POLYMERIC-BASED MULTILAYER FOOD PACKAGING FILMS FOR PRESSURE-ASSISTED AND MICROWAVE-ASSISTED THERMAL STERILIZATION
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Advanced food technologies such as Microwave-Assisted (MATS) and Pressure-Assisted Thermal Sterilization (PATS) of foods have the advantage of reducing processing times and the detrimental effects on food quality. However, these processes require food to be processed inside their packaging and thus, the interaction between food and its packaging during processing must be studied to ensure package integrity. Gas barrier, thermal, morphological, and free volume properties are critical packaging characteristics that help determine packaging selection for the advanced thermal processes. Selecting the appropriate packaging material will help extend the shelf-life of foods processed with such technologies. The overall objective of this study was to investigate the performance of multilayered polymeric films after MATS and PATS in terms of gas barrier, morphological and free volume properties. Influence of microwave processing on silicon (Si) migration from metal-coated multilayer polymeric films into selected food simulating liquids (FSL, water and 3% acetic acid) using inductively coupled plasma-mass spectroscopy (ICP-MS), as compared with conventional thermal processing was investigated. Polyethylene terephthalate (PET) and ethylene vinyl alcohol (EVOH) based multilayered structures were filled with model foods (mashed potato and water) and subjected to MATS and PATS, respectively. MATS was performed in a 40kW 915MHz single mode semi-continuous system. PATS was carried out in a 1.7 L cylindrical high pressure chamber with processing conditions of 680 MPa for 3 min at 105oC. X-ray diffraction and positron annihilation lifetime spectroscopy (PALS) were applied to investigate film morphology and free volume characteristics, respectively.In conclusion, MATS processing had a lesser influence on gas barrier property of PET based multilayer structures compared to the conventional retort process. EVOH based structures could be a suitable for PATS applications in terms of gas barrier requirements. Additionally, X-ray diffraction and PALS are powerful techniques that can be used in combination to help understand the gas barrier changes after food sterilization operations. No significant differences (P>0.05) between the level of Si migration from films to FSL during microwave processing as compared to the retort processing. This work provides the basis for understanding the gas-barrier changes after MATS and PATS application.