations were used for moisture sorption modeling of samples. The effect of glycerol concentration on water vapor permeability was investigated and the experimental data were fitted with an exponential model.Results and Discussion: By increasing the concentration of CNC, moisture content of the nanocomposite films declined. Effective moisture diffusion coefficient values for nanocomposite samples were higher than the pure starch film. The coefficient increased from 0.293×10-13 to 0.547×10-13 m2/s by increasing CNC concentration from 0 to 9%. This result can be attributed to the influence of cellulose nanofibers on the polymer matrix and gaps creation in the polymer amorphous regions. This, in turn, would facilitate moisture diffusivity into the polymer structure. It should be noted that plasticizer presence in the nanocomposite structure can be an important factor. Regarding that plasticizer lead to increase in polymer chain mobility, simultaneous presence of CNC and plasticizer could lead to create gaps in the structure of nonocompositefim. As expected, in the absence of plasticizer, the effective moisture diffusion coefficient in nanocomposite samples decreased by increasing the concentration of nanoparticles due to high immobility of polymer chains. In addition, the initial stages of moisture sorption were well described by the Fickʹs law but due to the polymer relaxation between 2.5 - 9 h interval, its behavior was deviated from this law. Finally, after about 9 hours, it was observed that the equilibrium moisture content of the nanocomposite samples were consistent with the values predicted by the Fickʹs model. Equilibrium moisture content depends on the hydrophilic locations of the nanocomposite structure. These locations have the ability to absorb moisture and this ability is not influenced by changes in the structure of the polymer during the moisture sorption process. Despite higher levels of effective moisture diffusion coefficients in starch-nanocrystalline cellulose nanocomposites compared to pure starch film, moisture content was lower in nanocomposite films. These results are probably due to the nature of nanocrystalline cellulose which is resistant to water and is compatible with the starch polymer. Nanocrystalline cellulose has the ability to make many hydrogen bonds with the hydrophilic polymer matrix. This results in decreasing hydrophilic property of starch. On the other hand, in all samples, the permeability to water vapor reduced with increasing nanoparticles concentration. For example, in the starch film which contained 0.4% glycerol, water vapor permeability was 2.62×10-7g.m/m2.h.Pa; with the addition of nanocrystalline cellulose to 9%, its value was decreased to 1.8×10-7g.m/m2.h.Pa. Moreover, the permeability to water vapor in all cases increased by increasing the concentration of plasticizer. Results also showed that there is an exponential relationship between the water vapor permeability and plasticizer content.Conclusion: By increasing the concentration of CNC, moisture content of the nanocomposite films declined. Effective moisture diffusion coefficient values for nanocomposite samples were higher than the pure starch film. The coefficient increased by increasing CNC concentration. The initial stages of moisture sorption were well described by the Fickʹs law but due to the polymer relaxation, its behavior was deviated from this law. Finally, after about 9 hours, it was observed that the equilibrium moisture content of the nanocomposite samples were consistent with the values predicted by the Fickʹs model. In addition, in all samples, the permeability to water vapor reduced with increasing nanoparticles concentration. However, the permeability to water vapor increased by increasing the concentration of plasticizer. Results also showed that there is an exponential relationship between the water vapor permeability and plasticizer content
Leila Abolghasemi Fakhri; Babak Ghanbarzadeh; Jalal Dehghan nia; Ali Akbar Entezami
Abstract
The high hydrophilic property of biopolymer based plastics is one of the most important defects of them. Blending biopolymers with compatible synthetic polymers and using nano particles such as nanoclay as nanofiller are improving methods that have been extensively considered in recent years. Carboxymethyl ...
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The high hydrophilic property of biopolymer based plastics is one of the most important defects of them. Blending biopolymers with compatible synthetic polymers and using nano particles such as nanoclay as nanofiller are improving methods that have been extensively considered in recent years. Carboxymethyl cellulose (CMC) is one of the lowest cost biopolymers that have enormous applications in different industries and polyvinyl alcohol (PVA) is a synthetic polymer which has a high compatibility with biopolymers. In this research, CMC-PVA nanocomposites containing 3-10% Montmorillonite (W/W CMC) were prepared by casting method. The X-ray diffraction (XRD) results indicated the formation of an exfoliated nanostructure in all MMT content samples. Nanocomposites containing 10% MMT exhibited 29.06% reduction in water vapor permeability (WVP) compared to the blend film without nanoclay. Samples with 10% MMT, showed the lowest surface hydrophilisity (contact angle = 65.1o). The differential scanning calorimetry (DSC) results indicate that by increasing of MMT contents, the glass transition disappeared gradually and no glass transition was observed in the thermograms of the films containing 5, 7 and 10% MMT.
Babak Ghanbarzadeh; Ali Akbar Entezami
Abstract
The starch based films have some disadvantages such as weak mechanical and poor water barrier properties that restrict their applications in food packaging. In the present research, the polyvinyl alcohol (POVH), as a compatible polymer, and montmorillonite (MMT) nanoclay, as a nanofiller, were added ...
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The starch based films have some disadvantages such as weak mechanical and poor water barrier properties that restrict their applications in food packaging. In the present research, the polyvinyl alcohol (POVH), as a compatible polymer, and montmorillonite (MMT) nanoclay, as a nanofiller, were added to plasticized starch film (PS) to improve its properties and also to produce PS-MMT-PVOH nanocomposits with different MMT content (3,5,7%). The results of X-ray diffraction (XRD) villustrated that the nanostructure of investigated starch based nanocomposites films has an exfoliated structure which can be attributed to the good dispersing of filler in polymer matrix. DSC results showed that with adding MMT and increasing its content from 0 to 7%, melting point and Tg increased from 242ᵒC to 262ᵒC and 148ᵒC to 188ᵒC. The results of tensile test showed that addition of PVOH and MMT increased the ultimate tensile strength (UTS) and decreased the water vapor permeability (WVP) of nanocomposite films.
