Starch from the new sweetpotato cultivar Konamizuki (KM) was evaluated as a food material, and its basic properties were characterized. Change in elastic modulus during cold storage of KM starch gels and syneresis after freeze-thaw treatment were limited and indicated slow retrogradation properties. In addition, KM starch paste had higher and more stable storage modulus than other starches, suggesting desirable gel-forming properties. These KM gel properties reflected distinctive structural properties, including larger quantities of short unit chains with degree of polymerization 6-10 and amylose-like long chains of the amylopectin, as well as longer amyloses and longer amylose-like chains of the amylopectin compared with other starches. Finally, KM starch was used in the production of tapioca pearls and starchy noodles, and subsequent sensory analyses indicated highly desirable properties as a food material for starchy gel products.
α-1,6-Glucosidase (isomaltase) belongs to glycoside hydrolase (GH) families 13 and 31. Genes encoding 3 isomaltases belonging to GH family 13 were cloned from filamentous fungi, Aspergillus oryzae (agl1), A. niger (agdC), and Fusarium oxysporum (foagl1), and expressed in Escherichia coli. The enzymes hydrolyzed isomaltose and α-glucosides preferentially at a neutral pH, but did not recognize maltose, trehalose, and dextran. The activity of AgdC and Agl1 was inhibited in the presence of 1 % glucose, while Foagl1 was more tolerant to glucose than the other two enzymes were. The three fungal isomaltases did not show transglycosylation when isomaltose was used as the substrate and a similar result was observed for AgdC and Agl1 when p-nitrophenyl-α-glucoside was used as the substrate.
The synthesis of the saccharide β-D-fructopyranosyl-(2→6)-D-glucopyranose, which was isolated from Super Ohtaka®, has recently been reported. During the synthesis of this saccharide, the formation of two novel saccharides from D-glucose and D-fructose was observed. The present study aimed to confirm the structures of the two disaccharides synthesized from D-glucose and D-fructose by thermal treatment. Furthermore, various properties of the saccharides were investigated. Both saccharides were isolated from the reaction mixture by carbon-Celite column chromatography and an HPLC system and were determined to be novel sucrose-isomers, β-D-fructopyranosyl-(2↔1)-β-D-glucopyranoside (1) and β-D-fructofuranosyl-(2↔1)-β-D-glucopyranoside (2), by MALDI-TOF MS and NMR analyses. Both saccharides showed low digestibility in vitro, and the sweetness of saccharide 2 was 0.45 times that of sucrose.