Interactions between water and EVOH food packaging films / Interacciones entre el agua y películas de EVOH para el envasado de alimentos

The transport of water in four EVOH copolymers commonly used in high barrier food packages was characterized through permeation (continuous flow) and gravimetric experiments at different rela tive humidities and 23 ± 2°C. Water sorption isotherms were fitted with the D'Arcy and Watts' equa tion. From these data, the value of the solubility coefficient (S, as defined by Henry's law) was deter mined and was found constant within a 0.2-0.75 water activity ( aw) range. Water uptake at the same aw increased as the EVOH ethylene content decreased. The permeability coefficient ( P) for water through EVOH was determined as a function of water activity. The permeability was constant within the range of 0.3-0.75 aw and decreased with EVOH ethylene content. At high relative humidities ( aw > 0.75) the value of permeability increased by up to two orders of magnitude. In this range, the higher the ethylene content the lesser the value of P.

Titanium-Passivated Tinplate for Canning Foods

Chromium-based treatments are currently used for the passivation of tinplate, which produces a protective surface layer consisting of a mixture of metal chromium and chromium oxide. This passivation film is effective against the formation of tin oxides and corrosion by food media, and offers a good substrate for the adhesion of protective organic coatings. However, there is an increasing concern about environmental and health risks with this passivation treatment. The aim of this paper was to study a new environmental friendly passivation treatment based on a titanium compound, applied on tinplate and afterwards lacquered with a conventional epoxyphenolic lacquer used for food can applications. The mechanical and electrochemical characteristics of the lacquered material and the metallic dissolution in canned sardines in tomato juice and peeled tomato were similar to those obtained with conventional Cr-passivated tinplate. According to these results titanium treatment could be considered an alternative to chromium for practical applications.

Review: Alternative high barrier polymers for food packaging Revisión: Polimeros de alta barrera para el envase de alimentos

PVdC and aluminium foil (or aluminium metallization) have traditionally been used as flexible high barrier materials in the design of packages for perishable foodstuffs. During recent years new polymers, treatments and coatings have been developed and are presently considered as alternative materials in the design of high barrier packages. These materials are reviewed, their water and oxygen permeability or permeance data are collated, and structures commercially avail able and their main applications are listed.

Modelling permeation through porous polymeric films for modified atmosphere packaging

The use of perforated packaging films is increasing with the application of modified atmosphere packaging for fresh produce. These films provide high to very high mass exchange rates. However, irrespective of the chemistry of the material, mass transport through such films cannot be described using conventional permeability equations (Henry's plus Fick's laws). Other expressions such as Knudsen's law, gas diffusivities or Poiseuille's hydrodynamic flow can be applicable. The application of these laws is discussed and their corresponding range of validity is provided. These laws were also applied to model experimental permeation rates of oxygen and water and were further used to describe the headspace evolution of two fruit products in modified atmosphere packaging. In the light of these results, the contribution of different factors to the headspace evolution is discussed.

Simple method for the selection of the appropriate food simulant for the evaluation of a specific food/packaging interaction

Knowledge of the extent of food/packaging interactions is essential to provide assurance of food quality and shelf life, especially in migration and sorption processes that commonly reach equilibrium during the lifetime of a commercial packaged foodstuff. The limits of sorption and migration must be measured in the presence of the specific food or an appropriate food simulant. The partition equilibrium of food aroma compounds between plastic films and foods or food simulants (K(A,P/L) has been characterized. Two polymers (LLDPE and PET), three organic compounds (ethyl caproate, hexanal and 2-phenylethanol), four food products with varying fat content (milk cream, mayonnaise, margarine and oil) and three simulants (ethanol 95%, n-heptane and isooctane) were selectedfor study. The results show the effect of the aroma compound volatility, and polarity, as well as its compatibility with the polymer and the food or food simulant. Equilibrium constants for the organic compound between the polymers and a gaseous phase (K(A,P/V)) as well as between the food (or food simulant) and a gaseous phase (K(A,L/V)) were also determined. An approach is presented to estimate K(A,P/V) from the binary equilibrium constants K(A,P/V) and K(A,L/V). Calculated results were shown to describe experimental data very well and indicated that compatibility between the aroma and the food or food simulant is the main contributing factor to the partition equilibrium describing the extent of food/packaging interactions. Therefore, the measurement of liquid/vapour equilibrium can be regarded as a powerful tool to compare the effectiveness of food simulants as substitutes of a particular food product and can be used as a guide for the selection of the appropriate simulant.

