オオムギについて XVI－歴史・文化・科学・利用

抄録

The physical properties of starch granules of cereals (barley, rice, wheat, corn), pseudocereal (quinoa), rhizomes (potato, sweet potato, yam, cassava, lotus) and beans (azuki, kidney bean, pea) were compared. The shapes of starch granules were characteristic of the respective plant species. The granule sizes ranged from 1 μm to less than 100 μm. Generally, the distribution patterns of granule sizes showed a single peak, but the distribution patterns of barley and wheat granules showed three peaks. The gelatinization temperature and enthalpy showed a tendency to increase in order from cereals to beans to rhizomes. The water absorption power of the granules increased in the order of azuki, wheat, barley and potato at 20°C. The digestion of raw starch granules by β-amylase resulted in two patterns of degradation, the outer and interior degradation types. The results suggest that the structures of plant starches are diverse and complex.
The structure and functionality of large, medium and small 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 starches, 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 apparent amylose content ranged from 2.9〜3.3% and was similar among the granules. The average chain length (DPn) of amylopectin was 6100〜8900, and similar between the varieties but differing among the granules. The chain length (CL) of amylopectin was 17〜20 glucose residues, being 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 susceptibility to enzymes and the fastest retrogradation both in normal and waxy starch granules. The difference in functionally among granules of the same variety exceeded the differences between the same granule sizes of different varieties.