Development of Antimicrobial Gelatin-Based Edible Films by Incorporation of <Emphasis Type="Italic">Trans</Emphasis>-Anethole/β-Cyclodextrin Inclusion Complex

Antimicrobial activity is an attractive property for packaging materials which can extend the shelf life of products and provide microbial safety for consumers. The study aimed to analyze the physicochemical and antimicrobial properties of gelatin-based edible films containing trans-anethole as the active additive. Encapsulation with β-cyclodextrin was used as an effective way to introduce trans-anethole into gelatin matrix. The results showed that the trans-anethole/β-cyclodextrin inclusion complex could be evenly dispersed in the gelatin-based edible films with appropriate addition. The incorporation of trans-anethole conferred the edible films with good antimicrobial activity as expected, which increased with the content of trans-anethole increasing. Moreover, the addition of inclusion complex improved the tensile strength and surface hydrophobicity and reduced the moisture content of the edible films. It was interesting that the edible films presented great UV light barrier property and it was increased by the addition of inclusion complex. Overall, the antimicrobial gelatin-based edible films showed great potential as bioactive packaging materials to extend food shelf life.     

Antimicrobial activity of Zataria multiflora Boiss. essential oil incorporated with whey protein based films on pathogenic and probiotic bacteria

The antimicrobial potential of whey protein isolate (WPI) edible films containing 1–4% (v/v) Zataria multiflora Boiss. essential oil (EO) on food‐borne pathogenic bacteria (Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Bacillus cereus) and probiotic bacteria (Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus casei subsp. casei) was evaluated. WPI films incorporated with 2% (v/v) of this EO inhibited the growth of all tested pathogenic bacteria and gram‐negative bacteria were more sensitive than gram‐positive bacteria. Incorporation of the EO at higher than 2% (v/v) showed significant antimicrobial effects (P < 0.05) for S. enteritidis and L. acidophilus. The growth of all probiotic lactic acid‐producing bacteria also inhibited when 2% of the EO was added. Comparison of an image processing‐based method with conventional method for measuring of inhibitory effects of edible films exhibited high correlations (R² ≥ 0.876) between the two methods. These results revealed that Z. multiflora Boiss. EO is a good antimicrobial additive for some food applications when included into WPI edible films.     

Antimicrobial effectiveness of oregano and sage essential oils incorporated into whey protein films or cellulose‐based filter paper

BACKGROUND: In this study the antimicrobial effectiveness of oregano and sage essential oils (EOs) incorporated into two different matrices, whey protein isolate (WPI) and cellulose‐based filter paper, was analysed. RESULTS: Antimicrobial properties of WPI‐based films containing oregano and sage EOs were tested against Listeria innocua, Staphylococcus aureus and Salmonella enteritidis. Oregano EO showed antimicrobial activity against all three micro‐organisms. The highest inhibition zones were against L. innocua. However, sage EO did not show antimicrobial activity against any of the micro‐organisms. Antimicrobial activity was confirmed for both EOs using cellulose‐based filter paper as supporting matrix, although it was significantly more intense for oregano EO. Inhibition surfaces were significantly greater when compared with those of the WPI films. This finding is likely due to the higher porosity and diffusivity of the active compounds in the filter paper. CONCLUSION: The interactions between the EOs and the films have a critical effect on the diffusivity of the active compounds and therefore on the final antimicrobial activity. As a result, to obtain active edible films, it is necessary to find the equilibrium point between the nature and concentration of the active compounds in the EO and the formulation of the film. Copyright © 2010 Society of Chemical Industry     

Antimicrobial activity of whey protein based edible films incorporated with oregano,rosemary and garlic essential oils

The use of edible films to release antimicrobial constituents in food packaging is a form of active packaging. Antimicrobial properties of spice extracts are well known, however their application to edible films is limited. In this study, antimicrobial properties of whey protein isolate (WPI) films containing 1.0–4.0% (wt/vol) ratios of oregano, rosemary and garlic essential oils were tested against Escherichia coli O157:H7 (ATCC 35218), Staphylococcus aureus (ATCC 43300), Salmonella enteritidis (ATCC 13076), Listeria monocytogenes (NCTC 2167) and Lactobacillus plantarum (DSM 20174). Ten millilitres of molten hard agar was inoculated by 200 μl of bacterial cultures (colony count of 1 × 10⁸ CFU/ml) grown overnight in appropriate medium. Circular discs of WPI films containing spice extracts, prepared by casting method, were placed on a bacterial lawn. Zones of inhibition were measured after an incubation period. The film containing oregano essential oil was the most effective against these bacteria at 2% level than those containing garlic and rosemary extracts (P < 0.05). The use of rosemary essential oil incorporated into WPI films did not exhibit any antimicrobial activity whereas inhibitory effect of WPI film containing garlic essential oil was observed only at 3% and 4% level (P < 0.05). The results of this study suggested that the antimicrobial activity of some spice extracts were expressed in a WPI based edible film.     

