Water vapor and oxygen-barrier performance of corn–zein coated polypropylene films

A novel corn–zein coating structure on polypropylene (PP) films was developed to examine its feasibility as an alternative water vapor and oxygen-barrier for flexible packaging industry. The barrier properties of the resulting films were evaluated as affected by coating formulation (solvent, corn–zein, plasticizer concentration and plasticizer type). Corn–zein with different amounts (5% and 15%) was dissolved in 70% and 95% aqueous ethanol solution at 50 °C, respectively. Solutions of corn–zein plasticized by polyethylene glycol (PEG) and glycerol (GLY) with various levels (20% and 50%) were applied on corona-discharged-treated PP by using solvent-casting method. The significant improvements in water vapor and oxygen-barrier properties of uncoated PP films were obtained with corn–zein coating. Water vapor permeability (WVP) of the coated films decreased significantly with increasing corn–zein concentration. The application of plasticized corn–zein coating on PP films showed nearly more than three order of reduction in oxygen permeability (OP). The high water vapor and oxygen-barriers were obtained for films coated with coating formulation consisting of higher amounts of corn–zein plasticized by GLY. The statistical analysis defined the key parameters of coating formulation that had major effect on the final properties of coated PP films as corn–zein, plasticizer concentration, and plasticizer type.     

Study of physical and mechanical properties of polypropylene nanocomposites for food packaging application: Nano-clay modified with iron nanoparticles

Polypropylene (PP) nanocomposites were prepared via melt interaction of clay in a twin screw extruder. The evaluation of PP nanocomposites containing montmorillonite (OMMT) with or without iron nanoparticles modification was studied for food packaging applications. The nanocomposites were investigated by thermal, mechanical, morphological and gas barrier analyses. The X-ray diffraction patterns of all nanocomposites revealed an increment in d-spacing of the OMMT layers and proved the compatibility of neat PP and clay, along with the intercalation and partial exfoliation of the layers. Addition of nanoparticles had reverse effect on the intercalation and exfoliation of the clay to some extent. Transmitting optical and scanning electron microscopy revealed certain homogeneity with uniform distribution of OMMT and nano-particles in the PP matrix. According to the acquired thermal properties, a tendency for the melting temperatures increased with the clay concentration. Also, crystallization temperature and crystallinity decreased with the clay concentration; however, nanoparticles compensated the effect of clay. Despite of no significant change in the ultimate tensile strength and elongation properties were observed in nanocomposites, the yield strength presented a substantial enhancement and the rigidity as well. Melt flow index (MFI) examination revealed decreasing melt viscosity of nanocomposite through increasing OMMT and iron nanoparticles. Besides, OMMT showed a high capacity to improve oxygen and water vapor barrier properties of PP. The use of clay increased the mobility distance of the gas molecules, led to oxygen permeability of neat PP being reduced whereas nanoparticle acted as an active oxygen scavenger and was capable of intercepting and scavenging oxygen by undergoing a chemical reaction with. Migration test also showed no restrictions in the use of nanocomposite films in food packaging.     

Corn Zein Packaging Materials for Cooked Turkey

Mechanical and barrier properties of corn zein films with butylated hydroxyanisole (BHA), bacterial enzyme, and emulsifier additives were investigated and compared to those of polyvinylidine chloride (PVDC) films. No significant differences (P < 0.05) occurred in elongation, tensile strength, or Young's modulus among corn zein films. PVDC had the lowest apparent water vapor permeability (WVP_app), and no significant differences in WVP_app were found between zein films and PVDC. Cooked turkey breast was packaged, evaluated by a trained sensory panel, and analyzed for hexanal content. Turkey breast wrapped in corn zein film with antioxidant and emulsifier had lower hexanal content than samples packaged in PVDC.     

Edible oxygen barrier bilayer film pouches from corn zein and soy protein isolate for olive oil packaging

An edible oxygen barrier film pouch was fabricated from a heat sealable corn zein (CZ) layer laminated on soy protein isolate (SPI) film and used to package olive oil condiments for use with instant noodles. The mechanical, barrier, and physical properties of the CZ/SPI bilayer films were then investigated and the oxidative stability of olive oil in the pouches was measured during storage under dry and intermediate relative humidity conditions. When compared to the SPI film, lamination with an additional layer of CZ film led to increased tensile strength and water barrier properties, while it had a lower elongation at break and decreased oxygen barrier properties. Nevertheless, the oxygen permeability of the CZ/SPI film (0.81 × 10⁻¹⁸ m³ m/m² s Pa) was lower than that of nylon-metalocene catalyzed linear low-density polyethylene (NY/mLLDPE) film (3.51 × 10⁻¹⁸ m³ m/m² s Pa) which is the material usually used for such condiments. The CZ/SPI bilayer films generated here were heat sealable at 120-130 °C and produced a seal strength greater than 300 N/m. The higher oxygen barrier property of the CZ/SPI bilayer films resulted in reduced oxidative rancidity of olive oil packaged in the CZ/SPI film when compared to olive oil packaged in NY/mLLDPE films.     

