Application of humidity-regulating trays for packaging of fresh strawberry and tomato

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