Surface reflectivity, viscoelasticity, and degree of gelatinization of cooked rice prepared by additions of 1.3-, 1.5-, and 1.7-fold water were measured to find an easy and convenient estimation of the retrogradation of cooked glutinous or non-glutinous rices. When changes of surface reflectivity of cooked glutinous or non-glutinous rices with time were measured upon changing the water content from 1.3- to 1.7-fold, the values of surface reflectivity increased with the storage time, accompanying characteristic changes in their early stages. And, the more the water added to the non-glutinous rice cooking, the higher the surface reflectivity observed. The reproducibility of the results was confizmed by heating the retrograded cooked rice in an electro-microwave oven. That is, the value restored in 3 min, and reached its original and stationary levels after 4-min treatment, with a similar curve to that of gelatinization. When time course of gelatinization of cooked and powdered non-glutinous and glutinous rices were tested by enzyme methods using pullulanase and β-amylase, the values of gelatinization increased with the water added to the rice cooking, but decreased with the in crease of storage time. The speed of the retrogradation is independent of the water content in the rice cooking. The degree of retrogradation of non-glutinous rice correlated well with the surface reflectivity, but that for glutinous rice did not. The time courses of instantaneous elasticity and steady flow viscosity of non-glutinous rice cooked with the addition of 1.5-foldwater correlated with those of the surface reflectivity. From these results, we suggest the presence of some advantageous correlation between the degree of retrogradation and surface reflectivity, and viscoelasticity of cooked non-glutinous rice.

View full abstract

The polysaccharide composed of only D-glucose was extracted with cold water from the endosperm of Italian millet and purified through a column of DEAE-cellulose (borate form). It was revealed to be a phytoglycogen from the results of IR-analysis, methylation study, and enzymic hydrolysis. The weight average molecular weight of the polysaccharide was determined to be about 11, 000 by gel chromatography. β-Limit dextrin prepared from the polysaccharide by treating with β-amylase was digested with pullulanase and then isoamylase. A ratio of maltose and maltotriose to higher oligosaccharides in the digest supported Meyer's model for the structure of this polysaccharide.

View full abstract

The effect of sodium dodecyl sulfate (SDS) on the viscosity of a dilute waxy corn starch paste was measured with a B (Brookfield) type viscometer. The addition of SDS to the paste increased the viscosity. The increase in the viscosity of the paste was inhibited by an increase in the ionic strength and was influenced by heating temperatures or times . Although the binding isotherm of SDS to gelatinized starch had almost the same degree as that to dispersed starch, an increase in the viscosity might be essentially caused by the interaction between swollen starch granules and SDS. Pretreatment of the paste with j3-amylase resulted in the disappearance of the increase in the viscosity. We concluded that an interaction between amylopectin and SDS leads to a further expansion of the swollen granules due to an electrostatic repulsion between adjacent branches of amylopectin molecules, holding sulfate ions, which may be attributed to the increase in the viscosity of the paste.

View full abstract

Fourteen samples of synthetic amylose having molecular weight ranging from 2.71×10⁵ to 1.18×10⁶ were prepared from maltopentaose and glucose-l-phosphate by the action of potato phosphorylase. Light-scattering measurements, gel permeation chromatography, and viscometry have been made on these samples in aqueous solvents to establish the Mark-Houwink-Sakurada equation ; [η] =KM_wa ([n] and M_w are intrinsic viscosity and weight-average molecular weight, and K and a are constants, respectively). The values of K in ml g^-1 and a for the amylose in 0, 25 M aqueous KCl at 40°Cwere determined to be 2.15×10^-2 and 0. 63, respectively, in good agreement with the values for lily amylose reported by Takagi and Hizukuri [J. Biochem., 95, 1459 (1984) ]. It was shown that the smaller [η] values reported previously can be interpreted in terms of the presence of amylose with long branched chains in the samples by simulating [η] at given M_w for randomly branched amylosic chain.

View full abstract

Some chemical and physical properties of starch prepared from bulbs of katakuri, which were collected in Hokkaido and Iwate, were investigated. The results obtained were as follows; 1) The mean particle size of katakuri starch was 19.9 μm, and was bigger than that of sweet potato starch and smaller than that of potato starch. 2) The susceptibility of katakuri starch granules to hog pancreatin was similar to that of sweet potato starch granules having relatively high susceptibility. By scanning electron micros-copy (SEM), stripe structure and large holes on the surface of katakuri starch granules were observed after attack by pancreatin. The large holes were observed in the early stage of the attack. This was quite different from the case of normal maize starch granules, for which the enzymatic attack usually started with small pits on the surface of the granules and then the pits increased in number and in size during the subsequent enzyme attack. 3) The initiation temperatures for gelatinization of katakuri starch, by photopastegraphy, differential scanning calorimetry (DSC), and Brabender's amylography of 6% concentration, were 44, 47, and 53.5°C, respectively. These temperatures were 10 to 20°C lower than the respective values of kuzu, sweet potato, and potato starches. The enthalpy change, 4H, de-termined by DSC was 3.3 cal/g, which was relatively lower than that of the other three starch-es. The maximum viscosity by Brabender's amylography (6 %) was 900 BU and breakdown was 620 BU. 4) The amylose contents of katakuri starch, determined by amperometric titration and en-zyme-chromatographic method, were 22.1 and 22.6%, respectively. The Fr. III/Fr. II, which was determined by enzyme-chromatographic method, was low in spite of the susceptibility of katakuri starch granules being relatively high. 5) Katakuri starch showed B-type X-ray diffractogram.

