Properties and postharvest behavior of the vegetable cactus Nopalea cochenillifera

Flattened stem segments (cladodes) of certain cactus species are eaten in Mexico as a vegetable, when still at the young tender stage (nopalitos). This study focuses on the properties and response under storage of vegetable cladodes of a spineless cactus species newly introduced to Israel, Nopalea cochenillifera (L.) Salm-Dyck. Cladodes of N. cochenillifera were found to be suitable for harvest at the end of the rapid growth phase, at which time they were 11-13 cm long, weighed about 40 g, and had a chemical composition similar to that of certain Opuntia species used as a vegetable. The cladodes exhibited typical acidity changes of CAM plants, with titratable acidity measured at harvest fluctuating from a morning high level of 620 mmol H+ m(-2) to an evening low level of 69 mmol H+ m(-2) (155 and 17 mmol H+ kg FW-1, respectively). Acidity of fresh morning-harvested cladodes stored in an open place or a room declined to an acceptable level of 400 mmol H+ m(-2) (100 mmol H+ kg FW-1) by the second day. Storage studies (dark conditions) indicated that cladodes have to be protected from low temperature (4 degrees C) because of chilling injuries and maintenance of acidity, and also that CO2-free air does not influence acidity changes. In a long-term storage study, cladodes were either left uncovered, placed in polyethylene bags, or wrapped in PVC film, then kept in darkness for up to 21 days at 12 or 20 degrees C. Acidity, while declining with time, tended to be higher at the lower temperature and in cladodes placed in plastic bags. It dropped markedly when the cladodes were transferred from dark storage to a room held at 20 degrees C and a light regime of 12 h dim light/12 h dark (4 days). Plastic bags significantly reduced weight loss, but they were not recommended for storage because cladodes under this treatment tended to be wet and to develop roots. With respect to both acidity and weight loss, the most favourable treatment for long-term storage is wrapping the cladodes in PVC film and storing them at either 12 or 20 degrees C. (C) 1997 Elsevier Science B.V.