Weaning rats were fed diets containing 59% starch granules, 25% casein, 5% corn oil, 5% fiber, and adequate quantity of minerals and vitamins for 4 weeks. Growth responses of rats to four kinds of starch granules were as follows; high-amylose corn≤ potato<yamanoimo<corn. In vitro digestibility of these starch granules to pancreatin was as follows; potato<yamanoimo≤ high-amylose corn<corn. Starch granules were separated from feces and contents of stomach, intestine (small and large) and cecum of rats fed each one of diets containing starch granules as the main carbohydrate source and observed under a scanning electron microscope (SEM). On the surface of potato and yamanoimo starch granules isolated from stomach of rats, shallow holes were observed under SEM and supposed to be results of the attack by salivary amylase. Many pin holes, in small and large size, were observed on the surface of potato and yamanoimo starch granules isolated from feces and contents of intestine and cecum, and sometimes step-shaped or terraced inner structures of starch granules could be seen. These observations suggested that starch granules of potato and yamanoimo were attacked by a-amylase (s) of gastrointestinal tract of rats including those of entero-microorganisms. SEM observations of the cross-section of a grain of feces of rats fed each one of diets containing starch granules of potato, yamanoimo, and high-amylose corn revealed that damage of starch granules could be seen without the tedious procedure separating starch granules from feces.*1 To whome requests for reprints should be addressed.

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Potato starch examined contained 0.015% of lipid. The ratio of non-polar to polar lipid was about 60 : 40. Principal lipids in potato starch were free fatty acid, sterylglycoside, unidentified neutral lipid and diglycosyldiglyceride in the decreasing order. Major fatty acids of total lipid in potato starch were palmitic, linoleic and linolenic acids, among which palmitic acid was predominant.

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(1) Raw starch digestion by black-koji amylase system was studied. a) The ability of the black-koji amylase system to digest raw starch may be associated with the ability to adsorb on raw starch. b) Alpha-amylase had an extremely weak activity to digest raw starch, but glucoamylase had a strong activity to digest raw starch. c) Alpha-amylase and glucoamylase, when used jointly, interacted with each other increasing digestion of raw starch to about 3 times the sum of their separate activities. d) Glucoamylase consisted of two kinds of glucoamylase, that is, glucoamylase I and glucoamylase II. The raw waxy corn starch digestion by glucoamylase I was accelerated by adding a-amylase or isoamylase. The raw non waxy corn starch digestion by glucoamylase I was accelerated by a-amylase but not so much by isoamylase as by a-amylase. The raw waxy corn starch digestion by glucoamylase II was very weak, but was accelerated extremely by adding isoamylase, but not by a-amylase. (2) Alpha amylase adsorption on raw starch and its relation to raw starch digestion were investigated. a) Pancreatic a-amylase digested raw starch most strongly and was adsorbed on raw starch most easily. In the case of a-amylases from bacteria and malt, α-amylase adsorption curves reversed positions from those shown for digestion. b) Glucose and maltose, especially the latter, inhibite both amylase adsorption and raw starch digestion, and so the raw starch digestion was accelerated by dialysis . (3) Raw starch digestion by Rhizopus amylase system was studied. a) The glucoamylase system of Rhizopus sp. was fractionated into two kinds of glucoamylase, that is, glucoamylase I and II. b) Glucoamylase I could be adsorbed on raw starch and was highly active in raw starch digestion. The raw waxy corn starch digestion by glucoamylase I was accelerated by adding α-amylase or pullulanase. c) Glucoamylase II could not be adsorbed on raw starch. The raw waxy corn starch digestion by glucoamylase II was very weak, but was accelerated by adding α-amylase contrary to the case of glucoamylase II of black-koji.

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B. macerans enzyme has been known by the name of BMA or cyclodextrin glycosyltransferase which has three different actions on α-1, 4-glucan. These actions are cyclization, coupling and disproportionation. As these actions occur simultaneously, a fewer study of the mechanism of macerans enzyme actions has been done. 1) The author has studied on the action of macerans enzyme using various maltooligosaccharides and cyclodextrins (CDs) in order to prepare various CDs selectively, and tried to clarify some action mechanisms and action pattern . Cyclization proceeded as exo-type attack from non-reducing end of oligosaccharides, α-CD was easily transfered to G₁-G₄ to form G₇, G₈, ---by coupling reaction at the initial stage of the reaction. G₂ was the most effective acceptor in the maltodextrins we examined. The rate of coupling reaction of β-CD was extremely slower than α-CD . Disproportionation which is the transferation between maltooligosaccharides showed a certain pattern in which primarily G_n-2 moiety was transfered to another G_nmolecule to form G_2n-2 and G₂. From the experiments of the effects of complexing agents, we observed that the addition of SDS induced strongly the formation of α-CD from maltodextrin and other hand, β-CD was produced by the existence of Triton X-100. Stubbed CD which connected glucosyl, maltosyl---by α-1, 6 linkage with CD was also formed by the addition of complexing agents such as SDS to branched substrates . From the above results, the author infered that the action pattern of macerans enzyme may be changed by the conformational change of substrate . 2) The author proposed a scheme of α, β-CD formation. Accumulation of β-CD by the prolonged period of the reaction was elucidated by the scheme. 3) A new method of CD preparation was proposed . The principle of the method is that unreacted linear and branched dextrin in the macerans enzyme digest of starch are hydrolyzed to glucose by incubation with glucoamylase. CDs were fractionated by precipitation by addition of organic solvents such as acetone .

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