Preparation and characterization of guluronic acid oligosaccharides degraded by a rapid microwave irradiation method.

Guluronic acid oligosaccharides (GOS) with degree of polymerization (DP) ranging from 1 to 10 were prepared by a rapid microwave degradation method. Polyguluronic acid, fractionated from alginate hydrolysate, was dissolved in dilute ammonia water at a concentration of 20 mg/mL (pH 5) and then hydrolyzed under microwave irradiation (1600 W) at 130°C for 15 min to produce GOS mixture. The GOS mixture was separated by a Bio-Gel P6 column and ten fractions were obtained. Each GOS fraction was further characterized by electrospray ionization mass spectrometry, (1)H NMR, (13)C NMR, and 2D NMR spectroscopy techniques. The data showed that the GOS fractions were saturated oligoguluronates with general molecular formula C(6n)H(8n+2)O(6n+1) (n=1-10). This microwave degradation method was not only convenient, less time consuming, and environment-friendly, but also produced GOS with high yield (71%) and eliminating a desalting procedure compared to conventional acid hydrolysis method.