Effect of plasticizing sugars on water vapor permeability, surface energy and microstructure properties of zein films

Sugars are natural plasticizers for food biopolymers and zein is the most important protein of corn. In this research, sugars (fructose, galactose and glucose) were used as plasticizers and the water vapor permeability (WVP), contact angle and microstructure of the zein films were studied. The pure zein film had high WVP and adding of sugars to 0.7 g/g zein caused to decrease of WVP. Films containing galactose had the lowest WVP.All samples had the lowest contact angle with ethanol and the highest contact angle with water. The zein films containing galactose had the highest water contact angle within the plasticized films. The pure zein films and the films containing fructose had higher critical surface tension of wetting (γ_c) than the films containing glucose and galactose. Adding sugar plasticizer to zein films increased the surface tension of zein films. In the unplasticized zein films, loose structures with a lot of cavities and voids were observed. The films plasticized by fructose had smooth surface and plasticizer particles distributed throughout of the films.     

Physical and mechanical properties of peanut protein films

The properties of peanut protein films were modified using physical and chemical treatments, and their effects on color, mechanical strength, water solubility and barrier to water vapor and oxygen of the films were investigated. Physical treatments consisted of heat denaturation of film-forming solution for 30 min at 60°C, 70°C, 80°C and 90°C, ultraviolet irradiation of films for up to 24 h, and three ultrasound processes of film-forming solution. Chemical treatments consisted of addition of aldehydes and anhydrides. Heat curing at 70°C, ultraviolet irradiation for 24 h, ultrasound for 10 min in a water-bath, and formaldehyde and glutaraldehyde addition caused a significant increase in the tensile strength of the films. The water vapor permeability (WVP) and oxygen permeability (OP) of the films decreased after heat denaturation and aldehyde treatment. OP also decreased with UV treatment. Heat curing was the most effective treatment, making the films stronger, more resistant to water and less permeable to water vapor and oxygen.     

Mechanical and barrier properties of biodegradable soy protein isolate-based films coated with polylactic acid

Polylactic acid (PLA)-coated soy protein isolate (SPI) films were prepared by dipping SPI film into PLA solution. The effects of coating on improvements in mechanical and water barrier properties of the film were tested by measuring selected film properties such as tensile strength (TS), elongation at break (E), water vapor permeability (WVP), and water solubility (WS). TS of SPI films increased from 2.8±0.3 up to 17.4±2.1 MPa, depending on the PLA concentration of the coating solution, without sacrificing the film's extensibility. In contrast, the extensibility of SPI film coated with solution containing more than 2 g PLA/100 ml solvent, increased. WVP of PLA-coated SPI films decreased from 20 to 60 fold, depending on the concentration of PLA coating solution. Water resistance of SPI films was greatly improved as demonstrated by the dramatic decrease in WS for PLA-coated films. The improvement in water barrier properties was mainly attributed to the hydrophobicity of PLA.     

Preparation and properties of dialdehyde carboxymethyl cellulose crosslinked gelatin edible films

Glycerol-plasticized gelatin edible films with a new kind of dialdehyde polysaccharide, dialdehyde carboxymethyl cellulose (DCMC) as crosslinking agent are successful prepared using casting techniques. The mechanical properties, thermal stability, light barrier properties, swelling behavior as well as water vapor permeability (WVP) of the gelatin-DCMC films are investigated. The results indicate that the addition of DCMC causes tensile strength (TS) and thermal stability to increase and elongation at break (EB) to decrease, suggesting the occurrence of crosslinking between gelatin and DCMC. The light barrier measurements present high values of transparency at 280 nm and low values of transparency at 600 nm of the gelatin-DCMC films, indicating that gelatin-DCMC films are very transparent (lower in transparency value) while they have excellent barrier properties against UV light. Moreover, the values of transparency at 280 nm increase with the increased DCMC and glycerol content, suggesting the potential preventive effect of gelatin-DCMC films on the retardation of product oxidation induced by UV light. Furthermore, the addition of DCMC can greatly decrease the water vapor permeability (WVP) and equilibrium swelling ratio (ESR) down to values about 1.5 × 10⁻¹⁰ g m/m² s Pa and 150%, revealing the potential of DCMC in reducing the water sensitivity of gelatin-based films. In common for hygroscopic plasticizer in edible films, the addition of glycerol gives increase of EB and WVP and decrease of thermal stabilities and ESR of the gelatin-DCMC films.     

