Kinetics Of Acid Hydrolysis Of Glucomannans From Bletilla Striata

Bletillan was a kind of heteropolysaccharide composed of mannose and glucose which could be obtained from Bletilla striata. It was a novel biodegradable polymers with some pharmacological activities such as anti-ulcer, anti-gastrointestinal bleeding, intestinal adhesion prevention. In this paper, recent techniques for molecular weights (Mw) analysis of polysaccharides had been reviewed, the kinetics of acid hydrolysis of bletillan (BT01) was studied, BT20 was prepared as one example by controlled acid hydrolysis of BT01 to illustrate potential developments of hydrolysis products.Purified bletillan BT01 was obtained from raw tubers of Bletilla striata, which was used as start materials to undertake system reactions at various temperatures and acid concentrations using HCl. The degradation process was monitored by determination of Mw of samples taken out at definite reaction time during the hydrolysis, using a gel permeation chromatography - evaporative light scattering detection (HPGPC-ELSD) method. A first-order kinetic model was found to match the reaction, indicating that acid hydrolysis of BT01 is a random process. The reaction rate constants at various conditions were calculated on the basis of this model, and the kinetic function was further established. The activation energy, Ea, was calculated to be 131.0 kJ·mol?1 for acid hydrolysis of bletillan. The rate constant increased by a factor of 10 with a decrease in pH by 1 unit, regardless of temperature. The quantitative relationship between viscosity, Mw and reaction time was also established to monitor the reaction process conveniently. A process for BT20 was developed by controlled acid hydrolysis methods accordingly, with high purity and good reproducibility.Gel permeation chromatography-refractive index/multi-angle laser light scattering (GPC-RI/MALLS), hydrophilic interaction chromatography-evaporative light scattering detection (HILIC-ELSD), ultraviolet spectrophotometry (UV), infrared spectrophotometry (IR), and nuclear magnetic resonance (NMR) techniques were applied for structure characterization of BT07 and other samples. The results indicated Mw of BT07 to be 24.2 kDa, with narrow distribution (1.263). BT07 was composed of glucose and mannose in the molar ratio 1∶2.88, with a backbone ofβ-(1→4)-linked mannopyranosyl and glucopyranosyl units. The DS of acetyl groups was 0.2046. The intrinsic viscosities of five polysaccharides standards were measured in pure water at 25℃by capillary viscosimetry, and the Mark-Houwink equation was thus determined to be [η] = 7×10-4M 1.10. The universal calibration curve for TSK-gel G4000PWXL column was established to be lg[η]M = -0.7788Ve + 12.7444 accordingly.