Abstract
The mechanism of chilling injury in Cucurbitaceae fruits including cucumber, oriental pickling melon, marrow, squash, balsam pear, white gourd and chayote was investigated by using an Arrhenius equation for the rate of potassium ion leakage from the tissue slices at 0-30°C.
1. The symptoms of chilling injury were pitting, surface pitting and watery breakdown following the decay by the secondary infection of microorganisms. There was observed to be a significant deviation among chilling tolerance of cucurbits fruits at 0-5°C. The fruit of balsam pear showed the most sensitive to chilling and Cucurbita fruit was observed to be the most chilling tolerant species. In general, chilling sensitivity might depend on fruit maturity, and fruit harvested commercially at mature stage showed much more tolerant to chilling than the fruit that was harvested at immature stage.
2. In all species, there were break points at ranging 5-12°C in the Arrhenius plot of rate of potassium ion leakage from the tissues. A higher rate of potassium ion leakage was observed at the lower temperatures below the break points. These breaks corresponded nearly with the critical temperatures for chilling injury of these fruits.
3. The break points were observed in the Arrhenius plot for the tissues of cucumber fruit stored at 20°C (safe temperature) throughout storage period. On the other hand, the break points became obscure during storage at 5°C (chilling temperature) and became hard to distinguish after storage for 15 days.
The abrupt breaks at the critical temperatures observed in the Arrhenius plots may suggest that the occurrence of phase change of membrane lipid in the fruit tissues might be primary event of chilling injury of the Cucurbitaceae fruit.
