Physicochemical properties and biological activities of mucilaginous substances from selected Thai medicinal plants

Abstract

As a continuous searching for anti-diabetic (type II) potential substances, seven mucilaginous polysaccharides from selected plants were studied as follow: aerial parts of Basella alba Linn., fruits of Hibiscus esculentus Linn., leaves of Litsea glutinosa (Lour.) C.B. Robinson, seeds of Ocimum canum Sims., seeds of Plantago ovata Forssk., fruits of Scaphium scaphigerum G. Don. and seeds of Trigonella foenum-graecum Linn. The bioactive properties for entrapping glucose against dialysis, inhibiting enzyme α-glucosidase, pancreatic lipase, disturbance on micellar lipids solubilization and free radical scavenger were in vitro studied compared to glucomannan. The physical characteristics for swelling properties, viscosity and average molecular weight were determined. The chemical characteristics were analyzed for monosaccharide composition using gas chromatography after methanolysis and TMS-derivatization. B. alba mucilage was further investigated by 1H NMR spectroscopy. O. canum mucilage superiorly entrapped glucose compared to glucomannan. This activity was relevant to its highly viscous gelation. S. scaphigerum showed another property of α-glucosidase inhibition. Its mucilage (0.5%) inhibited the enzyme activity by 82.6%, compared to 1-Deoxynorjirimycin (by 47.6%). The IC₅₀ of α-glucosidase inhibitory activity was found as 1.7 mg/ml. Mucilages from O. canum and T. foenum-graecum as well as glucomannan showed around 20% inhibition on cholesterol solubility in bile acid micelles. All mucilages decreased oleic acid micellar solubilization whilst most of them increased stearic acid micellar solubilization. The studied mucilages had no effect on the lipase activity but affected on the micellar interface. Most mucilages, except from O. canum and P. ovata, showed DPPH scavenging activity higher than glucomannan. Especially L. glutinosa, S. scaphigerum and H. esculentus mucilages had IC₅₀ less than 1 mg/ml. Galacturonic acid was found in 3 from 7 mucilages namely B. alba, P. ovata and S. scaphigerum. Whereas rhamnose was common sugar found in all seven mucilages. Monosaccharide components of these mucilages were compared to another reports from distinguished techniques B. alba mucilage was revealed to be β-galactan with the composition of arabinose (24%), rhamnose (5%), galactose (41%), galacturonic acid (13%) and glucose (16%)