Characterizing the migration of antioxidants from polypropylene into fatty food simulants

The migration (diffusion and equilibrium) processes of antioxidants (AOs) from polypropylene (PP) films of different thicknesses into n-heptane and 95% ethanol as fatty food simulants were analysed at 20, 37 and 60 degrees C. Heptane fully extracted the AOs from the polymer while a partition equilibrium described the migration to ethanol. The kinetics of migration were also studied via the diffusion coeffcients. As expected, diffusion was found to be faster when the polymer was in contact with heptane, due to polymer swelling by the solvent. The kinetics of the process in ethanol was described by different theoretical expressions which are discussed. Equations disregarding partition equilibrium failed to describe the process and the diffusion coefficient values obtained through them were much smaller than the actual ones and dependent on film thickness. The results also showed the significance of food simulant selection in the analysis of food-packaging interactions and migration variability with thickness.

Food aroma partition between packaging materials and fatty food simulants

By means of thermal desorption experiments, the partition equilibrium (partition coefficient, K) was analysed for six food aroma components (d-limonene, n-decane, ethyl caproate, phenylethanol, n-hexanol and hexanal) between three sealable pollymer films suitable for direct food contact (ultra-low density polyethylene, ULDPE; ionomer, ION; and polyester, PET) and four fatty food simulants (ethanol 95%, EtOH; sunflower oil, Oil; n-heptane, HEP, and iso-octane, OCT). The results showed that aroma scalping is highly dependent on the fatty food simulant utilized. Polar aroma components were more sorbed into polymers in the presence of a non-polar fatty food simulant, and vice versa. K values in the presence of Oil were always between those in EtOH and in HEP or OCT. In general, PET was the packaging film which showed the lowest partition coeffecient for non-polar components while ULDPE showed the lowest partition for polar aromas. The partition equilibrium of mixed d-limonene, ethyl caproate, and n-hexanol was also determined. The differences in K values between isolated aromas and mixed aromas were small. In general, the most sorbed aroma showed increased partition by mixture while the partition of the least sorbed was reduced.

Developmental and stress regulation of RCI2A and RCI2B, two cold-inducible genes of arabidopsis encoding highly conserved hydrophobic proteins

The capability of most higher plants to tolerate environmental conditions strongly depends on their developmental stage. In addition, environmental factors have pleiotropic effects on many developmental processes. The interaction between plant development and environmental conditions implies that some genes must be regulated by both environmental factors and developmental cues. To understand their developmental regulation and obtain possible clues on their functions, we have isolated genomic clones for RCI2A and RCI2B, two genes from Arabidopsis ecotype Columbia (Col), whose expression is induced in response to low temperature, dehydration, salt stress, and abscisic acid. The promoters of RCI2A and RCI2B were fused to the uidA (GUS)-coding sequence and the resulting constructs used to transform Arabidopsis. GUS activity was analyzed in transgenic plants during development under both stressed and unstressed conditions. Transgenic plants with either the RCI2A or RCI2B promoter showed strong GUS expression during the first stages of seed development and germination, in vascular bundles, pollen, and most interestingly in guard cells. When transgenic plants were exposed to low temperature, dehydration, salt stress, or abscisic acid, reporter gene expression was induced in most tissues. These results indicate that RCI2A and RCI2B are regulated at transcriptional level during plant development and in response to different environmental stimuli and treatments. The potential role of RCI2A and RCI2B in plant development and stress response is discussed.

High-yield expression of a viral peptide vaccine in transgenic plants

A high-yield production of a peptide vaccine in transgenic plants is described here. A 21-mer peptide, which confers protection to dogs against challenge with virulent canine parvovirus, has been expressed in transgenic plants as an amino-terminal translational fusion with the GUS gene. Transformants were selected on the basis of their GUS activities, showing expression levels of the recombinant protein up to 3% of the total leaf soluble protein, a production yield comparable to that obtained with the same epitope expressed by chimeric plant viruses. The immunogenicity of the plant-derived peptide was demonstrated in mice immunized either intraperitoneally or orally with transgenic plant extracts, providing the suitability of the GUS fusions approach for low-cost production of peptide vaccines.

Effect of sorbed oil on food aroma loss through packaging materials

Mass transport of six food aroma components, D-limonene, n-decane, ethyl caproate, phenylethanol, 1-hexanol, and hexanal, through three sealable polymer films suitable for direct food contact, ultra-low-density polyethylene (ULDPE), ionomer (ION), and modified polyester (mPET), was analyzed by permeation experiments. Transport was characterized by the permeability coefficient and its two contributing factors, the diffusion coefficient (related to kinetics) and the solubility coefficient (related to equilibrium). The results show that ULDPE is more permeable to aromas that ION, which is more so than mPET. Differences in diffusivity are mainly responsible for barrier improvement. With aromas, nonpolar compounds permeate faster than polar ones through ULDPE. The effect of sorbed oil on the behavior of these materials as food aroma barriers was investigated. The sorption of oil apparently resulted in polymer swelling, increasing the solubility of aromas into the polymer matrixes. Little or no effect was found on the values of the diffusion coefficient. The permeability coefficient was affected as a consequence of changes in solubility. When aromas were compared, the transport of nonpolar penetrants showed a considerable increase while permeability values for the polar ones were either unaffected or even reduced. This behavior has been discussed in terms of polymer/oil/aroma compatibility.

