Effect of polysaccharide chain conformation on ultrasonic degradation of curdlan in alkaline solution.

This study was to investigate the effects of polysaccharide chain conformation on ultrasonic degradation of curdlan, a high MW ß-glucan with wide applications. The ultrasonic degradation was performed in alkaline solution at 0.1 M and 0.3 M NaOH, in which the curdlan chain was mainly in triple helical conformation and random coil form, respectively. The degradation rate was represented by the kinetic model, 1/Mt - 1/Mo = kt, with the rate constant k increasing with the ultrasonic power. The degradation rate was much higher in 0.3 M NaOH than in 0.1 M NaOH, suggesting that curdlan in random coil conformation was more liable to degradation than in helical conformation. Curdlan in 0.1 M NaOH was changed from triple helices to single helices and eventually to random coils with a higher solubility. In summary, ultrasonic degradation of curdlan in alkaline solution had a close and complex relationship to the chain conformation changes.

Ultrasonic disruption of fungal mycelia for efficient recovery of polysaccharide-protein complexes from viscous fermentation broth of a medicinal fungus.

High-intensity ultrasound (US) was applied to facilitate the extraction of intracellular and extracellular polysaccharide-protein complexes (PSPs) from the viscous mycelial fermentation broth of a medicinal fungus Cordyceps sinensis Cs-HK1. The US treatment caused the disruption of fungal mycelia, a dramatic reduction of the apparent broth viscosity, and the release of intracellular products into the liquid medium. The degree of mycelium disruption and the rate of intracellular product release were dependent on US power intensity, treatment period and biomass concentration of broth. The extraction or release kinetics of total water-soluble products and PSPs (yield Y versus time t) under the effect of US was fitted closely to the Elovich model Y=Yo+Y1 lnt and parabolic model Y=Yo+Y1t(½), respectively. Another interesting effect of the US treatment was a notable increase in the antioxidant cytoprotective activity of PSP against H2O2 induced cell death.

Structure and properties of a (1→3)-ß-D-glucan from ultrasound-degraded exopolysaccharides of a medicinal fungus.

A high molecular weight (MW) exopolysaccaride (EPS) fraction EPS1 was isolated from the fermentation broth of a medicinal fungus Cordyceps sinensis Cs-HK1 and partially degraded by high-intensity ultrasound (US) into a lower MW fraction EPS1U. EPS1U exhibited a single, symmetric peak on size exclusion chromatography with an average MW of 730kDa by light scattering analysis. It had a much lower intrinsic viscosity (1.7 versus 15.6dL/g) but a much higher solubility in water (77.5 versus 5.1g/L) than EPS1. Based on methylation analysis and NMR spectrometry, the structure of EPS1U was deduced as a (1→3)-ß-d-glucan with glucose side chains attached to O-6 position at the branching points. EPS1U showed a high moisture absorption capability comparable to chitosan and urea, suggesting its potential as a moisturizing agent for food and cosmeceutical application. This is the first report on a high MW (1→3)-ß-d-glucan isolated from EPS produced by Cordyceps sinensis.

Ultrasonic treatment for improved solution properties of a high-molecular weight exopolysaccharide produced by a medicinal fungus.

High-power ultrasound (20 kHz) was applied to modify the physicochemical properties of a high-molecular weight (MW) exopolysaccharide (EPS) from mycelial culture of a medicinal fungus. At 35 W/cm(2) or higher ultrasound power, the apparent and intrinsic viscosities of EPS solution dropped by nearly 85% within 10 min, and the water solubility was increased by more than fourfold. The ultrasonic treatment led to a notable reduction of the maximum MW and a more uniform MW distribution, but no significant change in the primary structure of the EPS molecules. In contrast, the intrinsic viscosity of EPS was reduced by only 20% in 1.0M sulfuric acid at 50 degrees C for 9h. Ultrasound was proven an effective and favorable means for improving the solution properties of high-MW bioactive polysaccharides in mild conditions.