Nada Ciković

Gas permeability and DSC characteristics of polymers used in food packaging

The work is an experimental study of gas permeability and DSC characterisation of polymers used in food packaging. For this purpose polyethylene (0.03 and 0.1 mm), polypropylene (0.03 mm), and coextruded polypropylene (0.1 mm) were studied. The permeabilities of polymers to oxygen and nitrogen were measured at 20 oC, 40 oC and 60 oC using the manometric method. From the obtained permeability data, permeation, diffusion and solubility constants were calculated while temperatures and enthalpies of the phase change were determined by the DSC method. Permeability of oxygen and nitrogen increase with temperature for all investigated samples. Permeation data for the polypropylene (0.03 mm) and polyethylene (0.03 mm) showed good agreement with the Arrhenius equation. Upon temperature increase starting from 40 0C all samples undergo phase change in the temperature range from 107 0C to 173 0C with enthalpies in the range of 40 to 85 J g^-1. Experiments, where simulated conditions of food sterilisation were used as well as exposition to radiation in a microwave oven, showed negligible changes in DSC indicating structural stability of the polymers.

Permeability characterisation of solvent treated polymer materials

The permeability of gases is reported for some monofilms as well as laminated polymers at temperatures from 20 to 60°C. In order to simulate the effect of food/packaging interaction on permeability of polymeric materials, all investigated samples were subjected to 15% (v/v) ethanol and 3% (w/v) acetic acid aqueous solution prior to permeability measurements. The activation energy for permeability is also reported for each gas. The permeability of the selected polymers treated with food simulants increased significantly compared to untreated ones, mainly due to the swelling effect of the water molecules. All investigated samples showed behaviour predicted by the Arrhenius equation when in the dry condition.

The effect of inhibitors on the corrosion of tin in sodium chloride solution

Abstract The corrosion behavior of tin in salt solutions at various temperatures and in the presence of air, nitrogen and oxygen atmosphere was investigated. For this purpose, model salt solutions containing sodium chloride (2 wt%) and sodium chloride with 0.002 wt% nitrite and nitrate were prepared. The system was chosen to perform the corrosion processes which could take place during the thermal treatment of some food products in tin plate cans, in the presence of oxidizing salts and different atmospheres. Electrochemical investigations were performed using potentiostatic and galvanostatic polarization methods. From the experimental data, the corrosion current, corrosion potential, polarization resistance and electron number were calculated. Auger electron spectroscopy and the XPS technique were used to determine the chemical composition investigations of solid surface. A possible corrosion mechanism was proposed.

Redox-potential and browning of tomato paste in aluminium tubes during storage at different temperatures

ZusammenfassungEs wurden der Einfluß der Temperatur und der Alu-Verpackung auf physikalisch-chemische Änderungen des Tomatenkonzentrates während der Lagerung untersucht. Dabei wurde festgestellt, daß die Verpackung und die Lagerungsbedingungen auf die oxydativen Veränderungen des Tomatenkonzentrates und der Korrosionsprozeß in der Alu-Verpackung einen großen Einfluß haben. Die größte Änderungen während der Lagerung wurde im Gehalt an Askorbinsäure und Hydroxymethylfurfural festgestellt. Die genannten Verbindungen haben gewisse Redox-Eigenschaften. Die Redox-Reaktion während der Lagerung hat Einfluß auf die Veränderung des Redox-Potentials, und zwar ist dieses um so höher, je niedriger die Reduktionskraft der anwesenden Verbindungen ist.AbstractThe influence of temperature and applied lacquer on aluminium (Al) tubes on physico-chemical changes of tomato paste during storage was studied. Packaging and storage conditions have a considerable influence on both the oxidative changes in the product and corrosion behaviour of the Al tubes. The greatest changes during storage were the ascorbic acid and hydroxymethylfurfural contents; the compounds known to possess certain oxido-reduction power. The consequence of oxidation-reduction reactions taking place during storage was the establishment of particular redox values: the lower the reducing power of the compounds present, the higher the rH value obtained.

Der Einfluß wäßriger Gewürzextrakte auf die Aluminiumkorrosion in NaCl-Lösung

SummaryThe influence of water-space spice extracts on the corrosion of aluminum in sodium chloride solution was investigated. Model solutions of spice extracts (paprika, pepper, garlic, rosemary) and mixtures in sodium chloride solution were prepared for the determination of corrosion current versus corrosion potential of aluminum. Simultaneously, pH and conductance of the solutions as a function of each spice and its concentration were measured.ZusammenfassungEs wurde der Einfluß wäßriger Gewürzextrakte und deren Mischungen auf die Aluminiumkorrosion in NaCl-Lösungen untersucht. Zur Bestimmung der Korrosionsströme und Korrosionspotentiale des Aluminiums wurden Modellösungen aus wäßrigen Gewürzextrakten (Pfeffer, Paprika, Knoblauch, Rosmarin) sowie ihre Mischungen, mit NaCl-Lösung hergestellt. Gleichzeitig wurden pH und spez. Leitfähigkeit der Lösungen in Abhängigkeit von Art und Masseanteil der Gewürze gemessen.