Analysis of antioxidants extracted from polypropylene by supercritical fluid extraction

Maximal potential migration of six antioxidants (AO) from five polypropylene (PP) formulations was determined by two supercritical fluid extraction (SFE) procedures, both of which contained static and dynamic steps. All analytical conditions affecting the extraction were studied and optimized using Irgafos 168 as standard. SFE was more efficient as temperature and fluid density increased. During the static step in which the samples were exposed to the fluid without flux, the introduction of hexane and methanol as fluid modifiers significantly improved the extraction. Hexane appears to facilitate polymer swelling while methanol solvates the antioxidants. In the dynamic step (in which the extraction actually occurs) time is the key parameter. Extraction for 90 min results in an efficiency of around 75%. The introduction of modifiers during this step (by an HPLC-SFE procedure) did not produce any significant improvement. When SFE was carried out on all samples, extraction efficiency was around 75% except for Irganox 1010 and Hostanox O3. The large molecular volume of these antioxidants may be responsible for the considerable reduction of extraction efficiency. Particle size and shape of polymer sample were also important. The greater the surface to volume ratio the greater the extraction efficiency.

Global and specific migration of antioxidants from polypropylene films into food simulants

Global migration and specific migration of antioxidants (AOs--Irgafos 168 [tris(2,4-di-tert-butylphenyl) phosphite], Irganox 1076 [octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl-propionate], and Hostanox SE2 (distery thiodipropionate)--from polypropylene (PP) films into food simulants (water, 3% acetic acid, 95% ethanol, olive oil, and heptane) were studied. Films (50, 100, and 200 microns thick) were exposed to simulants at temperature-time conditions simulating migration under retorting and long-term storage. Global migration into aqueous simulants was independent of film thickness and conditions of exposure, so it seems as if the migration process was limited to the dissolution of migrants on the contacting surface. Global migration to fatty food simulants was dependent on simulant, conditions of exposure, and in some cases film thickness. Specific AO migration was analyzed from dry residues obtained from global migration analysis. Migration of AOs into aqueous simulants was below the detection limit (0.01 mg/dm2). Migration into fatty food simulants was dependent on the simulant. The extractive power of simulants was similar to that observed in global migration studies. Specific migration into heptane was independent of the polymer mass, though dependent on the thickness. Migration into ethanol was dependent on both mass and thickness. A theoretical discussion about the controversial effect of thickness on migration results, based on the kinetics of the process, is presented.

Expression of the plastid ndhF gene product in photosynthetic and non-photosynthetic tissues of developing barley seedlings

A fragment of the NDH-F subunit of the plastid NAD(P)H dehydrogenase complex (NAD(P)H-plastoquinone-oxidoreductase) from barley was expressed as a fusion protein in Escherichia coli and an antibody to the fusion protein was prepared. Western blot analysis using the anti-NDH-F antibody showed specificity towards a plastid polypeptide of approximately 70 kDa present in both photosynthetic and non-photosynthetic barley tissue. The polypeptide was found in thylakoid membranes of green leaves whereas in etiolated leaves it was shown to be associated with the membrane fraction of etioplasts. NDH-F levels were higher in roots and etiolated tissue than in greening or young leaves. During leaf ontogeny, NDH-F levels decreased from young to mature tissue but increased during senescence. The accumulation of NDH-F in thylakoids of young leaves was stimulated by photooxidative treatment. The results indicate a high degree of expression of plastid ndh genes (which encode NAD(P)H dehydrogenase subunits) in non-photosynthetic plastids and under conditions which impair the photosynthetic activity of chloroplasts. In addition to its putative implication in photosynthetic electron transport, a non-photosynthetic role, such as chlororespiration, is proposed for the plastid NAD(P)H dehydrogenase complex.

Study of aroma scalping through thermosealable polymers used in food packaging by inverse gas chromatography

Scalping of aroma components in polymers used for food packaging was determined by solubility experiments. Aromas were selected from different families: esters, alcohols, hydrocarbons and ketones. Polymers were a linear low density polyethylene (LLDPE), an ionomer and a new thermosealable polyester (PET). Polymers were selected from thermosealable materials because of their resistance to fats and oils. Sorption isotherms (low sorbate activity range) for every system aroma (vapour)/polymer were determined by inverse gas chromatography. Isotherms were found to be linear. Hence, solubility coefficients (S) as defined by Henry's law were calculated from the isotherm slopes. According to S values, PET appears to be the best choice to minimize aroma scalping by sorption in the packaging inner layer, Ionomers improve the barrier to aroma when compared with LLDPE except for polar sorbates. Sorption of aroma components was shown to be selective, e.g. limonene was preferentially sorbed in LLDPE. The value of S for the limonene/LLDPE system was 2.5 times the value of S for ethyl caproate/LLDPE. This selectivity may lead to an imbalance in the flavour and may be more important than the prevention of overall scalping.