RVA and the pseudoplastic behavior of guar gum and xanthan gum

Ragini Chaudhary
Scientific and Digital Systems, New Delhi, India

Polysaccharides are used widely in the food, cosmetic and pharmaceutical industries, and many exhibit interesting and useful visco-elastic properties when dissolved in water at very low levels. They have a viscous appearance when stationary, and fluidity when shear is applied, such as wiping, pouring or brushing.

In the pharmaceutical industry, polysaccharides are used in ocular drug delivery gel systems for controlled drug delivery. In tablet manufacturing, they are used as binders and disintegrating agents and in micro-encapsulation of drugs. They are also used in suspensions and anti-acid formulations. In slimming aids and nutritional foods they are an important non-caloric source of soluble dietary fiber. A synergistic mix of guar gum and fiber mixture when taken with water expands in the stomach to produce a feeling of fullness.

RVA Method

A series of RVA experiments at different shear rates (160, 225, 300, 500 and 750 rpm) examined the shear thinning (pseudoplastic) behavior of guar gum and xanthan gum.

Time Type Value
00:00:00  Temperature 25°C
00:00:00 Speed  960 rpm
00:00:20 Speed * rpm
00:02:00 Temperature 25°C
00:12:00 Temperature 95°C
00:14:00 Temperature 95°C
00:24:00  Temperature 25°C
00:26:00 Temperature 25°C
00:26:00 End

Table 1. RVA test profile for guar gum and xanthan gum.
* 160 rpm, 225 rpm, 300 rpm, 500 rpm, 750 rpm.

Results

When the final viscosity is an essential criterion for a product, then shear rate applied during manufacture and use must be considered (Figure 1, Figure 2). Both guar gum and xanthan gum exhibit pseudoplastic behavior at the concentrations used with final viscosity reduced at higher shear rates (Figure 3, Figure 4).

The RVA is a simple and rapid tool for the study of pseudoplastic behavior of guar gum and xanthan gum used in the food, cosmetic and pharmaceutical industries.

Figure 1. Guar gum behavior at different shear rates.


Figure 2. Xanthan gum behavior at different shear rates.

Figure 3. Final viscosity vs shear rate for guar gum.

Figure 4. Final viscosity vs shear rate for xanthan gum.