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 funct ion of pretreatment and concentration using a glass capillary viscometer. I t was found that the onset of molecular entanglements varied with pretreatm ent, 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 specifi c viscosity of hsian-tsao leaf gum exhibited a power-law dependence on conc entration. 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 sal t tolerance and chain stiffness parameters. It was found that the chain sti ffness 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 ri ghts reserved.