Food Packaging and Shelf Life 26 (2020) 100566 Available online 25 September 2020 2214-2894/© 2020 Elsevier Ltd. All rights reserved. Designing thinner wall ethylene-vinyl alcohol copolymer and polypropylene-based semi-rigid trays for microwave-assisted thermal sterilization and pasteurization processes Saleh Al-Ghamdi a, b , Ashutos Parhi a , Chandrashekhar R. Sonar a , Michail K. Dolgovskij c , Barbara Rasco d , Juming Tang a , Shyam S. Sablani a, * a Department of Biological Systems Engineering, Washington State University, Pullman, WA, 99164-6120, USA b Agricultural Engineering Department, College of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh, 11451, Saudi Arabia c Kuraray America, Inc., Pasadena, TX, 77507, USA d College of Agriculture and Natural Resources, University of Wyoming, 1000 University Ave., Laramie, WY, 82073, USA A R T I C L E INFO Keywords: Oxydots Oxygen ingress Polymer packaging Semi-rigid trays Thermal processing ABSTRACT The goal of this research was to design a thinner wall tray for microwave-assisted thermal processing technol- ogies. Three-layer (PP//EVOH//PP) sheets of different EVOH- and PP-layer thicknesses were coextruded. The sheets were then thermoformed into 8-oz trays with dimensions of 150 × 100 × 50 mm (L × W×D). Trays were flled with model foods and subjected to conventional and microwave-assisted pasteurization and sterilization processes. Barrier and mechanical properties were assessed before and after processing. Oxygen ingress, weight loss, and color kinetics were measured over a storage period of 3–6 months at 7, 23, and 37 ◦ C. The newly- designed trays showed comparable or better performance in terms of O 2 ingress and weight loss, with a 24 % reduction in wall thickness. Therefore, thinner EVOH and PP-based trays hold promise for use in microwave- assisted sterilization and pasteurization processes. This will result in a reduced carbon footprint and provide more economical alternatives to other forms of packaging that are currently available. 1. Introduction Semirigid polymeric trays are widely used for packaging of ready-to- eat (RTE) pasteurized, sterilized and frozen meals, baby food, and soups. There is a signifcant interest in high barrier polymeric trays to replace glass jars, bottles, and metal cans for food packaging applications (Humbert, Rossi, Margni, Jolliet, & Loerincik, 2009). This is because polymeric packaging is lightweight, transparent, and economical. It can also be microwaved, and is easy to form and process (Selke & Culter, 2016). Thermoformed plastic trays have evolved to meet market de- mand for different shapes and designs. These trays can be designed to have high oxygen and water vapor barrier properties, to withstand high processing temperatures, and to maintain their original functionality. Multilayer thermoformed trays and cups have been developed for high barrier and high-temperature applications, such as shelf-stable RTE meals and baby foods that undergo sterilization at 121.1 ◦ C or pasteurization at 90 ◦ C. For these trays, a layer of ethylene-vinyl alcohol copolymer (EVOH) is sandwiched between layers of polypropylene (PP), resulting in high barrier trays that provide long shelf-life storage of food (Buntinx et al., 2014). These trays are designed for conventional in-package thermal processing operations (Ramaswamy & Grabowski, 1996). Microwave-assisted thermal sterilization (MATS) and pasteurization (MAPS) are emerging technologies that require shorter processing times than traditional thermal sterilization food processes due to volumetric heating. This provides food safety without compromising food quality (Tang, 2015; Tang, Hong, Inanoglu, & Liu, 2018; Zhang et al., 2019). It is uncertain whether redesigning semirigid trays with thinner EVOH- and PP-layer would provide better barrier trays for MATS processing than conventional retorting while maintaining shelf-life. Optimizing the thickness of the EVOH layer is imperative, since it is an expensive copolymer, whereas the PP layer thickness can infuence the relative humidity/moisture content of the EVOH layer, which can affect its barrier performance. Decreasing the tray wall thickness would reduce the amount of plastic in the package, thus lowering manufacturing and transportation * Corresponding author. E-mail address: ssablani@wsu.edu (S.S. Sablani). Contents lists available at ScienceDirect Food Packaging and Shelf Life journal homepage: www.elsevier.com/locate/fpsl https://doi.org/10.1016/j.fpsl.2020.100566 Received 18 May 2020; Received in revised form 21 August 2020; Accepted 8 September 2020