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

Abstract

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 × 10³ kDa and a radius of 123 nm. The primary structural analysis indicated that APPS composed of a →2)-α-l-Rha<i>p</i>-(1→4)-α-d-Gal<i>p</i>A-(1→ backbone with 12% branching point at C-4 of Rha<i>p</i> 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 (<i>E</i>_a) of 226.5 kJ/mol and a pre-exponential factor (<i>A</i>) of 2.10 × 10²⁵/s, whereas its primary degradation occurred in the temperature range from 215.6 to 328.0 °C. In addition, APPS showed significant anti-inflammatory effect against mRNA expressions of the pro-inflammatory cytokine genes, especially for IL-1β, suggesting its potential utilization in functional foods and dietary supplement products