Effects of murta (Ugni molinae Turcz) extract on gas and water vapor permeability of carboxymethylcellulose-based edible films

The effect of murta (Ugni molinae Turcz) leaves extract on water vapor permeability (WVP) and gas permeability (GP) of carboxymethylcellulose (CMC)-based films was studied. Two ecotypes of murta leaves “Soloyo Grande” (SG) and “Soloyo Chico” (SC), were analyzed for their composition (HPLC-MS) and SC extract revealed a higher concentration of flavonols than the SG extract. The film forming solution was prepared with 2 g of CMC, 0.4 ml of glycerol and 0.5 ml of sunflower oil in 100 ml of water (Control), 50 ml of water and 50 ml of each exctract (SC50 or SG50) and 100 ml of each extract (SC 100 or SG 100). The addition of murta leaves extract modified the WVP and GP of the films. The WVP decreased significantly (P?0.05) with the incorporation of SG extract in the film but not with the SC extract (P>0.05). The CO₂ and O₂ permeability of the films were influenced by the kind and concentration of murta leaves extract used. The CO₂ permeability, with SG extract was higher than without extract (P?0.05) and with SC extract was not modified. The O₂ permeability with murta leaves extract were lower than without extract. Therefore, it is possible to consider that films with SC acts only as barrier to the oxygen, but with SG the water vapor and gas barrier properties were modified, being more permeable to the CO₂ and acting as barrier to O₂ and water vapor.     

Effect of ferulic acid and α-tocopherol antioxidants on properties of sodium caseinate edible films

Edible films, based on sodium caseinate containing three different concentrations of ferulic acid or α-tocopherol (20, 40 and 60 mg/g sodium caseinate), were obtained in order to evaluate the effect of these compounds on properties of the caseinate matrices. Special emphasis was placed on their effect on the films’ oxygen barrier properties, which are decisive in the prevention of the oxidation of foods containing lipids. Films were characterized as to their tensile, optical and surface properties as well as their barrier properties to water vapor, oxygen and aroma compounds (n-hexanal and n-hexanol). Ferulic acid was more efficient at reducing oxygen and n-hexanal permeability than α-tocopherol. Although ferulic acid slightly increased the stiffness of films at low concentration, in general, both antioxidants slightly reduce mechanical resistance, water vapor permeability, gloss and transparency of the films.     

Influence of plasticizers on the water sorption isotherms and water vapor permeability of chicken feather keratin films

Biodegradable films from many protein sources have in recent decades attracted a lot of attention for their potential use in food protection because they have several advantages over synthetic films, including those related to the environment. The effects of type and concentration of plasticizers on microstructure, sorption isotherms and water vapor permeability (WVP) of films obtained from chicken feather keratin (CFK) were investigated. Keratins were extracted with an aqueous solutions of urea, 2-mercaptoethanol and surfactant. The protein was dosed and the maximum concentration achieved was 12 g/100 ml. The protein concentration in the keratin film solution was standardized at 7 g/100 ml for the preparation of the films by casting. The results showed that increasing the plasticizer concentration caused a decrease in barrier properties and favored water adsorption by the polymeric network, increasing the moisture content of the films. The monolayer moisture content was 8.76 times higher for films made with glycerol than films made without plasticizer and 12 times higher than films plasticized with PEG 4000. The same behavior was observed for the water solubility coefficient, which increased with increasing plasticizer concentration.     

