Structural, thermal and viscoelastic characteristics of starches separated from normal, sugary and waxy maize

Starches separated from five types of maize (two normal, one sugary and two waxy) were investigated for physicochemical, thermal, amylopectin structure and viscoelastic properties. Kisan and Paras were normal maize while Parbhat and LM-6 were waxy maize type. Apparent amylose content of normal and sugary maize was 29.5-32.6 and 41.0%, respectively. Swelling power of normal, sugary and waxy maize starches was 11.6-15.2, 7.8 and 30.2-39.2 (g/g), respectively. X-ray diffraction of maize starches indicated typical A-pattern. Maize starch showed a single broad peak at 2 theta=23.2 degrees and a dual peak 2 theta=17 degrees-18.1, respectively. Waxy maize starches showed the presence of greater crystallinity than other starches while sugary maize starch showed the presence of lower crystallinity and a large amount of amylose-lipid complex. Intrinsic viscosity [B] of starches in 90% DMSO at 2 degrees C was 79.7-119.5 ml g(-1) for normal, 70.5 ml g(-1) for sugary and 107.2-118.1 ml g(-1) for waxy starches. Branch chain-length distribution of amylopectin revealed that the apparent amylose, long side chain- and short side chain-amylopectin proportion ranged between 0.0-41%, 13.4-31.5% and 41.5-66.8%, respectively, among the various maize starches. Maize sugary showed the highest apparent amylose content and the least amount of short- and long-side chains of amylopectin. LM-6 and Parbhat showed higher proportion of both long and short-chain amylopectin as compared to other starches. Distribution of alpha-1, 4-chains of amylopectin (short-/long-chain) ranged between 2.1 and 3.4, the least for LM-6 and the highest for Paras starch. The transition temperatures (T-o-T-c) ranged between 60.5 and 76.1 degrees C for sugary, 63.5-76.3 degrees C for normal and 64.4-81.3 degrees C for waxy maize starch. The enthalpy of gelatinization (Delta H-gel) of sugary, normal and waxy maize starches was 2.47, 3.7-4.75 and 4.15-5.4 J/g, respectively. Normal and sugary maize starches showed higher G' and G than waxy type starches. The change in the moduli during cooling and reheating of pastes cooked at different temperatures revealed low disintegration of granular structure in starch with higher amylose and amylose-lipid complex as well as low crystallinity. The changes in moduli during 10 h at 10 degrees C revealed highest retrogradation in maize sugary followed by Paras and Kisan starch. (c) 2005 Elsevier Ltd. All rights reserved.