Structure and functionality of large, medium and small granule starches in normal and waxy barley endosperms

The structure and functionality of large, medium and small starch granules from normal and waxy barley were examined. The median size of large, medium and small granules was 18.1, 11.4 and 2.2 μm and 17.2, 9.2 and 2.0 μm in normal and waxy starch, respectively. The amylose content was 25.9% for normal small starch granules, about 4% lower than that of large and medium granules. For waxy starches, the amylose content ranged 2.9–3.3% and was similar among the granules. The DPn of amylopectins was 6100–8900, and similar between the varieties but differing among the granules. The CL of the amylopectins was 17–20 glucose residues, and in both starches, shorter in small granules than in large and medium granules. The relative crystallinity was 20.3–23.9% for normal starch granules, and 33.0–37.1% for waxy starch granules. The transition temperatures and enthalpy changes were 55.6–71.7°C and 7.4–8.5 J/g and 58.9–77.2°C and 10.1–12.1 J/g for the normal and waxy starch granules, respectively. The small granules displayed the greatest swelling power and susceptibility to enzymes, and the fastest retrogradation both in normal and waxy barley. The difference of functionality among granules of the same variety exceeded those between the same granule sizes of different varieties.