Development of Antimicrobial and Controlled Biodegradable Gelatin-Based Edible Films Containing Nisin and Amino-Functionalized Montmorillonite

The utilization of petroleum-derived synthetic materials causes severe ecological problems, such as environmental pollution and soil degradation. Hence, using naturally derived and renewable materials to fabricate novel biodegradable films for safe and effective food packaging has been a subject of interest over the years. Here, the novel antimicrobial and controlled biodegradable gelatin-based edible films were developed using nisin as the antimicrobial agent, amino-functionalized montmorillonite as the nanoparticle filler, and dialdehyde xanthan gum as the crosslinking agent. The results indicate that the ultraviolet barrier ability, water resistance, and mechanical properties of gelatin-based edible films are obviously improved on account of the crosslinking effect. Moreover, the resulting films demonstrate antimicrobial activity against Staphylococcus aureus owning to the addition of nisin. Furthermore, the crosslinking can slow down the erosion of the edible films by fungi due to the improved hydrophobicity and compact structure. Particularly, the edible films can be completely biodegraded in soil within 30 days. Meanwhile, the rate of soil biodegradation can be well controlled by adjusting the crosslinking degree. Overall, this novel gelatin-based edible films have potential applications in food packaging.     

Covalent Whey Protein–Rosmarinic Acid Interactions: A Comparison of Alkaline and Enzymatic Modifications on Physicochemical,Antioxidative, and Antibacterial Properties

The covalent interactions between whey protein isolate (WPI) and rosmarinic acid (RosA) at two different conditions, alkaline (pH 9) and enzymatic (in the presence of tyrosinase, PPO), at room temperature with free atmospheric air were studied. The conjugates formed between WPI and RosA were characterized in terms of their physicochemical and functional properties. The changes in protein structure were analyzed by intrinsic fluorescence and binding of 8‐anilino‐1‐naphthalenesulfonic acid. The findings show that the covalent interactions caused a decrease in free amino and thiol groups and tryptophan content at both conditions. The decrease at enzymatic conditions was lower than at alkaline conditions. In addition, modified WPI at alkaline conditions exhibited higher antioxidative capacity compared to the modification at enzymatic conditions. However, WPI modified at enzymatic condition showed mild antimicrobial activity against Staphylococcus aureus LMG 10147 and MU50 compared to WPI modified at alkaline conditions and unmodified WPI (control). The modified WPI can be used as multifunctional ingredient into various food products with an additional health promoting effect of the bound phenolic compounds.     

Evaluation of Antibacterial Activity of Whey Protein Isolate Coating Incorporated with Nisin,Grape Seed Extract,Malic Acid,and EDTA on a Turkey Frankfurter System

ABSTRACT: The effectiveness of whey protein isolate (WPI) coatings incorporated with grape seed extract (GSE), nisin (N), malic acid (MA), and ethylenediamine tetraacetic acid (EDTA) and their combinations to inhibit the growth of Listeria monocytogenes, E. coli O157:H7, and Salmonella typhimurium were evaluated in a turkey frankfurter system through surface inoculation (approximately 10⁶ CFU/g) of pathogens. The inoculated frankfurters were dipped into WPI film forming solutions both with and without the addition of antimicrobial agents (GSE, MA, or N and EDTA, or combinations). Samples were stored at 4 °C for 28 d. The L. monocytogenes population (5.5 log/g) decreased to 2.3 log/g after 28 d at 4 °C in the samples containing nisin (6000 IU/g) combined with GSE (0.5%) and MA (1.0%). The S. typhimurium population (6.0 log/g) was decreased to approximately 1 log cycles after 28 d at 4 °C in the samples coated with WPI containing a combination of N, MA, GSE, and EDTA. The E. coli O157:H7 population (6.15 log/g) was decreased by 4.6 log cycles after 28 d in samples containing WPI coating incorporated with N, MA, and EDTA. These findings demonstrated that the use of an edible film coating containing nisin, organic acids, and natural extracts is a promising means of controlling the growth and recontamination of L. monocytogenes, S. typhimurium, and E. coli O157:H7 in ready‐to‐eat poultry products.     

