Dry matter content of apical and basal portions of Russet Burbank potatoes
Studies were made over a 4-year period of some factors affecting the dry matter content of the apical and basal portions of growing Russet Burbank potatoes. The greatest difference between portions was obtained from tubers of the normally irrigated plots of 1969. The amounts in the two portions in 1970 were nearly equal throughout the growing season. The major differences between the 2 years was a slightly cooler June and warmer maximum temperatures in July of the 1970 growing season. Moisture stress, particularly, early in the stage of tuber development (1972 season) caused a switch in amount of dry matter in the apical and; basal portions. Stress later in the development stage (1969 season) did not cause a switch. Fertility level was not as influential as moisture stress in affecting the ratio of dry matter in the two ends, whether under stress or normal moisture conditions.
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.
On the fractionation of β-lactoglobulin and α-lactalbumin
Abstract Existing methods for the preparation of α-lactalbumin and β-lactoglobulin are examined critically. It is proposed that the most satisfactory method for the preparation of the whey protein fraction from bovine milk is (NH 4 ) 2 SO 4 fractionation. A number of new gentle procedures for the fractionation of the whey proteins are compared with some existing methods. The distribution of total protein at various stages is determined by total Kjeldahl nitrogen and the kind of protein by starch-gel electrophoresis. The effect of variables, such as pH, salt concentration and temperature on the separation of α-lactalbumin and serum albumin from β-lactoglobulin is studied. Differences in the behavior ( e.g. solubility) of genetic variants of β-lactoglobulin are noted. The solubility of each of the major whey proteins, under similar conditions to those used in the fractionation, is compared with its solubility in the whey protein mixture. The understanding gained of factors important in the fractionation is used in recommending new procedures for α-lactalbumin and β-lactoglobulin isolation.