Effect of annealing on the molecular structure and physicochemical properties of bread wheat starches varying in amylose content

Starch from normal (CDC teal), high amylose (line 11132) and waxy (99WAX27) 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°C) ranged from 2-38μm, 0.007-0.058%, 26.9-32.3%, 13.4-18.7%, 28.6-42.8%, 12.7-14.3°C, 11.3-13.3 J/g, 27.6-72.1 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 >WAX27, CDC teal >99WAX27 >11132, and 99WAX27 >11132 >CDC teal, respectively. Susceptibility towards α-amylase hydrolysis followed the order: 99WAX 27 > 11132 > CDC teal ( CDC teal >99WAX27 (>24h). 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 amylase (apparent & total), lipid complexed amylose chains, gelatinization temperature range, swelling factor, amylose leaching, peak viscosity, final viscosity, set-back, light transmission, susceptibility towards α-amylase and acid hydrolysis and the proportion of small (2 to 8 μm) B-type granules decreased on annealing. However, thermal stability and crystallinity increased on annealing, whereas enthalpies of gelatinization and retrogradation and the amylopectin chain length distribution remained unchanged in all starches. Pores and indentations were formed on the granule surfaces of CDC teal and 99WAX27 starches on annealing.