AN EVALUATION OF WET PROCESSING METHOD ABOUT STEADY STATE RHEOLOGICAL PROPERTIES OF GUAR GUM

Guar is processed to extract endosperm which is pulverised to powder, popularly known as guar gum. Presently guar gum is extracted using dry milling method in which 12-17% gum is lost during dehulling. A new wet pretreatment process comprising soaking guar seeds to 72-78% moisture content (dry basis) followed by dehulling using a new machine resulted into more than 90% dehulled seeds with less than 3% broken and powder formation. The guar gum powder obtained by this pretreatment method was evaluated and its physico-chemical and rheological properties were compared with commercial guar gum sample. Rheological properties of 1% aqueous solutions were studied in the temperature range of 20-60°C. Powder obtained by wet process was darker in colour, while proximate composition and pH of solution was equal to that of dry-milled gum. Rheological behaviour of both samples was similar (P≥0.05) with respect to apparent viscosity, yield stress, and consistency index. Yield stress decreased with increased temperature obeying the Arrhenius relationship (E=3.63 kJ/mol) and varied between 4.78-5.79 Pa for gum prepared by wet process. Generalized Herschel-Bulkley model described adequately the flow behaviour of both samples. This study showed that the guar gum obtained by wet pretreatment process exhibited rheological properties similar to those of commercial guar gum with fewer losses in gum production process.