Mechanical and thermal behaviour of flexible food packaging polymeric films materials under high pressure/temperature treatments

The effect of high‐pressure processing on mechanical and thermal properties of four complex packaging materials (polyethylene/ethylene vinyl alcohol/ polyethylene: PE/EVOH/PE; metallized polyester/polyethylene: PETmet/PE; polyester/polyethylene: PET/PE; polypropylene SiOx recovered: PPSiOx) was studied. Pouches of the different materials containing distilled water or olive oil as food simulants, as well as empty ones, were subjected to 400 MPa for 30 min, at temperatures of 20 or 60°C. Delamination and wrinkling were a general consequence of the high‐pressure processing of multilayer polymeric systems. However, no significant changes were observed regarding the mechanical properties of PE containing laminates after pressurization. PPSiOx underwent significant modifications as SiOx completely broke down. Neither thermal property was affected by pressure, as it was the processing temperature that induced tempering effects on the crystallization behaviour of polymeric components. Only PE/EVOH/PE, when in contact with water as a simulant, presented a decrease in the melting point temperature. Copyright © 2008 John Wiley & Sons, Ltd.     

Development of Cellulose Eco‐nanocomposites with Antimicrobial Properties Oriented for Food Packaging

Nanocomposites based on cellulose acetate, a commercial organoclay (Cloisite30B), triethyl citrate and variable content of antimicrobial agents (thymol and cinnamaldehyde), were obtained using a solution casting technique. The properties of the nanocomposites were evaluated using X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, mechanical (modulus of elasticity, tensile strength and elongation at break), scanning electronic microscopy, global migration and microbiological testing. A reduction of glass transition (T_g), melting temperature (T_m) and melting enthalpy (?H_m) was also observed when the content of thymol and cinnamaldehyde was increased in the cellulose acetate nanocomposites. In contrast, thermal stability, mechanical performance and morphology of material did not show important differences when the content was modified. Results of global migration were dependent of the kind of simulant used. Finally, the antimicrobial activity was dependent of the essential oil used and its content inside the nanocomposite. An important effect of organoclay on the antimicrobial activity was also observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of high‐pressure food processing on the mass transfer properties of selected packaging materials

The effect of high‐pressure processing (HPP) on the total migration into distilled water and olive oil and on the barrier properties of four complex packaging materials were evaluated. The films were polyethylene/ethylene‐vinyl‐alcohol/polyethylene (PE/EVOH/PE), metallized polyester/polyethylene, polyester/polyethylene (PET/PE), and polypropylene‐SiOx (PPSiOx). Pouches made from these films were filled with food simulants, sealed and then processed at a pressure of 400 MPa for 30 min, at 20 or 60°C. Pouches kept at atmospheric pressure were used as controls. Prior to and after treatment, all films were evaluated for their barrier properties (oxygen transmission rate and water vapour transmission rate) and ‘Total’ migration into the two food simulants. In the case of water as the food stimulant, a low ‘Total’ migration was observed and even a lower one after the HPP treatment. In the case of oil as the food simulant, a higher ‘Total’ migration was found compared to the control as a result of damage to the structures during the HPP treatment. The gas permeability of the films increased after the HPP, compared to the control, due to damages in the structure caused during the treatment. The PET/PE film presented minimum changes in properties after HPP. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and theoretical study of LDPE versus different concentrations of Irganox 1076 and different thickness

This work presents a theoretical and experimental study on the specific migration process, describing the mass transfer of a model migrant Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (I-1076), an antioxidant commonly used in the polyolefins processing. Film samples (LDPE), with initial concentration of Irganox between 1000 and 6000 (mg/kg), and thickness of 50-190 ??m, were placed in contact with fatty (EtOH 95%) and aqueous (EtOH 10%) food simulants at 40 °C for 20 days, in order to obtain the concentration evolution in the food simulant which was measured by HPLC. On the other hand, a phenomenological model based on a resistances-in-series approach was developed considering the diffusion through the polymer film, natural convection in the food simulant and the thermodynamic equilibrium between the polymer and the liquid simulant phase. For the thickest films, the diffusion coefficient of I-1076 through the polymer phase was estimated varying between 1.95·10^− 13 (m² s^− 1) and 2.0·10^− 13 (m² s^− 1) at 40 ºC. On the contrary, the thinnest one shows a significant decrease of the diffusion coefficient value, which was evaluated in 1.0·10^− 14 (m² s^− 1). This modification can be explained by means of a crystal distribution and size in the thinnest polymer film prepared by CAST extrusion. The mathematical model developed is a tool for prediction and analysis which can be used to facilitate the characterization of polymers, and it could predict the response as packaging for food in a specific application.     

