Structural, Thermal, and Anti-inflammatory Properties of a Novel Pectic Polysaccharide from Alfalfa (Medicago sativa L.) Stem

A pectic polysaccharide (APPS) was purified from the cold alkali extract of alfalfa stem and characterized to be a rhamnogalacturonan I (RG-I) type pectin with the molecular weight of 2.38 x 10(3) kDa and a radius of 123 nm. The primary structural analysis indicated that APPS composed of a -> 2)-alpha-L-Rhap-(1 -> 4)-alpha-D-GalpA-(1 -> backbone with 12% branching point at C-4 of Rhap forming side chains by l-arabinosyl and d-galactosyl oligosaccharide units. Transmission electron microscopy (TEM) analysis revealed a primary linear-shaped structure with a few branches in its assembly microstructures. The thermal decomposition evaluation revealed the stability of APPS with an apparent activation energy (E-a) of 226.5 kJ/mol and a pre-exponential factor (A) of 2.10 x 10(25)/s, whereas its primary degradation occurred in the temperature range from 215.6 to 328.0 degrees C. In addition, APPS showed significant anti-inflammatory effect against mRNA expressions of the pro-inflammatory cytokine genes, especially for IL-1 beta, suggesting its potential utilization in functional foods and dietary supplement products.