(567g) Effect of Low Power-Ultrasonic On the Supramolecular Aggregation of Exopolysaccharide From Cordyceps Sinensis Mycelial Culture

Aggregation formed based on the self-association of macromolecules through internal weak interaction is commonly existed in biopolymers. The presence of aggregation in polysaccharide has led to low solubility and high viscosity in aqueous solution. However, a recent publication pointed out that the biological activities of some biopolymers were aggregates-related. The aim of this study was to examine the supramolecular association state of an exopolysaccharide(EPS) produced from a medicinal fungus Cordyceps sinensis under low power ultrasound condition. The high MW and hard soluble EPS separated from Cordyceps sinensis mycelial culture was treated by ultrasound probe (20 kHz) with a low power level of 20%(4.0 W) for 0.5, 1, 2, 3, 5, 8, 13 and 60 min respectively. The intrinsic viscosity of EPS was decreased by about 80% and its water solubility increased by 4 times after ultrasonic treatment for 8 mins. Dynamic light scattering (DLS) showed the transferring transition in DLS spectra from 4 separated peaks to 1 single symmetrical peak. The size of aggregation decreased from mainly 10000~100000nm to a dominant 100~1000nm. The molecular weight of EPS was moderately reduced and the molecules distribution was narrowed as evidenced by the increasingly prolonged retention time and area percentage of high MW peak in GPC profiles with the progress of ultrasonic treatment. Atomic force microscopy (AFM) observation disclosed that ultrasonic irradiation converted EPS from highly aggregated state into the stretched strand, which was composed of multiple helices according to Congo red analysis. No significant change was made on the primary chemical structure of EPS as indicated by chemical analysis and IR spectra. The ultrasonic induced modification of the viscosity and solubility of EPS can be attributed to the change of molecule size and the aggregation state in aqueous solution, as a result of the disruption and reformation of chemical bonds, especially the weak hydrogen bonds, affected by ultrasonic energy.