Article,
HYDROLYSIS OF XANTHAN IN DILUTE ACID - EFFECTS ON CHEMICAL-COMPOSITION, CONFORMATION, AND INTRINSIC-VISCOSITY
Carbohydr. Res., 214 (1): 55 -- 69 (July 1991)
Abstract
The polysaccharide xanthan has been depolymerized by mild acid hydrolysis
(pH 1-4) at 80-degrees. The conformational state was varied from
fully ordered to partially disordered by varying the ionic strength
and pH. Hydrolysis occurred mainly in the side chains, with the terminal
beta-mannose as the most susceptible unit, yielding a continuous
series of modified xanthans from the intact ''polypentamer'' to the
''polytetramer'', while retaining a high molecular weight. Depolymerization
of the glucan backbone was analysed by monitoring the intrinsic viscosity
(eta). For ordered xanthan the calculated changes in the degree
of polymerization (X(w)) as a function of time deviate strongly from
that expected for random depolymerization of a single-stranded, linear
polymer, but the data are in qualitative agreement with the behaviour
of such double-stranded polymers as DNA. The conformational properties
of partly hydrolysed xanthan were investigated by optical rotation.
For the series degraded at pH 2, the midpoint of the temperature-driven
transition (T(m)) was > 95-degrees in all cases, but the absolute
value of the specific optical rotation (alpha) increased by increasing
hydrolysis time, a change partly ascribed to an increase in the fraction
of disordered chains, but also to the loss of beta-mannose. This
loss itself did not appear to influence the conformational state
or the depolymerization rates of the xanthan backbone.
Tags
- ;;
- aqueous
- bacterial
- bronchial
- dependence
- double-stranded
- electron-microscopy;
- elevated-temperature;
- gum;
- helix;
- mucin;
- polysaccharide;
- sodium-chloride;
- thermal-stability;
- xanthomonas-campestris;
- [isi:]
