Structural characterization of noni ( Morinda citrifolia L.) pectin and its inhibitory activity on pancreatic lipase

This study aimed to investigate the physicochemical properties and biological activities of noni pectin (NP) extracted using various solvents, three fractions of noni pectin were obtained using traditional chemical and deep eutectic solvents. NPs are composed of various ratios of galacturonic acid, arabinose, rhamnose, xylose, glucose, and galactose with different yields, molecular weights, esterification degrees (DE), and microstructures. Among the fractions, noni pectin extracted with Betaine-citric acid (BNP) exhibited higher molecular weight, degree for esterification and pancreatic lipase (PL) inhibitory activity than the other fractions. Enzyme kinetic analysis indicated that BNP inhibited PL via a noncompetitive mechanism. BNP significantly altered the secondary structure of PL and quenched PL fluorescence, suggesting a static quenching mechanism. Isothermal titration calorimetry (ITC) further demonstrated that the binding of BNP to PL was spontaneous and driven by enthalpy, primarily mediated by hydrogen bonding and van der Waals forces. Molecular docking simulations also confirmed strong noncovalent interactions (hydrogen bonding and van der Waals forces) between BNP and PL. This study validated the high efficiency of the deep eutectic solvent-extracted noni pectin fraction in pancreatic lipase inhibition.