Starch from hull-less barley: I. Granule morphology, composition and amylopectin structure

Starch was extracted from 10 hull-less barley (HB) genotypes [waxy (CDC Can dle, CDC Alamo, SB 94912, and SB 94917), normal amylose (Phoenix, CDC Dawn, SR 93102, and SB 94860), and high amylose (SB 94893 and SB 94897)]. Starch content ranged from 56 to 65%. The purity of the isolated starches was gre ater than 96%. Average starch yield and extraction efficiency were 44 and 7 1%, respectively. The starches from all genotypes consisted of a mixture of large lenticular and small irregularly shaped granules. The granules of mo st starches were intact, whereas in others (SB 94917, SR 93102, and SB 9486 0) they were compound (clustered), The proportions of small (diameter less than or equal to 10 mum) and large granules (diameter > 10 mum), by total n umber and by total weight differed among genotypes. Bound lipid content was positively correlated (r=0.92, P < 0.01) with total amylose content. Free and bound lipid contents ranged from 0.1-0.3% and 0.3-1.7%, respectively. T he apparent and total amylose contents ranged from 0-39% and 0-45%, respect ively. The amounts of amylose complexed with native lipids (total amylose-a pparent amylose) ranged from 0.5 to 7.8%. The proportion of small granules was correlated with total amylose content (r=0.59, P < 0.1). However, the a verage granule diameter was negatively correlated (r=-0.65, P < 0.05) with total amylose content. The debranched amylopectins of all starches exhibite d the highest peak in the MALDI-MS spectrum at DP 12. The average chain len gth (CL) and degree of branching ranged from 17.6-22.7% and 4.4-5.5%, respe ctively. The short (DP 5-17) and long (DP greater than or equal to 35) chai ns ranged from 58.2-59.1% and 3.0-12.8%, respectively. The study showed tha t amylose/amylopectin ratio and amylopectin branch chain length have high c orrelation with granule size and size distribution in this set of barley ge notypes. (C) 2001 Elsevier Science Ltd. All rights reserved.