Chitosan films as pH-responsive sustained release systems of naturally occurring antifungal volatile compounds.

Reversible imine bonds have been used as a strategy to develop pH-dependent antifungal systems based on grafting benzaldehyde and citral onto the surface of chitosan films. Formation of imine bonds was confirmed by ATR-FTIR and XPS. Aldehyde unit incorporation respect to glucosamine units of chitosan polymer was estimated by elemental analysis. The rate and extent of imine bond hydrolysis depended on the pH of the media and the chemical structure of the aldehyde. The release of the aldehydes was monitored by gas chromatography observing acidic media favours the release. Imine bond obtained from benzaldehyde was more prone to be hydrolysed than citral. Chitosan films grafted with benzaldehyde and triggered at acidic pH controlled in vitro growth of common fruit and vegetable spoilage and pathogenic fungi. The films developed could be applied in the design of food packages intended to prevent postharvest fungal spoilage.

Covalent immobilization of lysozyme on ethylene vinyl alcohol films for nonmigrating antimicrobial packaging applications.

The objective of this study was to develop a new antimicrobial film, in which lysozyme was covalently attached onto two different ethylene vinyl alcohol copolymers (EVOH 29 and EVOH 44). The EVOH surface was modified with UV irradiation treatment to generate carboxylic acid groups, and lysozyme was covalently attached to the functionalized polymer surface. Surface characterization of control and modified films was performed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and dye assay. The value of protein loading after attachment on the surface was 8.49 µg protein/cm(2) and 5.74 µg protein/cm(2) for EVOH 29 and EVOH 44, respectively, after 10 min UV irradiation and bioconjugation. The efficacy of the EVOH-lysozyme films was assessed using Micrococcus lysodeikticus. The antimicrobial activity of the films was tested against Listeria monocytogenes and was similar to an equivalent amount of free enzyme. The reduction was 1.08 log for EVOH 29-lysozyme, 0.95 log for EVOH 44-lysozyme, and 1.34 log for free lysozyme. This work confirmed the successful use of lysozyme immobilization on the EVOH surface for antimicrobial packaging.

Photoactivated chlorophyllin-based gelatin films and coatings to prevent microbial contamination of food products.

The aim of this work was to develop antimicrobial photosensitizer-containing edible films and coatings based on gelatin as the polymer matrix, incorporating sodium magnesium chlorophyllin (E-140) and sodium copper chlorophyllin (E-141). Chlorophyllins were incorporated into the gelatin film-forming solution and the inhibiting effect of the cast films was tested against Staphylococcus aureus and Listeria monocytogenes. The results demonstrated that water soluble sodium magnesium chlorophyllin and water soluble sodium copper chlorophyllin reduced the growth of S. aureus and L. monocytogenes by 5 log and 4 log respectively. Subsequently, the activity of self-standing films and coatings containing E-140 was assessed on cooked frankfurters inoculated with S. aureus and L. monocytogenes. These tests showed that it was possible to reduce microorganism growth in cooked frankfurters inoculated with S. aureus and L. monocytogenes by covering them with sodium magnesium chlorophyllin-gelatin films and coatings.

Characterization of antimicrobial properties on the growth of S. aureus of novel renewable blends of gliadins and chitosan of interest in food packaging and coating applications.

The biocide properties of chitosan-based materials have been known for many years. However, typical antimicrobial formulations of chitosan, mostly chitosonium salts, are known to be very water sensitive materials which may impair their use in many application fields such as food packaging or food coating applications. This first work reports on the development and characterization of the antimicrobial properties of novel fully renewable blends of chitosan with more water-resistant gliadin proteins isolated from wheat gluten. Chitosan release to the nutrient broth from a wide range of blends was studied making use of the ninhydrin method. The results indicated that both pure chitosan and its blends with gliadins presented significant antimicrobial activity, which increased with increasing the amount of chitosan in the composite formulation as expected. The gliadins-chitosan blends showed good transparency and film-forming properties and better water resistance than pure chitosan. The release tests revealed that dissolution of the biocide glucosamine groups, i.e. the chitosan water soluble fractions, also increased with the amount of chitosan present in the formulation. The release of these groups was for the first time directly correlated with the antimicrobial properties exhibited by the blends. Thus, incorporation of chitosan into an insoluble biopolymer matrix was revealed as a very feasible strategy to generate novel chitosan-based antimicrobial materials with potential advantages, for instance active food packaging applications.

Improving packaged food quality and safety. Part 1: synchrotron X-ray analysis.

The objective was to demonstrate, as an example of an application, the potential of synchrotron X-ray analysis to detect morphological alterations that can occur in barrier packaging materials and structures. These changes can affect the packaging barrier characteristics when conventional food preservation treatments are applied to packaged food. The paper presents the results of a number of experiments where time-resolved combined wide-angle X-ray scattering and small-angle X-ray scattering analysis as a function of temperature and humidity were applied to ethylene-vinyl alcohol co-polymers (EVOH), polypropylene (PP)/EVOH/PP structures, aliphatic polyketone terpolymer (PK) and amorphous polyamide (aPA) materials. A comparison between conventional retorting and high-pressure processing treatments in terms of morphologic alterations are also presented for EVOH. The impact of retorting on the EVOH structure contrasts with the good behaviour of the PK during this treatment and with that of aPA. However, no significant structural changes were observed by wide-angle X-ray scattering in the EVOH structures after high-pressure processing treatment. These structural observations have also been correlated with oxygen permeability measurements that are of importance when guaranteeing the intended levels of safety and quality of packaged food.

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.

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.

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.

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.