The rheological properties of starch pastes of small, middle and large granule potato starch studied. During gelatinization of starch granules in water, paste properties of all three classified potato starches changed as follows. (1) The patterns of flow curves changed from thixotropic flow to particular flow through plastic flow, which is independent of time. (2) T₃₀/T₀ values, evaluated time-torque dependence curves, increased. (3) Dynamic modulus and viscosity decreased. paste of the large granule starch showed a plastic flow curve by shorter time of heating 95°C than that of the small granule starch. Higher T₃₀/T₀ value, lower dynamic modulus and viscosity of starch pastes, and lower Young's modulus of starch gels were observed by the increase of granular size, when starch pastes were prepared under the same conditions. Young's modulus of starch gels decreased with increased temperature and heating time for the pasting. The temperature at peak value in breaking strength of starch gels was close to the one peak viscosity in amylograms. The large granule starch showed larger strain ratio of gel at breaking than the small granule starch.

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The action of four preparations of glucoamylase [α-1, 4-glucan glucohydrolase, EC 3. 2. 1. 3], crude glucoamylases of Rhizopus amagasakiens and Endomyces and crystalline glucoamylases of Rhizopus niveus and Endomyces, on starch granules of less susceptible [potato, anaylose-extender (ae) mutant of maize and heat-moisture treated potato] and more susceptible [sugary-2 (su₂) and sugary-2 opaque-2 (su₂ o₂) mutants of maize] types to the action of a-amylase than normal maize was studied to characterize the action of these enzymes on native starch granules. The extent of hydrolysis (percent degradation) was followed by measuring the amount of glucose liberated. Patterns of degradation were observed by scanning electron microscopy (SEM). Each preparation showed qualitatively similar time courses of degradation specific for each respective type of starch granules although each preparation contained different amounts of a-amylase. Relative rate of digestion by glucoamylases of the six types of starch granules showed that su₂ and su₂ o₂ cmutants of maize were most rapid, followed by normal maize, heat-moisture treated potato, ac maize, and potato in decreasing order respectively. Four preparations of glucoamylase showed, in general, similar patterns of attack on the normal maize starch granules. Namely, small pits appeared on the surfaces of the granules, pits increased in number and size and holes penetrated into the inner portions of the granules toward the center of the granules. The points of attack were uniformly distributed on the surfaces of the granules.

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The isolation and characterization of glycogen-type polysaccharide from the Sclerotia of Corticium rolfsii are described. The purified polysaccharide ([α]D+198°) was shown to be homogeneous by zone electrophoresis and ultracentrif ugation. The molecular weight, estimated by gel filtration, was larger than 2.0×10⁶ and the sedimentation coefficient was 5 .39×10^-12 The results from enzymatic hydrolysis with various amylases (α-, β- and isoamylase) and methylation analysis indicate that the polysaccharide was a highly branched glycogen. The average chain length of this glycogen was calculated to be 8, and the exterior and interior chain length were 5 and 2, respectively.

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The various cationic tapioca starch derivatives were prepared by the reactions of tapioca starch with the tertiary amine chloride (1) or the glycidyl tertiary amine (2). The degree of substitution (DS) of amine in the product obtained by the reaction system of (1) was reduced by an increase of one methylene group from ethyl group to propyl group. In the reaction system of (2), the difference of DS was little observed between diethyl group and pyrrolidyl group at the glycidyl tertiary amine, but the DS was decreased largely by the reaction with a glycidyl piperidine bearing a more bulky group. The viscograms in the reaction system of (1) showed that the gelatinization temperature was lowered and the maximum viscosity was increased with an increase of DS. On the other hand, the viscogram of the cationic starch derivatives especially prepared by the treatment with a glycidyl diethyl amine showed a property that the viscosity increased greatly when the temperature of the paste was maintained at 95°C for 30 min. This behavior of viscosity may be due to the cross-linking of starch molecules resulting from scission of the epoxy group in the tertiary amine. The swelling power of the cationic starch derivatives prepared by the reaction system of (2) was generally increased by formation of hydroxyl group resulting from scission of epoxy group. The SEM observation showed that the surface of the starch granules was decomposed greatly with an increase of the number of reactions repeated.

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