Effect of granular characteristics on the viscoelastic properties of composites of amylose and waxy starches

For elucidating the influence of granular properties on the viscoelastic characteristics of starch gel, in this study waxy corn and waxy rice starches pre-heated at different temperatures were mixed with amylose isolated from normal corn starch to form amylose-waxy starch composites. Rheological properties of the amylose, the waxy starches and the composites during aging at 25 degrees C were determined and compared. Results showed that the storage modulus (G) of amylose solution (2%, w/w) during aging was lower than 48 Pa, and the rheological properties during aging o $($$$) over barf waxy starches pre-heated at 60 degrees C were too weak to be detected. The G' of waxy starches during aging decreased with increasing pre-heating temperature from 70 to 90 degrees C, and the decrement on G' value was more obvious for waxy corn starch. The amylose-waxy starch composites had higher gel strength than that of amylose or waxy starch alone. The C of amylose-waxy corn starch composite increased with increasing pre-heating temperature from 60 to 80 degrees C and then decreased at 90 degrees C, however, the G of amylose-waxy rice starch composite increased with increasing pre-heating temperature from 60 to 90 degrees C. Waxy corn starch had lower hot paste and final viscosities, but higher breakdown than waxy rice starch. Waxy corn starch also showed a rapid increase on the swelling power at temperature above 70 degrees C while waxy rice starch increased slowly. The rigidity and integrity of waxy corn starch granules was found lower than waxy rice starch at 90 degrees C. Results indicate that granule properties and interaction occurred between amylose and starch granules play important roles during gelation of starch. (C) 2007 Elsevier Ltd. All rights reserved.