Taro (Colocasia antiquorum Schott var . esculenta Engler) root starch was isolated and puri-fied by washing grated taro root three times with 0.2 M sodium chloride (pH 8 .6) followed by successive washing with water and finally with ethanol . The deproteinized starch by three times repeated steeps in 0.3% sodium hydroxide for 24 hr at 14°C contained 24 mg% of phosphorus. The approximate content of amylose was estimated to be about 14% by amethod of iodine coloration. Scanning electron micrographs of the starch preparation revealed polyhedral granules having an average diameter of 1 to 2μ. The shape of Brabender's amylogram of the starch was similar to that of glutinous rice starch and the temperature for gelatinization was as high as 73-74°C . A 1% solution of taro starch was also much more opaque than that of glutinous rice starch . Sixty eight per cent of the taro starch was hydrolyzed by β-amylase and 18% of 6³-α-glucosylmaltotriose was produced from the β-limit dextrin by the action of saccharifying α-amylase of Bacillus subtilis. The yield of this singly branched tetraose was considerably less than that from waxy maize starch-β-limit dextrin, and the implication was discussed .

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Although epichlorohydrin has been used as one of the most common cross-bonding reagents of starch, to inhibit swelling of starch granules during cooking, only a little is known about the relation between physical properties of cross-bonded starch and the site of crossbonding in starch molecule. The samples of various degree of cross-bonding in the range of 1 cross-bonding/110 AGU-1 cross-bonding/2300 AGU were prepared by the reaction of epichlorohydrin with corn starch at room temperature. The reaction efficiency of epichlorohydrin was about 70%. There were good relationships between the degree of cross-bonding and the absorbance at 95°C of photopastegrams, and also swelling power at 100°C. In order to determine the site of the cross-bonding in starch molecule, the samples were treated with exo-amylases, then the limits of the hydrolysis were determined. The extent to which cross-bonded starch was hydrolyzed by exo-amylases was greatly decreased depending upon the degree of cross-bonding produced. Therefore, it may be concluded that the decrease in the hydrolysis extent of starch by the enzymes is due to inability of starch to swell as well as to insusceptibility of starch to the enzyme by formation of the cross-bondings, presumably at the nonreducing ends of starch molecules.

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Glucoamylase (Rhizopus-niveus) was fixed by methylimidate-hydrochloride group of polyacrylonitrile (PAN) which had been preliminarily treated by dry hydrogen chloride gas in methanol. The activity of the fixed-enzyme was dependent on the conditions of the fixation reaction (pH, temperature and reaction time). The optimum reaction conditions corresponding to maximum initial enzyme activity for 1 mg of PAN matrix was as follows: pH 6.0, reaction temperature of 50°C, reaction time for 30 min. The optimum reaction conditions to illustrate the longest half-life of the fixed-enzyme were as follows: pH range from 6 to 8, reaction temperature from 15°C to 30°C, reaction time being longer. As the decay in the activity of the fixed-enzyme during the durability test runs was found to be due to the split off of the fixed-enzyme molecule which had been promoted by the co-presence of the reversible orthoamide bridge structure vs. the stable amidine bridge structure among resin and enzyme, it was suggested that the more the irreversible amidination reaction had been proceeded in the fixation, the better durability would be expected. In so far as our experimental results were concerned, the above optimum reaction condition for the better durability in the enzyme-fixation was specified for PAN carrier easily soluble in dimethyl formamide (DMF) and the durability was very much improved when other kind of PAN carrier scarcely soluble in DMF were used.Therefore, the most responsible factor to obtain the amidine bridge structure was the structure of the PAN resin besides pH, bath-temperature and reaction time and majority of the fixed-enzyme molecules were considered to possess the amidine structure in the latter matrix. Compensation relation was observed among the initial activity and the half-decay time in the durability of the fixed-enzyme.

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Our studies on starch started during the Second World War with the large scale manufacture of pre-cooked field ration, called “Kansohan, ” which became edible boiled rice when mixed with cold water. That was an pplication of KATZ'S alpha-starch theory. Thereafter, our interest spread to X-ray studies on many kinds of starch granules and their physico-chemical properties in the raw and cooked states. My special interest tended to focus on the structure of starch granules, when the electron microscope became available for studies on the surface and inner structure of starch granules. I went to Dr. WHISTLER'S laboratory at Purdue University, U. S. A., for one year and observed about 10, 000 ultra-thin sections, mainly of corn starch granules. From this work I came to the conclusion that raw cereal starch granules might be digested from the inner part of the granules. Returning to Osaka University in 1956, I continued physico-chemical and enzymatic studies on starch with many co-workers. In 1958, we confirmed the appositive growth of starch granules in string beans and red beans cultivating these plants with radio-active carbon dioxide. We obtained radio-active starch granules from the beans and imbedded them in methacrylate resin and cut them into ultra-thin sections of about 0.5 micron thickness. Then we placed the sections on a slide glass and covered them with thin X-ray stripped film and kept them in the dark for 30 to 60 days. Then we developed the film on the slide glass and observed it under a light microscope. In this way, we saw many black rings caused by C-starch deposited on the periphery of the sections. Then we stained the same sections blue with iodine through the Xray film to show the starch in the center of the sections. During our work, however, BADENHUIZEN and DUTTON reported the same result in 1956, obtained in almost the same way, using radio-active whole potato starch granules. In 1959, we found that short chain amylose (degree of polymerization: 10 to 15)can be recrystallized as spheroids with cross polarization. These spheroids obtained from dilute solution showed a very sharp X-ray diffraction pattern of the B-type, and of the A-type when recrystallized from concentrated solution. These findings lead us to the idea that the X-ray diffraction pattern of starch granules from different plant species are not specific for these different species but are due to the conditions in which the starch granules are grown. We proved this clearly using soy bean seedlings budded at different temperatures. Then we ripened sweet potato roots, potato tubers and rice ears at different temperatures and examined their starch granules by X-ray diffractometric, viscosimetric and biological methods. In general, we found that lower temperatures caused formation of potato-type starch and higher temperatures led to formation of corn-type starch . In 1962, we succeeded in recrystallizing amylose, amylopectin and a mixture of amylose and amylopectin prepared by SCHOCH'S method from concentrated aqueous gelatin solutions . he recrystallized granules of amylopectin and the mixture showed a B-type X-ray diffraction pattern but they did not show cross polarization. These two spheroids dissolved easily in warm water at 60°C and could be recrystallized again from gelatinous solution . The irregular-shaped small granules of the amylose fraction were insoluble even in hot water. These properties differ completely from those of natural starch granules. Then, I tried to make models of amylose and amylopectin using a metellic chain. Amylose of 1000 glucose units is supposed to be a random helical chain and an amylopectin molecule with 1000 glucose residues of 30 straight chains is supposed to be like the model shown in Fig. 19.

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