Corn starch was roasted at 150°C and 180°C for various periods of time to determine the changes in the chemical and physical properties during the heat treatment. The samples prepared by the above mentioned process were characterized by the determination of amylography, photopastegraphy, cold water solubility, iodine absorption, β-amylolysis and reducing value. The rheological properties which were determined by amylography were drastically changed even at the initial stage of the treatment both at 150°C and 180°C. On the other hand, the structural changes of the starch molecule, such as rebranching occured by heat, were easily estimated by the determination of the limit of β-amylase degradation, cold water solubility and the spectra of iodine absorption. We could observe slight depolymerization of starch molecule by the 150°C roasting, but almost no sign of rebranching or repolymerization of the liberated short chain was observed at this temperature. Evidences of the both reaction were observed in the sample roated at 180°C. It was considered that there was a critical temperature between 150°C and 180°C where rebranching and repolymerization reaction began to occur.

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The swelling ratio and solubility of potato starch with urea were studied to elucidate the effect of urea on the gelatinization of starch. The swelling ratio and solubility were increased with the increasing of urea concentration and raising the temperature. The concentration of urea required for the initial gelatinization decreased on elavating the temperature as follows; 6 M/l at 20°C, 4.5 M/l at 30°C, 3.2 M/l at 40°C and 1 M/l at 50°C. The initial gelatinization temperature of potato starch at zero concentration of urea was estimated about 56°C, and this agreed with the result obtained by Kofler microscope methods. The swelling ratio above 3.5 M/l urea at 60°C was lower than those at other temperatures (2050°C). A lower swelling ratio is due to the decrease in the amount of precipitates because of a higher solubility at a higher temperature. There was not the increase of swelling ratio between 3.5?`5.5 M/l urea at 50°C and 6.58 M/l at 40°C. These results suggest that the swelling ratio is not primarily connected only to the degree of gelatinization. The urea inhibited the starch-iodine reaction, and inhibition of starch-iodine reaction by urea was remarkable at the low iodine concentration.

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A special feature in this method is to use nylon cloth bag called Hyzex in stead of standard sieve. As the result, preparation of about 40 varieties become possible a day, recovery became higher too.

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Reaction of carbohydrate with o-phenylenediamine in alkaline solution (pH 10) at an elevated temperature (100°C) to produce quinoxaline derivatives can be utilized for the analysis of starch and other carbohydrates. The formation of various quinoxalines can be followed by polarography, ion-exchange chromatography, and thin-layer-chromatography, respectively. The reaction mechanisms of amylose and amylopectin with o-phenylenediamine are discussed. Application of the reaction to the determination of number-average molecular weights of amylose and amylopectin is described. The method is also applicable to the determination of carbonyl content of periodate oxidized starches. Applications to other glucans are briefly stated.

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