Molecular Characteristics and Functional Properties of Barley Starches with Varying Amylose Content

Molecular structures and functional properties of starches isolated from normal, waxy, and zero amylose barleys were examined. Amylopectins from zero amylose starch had the largest molecular weight (M_w), whereas those from high amylose starch, the smallest. A good correlation between the Mw and the radius of gyration (R_g) was observed among amylopectins from various starches, indicating similar polymeric conformation in solution even with the differences in the M_w. The debranched amylopectin molecules from different types of barley starches exhibited similar profiles, implying that the packing geometry of double helices in the different types of barley starches may be similar. Zero amylose starch showed the highest peak viscosity (326 RVU) in RVA viscograms at lower pasting temperature (67.6℃), compared to normal and high amylose starches. Relationship between RVA peak viscosity and amylose content suggested that the presence of amylose inhibited the development of granular swelling of barley starches during cooking. A rapid retrogradation, traced by differential scanning calorimetry (DSC) and strain-controlled rheometry, occurred in the high amylose starch sample during storage, while zero amylose starch showed a very good resistance to retrogradation, indicating excellent storage stability.