High Sucrose Concentrations (high + sucrose_concentration)

Distribution by Scientific Domains

Selected Abstracts

Combinatorial engineering to enhance thermostability of amylosucrase

Stéphane Emond
Abstract Amylosucrase is a transglucosidase that catalyzes amylose-like polymer synthesis from sucrose substrate. About 60,000 amylosucrase variants from two libraries generated by the MutaGen random mutagenesis method were submitted to an in vivo selection procedure leading to the isolation of more than 7000 active variants. These clones were then screened for increased thermostability using an automated screening process. This experiment yielded three improved variants (two double mutants and one single mutant) showing 3.5- to 10-fold increased half-lives at 50°C compared to the wild-type enzyme. Structural analysis revealed that the main differences between wild-type amylosucrase and the most improved variant (R20C/A451T) might reside in the reorganization of salt bridges involving the surface residue R20 and the introduction of a hydrogen-bonding interaction between T451 of the B, domain and D488 of flexible loop 8. This double mutant is the most thermostable amylosucrase known to date and the only one usable at 50°C. At this temperature, amylose synthesis by this variant using high sucrose concentration (600 mM) led to the production of amylose chains twice as long as those obtained by the wild-type enzyme at 30°C. [source]

Production of fructose and ethanol from media with high sucrose concentrations by a mutant of Saccharomyces cerevisiae

Hasan Atiyeh
Abstract The production of enriched fructose syrups and ethanol from a synthetic medium with high sucrose concentrations was studied in a batch process using Saccharomyces cerevisiae ATCC 36858. The results showed that the fructose yield was above 92% of theoretical values in synthetic media with sucrose concentrations between 180,g,dm,3 and 726,g,dm,3. Ethanol yield was about 82% in media with sucrose concentrations up to 451,g,dm,3. A product containing 178,g,dm,3 fructose, which represents 97% of the total sugar content, and 79,g,dm,3 ethanol was obtained using a medium with 360,g,dm,3 sucrose. The fructose fraction in the carbohydrates content in the produced syrups decreased with increases in the initial sucrose concentration. In a medium with initial sucrose concentration of 574,g,dm,3, the fructose content in the produced broth was 59% of the total carbohydrates. Glycerol and fructo-oligosaccharides were also produced in this process. The produced fructo-oligosaccharides started to be consumed when the concentration of sucrose in the media was less than 30% of its initial value. Complete hydrolysis of these sugars was noticed in media with sucrose concentrations below 451,g,dm,3. These findings will be useful in the production of ethanol and high fructose syrups using sucrose-based raw materials with high concentrations of this carbohydrate. © 2001 Society of Chemical Industry [source]


ABSTRACT Glucosyltransferases can be applied in the synthesis of prebiotic oligosaccharides. Enzymatic synthesis using acceptors can be used to obtain these carbohydrates. When maltose is the acceptor, oligosaccharides containing one maltose moiety and up to eight glucose units linked by ,-1,6-glycosidic bonds are obtained as the product of dextransucrase acceptor reaction. In this work, the enzymatic synthesis of isomalto-oligosaccharides using dextransucrase from Leuconostoc mesenteroides NRRL B-512F was optimized by response surface methodology. The effect of maltose and sucrose concentrations on the acceptor reaction was evaluated in a batch reactor system. Partially purified enzyme was used to reduce the enzyme purification cost. The results showed that high sucrose concentrations in conjunction with high maltose levels enhanced the isomalto-oligosaccharide synthesis. A productivity of 42.95 mmol/L.h of isomalto-oligosaccharides was obtained at the optimal operating condition (100 mmol/L of sucrose and 200 mmol/L of maltose). PRATICAL APPLICATIONS Oligosaccharides as prebiotic have a large application in food formulations, and their beneficial role in human health have been extensively studied. Although the acceptor mechanism of dextransucrase has already been extensively studied, an industrial process has not been developed yet for enzyme synthesis of isomalto-oligosaccharide. The process studied in this work allows the large-scale preparation of isomalto-oligosaccharide using partially purified enzyme. [source]