The physiologic utilizations of raw starches from corn, rice, sweet potato and potato were investigated by feeding them to rats in 66.8% level of the diet under strictly comparable conditions. It was found that the potato starch was the most difficult to digest of all samples and followed by the sweet potato starch. The starch content of feces attained to about 80% in the case of potato starch feeding and the value for sweet potato starch was about 20%, while those for corn and rice, were no more than 6 to 8%. In addition potato starch were separated into larger and smaller granul fractions, and also were disintegrated with ball mill for 5 hours. The same comparable feeding tests conducted on those kinds of potato starch showed that all of them evidenced the low degrees of digestibility, specially the large-sized granules were decidedly low digestibility as compared with small nes, and the original sample occupied something of an intermediate position . And thetreatment of ball mill improved scarcely the digestibility. The various starches were digested in vitro with glucoamylase, and the quantity of reducing sugar liberated by this digestion was estimated. The digestibility of these in vitro was shown to correlate well with these in vivo; the rice starch was the most easily digested, followed in order by the corn, the sweet potato, the small-sized potato, the ball milled potato, the original potato, the large-sized potato. Even though raw starch was digested considerably by glucoamy lase for 6 days, X-ray diff ractograms evidenced no significant differences between the damage starch granules digested and the original ones. The observation of fecal starches was also performed with a scanning electron microscope and the patterns that starch granules were attacked by intestinal flora, especially by some bacilli, could clearly be observed.

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Two Rhesus monkeys were fed only on raw potatoes for one week and the feces were recovered in the last 3 days. The apparent digestibility of raw starch by the two monkeys was 71.5 and 94.7%, respectively. These values are much higher than those obtained by rats, cocks and carp as reported in the previous literatures . The starch granules excreted in the feces were recovered and some of their properties were compared with those of native potato starch granules. The intrinsic viscosity was 92 .7% of the native starch. Photopastegrams showed that the temperature of starting clarification was 2° higher and its rate was lower than those of the native starch . The recovered starch was solubilized by 2.3% with pancreatin, while the native starch by 12 .0% under the same conditions. The blue value and the iodine affinity of the recovered starch were higher, and the λ max of the iodine color reaction was shifted to a longer wavelength, than the corresponding values of the native starch. Observation through a scanning electron micrograph of the recovered starch granules suggested that some microorganisms (probably bacilli) play an important role, in addition to the pancreatic α-amylase, in the digestion of raw potato starch by monkeys.

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Weaning rats were fed diets containing 59% starch granules (either laboratory prepared potato starch or commercial corn), 25% casein, 5% corn oil, 5% fiber and adequate quantity of minerals and vitamins for 3 weeks. Less growth responses (apparent body weight gain minus weight of contents of gastrointestinal tract) of rats fed the potato starch diet than those fed the corn starch diet were observed. In vitro digestibility of these starch granules to pancreatin was in order of decreasing, corn, commercial potato and laboratory prepared potato. Starch granules were separated from contents of stomach, small intestine, cecum and large intestine of rats fed the potato starch diet for either 7 or 21 days and observed under a scanning electron microscope (SEM). Pin holes of shallow and deep types were observed on the surfaces of potato starch granules isolated from stomach of rats. Sometimes, inner structures of the granules, which appeared to be terraced or step-shaped, could be seen. Many pin holes of smaller and larger sizes were visible on the surfaces of starch granules isolated from contents of small intestine of rats. Observation of the granules elucidated also, the inner structures. We could, thus, clearly show that potato starch granules were attacked by digestive enzymes of rats, probably salivary and/or pancreatic a-amylases. Potato starch granules isolated from contents of cecum of rats showed more damage than those isolated from contents of stomach or small intestine. Some starch granules isolated from contents of cecum were accompanied with cocci. These observations suggested that degradation of starch granules in cecum and large intestine depended on the attack by enzymes of enterobacteria and/or digestive enzymes of rats.*1 To whome requests for reprints should be addressed.

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The relationship between the various conditions for carboxymethylation of starch and the properties of the products was investigated, and the following results were obtained. 1) When the reaction temperature in carboxymethylation reaction of starch is 20°C (room temperature), the reaction velocity is very slow regardless of the amount of monochloroacetic acid. But as the temperature rises above 35°C, the reaction velocity increases gradually. 2) The degree of substution (DS) of products was generally proportional to the amount of monochloroacetic acid used, but the amount of the acid reacted with starch decreased in accor dance with the increasing amount of the monochloroacetic acid used in the reaction medium. 3) The concentration of sodium hydroxide in the reaction medium influenced the physical properties of the products. 4) The aqueous solution of crude sodium carboxymethylstarch (CMSNa) of higher DS was stable on the viscosity than that of lower DS. 5) CMS acid was easily precipitated from the paste of crude CMSNa by treating it with dilute sulfuric acid, but the CMS acid produced could not be washed with water ;because it swelled in water. The CMS acid was easily washed with methanol, but the difficulty of neutralization of CMS acid with sodium carbonate was recognized. Therefor, the washing with methanol without the sulfuric acid treatment was a desirable method for the purification of crude CMS Na.

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Potato starch has been known for its high phosphorus content, which is mainly bound to C₆ of glucose residue of amylopectin. Substitution of cations bound to the phosphate was carried out for the purpose of changing the physical properties of potato starch. Mother starch was substituted by hydrogen-, potassium-, sodium- and calcium ions, then physical properties were determined by means of photopastegraphy, amylography, swelling powers, solubility and stability for cold temperature storage. Potato starch showed higher viscosity by increase of alkali metal substitution, and on the other hand, by the introduction of alkaline earth metal, potato starch showed a typical two step swelling pattern and lower viscosity by amylography and increased paste stability against mechanical shearing. Cation substitutions are especially interested for high phosphate potato starch, which contains 90-110 mg naturally bound phosphorus per 100 g of starch, as food processing starch without any chemical modification such as esterification or etherificaton. Phi sical properties of the substituted starch were varied by the balance of alkali metal ions and alkaline earth metal ions. For the mechanism of the swelling inhibitions of potato starch by calcium-, magnesium ion substitution, we speculate that about two third of existing phosphate were cross-linked between two chains through an ionic bond of calcium or magnesium.

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