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
Mealiness and sogginess in sweet potato
Abstract Sweet potato (var. Jersey) and yam (var. Velvet) are ‘mealy’ and ‘soggy’ varieties, respectively, of Ipomoea batatas Poir. In the raw state the storage roots of both have virtually the same histological structure: more or less abundant starch grains in the parenchyma cells and few intercellular spaces. After baking, the sweet potato shows rounded cells which are full of gelatinised starch and are separated by numerous small, capillary-like intercellular spaces. The baked yam has very little starch, shrivelled cells, ruptured and shrunken cell walls and many large intercellular cavities. The relationships of histological structure to textural properties in these roots and in the mealy and soggy varieties of the tuber of the Irish potato are discussed.
Pore Size in Potato Starch
Silver crystals were produced in native potato starch by reduction from silver nitrate solution. The size of crystals ranged from less than 0.5 nm to 75 nm, in two distinct types of distribution. Considerations of nucleation and growth support the possibility that crystal size is an index of pore size. A model of free space distribution in the swollen starch grain relates lamellation of the grain to variations in the density of the starch substance.