Structural Characteristics, Antioxidant, and Immunostimulatory Activities of an Acidic Polysaccharide from Raspberry Pulp

The extraction and characterization of new bioactive plant-derived polysaccharides with the potential for use as functional foods and medicine have attracted much attention. In the present study, A novel acidic polysaccharide (RPP-3a) with a weight-average molecular weight (Mw) of 88,997 Da was isolated from the raspberry pulp. RPP-3a was composed of rhamnose, arabinose, galactose, glucose, mannose, and galacturonic acid at a molar ratio of 13.1:28.6:16.8:1.4:6.2:33.9. Structural analysis suggested that the RPP-3a backbone was composed of repeating units of -> 4)-beta-Galp-(1 -> 3,4)-alpha-Rhap-(1 ->[4)-alpha-GalAp-(1 -> 4)-alpha-GalAp-(1 ->](n) with branches at the C-4 position of rhamnose. The side chain of RPP-3a, containing two branch levels, was comprised of alpha-Araf-(1 ->, -> 5)-alpha-Araf-(1 ->, -> 3,5)-alpha-Araf-(1 ->, -> 3)-beta-Galp-(1 ->, -> 3,6)-beta-Galp-(1 ->, -> 4)-beta-Glcp-(1 ->, and -> 2,6)-alpha-Manp-1 -> residues. RPP-3a exhibited moderate reducing power and strong hydroxyl and superoxide anion radical scavenging abilities. RPP-3a significantly promoted the viability of RAW264.7 macrophages by increasing the production of nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-1 beta (IL-1 beta) at both the expression and transcriptional levels. In summary, the immunostimulatory and antioxidant activities make RPP-3a a viable candidate as a health-beneficial functional dietary supplement.