Solution properties of hsian-tsao (Mesona procumbens Hemsl) leaf gum

In order to characterize the coil overlap parameters of hsian-tsao leaf gum, the specific viscosity of the hsian-tsao leaf gum was measured as a function of pretreatment and concentration using a glass capillary viscometer. It was found that the onset of molecular entanglements varied with pretreatment, which occurred at a concentration around 1.0 g/dl for hsian-tsao leaf gum extracted from fresh or frozen hsian-tsao leaf, and around 3.5 g/dl for hsian-tsao leaf gum extracted from dehydrated hsian-tsao leaf. The specific viscosity of hsian-tsao leaf gum exhibited a power-law dependence on concentration. The exponent h ranged from 1.25 to 1.43 in the dilute domain and from 2.21 to 2.93 in the semi-dilute domain, depending on the pretreatment. The coil overlap parameter of the hsian-tsao leaf gum was found to be in the range of 1.79-2.17, which was closer to that of a rod-like polymer. The effects of ionic strength and ion types on the viscosity of the hsian-tsao leaf gum in the dilute regime were also measured. The extent of the ionic strength dependence of intrinsic viscosity was used to characterize the salt tolerance and chain stiffness parameters. It was found that the chain stiffness parameter of the hsian-tsao leaf gum was in the range of 0.026-0.03, which was lower than that of several polysaccharides, indicating the stiff backbone of the hsian-tsao leaf gum. (C) 2000 Elsevier Science Ltd. All rights reserved.