Impact of annealing on the molecular structure and physicochemical properties of normal, waxy and high amylose bread wheat starches

Starch from normal (CDC teal), high amylose (line 11132) and waxy (99 WAX 27) bread wheat cultivars was isolated and its morphology, composition, structure and properties were studied before and after annealing. Granule diameters, total phosphorus, total amylose, lipid complexed amylose chains, crystallinity, gelatinization temperature range, gelatinization enthalpy, swelling factor (at 90 C), and amylose leaching (at 90 degrees C, in the above starches ranged from 2-38 mu m, 0.007-0.058%, 26.9-32.3%, 13.4-18.7%, 28.6-42.8%, 12.7-14.3 degrees C, 11.3-13.3 J/g, 27.6-72.2 and 22.2-26.2%, respectively. Peak viscosity, thermal stability, set-back and susceptibility towards acid hydrolysis followed the order: 99WAX27 > CDC teal > 11132,11132 > CDC teal > 99WAX27, CDC teal > 99 WAX 27 > 11132, and 99WAX27 > 11132 > CDC teal, respectively. Susceptibility towards alpha-amylase hydrolysis followed the order: 99 WAX 27 > 11132 > CDC teal (< 24 h) and 11132 > CDC teal > 99WAX27 (> 24 h). The extent of retrogradation measured by spectroscopy and differential scanning calorimetry followed the order: 11132 > CDC teal > 99WAX27 and 99WAX27 > CDC teal > 11132, respectively. In all starches, concentration of amylose, lipid complexed amylose chains, gelatinization temperature range, swelling factor, amylose leaching, peak viscosity, final viscosity, set-back, light transmission, susceptibility towards a-amylase and acid hydrolysis and the proportion of small (2-8 mu m) B-type granules decreased on annealing. Thermal stability and crystallinity increased on annealing. In all starches, gelatinization, enthalpy, retrogradation rate and amylopectin chain length distribution remained unchanged on annealing. Pores and indentations were formed on the granule surfaces of CDC teal and 99WAX27 starches on annealing. (c) 2008 Elsevier Ltd. All rights reserved.