A review of cellular structure,starch, and texture qualities of processed potatoes

Certain combined characteristics of cellular structure and starch properties provide distinctions between varieties of potatoes and bear strong relation to their culinary qualities. Larger tissue cells and larger average starch granules are associated with mealiness. Smaller cells and starch granules characterize the less mealy and “waxy” varieties. Similarly, the same general relationships hold for the varietal characteristics of high vs. low solids and high vs. low starch contents. Within a variety, proportionately larger numbers of large starch granules are associated with tubers of high specific gravity, and more smaller granules, with low specific gravity. There also is a distinct reduction in percent of small granules during storage of tubers. Differences in starch granule size are accompanied by differences in amylose and amylopectin. Small granules contain less amylose and gel at higher temperatures than do the larger starch granules. Amylose content likewise appears to be a varietal characteristic. These variations in amylose content reflect fundamental differences in the properties of the starch gels formed when different varieties of potatoes are cooked. Likewise, there are similar distinctions between the starches within different tissue zones of individual tubers. Cell size also varies characteristically within different tuber regions. Starch gel properties may be manipulated during processing by such treatments as precooking-heating, chilling, freezing, and thawing. These treatments provide some measure of control of textural quality in the finished product. Additives such as stearates or glycerides complex readily with amylose and also influence gel properties and texture in processed potato products. Sucrose accumulated during tuber storage also may increase gel strength and influence texture. Varietal differences in cell structure and in starch granule size and composition offer opportunities for genetic exploitation. The merits of special processing for texture control vs. development of varieties for specific processed product qualities are briefly discussed.