The impact of microwave-assisted thermal sterilization on the morphology, free volume, and gas barrier properties of multilayer polymeric films

Effect of ohmic heating on the structure and properties of flexible multilayer packaging

Food-packaging-processing interactions define packaging materials' performance properties and product quality. This study evaluated the effect of ohmic heating (OH) processing and different food simulants on the properties of four multilayer flexible packaging materials (PETmet/PE, PETmet/PP, PET/Al/PE, and PET/Al/PA/PP). OH treatment was applied to the sealed packages containing the food simulants using a voltage gradient of 3.7 V/cm at a frequency of 20 kHz, resulting in a thermal process of at 80 °C for 1 min. The structure and performance of the different packages were then evaluated. The materials did not show changes in chemical groups nor thermal properties. However, the simulant-packaging-processing interaction resulted in changes in crystallinity, morphology, mechanical and barrier properties (water and oxygen), especially for metallized films in contact with acidic food simulants. The results indicate that although OH resulted in changes in packaging materials, these materials can be used under the conditions applied in this study.

Preserving Ready-to-Eat Meals Using Microwave Technologies for Future Space Programs

The crewed suborbital and space flights launched by private companies over the past three years have rejuvenated public interest in space travel, including space tourism. Ready-to-eat meals (MREs) are the main source of nutrients and energy for space travelers. It is critical that those meals are free of bacterial and viral pathogens and have adequate shelf life. The participation of private companies in space programs will create new opportunities and demand for high-quality and microbiologically safe MREs for future space travels. In this article, we provide a brief review of nutrition and energy requirements for human activities in space. We discuss the general thermal processing requirements for control of bacterial and viral pathogens in MREs and introduce advanced thermal preservation technologies based on microwaves for production of MREs with different shelf-lives under various storage conditions. We also present the latest advancements in the development of polymer packaging materials for quality preservation of thermally stabilized MREs over extended storage. Finally, we recommend future research on issues related to the sensory quality of specially formulated MREs, microbial safety of dried foods that complement high moisture MREs, and food package waste management in future space missions.

Lifting the Sustainability of Modified Pet-Based Multilayer Packaging Material with Enhanced Mechanical Recycling Potential and Processing

Sustainability and recyclability are among the main driving forces in the plastics industry, since the pressure on crude oil resources and the environment is increasing. The aim of this research is to develop a sustainable thermoformable multilayer food packaging, based on co-polyesters, which is suitable for hot-fill applications and allows for recycling in a conventional waste stream. As a polymer material for the outer layer, we selected a modified polyethylene terephthalate (PETM), which is an amorphous co-polyester with a high glass transition temperature (±105 °C) and thus high thermal stability and transparency. The inner layer consists of 1,4-cyclohexylene dimethanol-modified polyethylene terephthalate (PETg), which is allowed to be recycled in a PET stream. Multilayers with a total thickness of 1 mm and a layer thickness distribution of 10/80/10 have been produced. To test the recyclability, sheets which contained 20% and 50% regrind of the initial multilayer in their middle PETg layer have been produced as well. The sheet produced from virgin pellets and the one containing 20% regrind in the middle layer showed no visible haze. This was not the case for the one containing 50% regrind in the middle layer, which was confirmed by haze measurements. The hot-fill test results showed no shrinkage or warpage for the multilayer trays for all temperatures applied, namely 95, 85, 75 and 65 °C. This is a remarkable improvement compared to pure PETg trays, which show a visible deformation after exposure to hot-fill conditions of 95 °C and 85 °C.

Stability of vitamin C, color, and garlic aroma of garlic mashed potatoes in polymer packages processed with microwave-assisted thermal sterilization technology

