Heat conditioning before ultraviolet-C illumination improves decay control and the keeping quality of cold stored lemon fruit

In order to avoid rind damage following postharvest UV-C light treatment on sensible Citrus cultivars the illumination was performed after heat conditioning (HT). Experiments were performed with lemons (Citrus limon 'di Massa') harvested twice (April and June), graded and divided into 6 sets (each of 180 fruit) according to HT duration (hours) as follows: I) none; II) 3h; III) 6h; IV) 12h; V) 24h; and VI) 36h. HT was performed in a ventilated room at 36°C under saturated RH conditions. After HT, half of the fruit (90 lemons) of each set was treated with 6 kJ m-2 and half remained un-illuminated. Then, all fruit was stored for 2 months at 5°C and 90±5% RH, followed by a 6-day simulated marketing period (SMP) at 20°C and 75% RH. After 1 month, at the end of storage and SMP rind damage was scored and the percentage of decay monitored. Rind disorders caused by UV-C illumination varied upon harvest time and HT duration. In the combined treatments the restrain of UV-C induced damage was achieved from 12h HT on, and among 12, 24 and 36h of HT differences were not significant. Fruit subjected to 24 or 36h HT were free of rind disorders at the end of the experiment. During storage rots were mainly caused by Penicillium italicum while P. digitatum was the main cause of decay during the SMP. The combined treatments had synergistic interaction in controlling the decay when HT was performed for 12, 24 or 36h. The greatest weight loss after 1 month of storage was found in fruit subjected to 24 and 36h of HT followed by the UV-C illumination while, after 2 months and following SMP differences among treatments were negligible