Physical Characteristics,Release Properties,and Antioxidant and Antimicrobial Activities of Whey Protein Isolate Films Incorporated with Thyme (<Emphasis Type="Italic">Thymus vulgaris</Emphasis> L.) Extract-Loaded Nanoliposomes

The aim of the current research was to fabricate, characterize, and compare physical, mechanical, antimicrobial, antioxidant, and release properties of whey protein isolate (WPI)-based films containing free or nanoencapsulated thyme (Thymus vulgaris) extract (TE) at concentrations of 0, 5, 10, and 15% w/w of WPI. Nanoliposomes with an average size of 350 nm were prepared using thin-film hydration and sonication method. The data obtained from FTIR reflected the occurrence of some new interactions between WPI and nanoliposomes. XRD results approved the negative effect of free TE on the crystallinity of WPI. Besides, SEM images showed that free TE caused the cracks and holes in the WPI matrix to increase. However, the encapsulated TE did not show these negative effects. The nanoliposome incorporation improved the mechanical stiffness, leading to a decrease in the water vapor permeability (WVP). The possible antimicrobial activity of the films containing TE-loaded nanoliposomes against Staphylococcus aureus and Escherichia coli was decreased in comparison to the free TE-incorporated films, probably due to the inhibition effect of the encapsulation preventing the release of TE from the matrix. In addition, the antioxidant potential of the films containing TE-loaded nanoliposomes was lower than that of free TE-incorporated films. Release studies indicated that the migration of TE in ethanol 95% simulant decreased significantly by the nanoencapsulation of TE. However, the release rate increased by an increase in temperature in both types of active films. Therefore, this work showed that there is a potential for the production of antioxidant and antimicrobial controlled-release nanoactive WPI-TE films for use in food packaging and medical fields.     

Effect of temperature,pH and film thickness on nisin release from antimicrobial whey protein isolate edible films

BACKGROUND: An active packaging film based on whey protein isolate (WPI) was developed by incorporating nisin to promote microbial food safety. The effect of temperature and pH on the release of nisin from edible films of different thickness was investigated. The film mechanical properties and inhibitory effect were also evaluated. RESULTS: Nisin release was significantly favoured by low pH, with the highest release after 24 h (1325 IU), which was not significantly affected by temperature (5 or 10 °C). Thickness significantly affected film elongation, with thicker films showing the highest elongation (54.3 ± 2.7%). Water vapour permeability (0.15 ± 0.4 g mm m^?2 kPa^?1 h^?1) and elastic modulus were not significantly affected by thickness. The highest nisin effective diffusivity (5.88 × 10^?14 m² s^?1) was obtained using a solution at pH 4, 112 µm film thickness and a temperature of 5 °C. More than four log cycles of Brochotrix thermosphacta were reduced from the surface of a ham sample after 8 days of incubation at 4 °C by the active WPI film containing 473 IU cm^?2 nisin. CONCLUSION: Nisin diffusivity from WPI edible films was favoured at lower pH and film thickness. This active packaging film may be used to preserve the quality and safety of meat products. Copyright © 2009 Society of Chemical Industry     

Antimicrobial Effects of Lactoferrin, Lysozyme, and the Lactoperoxidase System and Edible Whey Protein Films Incorporating the Lactoperoxidase System Against Salmonella enterica and Escherichia coli O157:H7

Lactoferrin (LF), lysozyme (LZ), the lactoperoxidase system (LPOS), and edible whey protein isolate (WPI) films incorporating LPOS were studied for inhibition of Salmonella enterica and Escherichia coli O157:H7. Antimicrobial effects of LF (5 to 40 mg/mL), LZ (1 to 20 mg/mL), and LPOS (0.5% to 5.0% [w/v] [0.03–.25 g/g, dry basis]) were examined by measuring turbidity of antimicrobial‐containing media after inoculation and by examining cell inhibition by WPI films incorporating LPOS (LPOS‐WPI films) on an agar recovery medium. Elastic modulus (EM), tensile strength (TS), percent elongation (%E), oxygen permeability (OP), and Hunter L, a and b of WPI films incorporating 0.03 to 0.25 g/g of LPOS were compared with those of plain WPI films without LPOS. The growth of S. enterica and E. coli O157:H7 (4 log colony‐forming units [CFU]/mL) in tryptic soy broth (TSB) was not prevented by LF at ≥20 and ≥40 mg/mL, respectively. S. enterica and E. coli O157:H7 in TSB were not inhibited by LZ at ≥ 6 and ≥ 20 mg/mL, respectively. LPOS at concentrations of 2.75% (w/v) and 1.0% (w/v) reduced S. enterica and E. coli O157:H7 to below the limit of detection (1 CFU/mL) in TSB, respectively. LPOS‐WPI films (0.15 g/g) completely inhibited S. enterica and E. coli O157:H7 (4 log CFU/cm²), inoculated either onto agar before placing the film disc or onto top of the film disc. Incorporation of 0.25 g/g of LPOS decreased EM, TS, and %E. The oxygen barrier property of WPI films was improved with the incorporation of LPOS at 0.15 to 0.25 g/g.     

