A Novel Alkaline Hemicellulosic Heteroxylan Isolated from Alfalfa (Medicago sativa L.) Stem and Its Thermal and Anti-inflammatory Properties

A novel hemicellulosic polysaccharide (ACAP) was purified from the cold alkali extraction of alfalfa stems and characterized as a heteroxylan with a weight-average molecular weight of 7.94 × 103 kDa and a radius of 58 nm. Structural analysis indicated that ACAP consisted of a 1,4-linked β-d-Xylp backbone with 4-O-MeGlcpA and T-l-Araf substitutions at O-2 and O-3 positions, respectively. Transmission electron microscopy (TEM) examination revealed the entangled chain morphology of ACAP molecules. The evaluation of thermal degradation property revealed a primary decomposition temperature range of 238.8–314.0 °C with an apparent activation energy (Ea) and a pre-exponential factor (A) of 220.0 kJ/mol and 2.81 × 1024/s, respectively. ACAP also showed significant inhibitory activities on IL-1β, IL-6, and COX-2 gene expressions in cultured RAW 264.7 mouse macrophage cells. These results suggested the potential utilization of ACAP in functional foods and dietary supplement products.