Effect of urea, sodium nitrate and ethylene glycol addition on the rheological properties of corn starch pastes

摘要

The effects of the additives used in starch adhesives production on the pasting process and rheological properties of native corn starch were investigated. Suspensions of the starch of Indentata variety (6 %) prepared in distilled water or aqueous solutions of urea (2.5 %), sodium nitrate(V) (2.5 %) and ethylene glycol (1.5 %) were subjected to a controlled pasting in RVA viscometer. The obtained pastes were placed in a measuring cylinder of HAAKE rheometer and the viscosity measurements were performed using controlled shear rate (CR) mode at shear rates of 0-600 s(-1). The paste smears were analyzed under a microscope after staining with Lugol's solution. It was found that the addition of urea caused a reduction in the pasting temperature, change in the shape of pasting curve as well as 30 % increase in the final viscosity (Table 1). The addition of sodium nitrate(V) led to an increase in the pasting time, decrease of the viscosity drop and reduced viscosity increase during cooling (Fig. 1). The influence of ethylene glycol additive on the pasting process was less significant than that of urea and sodium nitrate(V). Corn starch forms pastes or shear thinning suspensions with a distinct change in the rheological properties over time.