Physical and thermo-mechanical properties of whey protein isolate films containing antimicrobials, and their effect against spoilage flora of fresh beef

The effectiveness of antimicrobial films against beef's spoilage flora during storage at 5 °C and the impact of the antimicrobial agents on the mechanical and physical properties of the films were examined. Antimicrobial films were prepared by incorporating different levels of sodium lactate (NaL) and -polylysine (-PL) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were affected only by the addition of NaL at all concentrations used since an increased water uptake and permeability were observed with the addition of NaL into the protein matrix. An increase of the glass transition temperature (5–15 °C) of the sorbitol region, as determined by Dynamic Mechanical Thermal Analysis (DMTA), was caused by the addition of -PL into the WPI specimens. Instead, incorporation of NaL into the protein matrix did not alter its thermo-mechanical behavior. The addition of NaL at concentrations of 1.0% and 1.5% w/w in the film-forming solution resulted in a decline of maximum tensile strength (σ_max) and Young modulus (E). A decrease of E and σ_max, accompanied with an increase in elongation at break (%EB), was also observed with increasing -PL concentration, at moisture contents higher that 10% (w/w). The antimicrobial activity of the composite WPI films was tested on fresh beef cut portions. The maximum specific growth rate (μ_max) of total flora (total viable count, TVC) was significantly reduced with the use of antimicrobial films made from 0.75% w/w -PL in film-forming solutions (p < 0.05), while the growth of Lactic Acid Bacteria was completely inhibited. Significant inhibition of growth of the total flora and pseudomonads was also observed with the use of films made with protein solutions containing 2.0% w/w NaL. These results pointed to the effectiveness of the antimicrobial whey protein films to extend the shelf life of fresh beef.     

Physicochemical, nutritional, and antimicrobial properties of wine grape (cv. Merlot) pomace extract-based films

Abstract: Wine grape pomace (WGP) (cv. Merlot) extract‐based films were studied in terms of their physicochemical, mechanical, water barrier, nutritional, and antibacterial properties. Pomace extract (PE) was obtained by hot water extraction and had a total soluble solid of 3.6% and pH 3.65. Plant‐based polysaccharides, low methoxyl pectin (LMP, 0.75% w/w), sodium alginate (SA, 0.3% w/w), or Ticafilm^® (TF, 2% w/w), was added into PE for film formation, respectively. Elongation at break and tensile strength were 23% and 4.04 MPa for TF‐PE film, 25% and 1.12 MPa for SA‐PE film, and 9.89% and 1.56 MPa for LMP‐PE film. Water vapor permeability of LMP‐PE and SA‐PE films was 63 and 60 g mm m^?2 d^?1 kPa, respectively, lower than that of TF‐PE film (70 g mm m^?2 d^?1 kPa) (P < 0.05). LMP‐PE film had higher water solubility, indicated by the haze percentage of water after 24 h of film immersion (52.8%) than that of TF‐PE (25.7%) and SA‐PE (15.9%) films, and also had higher amount of released phenolics (96.6%) than that of TF‐PE (93.8%) and SA‐PE (80.5%) films. PE films showed antibacterial activity against both Escherichia coli and Listeria innocua, in which approximate 5‐log reductions in E. coli and 1.7‐ to 3.0‐log reductions in L. innocua were observed at the end of 24 h incubation test compared with control. This study demonstrated the possibility of utilizing WGP extracts as natural, antimicrobial, and antioxidant promoting film‐forming material for various food applications. Practical Application: WGP extract‐based edible films with the addition of a small amount of commercial polysaccharides showed attractive color and comparable mechanical and water barrier properties to other edible films. The films also demonstrated their potential antioxidant and antimicrobial functions. Hence, they may be used as colorful wraps or coatings for food, pharmaceutical, or other similar applications.     

