Fundamental to u n d e r s t a n d i n g the behavior of starch-thickened food products is a more complete characterization of various food starches according to their behavior during food preparation. That starches from different botanical sources differ in certain of their properties has long been recognized.Since Nageli's observations (1 7) nearly one hundred years ago that potato and wheat starches are affected differently by certain chemicals, numerous later investigators (5,7,23) have compared some of the physical properties of different starches. The importance of these differences in physical properties to practical applications is well recognized and the variety of natural starches available has been augmented by many chemically modified starches of diverse characteristics.Despite the many studies of the physical and chemical properties of these various natural and modified starches, recorded data on certain properties of special importance in food products, such as gel strength and cold-paste viscosity, seem to be meager. For this reason, choice of a particular starch for use in a particular food has been largely an art in the past, and the effects of varying the conditions under which it was used have been little understood. The few studies along this line which have been reported serve to point out the value of further work.Woodruff and her associates (28,ZP) found that 5% pastes of corn, wheat, rice, potato, arrowroot and cassava starches all failed to form gels unless they were heated above 90" C. although cassava starch gave no gel even after heating to 99.5" C. Whittenberger and Nutting (26) and Hofstee and de Willigen (a), however, reported that gel strength of potato starch pastes heated to various temperatures passed through a maximum value, and the latter investigators indicated that maximum gel strength corresponded to maximum hot-paste viscosity. Seck and Fischer (21) found no correlation between gel strength and viscosity for a number of different starches, although they and others (4,18) found a relation between viscosity and the degree of swelling of the granules. These and other investigations (1,15,27) led to the conclusion that gel strength and viscosity are two distinct and different properties of the pastes.The present series of studies may help to furnish a sounder basis for selecting the best starch for a given use and also elucidate the conditions which will give the most desirable results with the particular starch chosen. The purpose of this study was to determine how the extent of cooking affected a number of properties of starch pastes and to compare a variety of starches and flours in this respect. To this end sixteen representative food starches a Journal Article No. 2127 from the Michigan Agricultural Experiment Station.

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Summary1. The mechanism involved in the inactivation of cat plasma, serum, and plasma euglobulin by different concentrations of SK has been demonstrated.2. Two different caseinolytic entities were graphically differentiated. They were characterized by their time of formation and stability studies.3. With suboptimal SK concentration the development of the caseinolytic activity consisted of an initial rapid phase, followed by a slowly rising activity ; beta plasmin. With optimal SK concentration only the initial rapid caseinolytic activity was obtained (alpha plasmin).4. It is suggested that beta plasmin was formed by a reversible reaction and was inactivated when substrate was not present. With increasing SK concentration alpha plasmin formation competed with the beta plasmin formation.5. A comparison of potential caseinolytic activity of cat plasma, serum, and plasma euglobulin to beta and alpha plasmin is present.

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