PHYSICO-CHEMICAL CHARACTERISTICS, CHEMICAL MODIFICATIONS AND POTENTIAL UTILIZATION OF SOME PLANT GUMS

Abstract

Exudate gum samples were collected from six different gum producing trees purified and studied. They were compared with two standard gums, Acacia senegal and Anacardium occidentale exudate gum. The crude gums were first examined for their toxicological parameters and were analyzed for their physicochemical characteristics, proximate, elemental and various sugar compositions. The gums were further modified via oxidation, acetylation and carboxymethylation and characterized using scanning electron microscopy (SEM), energy dispersive X-ray fluorescence spectrometry (EDX),X-ray powder diffraction analysis (XRPD), Fourier transform infra-red (FTIR), ultraviolet-visible spectroscopy (UV-visible), 1D and 2D Nuclear magnetic resonance spectroscopy (NMR) and solid state NMR. The LD50 of the gums in albino rats is greater than 5000mg/kg.The result of the physicochemical properties of the purified gums ranged thus; moisture content (10.71 to 15.25%), pH (7.50 to 8.35), water holding capacity (28.50 to 94.50%), emulsifying capacity (17.80 to 62.85%), swelling index (7.40 0.20 to 10.94 0.25%), viscosity (8.7 0.30 to 31.6 0.76), specific rotation (-95.50 to +46.400), refractive index (1.33to 1.34) and viscosity-averaged molecular weight (5.7 ×104 to 20.1×104gmol-1) and compared favourably with the standards. The stated values increased significantly (𝑃<0.05) for the modified gum samples. The physicochemical characteristics of the modified gums ranged thus: moisture content (4.20 to 8.35%), pH (6.50 to 7.05), water holding capacity (33.0 to 99.0) emulsifying capacity (30.75 to 73.25%), swelling index (12.80 to 11.34%), viscosity (20.00 to 43.90), specific rotation (-95.50to 46.400), refractive index (1.33 to 1.34) and viscosity molecular weight (6.2×104 to 22.10×104gmol-1) and were higher than that of the native gums. The proximate composition of the gums revealed that they have low protein, fat, fibre and ash (0.18-4.19; 0.04-6.38; 0.10-4.50; and 0.40-7.85 % respectively),But the gums are very high in carbohydrate (77.62-93.24 %). Elemental analysis of the gums revealed the content of sodium (74.4 to 254.4mg/g), potassium (76.7 to 729.5mg/g), calcium (0.11 to 0.19mg/g), manganese (0.11 to 0.22mg/g), iron (13.10to 19.50mg/g) and zinc (0.82 to 3.90mg/g),cadmium and zinc were below detection limit. SEM analysis suggested the gums have irregular particle sizes. The X-ray diffractogram of the gum samples confirmed the gums almost complete amorphous nature. The FTIR spectra showed broad band (O-H) located within the region of 3800-3500cm-1 which appeared in all the native gums. The other major functional groups in the native gums were 1736cm-1 (-C=O), 1625cm-1 (-COO-) 1427cm-1 (-COO-), 1227cm-1 (-C=O). 1162cm-1 (C-O stretching and C-H stretching). During oxidation, acetylation and carboxymethylation, there were introduction of new functional groups, 1800-1500cm-1 (-COOH), 1750cm-1 – 1730cm-1 (-COO-) and 1606cm-1 – 1632cm-1 (OCH2COONa) respectively. Application of 1D- and 2D- NMR spectroscopy to the original Sweitenia mycrophylla gum and its degraded products in combination with chemical data, led to the confirmation that the original gum contained a chain of 𝛽−𝐷−𝑚𝑎𝑛𝑛𝑜𝑝𝑦𝑟𝑎𝑛𝑜𝑠𝑦𝑙 residue linked at 1 4 which carried alternating ∝−𝐷−𝑔𝑎𝑙𝑎𝑐𝑡𝑜𝑝𝑦𝑟𝑎𝑛𝑜𝑠𝑦𝑙 residues at 0-6 mannopyranosyl unit. All the gum granules possessed good flow properties with Hausner ration of 1.10 to 1.30 and Carr’s index of 9.0 to 23.0%. Tablets prepared with 4-8% w/w gum had hardness 4kg while tablets prepared with 6-8% w/w binders had friability of <1% comparable to that prepared with 4% (w/w)acacia gum. The disintegration time of the tablet was <15 min. The tablets had fast dissolution in aqueous media with >94% drug dissolution in 45 min.