The U.S. Army and NASA need ready-to-eat meals with extended shelf-life for military operations and future manned space missions. For traditional heat sterilization methods, aluminum foil laminated pouches are used to achieve a shelf-life of 3 to 5 years at room temperature. However, those packages are not suited for advanced thermal processing technologies based on microwave energy. This research investigated the effect of polymeric packaging materials on storage stability of garlic flavor, vitamin C, and color of garlic mashed potatoes processed with microwave-assisted thermal sterilization (MATS) technology. Three types of high-barrier metal oxide-coated polymer pouches were used for MATS process, designed to achieve lethality approximately F₀ = 6 min. Aluminum foil-based pouches were used for retort process as control. Results demonstrated that both oxygen and water vapor barrier properties (oxygen transmission rate [OTR] and water vapor transmission rate [WVTR]) of the polymer pouches were affected by MATS processing. OTR increased by three to nine times, while WVTR increased by 5 to 20 times after processing. The MATS process resulted in 13% to 16% vitamin C loss, while retort process resulted in 18% loss in garlic mashed potato. The kinetics of vitamin C indicated that metal oxide-coated high-barrier packages (after processing OTR <0.1 cc/m² .day; WVTR <1.0 g/m² .day) could replace aluminum foil-based pouches for MATS processed shelf-stable ready-to-eat garlic mashed potatoes. PRACTICAL APPLICATION: Garlic mashed potatoes in polymer packages processed in a microwave-assisted thermal sterilization (MATS) system had better retention of vitamin C compared to samples packaged in aluminum laminated pouches and processed in retort. Polymer packages combined with MATS processing could potentially provide safe, better quality, and nutritious shelf-stable food products for military and space missions.

Multilayer packaging: Advances in preparation techniques and emerging food applications

In recent years, with advantages of versatility, functionality, and convenience, multilayer food packaging has gained significant interest. As a single entity, multilayer packaging combines the benefits of each monolayer in terms of enhanced barrier properties, mechanical integrity, and functional properties. Of late, apart from conventional approaches such as coextrusion and lamination, concepts of nanotechnology have been used in the preparation of composite multilayer films with improved physical, chemical, and functional characteristics. Further, emerging techniques such as ultraviolet and cold plasma treatments have been used in manufacturing films with enhanced performance through surface modifications. This work provides an up-to-date review on advancements in the preparation of multilayer films for food packaging applications. This includes critical considerations in design, risk of interaction between the package and the food, mathematical modeling and simulation, potential for scale-up, and costs involved. The impact of in-package processing is also explained considering cases of nonthermal processing and advanced thermal processing. Importantly, challenges associated with degradability and recycling multilayer packages and associated implications on sustainability have been discussed.

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 (SiO_x -coated PET), MOC (Overlayer-AlO_x -Organic-coated PET), MOD (Overlayer-SiO_x -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.

Microwave treatment regulates the free volume of rice starch

The aim of this work was to investigate the role of microwave parameters and moisture content on the free volume (FV) changes of rice starch by positron annihilation lifetime spectroscopy analysis (PALS) and to explore the potential relationship between the changes of FV and physicochemical properties of rice starch. Microwave heating and water molecules lead to the increasing of FV of starch. However, this result is largely influenced by the plasticization of water molecule. The anti-plasticization caused by water evaporation resulting in a decrease in the size and concentration of FV during microwave heating. Significant decrease (p < 0.05) in the thickness of amorphous region of microwave-heated rice starch was found by small angle X-ray scattering (SAXS), and the glass transition temperature (Tg) and gelatinization temperature significantly increase (p < 0.05) after microwave heating. According to correlation analysis, the power intensity and heating time were correlated negatively with the lifetime of o-Ps. In addition, the changes of amorphous region and Tg of rice starch were strongly related to FV changes. These results provided a theoretical basis for further research on the directional regulation of FV and improvement the quality of starch-based food by using microwave treatment.

Ultraviolet-C Light Sanitization of English Cucumber (Cucumis sativus) Packaged in Polyethylene Film

Food safety is becoming an increasing concern in the United States. This study investigated the effects of ultraviolet-C (UV-C) light as a postpackaging bactericidal treatment on the quality of English cucumber packaged in polyethylene (PE) film. Escherichia coli k-12 was used as a surrogate microbe. The microbial growth and physical properties of packaged cucumbers were analyzed during a 28-d storage period at 5 °C. Inoculating packaged cucumbers treated at 23 °C for 6 min with UV-C (560 mJ/cm(2) ) resulted in a 1.60 log CFU/g reduction. However, this treatment had no significant effect (P > 0.05) on the water vapor transmission rate or oxygen transmission rate of the PE film. Results show that UV-C light treatment delayed the loss of firmness and yellowing of English cucumber up to 28 d at 5 °C. In addition, UV-C light treatment extended the shelf life of treated cucumber 1 wk longer compared to untreated cucumbers. Electron microscopy images indicate that UV-C light treatment influences the morphology of the E. coli k-12 cells. Findings demonstrate that treating cucumbers with UV-C light following packaging in PE film can reduce bacterial populations significantly and delay quality loss. This technology may also be effective for other similarly packaged fresh fruits and vegetables.