Kata Galić

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.

Shelf Life of Packaged Bakery Goods—A Review

Packaging requirements for fresh bakery goods are often minimal as many of the products are for immediate consumption. However, packaging can be an important factor in extending the shelf life of other cereal-based goods (toast, frozen products, biscuits, cakes, pastas). Some amount of the texture changes and flavor loss manifest over the shelf life of a soft-baked good can usually be minimized or delayed by effective use of packaging materials. The gains in the extension of shelf life will be application specific. It is recognized that defining the shelf life of a food is a difficult task and is an area of intense research for food product development scientists (food technologists, microbiologists, packaging experts). Proper application of chemical kinetic principles to food quality loss allows for efficiently designing appropriate shelf-life tests and maximizing the useful information that can be obtained from the resulting data. In the development of any new food product including reformulating, change of packaging, or storage/distribution condition (to penetrate into a new market), one important aspect is the knowledge of shelf life.

Effect of relative humidity on carvacrol release and permeation properties of chitosan based films and coatings.

The influence of water vapour conditions on mass transport and barrier properties of chitosan based films and coatings were studied in relation to surface and structural properties. Water contact angles, material swelling, polymer degradation temperature, barrier properties (PO2, PCO2, WVP) and aroma diffusion coefficients were determined. The solvent nature and the presence of carvacrol influenced the surface and structural properties and then the barrier performance of activated chitosan films. Increasing RH from 0% to 100% led to a significant increase in material swelling. The plasticization effect of water was more pronounced at high humid environment, while at low RH the matrix plasticization was induced by carvacrol. The deposit of a thin chitosan layer on polyethylene decreased PO2 and PCO2 both in dry and humid conditions. The carvacrol release from the chitosan matrix was strongly influenced by RH. A temperature increase from 4 to 37°C also had an impact on carvacrol diffusivity but to a lesser extent than RH.

EFFECT OF TEMPERATURE AND MECHANICAL STRESS ON BARRIER PROPERTIES OF POLYMERIC FILMS USED FOR FOOD PACKAGING

The permeance of carbon dioxide, oxygen, nitrogen, and air through commercial polymers based on polyethylene (PE), biaxially oriented polypropylene (BOPP), and polyamide (PA) used for food packaging is reported. The influence of temperature (from 10 to 60°C) and crease stress cycles (30, 50, 70, and 110) on gas permeance is also analyzed. Generally, the highest changes in gas permeance changes with increased stress cycles are observed with films having a metallized layer in the structure, namely BOPPcoex/BOPPcoex.met and, to a lesser extent, BOPPcoex.met/PE laminate. The lowest crease stress influence on barrier properties is obtained for PE film. In this case, the highest activation energy for the permeability coefficient (P) is obtained. Normal progressions of activation energies for P are: N2 = Air>CO 2>O2.

Shelf life of packaged sliced dry fermented sausage under different temperature.

The aim of this study was to investigate the shelf-life of commercial sliced dry fermented sausage during storage at different temperatures. Different laminate composition was used for vacuum and nitrogen (100% N(2)) packaging. The microbiological, physico-chemical and sensory parameters were analysed during 120 days storage at 4, 22 and 37°C. Packaging materials were analysed for their barrier characteristic (oxygen permeability). Sensory quality limited the shelf-life of sliced dry fermented sausages before the limiting effects of microbial proliferation occurred. Nitrogen atmosphere packaging allowed longer storage (>120 days) than vacuum (95 days) packaged dry fermented sausages at 4°C.

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.

Carvacrol affects interfacial, structural and transfer properties of chitosan coatings applied onto polyethylene.

Different chitosan coating solutions were tested with the aim of investigating their adhesion and wettability onto polyethylene film to improve packaging performance and provide antimicrobial properties. Surface wetting kinetics was monitored by contact angle measurements. Addition of ethanol and carvacrol improved wettability and adhesion of the thin chitosan layer. Structure, water vapour, O2, CO2 and air permeabilities of self supported chitosan films and coated polyethylene were determined. The formation of a thin chitosan layer on polyethylene improved gas barrier properties decreasing the Permeability Coefficient for oxygen and carbon dioxide ( [Formula: see text] , [Formula: see text] ) from 100 to 10,000 times. Presence of carvacrol in the chitosan coating layer increased [Formula: see text] , [Formula: see text] and Pair by a factor of ten. Moreover, it influenced film microstructure. However chitosan was shown to be good gas barrier film in the dry state.

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.

Polyethylene/Polycaprolactone Nanocomposite Films for Food Packaging Modified with Magnetite and Casein: Oxygen Barrier, Mechanical, and Thermal Properties

ABSTRACT Polyethylene (PE) was modified and prepared as double-layer polyethylene/polycaprolactone (PE/PCL) film. Magnetite and casein were added to the PCL-coating film to improve barrier properties and prevent destruction of basic structure of primary polymer PE. Significant improvements were observed with regards to mechanical (tensile strength, elongation at break) and thermal properties, while barrier (O2 permeability) properties were slightly improved. Overall migration values into acetic acid were lower (from 1 to 4.6 mg/dm2) than the upper limit set by the legislation. Specific migration of iron in PE/PCL-Fe samples is also below (µg/L) specific migration limit value set by the legislation (mg/kg). GRAPHICAL ABSTRACT

Preparation and Properties of Low Density Polyethylene Film Modified by Zeolite and Nanoclay

PE-LD samples containing two types of filler in concentrations of 2–10 wt.% (zeolite TMAZ 7 and nanoclay Cloisite 20A). The microstructural and morphological changes as well as mechanical features of samples were characterized by scanning electronic microscopy (SEM) and by tensile tests. The thermal degradation of PE-LD composites were achieved using thermogravimetric analysis (TGA). The permeability, the diffusion and the solubility constants of the gases in modified PE-LD films were calculated and the gas separation (N2/O2; O2/CO2) ability was determined. In the presence of nanoparticles, at lower content, the value of oxygen permeability of PE-LD decreases.