Fungal Inactivation by Mexican Oregano (Lippia berlandieri Schauer) Essential Oil Added to Amaranth,Chitosan, or Starch Edible Films

ABSTRACT: Edible films can incorporate antimicrobial agents to provide microbiological stability, since they can be used as carriers of a wide number of additives that can extend product shelf life and reduce the risk of pathogenic bacteria growth on food surfaces. Addition of antimicrobial agents to edible films offers advantages such as the use of low antimicrobial concentrations and low diffusion rates. The aim of this study was to evaluate inhibition of Aspergillus niger and Penicillium spp. by selected concentrations of Mexican oregano (Lippia berlandieri Schauer) essential oil added to amaranth, chitosan, or starch edible films. Oregano essential oil was characterized by gas chromatography-mass spectrometry (GC/MS) analysis. Amaranth, chitosan, and starch edible films were formulated with essential oil concentrations of 0%, 0.25%, 0.50%, 0.75%, 1%, 2%, and 4%. Mold radial growth was evaluated inoculating spores in 2 ways: edible films were placed over inoculated agar, Film/Inoculum mode (F/I), or the edible films were first placed in the agar and then films were inoculated, Inoculum/Film mode (I/F). The modified Gompertz model adequately described growth curves. There was no significant difference (P > 0.05) in growth parameters between the 2 modes of inoculation. Antifungal effectiveness of edible films was starch > chitosan > amaranth. In starch edible films, both studied molds were inhibited with 0.50% of essential oil. Edible films added with Mexican oregano essential oil could improve the quality of foods by controlling surface growth of molds.     

QUALITY PRESERVATION OF COMMERCIAL FISH BALLS WITH ANTIMICROBIAL ZEIN COATINGS

ABSTRACT

To enhance the practical application of active edible coatings in the food industry, edible zein coatings incorporated with nisin (54.4 AU/cm²) or nisin/ethylenediaminetetraacetic acid (EDTA; 568 µg/cm²) were used to preserve the quality of commercially manufactured fish balls. The microbial load, total basic volatile nitrogen (TVB‐N) content and weight loss were served as quality indicators. The increase of microbial load of fish balls coated with antimicrobial zein during a 15‐day refrigeration storage period was less than 1 log cfu/g, while the microbial load increased about 3 log cfu/g for the control group without the coating treatment. The formation of TVB‐N was significantly (P < 0.05) reduced when fish balls were coated with antimicrobial zein. With or without antimicrobial agent, coated fish balls exerted significantly (P < 0.05) less weight loss than uncoated fish balls.

PRACTICAL APPLICATIONS

Although edible coatings or films containing bioactive substance have been intensively studied over the last few decades, most of these, still, have not had widespread commercial applications because the majority of studies were conducted with food‐simulated systems or food samples produced in laboratory. The fish balls commercially manufactured in a fishery product factory was used to demonstrate the efficacy of antimicrobial edible coating will enhance the confidence of food manufactures to apply the technology in their products.     

Effect of active packaging incorporated with triclosan on bacteria adhesion

ABSTRACT: Antimicrobial polyethylene and cellulose based films incorporated with triclosan were studied. The antimicrobial efficacy, the hydrophobicity, microscopic and the mechanical characteristics of the films, as well free energy of adhesion between bacteria and antimicrobial films were evaluated. It was observed that both polyethylene and cellulose based films incorporated with the antimicrobial were homogeneous. Furthermore, the addition of triclosan did not affect mechanical characteristics of the films (P > 0.05). However, triclosan incorporated into polyethylene films reduced its hydrophobicity while antimicrobial cellulose based films became more hydrophobic. The adhesion was thermodynamically favorable between tested bacteria and polyethylene films. On the other hand, the adhesion to triclosan cellulose based film was thermodynamically unfavorable to Staphylococcus aureus and Escherichia coli and favorable to Listeria innocua and Pseudomonas aeruginosa. Polyethylene and cellulose based films showed inhibitory effect against S. aureus and E. coli, being the inhibition halo higher for polyethylene films. This study improves the knowledge about antimicrobial films.     

