ISHS Acta Horticulturae 297: II International Symposium on Kiwifruit
CHARACTERISTICS OF THE IRRITANT (CATCH) FACTOR IN PROCESSED KIWIFRUIT |
| Authors: | C.O. Perera, I.C. Hallett |
| Keywords: | raphides, calcium, oxalate, crystals, irritation, acridity, kiwifruit |
| Abstract:
The irritant factor in certain processed kiwifruit products was found to be due to the presence of calcium oxalate crystals. These were found predominantly in the inner pericarp region of the fruit as sharp needle-shaped raphides, arranged in bundles and embedded in a mucilage within idioblast cells. Cells containing raphides are rarely found in the outer pericarp or in the core regions. The raphides in the fruit have an average length of 80 μm. They have rectangular cross sections in the central region and sharp cone shaped apices. They were found even at the flowering stage before fruit set. However, no mucilage or idioblast cell wall covering the raphides could be observed until about the sixth or the seventh week after fruit set. In ripe fruit, the mucilage surrounding the raphides prevented them from dispersing, even if the idioblasts were ruptured. Hence, in fresh ripe fruit or pulp which have undergone little processing, individual raphides are unlikely to be exuded and very little or no irritation is perceived in ingesting them. However, in more severely processed products such as nectars, the high shear forces applied during processing cause the idioblast cells to rupture and the raphide bundles are dispersed from the mucilage surrounding them, thus causing irritation when such products are ingested. In dehydrated kiwifruit products, the sharp ends of the raphides become exposed due to the shrinkage of the mucilage and easy breakage of the cells. Thus in dehydrated products, the perception of the irritation is accentuated. The evidence presented indicates that the irritation in certain processed kiwifruit products is due to a mechanical action of the raphides on the mucous membranes. | |
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