Physical,mechanical, and antimicrobial properties of ethylene vinyl alcohol copolymer/chitosan/nano-ZnO (ECNZn) nanocomposite films incorporating glycerol plasticizer

In this study the ethylene vinyl alcohol copolymer (EVOH) and chitosan polymers mixture film containing nano zinc oxide (nano-ZnO) and glycerol was developed for food packaging. Physical, mechanical and antimicrobial properties of the film matrix were evaluated at different ratios of the biodegradable polymers (0:100, 25:75, 50:50, 75:25, 100:0) which contain nano-ZnO and incorporate with glycerol as the plasticizer. Film topography and cross-sections were evaluated by FE-SEM and AFM examinations. To assess characterization of the nanocomposites structure and network chemistry, FTIR spectroscopy was considered. The results indicate that EVOH improved barrier properties, transparency and mechanical properties. The antimicrobial properties were improved by adding chitosan. With adding glycerol decreases in barrier properties and increases in percentage of elongation at break (ε_b) were observed. Adding nano-ZnO improved barrier, mechanical and antimicrobial properties and significantly reduced the adverse effects of glycerol. Taken together, these data reveal that the new nanocomposite provides the better properties and the less adverse effects of plasticizer on matrix film.     

Plastics used in food packaging and the rôle of additives

Whilst paper and derived products still dominate packaging and large quantities of glass are still used in containers, the usage of plastics is significant, particularly for food packaging. Plastics are advantageous in providing good barrier properties in packages of low density (low weight) and high durability at low cost.Primary packaging of foodstuffs utilises film and containers principally; secondary packaging involves a wider variety of forms, including tote boxes and crates. In a cost-sensitive market, the commodity thermoplastics—polyolefins, poly(vinyl chloride) and styrene plastics—are widely employed in food packaging but there is considerable application of more expensive polymers in more advanced forms for special requirements.Satisfactory plastics packaging should not adversely affect the food in contact with it. Whilst pure high polymers might be expected to be inert, residual monomer, residues from polymerisation ancillaries, adventitious impurities and deliberate additives, all of lower molecular weight than the polymer, might be migratory and require particular consideration.     

Functional barriers: Properties and evaluation

Functional barriers are multilayer structures deemed to prevent migration of some chemicals released by food-contact materials into food. In the area of plastics packaging, different migration behaviours of mono- and multilayer structures are assessed in terms of lag time and of their influence of the solubility of the migrants in food simulants. Whereas barriers to oxygen or to aromas must prevent the diffusion of these compounds under conditions of use, a functional barrier must also be efficient under processing conditions, to prevent diffusion of substances when the polymer layers are in contact at high (processing) temperatures. Diffusion in melted polymers at high temperatures is much slower for glassy polymers, than in polymers that are rubbery at ambient temperature. To evaluate the behaviour of functional barriers under conditions of use, a set of reference diffusion coefficients in the 40-60°C range were determined for 14 polymers. Conditions for accelerated migration tests are proposed based on worst-case activation energy in the 40-60°C range. For simulation of migration, numerical models are available. The rules derived from the models can be used both by industry (to optimize a material in terms of migration) or by risk assessors. Differences in migration behaviour between mono- and multilayer materials are discussed.     

Migration of styrene monomer, dimers and trimers from polystyrene to food simulants

Migration experiments with polystyrene were performed in two-sided contact with n-heptane and distilled water as the food simulants at temperatures of 10, 24 and 40, and 40, 60 and 90°C, respectively. The surface/volume ratios in the migration cell were set at 8.04 and 10.05 dm² l^-1 for n-heptane and distilled water, respectively. Styrene monomer, styrene dimers and styrene trimers migrating to the food simulants were determined by GC-FID analysis. Heptane fully extracted the styrene monomer and the oligomers from the polystyrene sheet, whereas in the distilled water only the migrated styrene trimers could be detected. To determine the apparent diffusion coefficient, the migration process was analysed based on Fick's law. The higher the molecular weight of the oligomers, the more significant the reduction in the diffusion coefficient. Higher molecular weight oligomers also had lower activation energy of diffusion when the temperature dependence of diffusivity was analysed by the Arrhenius equation. The diffusion coefficient of the trimers was much higher for heptane contact than for water. The activation energy of the diffusion of trimers for water contact was higher than that for heptane.     

