Development of an Oxygen Sensitive Model Gel System to Detect Defects in Metal Oxide Coated Multilayer Polymeric Films.

Metal oxide coated multilayered polymeric pouches provide a suitable alternative to foil-based packaging for shelf-stable products with extended shelf-life. The barrier performance of these films depends upon the integrity of the metal oxide coating which can develop defects as a result of thermal processing and improper handling. In this work, we developed a methodology to visually identify these defects using an oxygen-sensitive model gel system. Four pouches with different metal oxide coatings: MOA (Coated PET), MOB (SiOx -coated PET), MOC (Overlayer-AlOx -Organic-coated PET), MOD (Overlayer-SiOx -coated PET) were filled with water and retort-processed for 30 and 40 min at 121 °C. After processing, the pouches were cut open, dried and subsequently filled with a gel containing methylene blue that changes color in the presence of oxygen. The pouches were then stored at 23 and 40 °C for 180 and 90 days, respectively. Defects were identified by observing the localized color change from yellow to blue in the packaged gel. These observations were confirmed through measurement of oxygen and water vapor transmission rates, as well as SEM and CLSM analyses. The MOC pouches showed the least change in barrier properties after thermal processing. This was due to crosslinking in the organic coating and protection provided by the overlayer. The melting enthalpy of all films increased significantly (P < 0.05) after sterilization. This may increase the brittleness of the substrates after processing. Findings may be used to improve the barrier performance of metal oxide coated polymeric films intended for food packaging applications. PRACTICAL APPLICATION: In this study, we developed a methylene blue-based, oxygen-sensitive model gel system to identify defects in metal oxide coated polymeric structures induced by thermal processing and mechanical stresses. We also performed a comprehensive analysis of these defects through CLSM and SEM. The gel system and methodology developed may be useful in the design and development of high barrier metal oxide coated films.

A Fluorescence-based Method for Estimation of Oxygen Barrier Properties of Microspheres.

In this study, we developed a fluorescence method to quantify oxygen barrier properties for wall materials used in microencapsulation of oxygen-sensitive compounds. We used a reversible, oxygen quenching dye, tris (4,7-diphenyl-1, 10-phenanthroline) ruthenium(II) dichloride complex, as a marker to monitor oxygen transport across spray-dried and freeze-dried Hi-cap100 and maltodextrin microspheres. We fit the rate of oxygen transport to Fick's second law and extrapolated an effective oxygen diffusion coefficient Deff. Results show that the Deff for spray-dried maltodextrin and Hi-cap100 formulations were in the range of 6.46 × 10-15 to 7.45 × 10-15  m2 /s and 16.0 × 10-15 to 22.4 × 10-15 m2 /s, respectively. Results also show an increasing trend in thiobarbituric acid reactive substances reaction rate constants, with an increasing Deff for each formulation. Additionally, freeze-dried maltodextrin formulations had significantly higher Deff (31.1 × 10-15 to 36.0 × 10-15 m2 /s) compared to spray-dried matrices due to a more porous morphology. This new method provides a framework for the in situ estimation of Deff for wall materials in microspheres. Potential applications include the design and selection of wall materials for maximum oxidative stability of encapsulated ingredients. PRACTICAL APPLICATION: Currently, the selection of wall materials used in microencapsulation of lipids takes a trial-and-error approach, which can be time consuming and prone to error. In this study, we developed a new methodology to directly assess the oxygen barrier properties of wall materials in microspheres. This method can be used by food scientists to screen wall materials in order to optimize the oxidative stability of encapsulated lipids.

Headspace oxygen as a hurdle to improve the safety of in-pack pasteurized chilled food during storage at different temperatures.

