RSM-Modeling and Optimization of High Titer Functional Xylo-Oligosaccharides Production by Edible Gluconic Acid Catalysis

Xylo-oligosaccharides as a functional prebiotic have great value in food, feed fields. Previous studies have shown that organic acids catalyze the hydrolysis of xylan-rich sources for the production of xylo-oligosaccharides. In this study, gluconic acid of edible aldonic acid, generated xylo-oligosaccharides via hydrolysis of xylan from corncob. In order to maximize the efficiency of xylo-oligosaccharide production, a model was designed and optimal conditions were determined by Box-Behnken design-based response surface methodology. The developed process resulted in a maximum xylo-oligosaccharides yield of 57.73% using 4.6% gluconic acid at 167°C for 28 min, which was similar to the predicted value and fitted models of xylo-oligosaccharides production. The results showed that the reaction temperature was crucial to xylo-oligosaccharides production, and by-product yields (xylose and furfural) could be effectively controlled by both reaction temperature and time. In addition, 44.87 g/L XOS was achieved by decreasing the solid-liquid ratio. Overall, the described process may be a preferred option for future high concentration xylo-oligosaccharides production.

Reversible Self-Assembling of Comb-Like Functionalized Dextran Surfactant Polymers as an SPR-Sensing Surfaces

Novel surface plasmon resonance (SPR) sensing surfaces were developed from the perspective of reversible self-assembling of the mixed dextran surfactant polymers onto SPR gold chips. Two comb-like dextran surfactant polymers, which are different in their dextran molecular weight (MW) distribution and the presence of amine functional groups, and their characterization were synthesized. These structurally well-defined surfactant polymers include a bimodal amine dextran surfactant polymer and a monomodal dextran surfactant polymer. The bimodal one consists of poly (vinyl amine) (PVAm) backbone with amine functionalized high MW dextran, non-functionalized low MW dextran and hydrophobic hexyl pendant groups. Allyl high MW dextran aldonic acid and low MW dextran aldonic acid chains with various ratios were sequentially attached to PVAm. The unreacted amine groups on the backbone were further grafted with hexanoic acid and the allyl groups on the high MW dextran were finally converted to amine. The monomodal surfactant polymer, PVAm with non-functionalized low MW dextran and hexyl branches, was synthesized and characterized using similar procedures, except with the absence of allyl high MW dextran aldonic acid and the amine functionalization. The molecular compositions of the surfactant polymers were determined by FTIR and 1H-NMR. Surface active properties at the air-water interface were determined using tensiometer. Reduction in water contact angles was observed on the surfactant treated surfaces. Reversible self-assembling of the synthesized surfactant polymers on SPR gold chip surface was monitored using SPR analysis. Reproducibility of the mixed surfactant assembling process was preliminarily confirmed by a consistent increase in reflectivity change, while no detectable changes in the reflectivity under a 1-h buffer flow indicated stability of the absorbed surfactant layer. Moreover, a simple, quick flow of a basis regeneration solution completely removed the adsorbed surfactant from the surface. Our preliminary investigation also exhibited that the regenerated SPR gold chip was effectively reusable.

Kinetics and mechanism of the reduction of CrVI to CrIII by D-ribose and 2-deoxy-D-ribose

The oxidation of D-ribose and 2-deoxy-D-ribose by CrVI yields the aldonic acid and Cr3+ as final products when an excess of sugar over CrVI is used. The redox reaction occurs through CrVI–>CrIII and CrVI–>CrV–>CrIII paths. The complete rate laws for the CrVI oxidation reactions are expressed by -d[CrVI]/dt = kH[H+]2 [ribose][CrVI], where kH = (5.9 ± 0.1) × 10-2 mol-3 dm9 s-1, and -d[CrVI]/dt = (k0 + kH'[H+]2) [2-deoxyribose][CrVI], where k0 = (1.3 ± 0.5) × 10-3 mol-1 dm3 s-1 and kH' = (4.2 ± 0.1) × 10-2 mol-3 dm9 s-1, at 33°C. An intermediate sugar alkoxide radical could be trapped with DMPO and observed by EPR as a multiline signal at g = 2.003. CrV is formed in a rapid step by reaction of the sugar radical with CrVI. CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxochromate(V) intermediates are formed, and the distribution of these CrV species in the reaction mixture essentially depends on the solution acidity.Key words: ribose, 2-deoxyribose, chromium, redox, mechanism, kinetics.

Complexes of Cu(II) with D-aldonic and D-alduronic acids in aqueous solution

A quantitative study of the equilibria involved in the interaction of Cu(II) ion with D-glucoheptonic, D-gluconic, D-galactonic, D-ribonic, D-glucuronic, and D-galacturonic acids in aqueous medium has been carried out by means of potentiometric measurements of hydrogen ion concentrations at a constant temperature of 20 °C and an ionic strength of 0.10 (NaNO3). The equilibrium data were processed with the FORTRAN computer program BEST. It was found that Cu(II) interacts with D-aldonic acids to form 1:1, 2:2, and 1:2 (M/L) complexes. The copper(II) complexes with D-galacturonic and D-glucuronic acids are considerably weaker than those of D-aldonic acid. Possible structures of the complex species formed are discussed.