Application of passive refrigeration and gaseous ozone to reduce postharvest losses on red chicory

Red chicory is a leafy vegetable, currently used for the preparation of ready-to-eat salads that undergo heavy losses during cold storage mainly due to microbial soft rot development. In this work, chicory was stored at (1°C) in a passive refrigeration chamber with low doses of gaseous ozone (0.1-1 ppm) applied during 21 days in order to reduce postharvest losses. Conventional refrigeration in absence of gaseous ozone was used as the reference storage method. In addition, in order to evaluate the antimicrobial effect a challenge test was performed inoculating sound red chicory heads with a specific spoilage microbiota, accounting approximately 8 log cfu mL-1 bacteria and 7 log cfu mL-1 yeasts and moulds, responsible for soft rot development under cold storage. The results showed that soft rot developed from day 8, especially in the inoculated samples, even though the leaf appearance was unchanged. At the end of cold storage, non-inoculated red chicory heads stored under conventional conditions lost all characteristics related to vegetable fresh appearance; on the contrary, colour brightness and tissue turgidity were retained in samples stored under passive refrigeration. Oxidative discoloration of leaf margins was recorded in red chicory heads stored under 1 ppm ozone. At the day 21, microbial counts of spoiled vegetable regardless the different cold storage conditions did not show any significant difference. Conversely, as expected, evident difference in soft rot severity was recorded between inoculated and non-inoculated samples. Passive refrigeration determined a lower amount of food waste in comparison with conventional refrigeration. Control samples, inoculated or not, showed 100% of losses whereas those under passive refrigeration produced 40.09±4.24 and 90.69±12.03% of food waste for inoculated and non-inoculated samples, respectively. A further reduction of vegetable waste (ranging from 10 to 30%) was registered when passive refrigeration was associated with gaseous ozone treatment at 0.1 ppm. Higher ozone doses caused no significant additional improvements. Passive refrigeration alone was able to reduce significantly weight losses and preserve the quality of chicory up to 21 days. In addition, the combined application of gaseous ozone and passive refrigeration resulted a valid approach to counteract soft rot development on red chicory heads and to reduce the amount of food waste. However, ozone exposure needs to be carefully calibrated to preserve vegetable tissues from oxidative damages caused by this gas.