View full abstract

The colloidal solution of starch-borate complex was prepared by heating the mixtures of starch and sodium tetraborate. The viscosity of the colloidal solution was considerably larger than that of starch alone and showed a maximum at a concentration of sodium tetraborate of 3×10^-3 mol/g (starch), at which the mol ratio of anhydroglucose unit of starch to sodium tetraborate was 2 : 1. The relationship between log η and reciprocal of temperature (1/T) was divided into two straight lines in the range of 10-40°C. However, it showed a linear line by the addition of sodium chloride. The addition of alkaline solution to starch-borate solutions increased viscosity linearly with the increase of pH.

View full abstract

Unpowdered and finely powdered potato starches prepared by a native process were observed to satisfy the standards for the first degree. In the case of finely powdered starch by a large-scale production (usually called rationally produced potato starches), the same result was recognized. The amylographic patterns of the three kinds of potato starches were different from each other. Moreover, the sizes of granules observed by polarized microscope among the three kinds of potato starches were different from each other. Concerning combined lipids contained in the potato starches, among the three kinds of starches there was little difference in their total lipid contents and their ratios of eluted lipid fractions. The constituent fatty acids of principal lipid classes, such as free fatty acid, monoglycosyl monoacylglycerol, and lysophosphatidylcholine, were the most abundant in palmitic acid, thei stearic, and oleic acids. The fatty acid compositions of combined lipids in potato starches hay almost equivalent characteristics in spite of their different manufacturing processes or thei distinct lipid classes.

View full abstract

Enzymatic hydrolysis of "Polydextrose" (PD), a synthetic glucose polymer used as soluble dietary fiber in food, was examined by using several glucanases in high concentration and long reaction periods. Porcine pancreatic α-amylase, bacterial liquefying and saccharifying α-amy lases, and a fraction of bacterial cellulase showed hydrolysis of 2-3%. Isomaltodextranase and glucodextranase gave hydrolysis degree of 8-10%, and glucoamylase in high concentration gavea hydrolysis degree as high as 20%. The structure of PD was discussed on the basis of these results.

View full abstract

This review describes the progress of our recent studies on the conformation and the physical properties of amylose in solutions. In the first three sections, the equilibrium and dynamic aspects of the conformation are discussed in terms of the results obtained by hydrodynamic studies, computer modeling and fluorescence depolarization measurements. It was shown that the most reasonable model for the conformation is random coil having significant sequences of pseudohelical character. This model is compatible with the concept that the thermal segmental motion causes the imperfection of the helical structure and promotes a random-coil character of the amylose chain in solution. The following sections include two examples of the functional physical properties of amylose in aqueous solutions : the complex formation with a fluorescent dye and the retrogradation.

View full abstract

In many scientific careers, certain years have a special significance. For the writer, 1949 and 1989 are such years. In 1949, I began my research career in Cambridge, by studying the structure of glycogen, under the direction of the late Dr. D. J. Bell, who since 1934 had published a series of papers on this subject. At this time, periodate oxidation methods of anal-ysis and paper chromatography were being developed, and these techniques were amongst those widely used in these and later studies. The research also involved an examination of a series of dextrins prepared for me, by an amylolytic degradation of rabbit liver glycogen. One of these, a “β-dextrin, ” had an apparent chain length of nine glucose residues, compar-ed to 12 for the original glycogen, suggesting that on the average, three glucose residues were removed by β-amylase from each chain. How-ever, the “β-dextrin” was, in fact, further degraded by crystalline β-amylase, and the true β-limit dextrin had a chain length of seven. Although this observation was a disappointment at that time, it led to a lasting understanding of the importance of enzyme and substrate con-centrations, which was invaluable over the next four decades. The researches on glycogen also involved classical methylations by the Haworth and Purdie procedures, followed by chromatographic separations of the methylated sugars. From this work came an awareness of the great debt that is owed to the pioneers of polysaccharide chemistry for their painstaking efforts in the 1930 s and 1940s. This fact tends to be overlooked by many who use modern facile and rapid methods of analysis. In 1989, our researches on starch and glycogen have been greatly honoured by this Society. In this review, a selection of this work will be described in four sections. The first covers a period in the 1950s and 1960s when it seemed probable that both polysaccharides contained a small proportion of (1→3)-α-D-glucosidic lin-kages. This would have important implications with respect to the biosynthesis and degradation of these two α-D-glucans. Fortunately, but with one possible exception, the proposition appears to be untrue. However, there is no guarantee that newly discovered samples of starch and glycogen from unusual biological sources such as uncommon algae and protozoa will not contain some anomalous linkages. The second section describes briefly the detection of anomalous linkages in amylose, and their identification by enzymic rather than chemical methods. The key to this work was yeast isoamylase, a debranching enzyme first described by Japanese biochemists. Debranching enzymes also play a major part in the third section which describes studies on the degree of multiple branching in amylopectin and glycogen. Multiple branching originally described the presence of chains containing more than one branch point as an integral part of the molecular structure. This was later described in terms of the ratio of A-chains to B-chains. This ratio is an important parameter which relates to the actual molecular models for amylopectin and glycogen. This topic forms the final part of this review.

View full abstract