Diffusion of homologous model migrants in rubbery polystyrene: molar mass dependence and activation energy of diffusion

Published diffusion prediction models for the diffusion of additives in food packaging simplify reality by having a small number of parameters only. Therefore, extrapolation of such models to barrier polymers, larger ranges of temperature and/or additive molecular weight (M_W ) is questionable. Extra data is still required to generalize these existing prediction models. In this paper, diffusion of a specifically designed homologous set of model additives (from 236 to 1120 g mol^?1) was monitored in two polystyrenes in the rubbery state (from 100 to 180°C): syndiotactic semi-crystalline polystyrene and its amorphous equivalent. Variations in associated diffusion coefficient D and activation energy Ea with migrant M_W and temperature were surprisingly low. Comparison of experimental behaviour with model predictions was performed. In their actual form, none of the models is capable of describing all experimental data, but there is evidence of convergence of the different approaches.     

Diffusion Phenomena during Chemical (NaOH) Peeling of Tomatoes

The apparent diffusivity of NaOH (D) through the skin of processing tomatoes was estimated for various concentrations and temperatures as it relates to chemical peeling. For concentrations of 2M NaOH or greater, D was independent of concentration, which allows the Fick's law of diffusion to be used for simulation of the events during chemical peeling. The temperature dependence of D was of the Arrhenius type (for temperatures greater than 50°C) with an estimated activation energy Ea = 71.2 KJ/mol.     

Prediction of worst case migration: presentation of a rigorous methodology

An improvement of the Piringer model, allowing the prediction of a worst case migration from packaging to food is presented here. The authors are proposing other constants for the calculation of the upperbound value of the diffusion coefficient, using experimental data determined by a film to film method. Considering the plasticizing effects of food simulants, a model involving the variation of the diffusion coefficient versus space and time must be used. Future fields of investigation are discussed: the relationship between diffusion coefficients and the volume of the migrant (instead of molar mass), and the variation of diffusion coefficient activation energy with temperature.     

Active antioxidant packaging films: Development and effect on lipid stability of brined sardines

Active antioxidant food packaging films were produced by the incorporation of ascorbic acid, ferulic acid, quercetin, and green tea extract into an ethylene vinyl alcohol copolymer (EVOH) matrix. The characterisation of the thermal and barrier properties of the developed film showed that the addition of these bioactive compounds did not greatly modify their properties. However, the presence of ascorbic and ferulic acids resulted in a significant decrease in water vapour permeability, possibly due to the high affinity for water of these substances. Exposure of the films to various food simulants showed that the release from the films was dependent on the type of food simulant and the antioxidant incorporated: in the aqueous food simulant, materials containing ascorbic acid produced the largest release; in the fatty food simulant, quercetin and green tea extract presented the best performance. The efficiency of the films developed was determined by real packaging applications of brined sardines. The evolution of the peroxide index and the malondialdehyde content showed that, in general, the films improved sardine stability. Films with green tea extract offered the best protection against lipid oxidation.     

New materials for food packaging—The future

It is unlikely that there will be many new materials used in future food packaging, but there will be new combinations of materials and new uses to which they are put. Changes in relative costs may reverse certain trends.Developments in the following areas are covered: metals, such as tin-free steel and the combination of aluminium and plastics; paperboard, such as tubs and ovenable board; glass, such as ‘Plastishield’, and plastics, themselves, dealing with developments in processing, such as stretch blow moulding and solid phase pressure forming.Developments in the newer materials such as poly(ethylene phthalate), the nitriles, poly(vinyl alcohol) and ethylene/vinyl alcohol copolymer and polycarbonate, are also considered.     

Halloysite Nanotubes/Polyethylene Nanocomposites for Active Food Packaging Materials with Ethylene Scavenging and Gas Barrier Properties

Novel polymeric active food packaging films comprising halloysite nanotubes (HNTs) as active agents were developed. HNTs which are hollow tubular clay nanoparticles were utilized as nanofillers absorbing the naturally produced ethylene gas that causes softening and aging of fruits and vegetables; at the same time, limiting the migration of spoilage-inducing gas molecules within the polymer matrix. HNT/polyethylene (HNT/PE) nanocomposite films demonstrated larger ethylene scavenging capacity and lower oxygen and water vapor transmission rates than neat PE films. Nanocomposite films were shown to slow down the ripening process of bananas and retain the firmness of tomatoes due to their ethylene scavenging properties. Furthermore, nanocomposite films also slowed down the weight loss of strawberries and aerobic bacterial growth on chicken surfaces due to their water vapor and oxygen barrier properties. HNT/PE nanocomposite films demonstrated here can greatly contribute to food safety as active food packaging materials that can improve the quality and shelf life of fresh food products.     