This study investigated the use of headspace oxygen in a model food system to prevent the growth of anaerobic pathogenic bacteria in in-pack pasteurized food at various storage temperatures. Three model food formulations prepared with tryptic soy broth and three agar concentrations (0.1, 0.4 and 1.0%) were sealed without removing the air from the package in high oxygen barrier pouches (OTR=0.3cm3/m2·day·atm). Important properties influencing bacterial growth, including pH and water activity (aw) were determined. The oxygen sorption kinetics of each model food were obtained at three different storage temperatures (8, 12, and 20°C) using an OxySense Gen III 300 system. An analytical solution of Fick's second law was used to determine the O2 diffusion coefficient. Growth challenge studies at 12 and 20°C were conducted at three selected locations (top, center and bottom layers) in model foods containing 1% agar. Model foods were inoculated with Clostridium sporogenes PA 3679 (300spores/mL), and were classified as low-acid (pH>4.5, aw>0.85). When the storage temperature decreased from 20 to 8°C, the oxygen diffusion decreased from 0.82×10-9m2/s to 0.68×10-9m2/s. As the agar concentration was increased from 0.1 to 1.0%, the effective oxygen permeability decreased significantly (p=0.007) from 0.88×10-9m2/s to 0.65×10-9m2/s. When the inoculated model foods were stored at 12°C for 14days, C. sporogenes PA 3679 was unable to grow. As the storage temperature was increased to 20°C, significant bacterial growth was observed with storage time (p<0.0001), and the C. sporogenes PA 3679 population increased by around 6logCFU/g. However, the location of the food did not influence the growth distribution of C. sporogenes PA 3679. These results demonstrate that oxygen diffusion from the pouch headspace was primarily limited to the food surface. Findings suggest that the air/oxygen present in the package headspace may not be considered as a food safety hurdle in the production of pasteurized packaged food.

Improving functional properties of pea protein isolate for microencapsulation of flaxseed oil.

Unhydrolysed pea protein (UN) forms very viscous emulsions when used at higher concentrations. To overcome this, UN was hydrolysed using enzymes alcalase, flavourzyme, neutrase, alcalase-flavourzyme, and neutrase-flavourzyme at 50 °C for 0 min, 30 min, 60 min, and 120 min to form hydrolysed proteins A, F, N, AF, and NF, respectively. All hydrolysed proteins had lower apparent viscosity and higher solubility than UN. Foaming capacity of A was the highest, followed by NF, N, and AF. Hydrolysed proteins N60, A60, NF60, and AF60 were prepared by hydrolysing UN for 60 min and used further for microencapsulation. At 20% oil loading (on a total solid basis), the encapsulated powder N60 had the highest microencapsulation efficiency (ME = 56.2). A decrease in ME occurred as oil loading increased to 40%. To improve the ME of N60, >90%, UN and maltodextrin were added. Flowability and particle size distribution of microencapsulated powders with >90% microencapsulation efficiency and morphology of all powders were investigated. This study identified a new way to improve pea protein functionality in emulsions, as well as a new application of hydrolysed pea protein as wall material for microencapsulation.

Oxidation-reduction potential and lipid oxidation in ready-to-eat blue mussels in red sauce: criteria for package design.

BACKGROUND: Ready-to-eat in-package pasteurized blue mussels in red sauce requires refrigerated storage or in combination with an aerobic environment to prevent the growth of anaerobes. A low barrier packaging may create an aerobic environment; however, it causes lipid oxidation in mussels. Thus, evaluation of the oxidation-reduction potential (Eh) (aerobic/anaerobic nature of food) and lipid oxidation is essential. Three packaging materials with oxygen transmission rate (OTR) of 62 (F-62), 40 (F-40) and 3 (F-3) cm3 m-2 day-1 were selected for this study. Lipid oxidation was measured by color changes in thiobarbituric acid reactive substances (TBARS) at 532 nm (TBARS@532) and 450 nm (TBARS@450). RESULTS: Significantly higher (P < 0.05) TBARS@532 was found in mussels packaged in higher OTR film. TBARS@450 in mussels packaged with F-62 and F-40 gradually increased during refrigerated storage (3.5 ± 0.5 °C), but remained constant after 20 days of storage for mussels packaged with F-3. The Eh of pasteurized sauce was not significantly affected (P > 0.05) by OTR and remained negative (< -80 mV) during storage. Negative Eh values can support the growth of anaerobes such as Clostridium botulinum. The headspace oxygen concentration was reduced by about 50% from its initial value during pasteurization, and then further declined during storage. The headspace oxygen concentration was higher in trays packaged with higher OTR film. CONCLUSION: Mussels packed with high OTR film showed higher lipid oxidation, indicating that high barrier film is required for packaging of mussels. Pasteurized mussels must be kept in refrigerated storage to prevent growth of anaerobic proteolytic C. botulinum spores under temperature abuse. © 2016 Society of Chemical Industry.

Non-invasive measurement of oxygen diffusion in model foods.

