A regio- and stereo-selective parallel synthesis of oligosaccharides on a solid support was successfully achieved by a combination of a novel α-selective glycosidation procedure and a uni-chemo hydroxyl protection (UCHP) procedure. The α-selective glycosidation of dibutyl 3,4-di-O-benzoyl-2,6-di-O-benzyl-α/β-D-galactopyranosyl phosphate in cyclopentyl methyl ether (as an ethereal solvent for effective swelling of the polystyrene resin) proceeded smoothly and in relatively high yield. Five types of trigalactoses [Galα1-3Galβ1-3Gal, Galβ1-3(Galα1-4)Gal, Galα1-4Galβ1-3Gal, Galα1-3Galβ1-4Gal, and Galα1-4Galβ1-4Gal] were successfully synthesized on a solid support as a model of a combinatorial oligosaccharide library.
In this study, we analyzed the starch and free sugars eluted from polished rice soaked in hot water to determine if they are correlated with the eating quality of cooked rice. Two grams of polished rice was heated with 40 mL of water at 85ºC. Eluted starch varied widely among used cultivars and the amount of eluted starch was significantly correlated with overall eating quality in two years (r=0.62**, 0.77**). The amylose ratio of eluted starch, measured with high-performance size-exclusion chromatography (HPSEC), was significantly negatively correlated with overall eating quality (r=−0.84**). This fact showed that eating quality rose as the ratio of amylopectin in eluted starch increased. Although the differences in chain-length distribution of amylopectin and free sugar contents in eluted starch did not correspond to differences in eating quality, it was suggested that eating quality improved if the short–chain ratio of amylopectin in eluted starch rose. Eluted starch of rice can be analyzed using only 2 g of polished rice and does not require any special equipment. Thus, this method can be applied to the selection of high-quality rice lines in the early generations of a breeding population.
The present paper shows the effects of reaction temperature on the activity and chain-transfer properties of all three starch branching enzyme (BE) isozymes, BEI, BEIIa and BEIIb, from rice towards amylopectin as a glucan substrate. The activity of BEI increased with an increase in the reaction temperature from 10 to 30ºC, then the activity decreased at higher temperatures, and finally BEI lost its activity at 45ºC. Both BEIIa and BEIIb activities were optimum at 25ºC, and no significant activity was found at 45ºC. The decrease in the enzymatic activity at high temperatures between 35-40ºC was more significant in BEIIb than in BEIIa. Despite the temperature-dependent activity, no practical changes in distinct chain preferences of any of the three BE isozymes were found. These findings indicate that these responses could influence the starch production, structure and physicochemical properties affected by environmental temperatures during the growth of rice plants.
Nowadays, germinated brown rice (GBR) is known as a food of high nutritional value. Germination produces various nutrients which are effective for health promotion. With the diversification of the usage of GBR, to elucidate the germination conditions suitable to increase its desired factors will be important. To improve the palatability of GBR, we prepared it using different conditions and investigated the compositional changes. The glucose content of GBR prepared by the low-temperature method corresponded to 130% of that of brown rice; however, its content with the warm method fell to 62%. Therefore, we conclude low-temperature is a suitable germination condition with respect to palatability. The analysis of enzymatic activity indicated that among the starch degradation enzymes, α-glucosidase has the pivotal role for the production of glucose.
Cellobiose phosphorylase (EC 184.108.40.206, CBPase) is an enzyme that catalyzes the reversible phosphorolysis of cellobiose into α-D-glucose 1-phosphate (G-1-P) and D-glucose. As the acceptor specificity of the reverse reaction is broad, CBPase can synthesize hetero β-disaccharides from G-1-P and monosaccharides as acceptors. Here, in order to develop an efficient system for producing a rare β-disaccharide like 4-O-β-D-glucopyranosyl-D-xylopyranose (GX) using CBPase, two attempts were examined. Firstly, the CBPase gene from Cellvibrio gilvus was heterologously expressed as an intracellular enzyme using Aspergillus oryzae. The recombinant CBPase was enclosed in the mycelia of the host cell by cold acetone treatment and prepared as a mycelial dry powder. Secondly, to facilitate the synthesis of GX by removing glucose from the reaction mixture, a commercial dry yeast was added to the reaction mixture. The powdered CBPase-yeast combined system produced an approximately 3.5 times higher yield of GX from cellobiose than the reaction without yeast.