Depression of sorption of volatile compounds into EVA film by electron beam irradiation

Decrease in solubility of volatile compounds (octan-l-ol, octanal, ethyl hexanoate, octane and d-limonene) into a film liner was studied after electron beam irradiation up to 20 Mrad of ethylene vinyl acetate copolymer (EVA) film. The solubility coefficient decreased gradually during ageing despite no change immediately after the irradiation. In all films dosed with 5-20 Mrad the sorption was depressed about 40% in comparison with the unirradiated one after 4 months. The behaviour was consistent with that of the decay of the radicals in the films. The enthalpy change in sorption (ΔH) was ?18.0 kJ mol^?1 for 5 Mrad ethylene vinyl acetate copolymer film compared with ?48.1 kJ mol^?1 for the unirradiated one. In a homologous series, sorption was significantly depressed with increasing carbon chain length of the volatile compound. The specific sorption depression effect was observed for low polarity compounds such as hydrocarbons, aliphatic esters and d-limonene. The diffusion coefficient of the sorbed compounds increased about 1.6 times after 3 months when irradiated to 20 Mrad.     

Thermal Destruction of Pteroylglutamic Acid in Buffer and Model Food Systems

First order rate constants (k) and activation energies (Ea) of pteroylglutamic acid (PteGlu) were determined between 100 and 140°C in citrate buffer (pH 3–6) and model food systems. The rate constants (hr^-1) in citrate buffer ranged from 0.145–2.36 at pH 3; 0.074–0.840 at pH 4.0; 0.021–0.207 at pH 5.0, and 0.015–0.133 at pH 6.0. Corresponding Ea values were 22.6, 19.5, 17.8, and 16.8 kcal/mole at pH 3, 4,5, and 6, respectively. In an apple juice model (pH 3.4), the rate constants ranged from 0.063–0.822 and in tomato juice model (pH 4.3), from 0.056–0.723. Ea values in apple juice an tomato juice were 20.0 and 19.7 kcal/mole, respectively.     

Modelling of migration from multi-layers and functional barriers: Estimation of parameters

Functional barriers form parts of multi-layer packaging materials, which are deemed to protect the food from migration of a broad range of contaminants, e.g. those associated with reused packaging. Often, neither the presence nor the identity of the contaminants is known, so that safety assessment of the materials has to rely on predictive tools. Several complementary freeware described here allow one to model diffusion in multi-layer films. These tools require the input of parameters that are not easy to determine or predict. Previous work has focused on the prediction of diffusion coefficients at storage temperatures of packaging in contact with food. However, many other kinetic and thermodynamic parameters are needed to describe transport properties during the processing of a material at high temperature and during its shelf-life. All parameters needed for the calculations are discussed. In order to propose default values, the approach consists of (1) reviewing the available literature data, (2) running experiments on polypropylene, polyethylene and poly(ethylene vinyl alcohol) in typical conditions (separately diffusion during processing and migration) and (3) simulating numerical sets for typical situations. Several freeware are proposed to simulate migration from multi-layers and functional barriers using the default parameters.     

Thermal Destruction of 5-Methyltetrahydrofolic Acid in Buffer and Model Food Systems

Thermal kinetic data (rate constants, k, and activation energies, Ea) for 5-Methyltetrahydrofolic acid (5-CH₃-H₄PteGlu) were determined in citrate buffers (pH 3-6) and in model food systems between 100° and 140°C. As pH increased from 3.0 to 6.0, the rate constants decreased as the temperature increased from 100° to 130°C, the rate constants increased. Ea values were 19.0, 17.0, 19.7 and 19.8 kcal/mole at pH 3, 4, 5 and 6, respectively. In the model food systems, the Ea values (kcal/mole) were 7.85 in apple juice and 10.6 in tomato juice. When dissolved oxygen content was reduced to 5.3 ppm, the stability of the 5-CH₃H₄PteGlu was increased substantially.     