In this study, we developed a non-invasive method to determine oxygen diffusivity (DO2) in food gels using an Oxydot luminescence sensor. We designed and fabricated a transparent diffusion cell in order to represent oxygen transfer into foods packaged in an 8-ounce polymeric tray. Oxydots were glued to the sides (side-dot) and bottom (bottom-dot) of the cell and filled with 1, 2, and 3% (w/v) agar gel as a model food. After deoxygenation, local oxygen concentrations in the gels were measured non-invasively at 4, 12 and 22°C. Effective oxygen diffusivities in gels (DO2g) and water (DO2w) were obtained after fitting experimental data to the analytical solution (data from side-dot) and the numerical solution (data from bottom-dot) to Fick's second law. Temperature had significant positive influence (P<0.05) on oxygen diffusivity estimated for different medium and analysis methods. The DO2obtained from both methods were statistically different (P<0.05) at 12 and 22°C but not at 4°C. Results show that DO2g values decreased by 72-92%, compared to DO2w. Results also show that decreasing the temperature from 22 to 4°C reduced the DO2w and DO2g values by 55-60%. No significant difference (P>0.05) was found between the activation energy (Ea) of water and gels (1-3% w/v) for temperatures ranging from 4 to 22°C. We used a combined obstruction and hydrodynamic model to explain why DO2g decreased as gel concentration increased. The method developed in this study can be used to study the oxygen diffusivity in foods.

Migration of Chemical Compounds from Packaging Polymers during Microwave, Conventional Heat Treatment, and Storage.

Polymeric packaging protects food during storage and transportation, and withstands mechanical and thermal stresses from high-temperature conventional retort or microwave-assisted food processing treatments. Chemical compounds that are incorporated within polymeric packaging materials to improve functionality, may interact with food components during processing or storage and migrate into the food. Once these compounds reach a specified limit, food quality and safety may be jeopardized. Possible chemical migrants include plasticizers, antioxidants, thermal stabilizers, slip compounds, and monomers. Chemical migration from food packaging is affected by a number of parameters including the nature and complexity of food, the contact time and temperature of the system, the type of packaging contact layer, and the properties of the migrants. Researchers study the migration of food-packaging compounds by exposing food or food-simulating liquids to conventional and microwave heating and storage conditions, primarily through chromatographic or spectroscopic methods; from these data, they develop kinetic and risk assessment models. This review provides a comprehensive overview of the migration of chemical compounds into food or food simulants exposed to various heat treatments and storage conditions, as well as a discussion of regulatory issues.

Modeling the oxygen diffusion of nanocomposite-based food packaging films.

UNLABELLED: Polymer-layered silicate nanocomposites have been shown to improve the gas barrier properties of food packaging polymers. This study developed a computer simulation model using the commercial software, COMSOL Multiphysics to analyze changes in oxygen barrier properties in terms of relative diffusivity, as influenced by configuration and structural parameters that include volume fraction (φ), aspect ratio (α), intercalation width (W), and orientation angle (θ) of nanoparticles. The simulation was performed at different φ (1%, 3%, 5%, and 7%), α (50, 100, 500, and 1000), and W (1, 3, 5, and 7 nm). The θ value was varied from 0° to 85°. Results show that diffusivity decreases with increasing volume fraction, but beyond φ = 5% and α = 500, diffusivity remained almost constant at W values of 1 and 3 nm. Higher relative diffusivity coincided with increasing W and decreasing α value for the same volume fraction of nanoparticles. Diffusivity increased as the rotational angle increased, gradually diminishing the influence of nanoparticles. Diffusivity increased drastically as θ changed from 15° to 30° (relative increment in relative diffusivity was almost 3.5 times). Nanoparticles with exfoliation configuration exhibited better oxygen barrier properties compared to intercalation. The finite element model developed in this study provides insight into oxygen barrier properties for nanocomposite with a wide range of structural parameters. This model can be used to design and manufacture an ideal nanocomposite-based food packaging film with improved gas barrier properties for industrial applications. PRACTICAL APPLICATIONS: The model will assist in designing nanocomposite polymeric structures of desired gas barrier properties for food packaging applications. In addition, this study will be helpful in formulating a combination of nanoparticle structural parameters for designing nanocomposite membranes with selective permeability for the industrial applications including membrane separation techniques.