Tensile, water vapor barrier and antimicrobial properties of PLA/nanoclay composite films

PLA-based composite films with different types of nanoclays, such as Cloisite Na⁺, Cloisite 30B and Cloisite 20A, were prepared using a solvent casting method and their tensile, water vapor barrier and antimicrobial properties were tested. Tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) of control PLA film were 50.45 ± 0.75 MPa, 3.0 ± 0.1%, and 1.8 × 10⁻¹¹ g m/m² s Pa, respectively. TS and E of nanocomposite films prepared with 5 g of clay/100 g of PLA decreased 10-20% and 11-17%, respectively, depending on the clays used. On the contrary, WVP of the nanocomposite films decreased 6-33% through nanoclay compounding. Among the clay types used, Cloisite 20A was the most effective in improving the water vapor barrier property while sacrificing tensile properties the least. The effect of clay concentration tested using Cloisite 20A showed a significant decrease in TS and WVP, with increases in clay content. Among the PLA/clay composite films tested, only PLA/Cloisite 30B composite film showed a bacteriostatic function against Listeria monocytogenes.     

Evaluation of Zein Films as Modified Atmosphere Packaging for Fresh Broccoli

ABSTRACT: Modified atmosphere packaging (MAP) is increasingly used with minimally processed produce. Increased MAP usage coupled with negative environmental views associated with nondegradable synthetic packaging materials creates a need for biodegradable films. Zein films plasticized with oleic acid had been proposed for biodegradable packaging applications. Conversion treatments including lamination and coating films with tung oil were reported to improve water vapor and gas barrier properties of films. In this work, the ability of treated and untreated zein films to perform as MAP for fresh broccoli florets was investigated. Florets were packaged in glass jars sealed with zein films and stored under refrigeration for 6 d. Headspace oxygen and carbon dioxide concentrations were monitored during storage. Tested films allowed the development of modified atmospheres inside the packages. Broccoli florets packaged in the test films maintained their original firmness and color.     

Technical Note: A Method to Quantify Prolamin Proteins in Corn That Are Negatively Related to Starch Digestibility in Ruminants

Compared with floury or high-moisture corns, dry corn with a greater percentage of vitreous endosperm has been demonstrated to be negatively related to starch digestibility and milk yield of lactating dairy cows. Starch granules in corn are encapsulated by hydrophobic prolamin proteins that are innately insoluble in the rumen environment. Corn prolamin proteins are named zein, and laboratory methods to quantify zein exist but are seldom employed in ruminant nutrition because of their arduous nature. In this study, advances in cereal chemistry were combined with rapid turbidimetric methods yielding a modified turbidimetric zein method (mTZM) to quantify zein in whole corn. Ten dry corns containing unique endosperms were evaluated using the mTZM. Corns with flint, dent, floury, or opaque endosperms were found to contain 19.3, 11.3, 5.8, and 4.9 g of zein/100 g of starch, respectively. The ability of mTZM to differentiate corn endosperm types as defined by least significant difference was 2.6 g of zein/100 g of starch. Ten high-moisture corns of varying moisture content were also evaluated using the mTZM. Zein content of high-moisture corns as defined by mTZM ranged from 8.3 to 2.8 g of zein/100 g of starch with a least significant difference of 1.2 g of zein/100 g of starch. The mTZM determined that zein contents of high-moisture, floury, and opaque corns were markedly less than those of flint and dent dry corns, indicating that mTZM has the ability to quantify starch granule encapsulation by hydrophobic prolamin proteins in whole corn.     

Different Kinds of Microfibrillated Cellulose as Coating Layers Providing Fiber-based Barrier Properties

In this study,we investigated the barrier properties of different kinds of microfibrillated cellulose(MFC)coating layers.The air,oxygen,and water vapor permeability,as well as the water contact angles(WCA),were measured to quantify the barrier efficacy of the applied coatings.The WCA data showed that the surfaces of MFC-coated cardboards are more hydrophilic than those of uncoated cardboards.However,different MFC coatings realize different oxygen transmission rates(OTRs)and water vapor transmission rates(WVTRs).The MFC coating derived from bleached bamboo pulp subjected to carboxyethylation pretreatment(MFCCBP)gave the best oxygen and water vapor barrier performances.The OTR of the virgin cardboard(>16500 cm³/(m²·24 h))decreased to 4638 cm³/(m²·24 h)after coating with the MFCCBP.The WVTR similarly decreased from 1016.7 g/(m²·24 h)to 603.2 g/(m²·24 h).     

Use of a Mathematical Model to Describe the Barrier Properties of Edible Films

ABSTRACT: A study on the influence of the solubilization and diffusion process on the barrier properties of 4 different edible films is presented. The water and oxygen barrier properties of zein, alginate, casein, and chitosan films were measured at 25°C. A mathematical model was fitted to the experimental data to obtain quantitative information on both solubilization and diffusion process. Results suggest that alginate film, which shows the highest water and oxygen permeability coefficient, has both higher affinity with water and a higher macromolecular mobility than the other 3 films. The lowest water and oxygen permeability coefficient was detected for chitosan and zein films. The casein film has shown an intermediate behavior.     

