The effect of calcium gluconate on the loaf volume of bread, viscoelastic properties, and interactions between gluten and starch in the dough was studied using a home bakery . The addition of Ca-gluconate (0.3% (w/w)) to the wheat flour significantly increased the loaf volume. Farinograph datum of wheat flour with Ca-gluconate shortened the development time of dough as compared with that of control. Scanning electron microscopic observation of wheat dough after 25-min mixing with Ca-gluconate showed in part thick, stringy fibers compared with that of the control without an additive, and therefore the gluten molecules tended to change the covering of the surface of starch granule. The gelatinization temperature of starch granules tended to decrease slightly by the addition of Ca-gluconate. Considering these results, the improvement of loaf volume by the addition of Ca-gluconate may be caused by the formation of cross-linkages between gluten and Ca-gluconate.

View full abstract

The cecal contents were taken under anaerobic conditions from the rats fed on a diet containing 10% pullulan, 10% polydextrose or 10% pectin, and cultured to count the total number of microflora. Also, the short chain fatty acid concentration, soluble sugar content, pH and weight of cecal contents were determined . 1) The proportions of Lactobacillus and Bifidobacterium in cecal microflora increased in rats fed on the pullulan diet. The proportions of Lactobacillus, Bifidobacterium and Clostridium decreased in the rats fed 10% polydextrose and 10% pectin diets . Bifidobacterium increased only in rats fed on the 10% pullulan diet. 2) The concentration of total short chain fatty acids increased in the cecal contents of rats fed on the pullulan diet. From these results, we concluded that pulluan is more fermentable than polydextrose and pectin in the rat cecum.

View full abstract

Xylose isomerase (XIase, from Streptomyces phaeochromogenus)-catalyzed activity and the enzyme Rf value on gel-filtration chromatograms were found to be very dependent on the concentration of NaCl. As one of the most likely explanations for this, these findings suggest that XIase forms a larger subunit (tetramer) without NaCI, whereas at concentrations higher than 0.13 M NaCI the enzyme forms a smaller subunit (dimer), the specific activity of which is almost twice that of the tetramer . The dissociation constant Ka of the xylose-subunit complex was evaluated; the Kd's were almost identical (0.3 mM) for both the tetramer and the dimer. Mg2+ ions may be essential for the binding of substrate . In conclusion, the dimer appears to be more useful than the tetramer for the XIase-catalyzed conversion of glucose to fructose.

View full abstract

Starches from two new potato varieties, Jaga Kids Purple '90 (Purple) and Jaga Kids Red '90 (Red), which were selected through the protoplast breeding method, had similar properties as follows. Purple and Red contained 21.7 and 21.0% amylose, 840 and 800 ppm phosphorus and showed high maximum and breakdown viscosities by a Rapid Visco Analyzer (RVA) . The amylose molecules of Purple and Red respectively had d.p.n 2190 and 2110, d.p.w 5400 and 5130, apparent d .p.-distribution range 590-12, 150 and 560-11, 750, and branch linkages for both was 3 .9 mol-1. The amylopectin molecules of both starches had an average chain length of 23, the iodine affinity was 0.06 and 0.08, and the chain-length distribution was similar. To clarify the effect of phosphate groups on the pasting properties of potato starch, nine potato starches with different phosphorus contents were examined. Regression analysis suggested that maximum, minimum, and breakdown viscosities and the pasting temperature by an RVA increased with the increase of linked phosphate groups. The potato starches showed a greater tendency of retrogradation than other non-cereal starches .

View full abstract

Saccharomyces cerevisiae mannan was hydrolyzed with 0.2 N sulfuric acid at 100°C for 12 hr. Seven manno-oligosaccharides were obtained from the hydrolysates by carbon column chromatography followed by gel filtration and characterized by 1H-NMR. Two of them contained α-(1→2)- and α-(1→6)-mixed linkages. This result differed from those obtained by PEAT et al. but agreed with those obtained recently by us (0.33 N sulfuric acid was used for hydrolysis in each experiment). It has been considered that acid hydrolysis of the yeast mannan may cause preferential cleavage of α-(1→2)-linked side chains, consequently yield a homologous series of α-(1→6)-linked manno -oligosaccharide based on the results that (1→6)-glycosidic linkage is much more stable toward acid hydrolysis than the (1→2)-glycosidic one, but our results disproved this idea and suggested that acid hydrolysis of highly branched yeast mannan is complex.

