Structural and physicochemical properties of starch gels prepared from partially modified starches using Thermus aquaticus 4-α-glucanotransferase

The modified starch gels prepared from partial enzyme treatments (1, 3, and 6 U/g starch; 2-h incubation) of the corn and rice starch pastes using Thermus aquaticus 4-alpha-glucanotransferase (TA alpha GT) were investigated for their molecular characteristics, microstructures, and physicochemical properties. Unlike the native and partially modified normal starches, the native and partially modified waxy starches could not form gels strong enough for textural analysis after 24 h for gel setting. Features of the partially modified normal starches were the specific apparent amylose contents and maximum iodine absorption wavelength (lambda(max). similar to 567 nm), as well as the tri-modal molecular weight profiles and flatter side-chain distributions. Also, the partially modified normal starch gels possessed fractured surfaces with discontinuous crystalline fibrous assembly that differed from the native starch gels' porous continuous network, which resulted in more brittle, rigid, and resilient gels compared with the native gels. (C) 2011 Elsevier Ltd. All rights reserved.