Cryo-Scanning Electron Microscopy Investigation of the Texture of Cooked Potatoes
The texture of steam-cooked potatoes was investigated by examining the fracture planes of four different cultivars, using cryo-scanning electron microscopy (cryo-SEM), which yielded a good preservation of the hydrated structures in potato tissue . For all cultivars , fracturing after steam -cooking took place between cells preferentially alongside the cell walls. However, textural difference appeared from the degree of intercellular contact, the cell shape and the appearance of cell surfaces. Cells in the fracture planes of firm potatoes had large intercellular contacts. In this case, most of the cells were flat and cell surfaces showed folds and cracks . For mealy potatoes , it appeared that cells in the fracture planes had little intercellular contacts . The cells were round and turgid and had smooth surfaces . In conclusion, the structure of cell wall and middle lamella , and the starch content , appear to be important parameters to distingui sh firm and mealy cultivars. Key \Vords: Cell, cryo-scanning electron microscopy , potato, cultivar , steam-cooking, texture, fracture plane, pectin, starch, cell wall. Initial paper received March 19, 1992 Manuscript received September 8, 1992 Direct inquiries to J.T. van Marte Telephone number: 31 8370 75060 Fax number: 31 837
Pectic epitopes are differentially distributed in the cell walls of potato (Solanum tuberosum) tubers
Six monoclonal antibodies (mAbs) were used to map the distribution of pectic epitopes in the cell walls of potato (Solanum tuberosum L. cvs Kardal and Karnico) tuber tissue in both light and electron microscopes. Unesterified (mAb JIM 5 epitope) and methyl-esterified (mAb JIM 7 epitope) pectins were abundant and equally distributed in all parenchymal and vascular cell walls. Homogalacturonans (HGAs) involved in Ca 2+ -cross-linking (mAb 2F4 epitope) were localised to the middle lamella and abundant at cell corners. The tuber cortex was densely labelled, but parenchymal cell walls in the perimedullary region contained few epitopes of calcium pectate except at corners and pit fields. In contrast, pectic side-chains were not detectable in the middle lamella of all parenchymal cell walls, except in the cortex where mAb LM6 (arabinan epitope) labelled the entire wall. The galactan epitope (mAb LM5) was localised to a zone very close to the plasmalemma in cortical cell walls and was also less abundant at pit fields and in vascular cell walls. MAb CCRC-M2 (rhamnogalacturonan I epitope) did not cross-react. Our results show that the cell walls of potato tubers are not homogeneous structures and that the pectic composition of the walls is spatially regulated.
Versuche zur Quellung des Kartoffelstärkekorns
Depending on the nature of the swelling agents the potato starch granules swell differently. The way of reaction depends on the hydrolizing, solvatizing, and hydrogen-linksplitting capacity of the solvent. The differences are explained by a new more detailed structure model of the starch grain. This model consists of a combination of different concepts, taking into account a core-shell structure, density layers, and cristalline micells.