Sorption of ethyl acetate and d‐limonene in poly(lactide) polymers

Poly(lactide) (PLA) polymers have garnered increased attention in the last few years as food packaging materials because they are environmentally friendly polymers. As the production of PLA increases and price per pound drops, PLA is becoming a growing alternative as a green food packaging material. In this research, the organic vapor barrier properties of commercially available PLA polymers were studied. Gravimetric sorption tests in PLA films were carried out, and the diffusion (D), solubility (S) and permeability (P) coefficients for ethyl acetate and d‐limonene in PLA were determined. For ethyl acetate, values of P = 1.22 × 10^?17 kg m m^?2 s^?1 Pa^?1, D = 2.63 × 10^?15 m² s^?1, and S = 4.62 × 10^?3 kg m^?3 Pa^?1) at 45 °C and a partial pressure of 12 654 Pa were obtained. For d‐limonene, no trace was detected after 21 days of testing at 45 °C and 258 Pa, which indicates a permeability coefficient lower than 9.96 × 10^?21 kg m m^?2 s^?1 Pa^?1. Poly(lactide) polymers demonstrated good aroma barrier to ethyl acetate and d‐limonene, and will most likely be good aroma barriers. PLA is not likely to promote flavor loss by either permeation or scalping. Copyright © 2005 Society of Chemical Industry     

Aroma Sorption Evaluation of Aseptic Packaging

A headspace method was developed for evaluating aroma sorption by polymeric packaging materials. Partition coefficients for ethyl acetate, n-hexanal, d-limonene and α-terpineol at vapor activities of 0.2 were measured between air and the materials at 25°C and 40°C. Four different flexible aseptic packaging materials with barrier layers of aluminum foil, polyvinylidene chloride (SARAN), metallized polyester (MPET) and ethylene vinyl alcohol (EVOH) were evaluated. Temperature and aroma type had significant effects on partition coefficients. No significant interactions between aromas were observed in partition coefficients. The inner polyolefin sealing layer determined the aroma sorption behavior.     

Measurement of effective diffusivities of ionic and non-ionic solutes through beef and pork muscles using a diffusion cell

A diffusion cell in conjunction with a new mathematical model was used to measure the apparent diffusion coefficients of sodium chloride, potassium nitrate and glucose through beef semitendinosus and pork longissimus dorsi muscles. The apparent diffusion coefficient was obtained within less than 180 min with a coefficient of variation less than 10% in most cases. The influence of temperature can be adequately explained by the Arrhenius-type law with activation energy between 19 and 26 kJ/mol depending on the diffusant. However, these values were not significantly different. Finally, we showed that the apparent diffusion coefficient of sodium chloride is not affected by the direction of the muscle fibre to the axes of diffusion while glucose diffusion parallel to the muscle fibre can be three times greater than diffusion at a right angle to the muscle fibre.     

Release of Naturally Derived Antimicrobial Agents from LDPE Films

ABSTRACT: The migration of the naturally derived antimicrobial (AM) agents, linalool, carvacrol, and thymol, from low-density polyethylene (LDPE) films containing ethylene vinyl acetate (EVA) copolymer into the food simulants, isooctane and various ethanol/water mixtures, was studied with a view towards examining the applicability of a first-order kinetic approach as well as a diffusion model approach for describing these systems. The results suggest that the proposed models adequately describe the release of AM agents. The combination of kinetic and diffusion analyses can provide additional information about the release process using the same data set. The analyses suggest that the release of linalool from LDPE/EVA depends on the EVA content in the formulation and that an optimum level of EVA is required to minimize the rate of release. A modification of the existing “idealized diffusion” model is proposed that enables the model to be applied to systems that demonstrate a departure from linearity when subjected to conventional analysis. The applicability of the idealized diffusion model was compared with the “simulant-limited” model and the results suggest that the former model is appropriate for describing most real systems when the simulant (or foodstuff) is favored in the partitioning of the AM agent between the film and the simulant.     

Diffusion of limonene in polyethylene

Diffusion coefficients of limonene in various linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) resins have been determined from sorption data using a thermogravimetric methodology. From these data, one can determine whether polymer synthesis parameters such as the choice of catalytic process or co-monomer result in substantial differences in how much food packaging additives might migrate to food. For example, LLDPE is currently manufactured using either one of two distinct catalytic processes: Ziegler-Natta (ZN) and metallocene, a single-site catalyst. ZN catalysis is a heterogeneous process that has dominated polyolefin synthesis over the last half-century. It involves a transition metal compound containing a metal-carbon bond that can handle repeated insertion of olefin units. In contrast, metallocene catalysis has fewer than 20 years of history, but has generated much interest due to its ability to produce highly stereospecific polymers at a very high yield. In addition to high stereospecificity, metallocene-catalysed polymers are significantly lower in polydispersity than traditional ZN counterparts. Absorption and desorption testing of heat-pressed films made from LLDPE and LDPE resins of varying processing parameters indicates that diffusion coefficients of limonene in these resins do not change substantially.