Physico-chemical studies on a commercial food-grade xanthan. I. Characterisation by sedimentation velocity, sedimentation equilibrium and viscometry
1995
Dhami, R. | Harding, S.E. | Jones, T. | Hughes, T. | Mitchell, J.R. | To, K.
A popular commercially available xanthan polysaccharide 'Keltrol RD' has been characterised by sedimentation velocity (Schlieren optics), sedimentation equilibrium (Rayleigh interference optics) and viscometry with regard to: (i) homogeneity; (ii) molecular weight: (iii) gross conformation: and (iv) critical overlap concentration, c*. Studies were conducted in phosphate-chloride buffer (pH = 6.5, I = 0.30). Preparations were shown to be homogeneous with a characteristic hypersharp Schlieren peak from sedimentation velocity. Despite the low c* value (approximately 0.5 mg/ml) it was still possible to obtain meaningful physical measurements in the dilute solution regime with a weight average molecular weight Mw = (5.9 +/- 1.1) X 10(6) g/mol, the second thermodynamic ('osmotic pressure') virial coefficient of (3.4 +/- 0.3) X 10(-4) ml mol g-2, a sedimentation coefficient s(0)20.w = (12.97 +/- 0.26)S, a sedimentation concentration regression parameter k(s) of (2127 +/- 85)ml/g and an intrinsic viscosity [eta] = (7534 +/- 2717)ml/g. From these data it is also possible to estimate the two hydration independent shape parameters II and the Wales-van Holde ratio k(s)/[eta]; the values obtained (approximately 0.53 +/- 0.20 and approximately 0.28 +/- 0.10, respectively) are consistent only with a stiff, elongated molecule of aspect ratio approximately 70:1.
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