Structural characteristics of two pectic polysaccharides from Avicennia marina fruit

Pectic polysaccharides in A. marina fruit exhibit excellent prebiotic effects and may be the key to treating constipation and dysentery; however, their detailed structures still need to be clarified. In this study, we obtained two pectic polysaccharide fractions (AMFPs-3-2 and AMFPs-3-4) from this fruit for the first time and comprehensively investigated their fine structures using chemical methods, GC–MS, and 1D- and 2D-NMR. AMFPs-3-2 was identified as a type I rhamnogalacturonan (RG-I) with a backbone composed of →2)-α-Rha p -(1→4)-α-Gal p A-(1→, and the side chains mainly consisted of arabinan with non-reducing ends of α/β-Ara f . Meanwhile, AMFPs-3-4 was characterized as a homogalacturonan (HG) composed of galacturonic acid (Gal p A) and methyl-esterified Gal p A, with Gal p A, (un)saturated Gal p A and methyl-esterified (un)saturated Gal p A as non-reducing ends, and α/β-Gal p A or methyl-esterified α/β-Gal p A as reducing ends. These findings demonstrate that different types of pectic polysaccharides from A. marina fruit can be effectively separated and distinguished. The elucidation of these clear structural features provides a solid structural basis for further investigating the pharmacological activity and structure-activity relationship of polysaccharides from A. marina fruit.