Evaluation of mechanical and water barrier properties of transglutaminase cross‐linked zein films incorporated with oleic acid

In this study, four concentrations of transglutaminase were used in zein films incorporated with four oleic acid concentrations, and subsequently, the mechanical and water barrier properties were evaluated. Enzyme concentration significantly affected mechanical and barrier properties of the films. Transglutaminase concentration at 1% improved tensile strength of control sample from 17.5 to 26.9 MPa while solubility decreased from 6.4% to 4.4%. Incorporation of oleic acid into transglutaminase‐treated zein films irrespective of enzyme concentration decreased water vapour permeability and solubility with the 1% transglutaminase‐treated zein films incorporated with 3% oleic acid registering the lowest permeability (0.37 g mm m^?2 h^?1 kPa^?1) and solubility (2.8%) values while elongation at break was not significantly improved. The use of transglutaminase at 1% concentration in cross‐linking zein films coupled with incorporation of controlled concentrations of oleic acid can be an effective approach in improving mechanical and water barrier properties of zein‐based films.     

Effect of cellulose fibers addition on the mechanical properties and water vapor barrier of starch-based films

Starch-based films have promising application on food packaging, because of their environmental appeal, low cost, flexibility and transparency. Nevertheless, their mechanical and moisture barrier properties should be improved. The aim of this work was to enhance these properties by reinforcing the films with cellulose fibers. Besides, the influences of both the solubility coefficient of water in the films (β) and the diffusion coefficient of water vapor through the films (D^w) on the films' water vapor permeability (K^w) were investigated. Films were prepared by the so-called casting technique, from film-forming suspensions of cassava starch, cellulose fibers (1.2 mm long and 0.1 mm of diameter), glycerol and water. The influence of fibers addition on K^w was determined at three relative humidity gradient ranges, ΔRH (2–33%, 33–64% and 64–90%). Films reinforced with cellulose fibers showed higher tensile strength and lower deformation capacity, and presented lower K^w than films without fibers. K^w showed strong dependency of β and D^w, presenting values up to 2–3 times greater at ΔRH = 64–90% than at ΔRH = 33–64%, depending on the film formulation. Therefore, adding cellulose fibers to starch-based films is a viable alternative to improve their mechanical and water barrier properties. Besides, this work showed the importance of determining film's water vapor permeability simulating the real environmental conditions the film will be used.     

Functional properties of gelatin-based films containing Yucca schidigera extract produced via casting,extrusion and blown extrusion processes: A preliminary study

Gelatin-based films containing both Yucca schidigera extract and low concentrations of glycerol (0.25–8.75 g per 100 g protein) were produced by extrusion (EF) and characterized in relation to their mechanical properties and moisture content. The formulations that resulted in either larger or smaller elongation values were used to produce films via both blown extrusion (EBF) and casting (CF) and were characterized with respect to their mechanical properties, water vapor permeability, moisture content, solubility, morphology and infrared spectroscopy. The elongation of the EF films was significantly higher than that of the CF and EBF films. The transversal section possessed a compact, homogeneous structure for all of the films studied. The solubility of the films (36–40%) did not differ significantly between the different processes evaluated. The EBF films demonstrated lower water vapor permeability (0.12 g mm m⁻² h⁻¹ kPa⁻¹) than the CF and EF films. The infrared spectra did not indicate any strong interactions between the added compounds. Thermoplastic processing of the gelatin films can significantly increase their elongation; however, a more detailed assessment and optimization of the extrusion conditions is necessary, along with the addition of partially hydrophobic compounds, such as surfactants.     

玉米醇溶蛋白膜的降解性能和水蒸气透过率的研究

对玉米醇溶蛋白（zein）与3%油酸增塑的玉米醇溶蛋白（OA-zein）膜的降解性能和水蒸气透过率进行了研究,实验结果表明：zein膜和OA-zein膜具有良好的抗酸性,但在pH 10以上时开始发生降解,蛋白酶水解实验表明了24h内蛋白膜不被酶水解.这些数据说明了蛋白膜在人体内不能被消化,但在碱性环境中可以降解.水蒸气透过率实验证明了蛋白膜所具备良好的阻气性能,可以作为疏水性的包覆材料应用于医药、食品和化工领域.