POSTHARVEST PHYSIOLOGY OF PRICKLY PEAR CACTUS STEMS

The young succulent stems of the prickly pear cactus (Opuntia ficus-indica and Opuntia inermis), a specialty vegetable, were harvested at two stages of development ( 10 and 20 cm long) and stored at 5, 10, 15 and 20-degrees-C for up to 30 days. Cactus stems of both species maintained their visual quality for 3 weeks at 5 and 10-degrees-C. Longer term storage at 5-degrees-C resulted in occasional development of surface discoloration stems of O.ficus-indica. Small stems had higher carbon dioxide production rates than large stems, approximately 60-mu-l CO2 g-1 h-1 and 25-mu-l CO2 g-1 h-1 1 day after harvest decreasing to 40-mu-l CO2 g-1 h -1 and 20-mu-l CO2 g-1 h-1 after 10 days at 20-degrees-C and 10-degrees-C, respectively. Ethylene production rates were low, averaging 0.2 nl g-1 h-1 at 20-degrees-C. The titratable acid content of cactus stems was affected by time of day of harvest and the subsequent storage temperature. Small stems were crassulacean acid metabolism-inactive, whereas large cactus stems showed diurnal fluctuations in acid content (0.94% at 08: 00 h and 0.47% at 18: 00 h). Storage of large cactus stems for 9 days at 10, 15 and 20-degrees-C resulted in a decreased acid content, whereas storage at 5-degrees-C resulted in steady or increased acid content. Longer term storage resulted in decreased acid content at all storage temperatures, but the rate of decrease was less at low temperatures.