私どものでんぷん粒研究の今昔

Abstract

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.