Postharvest behaviour of five Sardinian prune varieties as affected by immersion in heated sodium bicarbonate solution

Storage behaviour of 'Core', 'Core Columbu', 'Fradis' and 'Meloni' white prunes, and a black one ('Sighera') of Sardinian germplasm were evaluated following immersion for 0 (control), 15, 30, 45 or 60 sec in water at 20, 50, 55 or 60 degrees C with or without 2% (w/v) NaHCO3 (SBC). As international varieties, fruit from one white plum ('Shiro') and one black prune ('Stanly') were subjected to the same treatments. Fruit was harvested at commercial maturity, treated and then stored for 1 month at 5 degrees C and 90% RH followed by a simulated marketing period at 20 degrees C and 80% RH for 6 days. Fruit appearance, external damage, firmness and decay percentage were monitored after storage and SMP. Treatments did not induce rind damage (browning or discoloration) to any variety. SBC at 20, 45, 50 or 55 degrees C for 15 or 30 sec was not effective in controlling decay and compared to controls no improvement was observed. Immersion for 45 or 60 sec with SBC at all temperatures improved decay control with respect to controls and best results were obtained at 50 or 55 degrees C. Immersions at 60 degrees C improved decay control, but differences were not significant compared to the control attained with solutions of SBC heated at 55 degrees C. The overall appearance of 'Core', 'Core Columbu', 'Fradis' and 'Shiro' decreased significantly after the SMP period, especially when treated at 55 or 60 degrees C for 60 sec. Fruit shrivel was the main cause of the low rating. SBC did not affect shrivel indicating that heat treatment may be the probable cause. In general, local varieties were less affected by decay than other varieties and they performed well during storage.