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Humidity-regulating trays: Moisture absorption kinetics and applications for fresh produce packaging

Guido Rux, Pramod Mahajan, Manfred Linke, Oluwafemi Caleb, Martin Geyer(Department of Horticultural Engineering, Leibniz Institute for Agricultural Engineering, Potsdam Bornim, Germany)Astrid Pant, Sven Saengerlaub(Fraunhofer Institute of Process Engineering and Packaging, Freising, Germany)

Most polymeric materials used in fresh produce packaging have lower water vapour transmission rate relative to the transpiration rate of fresh produce. The consequences are high humidity levels and condensation of water vapour inside the package. The humidity-regulating trays were developed and tested in this study. They were made from a thermoformed multilayer structure: polyethylene (outside)/foamed hygroscopic ionomer (active layer) with 0 or 12 wt.-% NaCl/hygroscopic ionomer (sealing layer, inside). These trays were used to study moisture absorption kinetics at 76, 86, 96 and 100% RH for 16 days. Furthermore, the trays containing 7 g of water were closed with the high barrier lidding film and headspace relative humidity was continuously monitored over time. Finally, strawberries and tomatoes were used to test the effectiveness of trays on humidity regulation and weight loss of product. The amount of moisture absorbed by the tray was directly proportional to the amount of salt embedded into the tray matrix e.g. 0 and 12 wt % salt trays absorbed 7.6 and 13.2 g of moisture, respectively. The headspace RH of trays covered with a lidding film was found to be 89.8, 99.6 and 100 % in the tray with 12 and 0 wt% salt and control-PP trays, respectively. The trays containing fresh produce were able to regulate humidity below 97% but at the expense of higher product weight loss (2-3% for strawberry, 1% for tomatoes) compared to control polypropylene tray (0.6%).

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