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Understanding the influence of pressure assisted thermal sterilization on metal-oxide coated polymer films

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2021 ASABE Annual International Virtual Meeting  2100802.(doi:10.13031/aim.202100802)
Authors:   Ashutos Parhi, Juhi Patel, Shyam S. Sablani
Keywords:   Food packaging, HPP, oxygen indicator, Shelf-life

Abstract Metal oxide coated-PET based multilayer films used for food packaging applications are highly efficient in preventing the oxygen and moisture ingress, thus can provide extended shelf life. However, when used as in-package sterilized food packaging for pressure assisted thermal sterilization (PATS) process, they are exposed to the high temperature and pressure during the processing. This can create defects in the metal-oxide coating and increase the oxygen and moisture permeation through the films, reducing their efficiency. In this study, we have investigated the effects of PATS on three metal-oxide coated multilayer polymer film pouches: A (Overlayer/AlOx-coated PET(12 µm)// Oriented-Nylon 6 (15 µm)// Cast-Polypropylene (60 µm)), B(Overlayer/AlOx-Organic-coated PET(13 µm)//Oriented-Nylon 6 (15 µm)// Cast-Polypropylene (50 µm)), C (AlOx-coated PET (12 µm)//AlOx-coated PET(12 µm)// Oriented-Nylon 6 (15 µm)// Cast-Polypropylene (70 µm)). Initially, pouches were filled with water and preheated for 10 min at 98 °C. These preheated pouches were then subjected to 600 MPa of pressure with 5 min of holding time in a pilot-scale high pressure machine set to an initial temperature of 90 °C. After processing, the pouches were cooled down by placing them under tap water for 5 min. Subsequently, the pouches were drained of the water, refilled with an oxygen indicator and stored in an incubator at 40 °C for 80 days. The gel changed color from yellow to blue where cracks and pinholes had formed in the metal-oxide coating. Film samples were extracted from the locations with color change and subjected to scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Overall, film C had fewer locations with color change in the oxygen indicator after 80 days of storage, indicating less damage after processing. All the other films showed higher color change after exposure to the PATS process. This could be due to the presence of the multiple coated-PET layers in film C that might have successfully prevented oxygen molecules from permeating through. The use of oxygen indicator and microscopic tools helped characterize the effects of PATS processing on the occurrence of defects in the films. Altogether, the study can help accelerate the design and development of high-performance packaging for PATS.

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