Preparation and characterization of whey protein isolate films reinforced with porous silica coated titania nanoparticles

Whey protein isolate (WPI) films embedded with TiO₂@@SiO₂ (porous silica (SiO₂) coated titania (TiO₂)) nanoparticles for improved mechanical properties were prepared by solution casting. A WPI solution of 1.5 wt% TiO₂@@SiO₂ nanoparticles was subjected to sonication at amplitudes of 0, 16, 80 and 160 μm prior to casting in order to improve the film forming properties of protein and to obtain a uniform distribution of nanoparticles in the WPI films. The physical and mechanical properties of the films were determined by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and tensile testing. Water vapor permeability (WVP) measurements revealed that the water vapor transmission rates are slightly influenced by sonication conditions and nanoparticle loading. The DMA results showed that, at high sonication levels, addition of nanoparticles prevented protein agglomeration. The thermal stability of the materials revealed the presence of 3–4 degradation stages in oxidizing the protein films. The addition of nanoparticles strengthens the WPI film, as evidenced by tensile stress analysis. Sonication improved nanoparticle distribution in film matrix; such films can potentially become effective packaging materials to enhance food quality and safety.     

Liquid and vapour water transfer through whey protein/lipid emulsion films

BACKGROUND: Edible films and coatings based on protein/lipid combinations are among the new products being developed in order to reduce the use of plastic packaging polymers for food applications. This study was conducted to determine the effect of rapeseed oil on selected physicochemical properties of cast whey protein films. RESULTS: Films were cast from heated (80 °C for 30 min) aqueous solutions of whey protein isolate (WPI, 100 g kg^?1 of water) containing glycerol (50 g kg^?1 of WPI) as a plasticiser and different levels of added rapeseed oil (0, 1, 2, 3 and 4% w/w of WPI). Measurements of film microstructure, laser light‐scattering granulometry, differential scanning calorimetry, wetting properties and water vapour permeability (WVP) were made. The emulsion structure in the film suspension changed significantly during drying, with oil creaming and coalescence occurring. Increasing oil concentration led to a 2.5‐fold increase in surface hydrophobicity and decreases in WVP and denaturation temperature (T_max). CONCLUSION: Film structure and surface properties explain the moisture absorption and film swelling as a function of moisture level and time and consequently the WVP behaviour. Small amounts of rapeseed oil favourably affect the WVP of WPI films, particularly at higher humidities. Copyright © 2010 Society of Chemical Industry     

Inhibition of Three Pathogens on Bologna and Summer Sausage Using Antimicrobial Edible Films

Whey protein isolate (WPI) films (pH 5.2) containing 0.5 to 1.0% p‐aminobenzoic acid (PABA) and/or sorbic acid (SA) were assessed for antimicrobial and mechanical properties while in contact with sliced bologna and summer sausage that were inoculated with Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica subsp. enterica serovar Typhimurium DT104. WPI films containing SA or PABA decreased L. monocytogenes, E. coli, and S. Typhimurium populations by 3.4 to 4.1,3.1 to 3.6, and 3.1 to 4.1 logs, respectively, on both products after 21 d at 4 °C. Background flora was inhibited compared with controls. Film tensile strength decreased while % elongation remained unchanged following 72 h of product contact.     

Wettability, surface microstructure and mechanical properties of films based on phosphorus oxychloride-treated zein

BACKGROUND: Zein, the predominant protein in corn, has been extensively studied as an alternative packaging material in edible and biodegradable films. However, films made from 100% zein are brittle under normal conditions. The aim of this investigation was to improve the film‐forming properties of zein by chemical phosphorylation. The surface hydrophobicity, surface microstructure and mechanical properties of films based on untreated and phosphorus oxychloride (POCl₃)‐treated zein were evaluated and compared. The effect of POCl₃ treatment on the rheological properties of zein solutions was also studied. RESULTS: POCl₃ treatment, especially at pH 7 and 9, led to an increase in the apparent viscosity of zein solutions. Atomic force microscopy (AFM) analysis showed that the film based on POCl₃‐treated zein at pH 7 had a stone‐like surface microstructure with a higher roughness (R_q) than the untreated zein film. The AFM data may partially account for the phenomenon that this film exhibited high surface hydrophobicity (H₀). POCl₃ treatment diminished the tensile strength (TS) of zein films from 4.83–6.67 to 1.3–2.29 MPa. However, the elongation at break (EAB) of the films at pH 7 and 9 increased from 3.0–4.5% (control film) to 150.1–122.7% (POCl₃‐treated film), indicating the potential application of zein films in wrapping foods or in non‐food industries such as sugar, fruit or troche that need good extension packing materials. CONCLUSION: The data presented suggest that the properties of zein films could be modulated by chemical phosphorylation treatment with POCl₃ at an appropriate pH value. Copyright © 2011 Society of Chemical Industry