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

• Oligoguluronates were prepared by a rapid microwave degradation method without any additional acids.
• Ten guluronate oligomers (DP 1–10) were obtained by one step column separation.
• The structures of oligoguluronates were characterized by ESI-MS and NMR techniques.
• This method avoids desalting procedure and is environment-friendly.

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, 1H NMR, 13C NMR, and 2D NMR spectroscopy techniques. The data showed that the GOS fractions were saturated oligoguluronates with general molecular formula C6nH8n+2O6n+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.

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