High hydrostatic pressure effect on chemical composition,color, phenolic acids and antioxidant capacity of Cape gooseberry pulp (Physalis peruviana L.)

The aim of this study was to evaluate the effects of high hydrostatic pressure (HHP) at 300, 400 and 500 MPa/1, 3 and 5 min on nutritional and antioxidant properties of Cape gooseberry pulp after immediate application and after 60 days of storage. Proximal analysis, color, phenolic acids content and antioxidant capacity were determined. When analyzing the immediate effect of different treatments, a clear influence of HHP was observed in all the components of the proximal analysis. Regarding color, none of the three chromatic parameters showed significant differences with control leading to a minimum ΔE at 300 MPa/3 min. Changes in bound and free phenolic acids were evidenced after treatments. The maximum levels of TPC as well as antioxidant capacity were observed at 500 MPa/5 min. By the end of storage, all treated samples discolored leading to ΔE = 14.9 at 500 MPa/5 min. The profile of free and bound phenolic acids presented differences compared to Day 0. The antioxidant capacity by means of ORAC increased for treatments above 300 MPa/5 min indicating the effectiveness of these treatments for the production of functional products based on gooseberry pulp. For treatments above 400 MPa/3 min, molds and yeasts were not detected.     

Natural antimicrobials and antioxidants added to polylactic acid packaging films. Part I: Polymer processing techniques

Currently, reducing packaging plastic waste and food losses are concerning topics in the food packaging industry. As an alternative for these challenges, antimicrobial and antioxidant materials have been developed by incorporating active agents (AAs) into biodegradable polymers to extend the food shelf life. In this context, developing biodegradable active materials based on polylactic acid (PLA) and natural compounds are a great alternative to maintain food safety and non-toxicity of the packaging. AAs, such as essential oils and polyphenols, have been added mainly as antimicrobial and antioxidant natural compounds in PLA packaging. In this review, current techniques used to develop active PLA packaging films were described in order to critically compare their feasibility, advantages, limitations, and relevant processing aspects. The analysis was focused on the processing conditions, such as operation variables and stages, and factors related to the AAs, such as their concentrations, weight losses during processing, and incorporation technique, among others. Recent developments of active PLA-based monolayers and bi- or multilayer films were also considered. In addition, patents on inventions and technologies on active PLA-based films for food packaging were reviewed. This review highlights that the selection of the processing technique and conditions to obtain active PLA depends on the type of the AA regarding its volatility, solubility, and thermosensitivity.     

Effect of High-Pressure Food Processing on the Physical Properties of Synthetic and Biopolymer Films

ABSTRACT:  The effect of high-pressure processing on 2 plastic food packaging films, a biopolymer (PLASiOx/PLA) and a synthetic polymer (PET-AlOx), was studied. Samples in direct contact with olive oil, as a fatty food simulant, and distilled water, as an aqueous simulant, were subjected to a pressure of 500MPa for 15 min at 50 °C. The mechanical, thermal, and gas barrier properties of both films were evaluated after the high-pressure processing (HPP) and compared to control samples that have not undergone this treatment. Significant changes in all properties were observed in both films after the HPP treatment and in contact with the food simulants. In both films an induced crystallization was noticed. In the PLASiOx/PLA film the changes were larger when in contact with water that probably acted as a plasticizer. In the PET-AlOx film the changes in properties were attributed to the formation of pinholes and cracks during the HPP treatment. In this film, most of the properties changed more in the presence of oil as the food simulant.     

Crack propagation during fatigue experiments

In the present paper a very simple phenomenological theory of crack propagation during fatigue experiments is presented. It is shown that an important role is played by work-hardening to explain both the existence of a fatigue limit and the well known deviations from Miner's Rule in the case of tests conducted at varying maximum applied stresses. Although approximate, the theory can account for the main phenomena involved in fatigue experiments.

