Identification of an arabinogalactan with special structure from Moringa Oleifera Lam. leaf and exploration of its immunomodulatory activity

Arabinogalactan exhibits many biological activities, which is the candidate for functional food ingredients. However, there is limited research on the arabinogalactan from Moringa Oleifera leaf, and its structure needs to be more accurately characterized. This study investigated structural characteristics and immunomodulatory activity of a high-purity polysaccharide from Moringa oleifera leaf (i.e. MOLP-PE) to further explore arabinogalactan from Moringa Oleifera leaf and its potential application area. The results showed that MOLP-PE was a unique type II arabinogalactan: the main chain consisted of → 3, 4)-α-D-Galp-(1→, →3)-β-D-Galp-(1→ and →2, 4)-β-D-Rhap-(1→, with branches at the C-4 position of →3, 4)-α-D-Galp-(1→ and →2, 4)-β-D-Rhap-(1→, consisting of →5)-α-L-Araf-(1→, →3)-α-L-Araf-(1→, →6)-β-D-Galp-(1→ and →4)-β-D-GalpA-(1→. Compared with arabinogalactan from larch, galactan and arabinan, MOLP-PE exhibited stronger ability in stimulating proliferation, phagocytosis and cytokines release of macrophages and bound with Toll-like receptor 4 closer via more binding sites, which might be due to its higher contents of 1,3-linked-Galp and 1,5-linked-Araf. These findings elucidated that MOLP-PE, as type II arabinogalactan with a unique structure, could be exploited as an immunomodulatory food ingredient.