SHEAR THINNING AND ANTITHIXOTROPIC BEHAVIOR OF A HEATED CROSS-LINKED WAXY MAIZE STARCH DISPERSION

Cross-linked waxy maize (CWM) starch dispersions (2.6%, w/w) were heated in the range 60 degrees C to 80 degrees C and in a retort at 120 degrees C. All the heated dispersions exhibited shear-thinning behavior except for that heated for 15 min at 60 degrees C which showed slight shear-thickening. The consistency index (K) increased with heating time and was exponentially correlated to the granule size and the notional volume fraction. CWM starch dispersions heated for 8, 15 and 30 min at 120 degrees C exhibited counterclockwise (antithixotropic) shear rate-shear stress hysteresis loops. Similar behavior was observed when dispersions were sheared in three continuous cycles and they became more viscous with each shear cycle. Clusters of granules were found in sheared retorted dispersions that may have been shear induced. Gelatinized granules viewed with SEM appeared to have folds and crevices which may have aided in cluster formation.