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Zusammenfassung Es wird eine sehr einfache Grundlagentheorie zur Beschreibung der Fortpflanzungsbedingungen eines Risses unter Dauerbeanspruchung dargelegt.Die Grundlage dieser Theorie besteht darin die Rissfortpflanzung mit der mechanischen Hysteresis in Zusammenhang zu bringen.Es wird auf die wichtige Rolle der Verformung hingewiesen, sowohl für der Begriff der Dauerfestigkeit als auch für die wohlbekannten Abweichungen von dem Miner Gesetz, im falle von Versuchen bei maximaler Beanspruchung mit veränderlichen Amplituden.Trotz einer Anzahl von Vereinfachungen, gibt these Theorie eine gute Beschreibung der wichtigsten Vorgänge beim Dauerversuch.

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Résumé On présente une théorie phénoménologique extrêmement simple pour décrire les conditions de propagation des fissures en fatigue. Cette théorie repose sur le principe d'associer la propagation des fissures an cycle d'hystérésis mécanique. On montre que l'écrouissage joue un rôle important, à la fois dans la notion de la limite d'endurance, et dans les inexactitudes, bien connues, de la règle de Miner, lorsque des essais sent conduits à des contraintes maximales d'amplitude variable.Quoique assez grossière, cette théorie rend compte des principaux phénomènes qui interviennent dans des expériences de fatique.

     

Evaluation of the Effectiveness of a New Antimicrobial Active Packaging for Fresh Atlantic Salmon (Salmo Salar L.) Shelf Life

Nowadays, consumers demand for fresh, high‐quality seafood products continues to climb, especially in affluent, developed nations. At the same time, there is increasing attention regarding improved utilization of seafood for human consumption; Atlantic salmon is the main species in Chile aquaculture, and most of the salmon are exported as fresh fish to USA. It is well documented that low storage temperature inhibit bacterial growth and biochemical degradation, thus facilitating prolonged shelf life. Partly freezing the outer fillet layer from ?0.5°C to ?2.0°C (superchilling) has proven to be more efficient in inhibiting biochemical changes and bacterial spoilage compared with traditional chilling. Nevertheless, antimicrobial active packaging offers the possibility to increase product shelf life through the reduction of the microbiological damage of the product during its transportation, and thus increasing consumer safety and health. The main objective of this study was to compare the effects of an active antimicrobial packaging on microbiological growth, sensory attributes and instrumental quality measurements of raw Atlantic salmon (Salmo salar) fillets. Flexible plastic films containing Thymol as antimicrobial agent were used for salmon packaging. Salmon were stored at 2°C, 4°C and 8°C. Analyses of aerobic mesophilic bacteria and psicrophilic bacteria count were carried out at 1, 3, 8, 11, 15 and 18 days. L*a*b* colour evolution, overall sensorial properties and chemical evolution were studied. Application of active antimicrobial packaging for fillet salmon reduced the microbial count for least 18 days at 2°C. No modification of the sensorial properties was detected by the sensorial panel, indicating that the antimicrobial compound used in the present study, thymol, is compatible with salmon packaging. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and Characterization of Cellulose Acetate Butyrate/Organoclay Nanocomposites Produced by Extrusion

Nanocomposite films based on cellulose acetate butyrate, modified montmorillonite (Cloisite^® 30B), plasticizer (triethyl citrate) and antimicrobial compounds (carvacrol and cinnamaldehyde) were prepared by extrusion. The effects of the Cloisite^® 30B content and antimicrobial compound types on the morphology of the nanocomposite films were investigated by X‐ray diffraction and transmission electron microscopy. The thermal characteristics of films were analysed by thermogravimetry and differential scanning calorimetry; oxygen and water vapour permeability and tensile strength were determined. The film's antimicrobial behaviour against Listeria innocua, Staphylococcus aureus, Escherichia coli O157:O7 and Saccharomyces cerevisiae was investigated and determined using a viable cell count method. Nanocomposites with a Cloisite^® 30B content of 3 wt% showed better dispersion than nanocomposites with a 5 wt% content. For films with antimicrobial compounds, tensile strength and Young's modulus decreased and water vapour permeability increased (150%) because of the plasticization effect of the antimicrobial compounds (essential oils). The nanocomposites with carvacrol and cinnamaldehyde were effective against the tested Gram‐positive bacteria (reduction of at least 3.0 log CFU/ml) and yeast (reduction of at least 4.0 log CFU/ml). This study demonstrates that antimicrobial cinnamaldehyde and carvacrol can be successfully incorporated into cellulose acetate butyrate nanocomposites and that they have an inhibitory effect against microbial growth in solid medium. It shows the potential use of cellulose acetate butyrate for food packaging applications. Copyright © 2013 John Wiley & Sons, Ltd.