View full abstract

Five topics were picked up from our studies with Rhizopus glucoamylase during 30 years, and briefly introduced. 1) From the study of pH profile, it was concluded that the same pair of carboxylate and carboxyl groups, whose pKa's are 2.9 and 5.9 respectively, are involved in the catalytic hydrolysis of both a-1, 4 and a-1, 6 glucosidic linkages. 2) Calorimetric measurement of enthalpies of hydrolysis of a-1, 4 and a-1, 6 linkages revealed that heats of hydrolysis of a-1, 4 and a-1, 6 linkages are -1.1 kcal/mol and + 1.3 kcal/mol, respectively. Therefore, the reverse reaction, the condensation of the two linkages, is more favored, at least enthalpically, for a-1, 6 linkage formation, which is actually the case. 3) The number-average molecular weight of amyloses can be determined from the analysis of the time course of glucoamylase-catalyzed hydrolysis of amyloses. 4) Glucoamylase is the first enzyme to which the subsite theory was successfully applied. The subsite affinities of each subsite and the intrinsic rate constant of glucosidic linkage splitting have been determined solely from the rate parameters (Michaelis constants and molar activities) of a series of linear substrates. 5) Stopped-flow kinetic studies down to millisecond region on the binding of the enzyme with various substrates (maltooligosaccharides) and inhibitors (gluconolactone and 1-deoxynojirimycin) were done successfully. The results are useful in considering the detailed mechanisms of the enzyme reaction.

View full abstract

Maltosyl-cyclodextrins (G2-CDs) were synthesized by the transglycosylation catalyzed by pullulanase and isoamylase from a mixture of α-maltosylfluoride and CDs. A variety of heterobranched CDs (α-Gal-CDs, α-Gal-G1-CDs, α-Gal-G2-CDs, β-Gal-G1-CDs, β-Gal-G2-CDs, α-Man-G1-CDs and α-Man-G2-CDs) were also synthesized by the transglycosylation catalyzed by α- and β-galactosidases, and α-mannosidase. The structures of these products were elucidated by hydrolysis with glycosidases, FAB-mass and ¹³C-NMR spectroscopies, and methylation analysis.

View full abstract

The predominant persistence of plastic materials based on petroleum in the environment has resulted in a wide range of pollution and waste disposal problems. Consequently, environmentally degradable plastic materials based on annually renewable biological products, such as starch, are considered by many people as a solution to these problems and, since the 1970's, the research and development of plastics based on starch are intensively conducted on a world scale . These biodegradable plastics are expected to replace conventional plastics currently used for many singleuse items such as garbage bags, shopping bags, diaper linings, bottles, sanitary applicators, fast food service items and so on. But the rate and extent of biodegradation of these starch-based plastics in various environments have not been clarified. Besides, the costs are much higher than conventional petroleum-based plastics and are resisted by consumers . However, we expect that our continued efforts may provide starch-based biodegradable plastics that provide comparable physical properties and resonable costs in comparison with conventional petroleum-based plastics. In this paper, we reviewed briefly the present conditions of starch-based biodegradable plastics about the following subjects : the standard definitions of biodegradability and standard regulations, the predominant situations of starch as a replacer for the conventional plastics, the physical and chemical modifications of starch for use in biodegradable plastics, and starch-based biodegradable plastics currently available on the market .

View full abstract

Some fine separations and analyses of oligo-and poly-saccharides by the use of recently developed tools for HPLC, namely separation on a graphitized carbon column and detection with a pulsed amperometric detector, are presented. In addition, structural analyses of branched cyclodextrins by FAB-MS and 13C-NMR spectroscopies are outlined.

View full abstract