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-Rhap-(1 → 4)-α-GalpA-(1→, and the side chains mainly consisted of arabinan with non-reducing ends of α/β-Araf. Meanwhile, AMFPs-3-4 was characterized as a homogalacturonan (HG) composed of galacturonic acid (GalpA) and methyl-esterified GalpA, with GalpA, (un)saturated GalpA and methyl-esterified (un)saturated GalpA as non-reducing ends, and α/β-GalpA or methyl-esterified α/β-GalpA 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.