Structural and thermal analysis of a hyper-branched exopolysaccharide produced by submerged fermentation of mushroom mycelium

Abstract

An exopolysaccharide (PTR-EPS1) purified from the culture medium of the mycelial fermentation of Pleurotus tuber-regium had a weight-average molecular mass of 173.6 kDa and a radius of 55.6 nm. Methylation analysis and NMR results indicated that PTR-EPS1 had a 81% degree of branching at O-2 and consisted of a backbone of 1,6-linked α-D-Manp residues branched at O-2 with either a terminal α-D-Manp or -(1,2)-α-D-Manp-(1,2)-α-D-Manp units. The morphology of PTR-EPS1 was found to be spherical by TEM. Thermal analysis indicated that the main thermal degradation (up to 77.56% dry mass) of PTR-EPS1 occurred within a temperature range of 205.7–331.2 °C. The apparent activation energy E_a and pre-exponential factor A of PTR-RES1 were found to be 223.4 kJ mol⁻¹ and 5.37 × 10²³ s⁻¹, respectively. This is the first report on the structural information and thermal degradation properties of PTR-EPS1. These results will facilitate the potential application of this mushroom polysaccharide as a novel biopolymer in the design of carbohydrate-based nanoparticles and food delivery systems.