Structures of Rice, Maize and Other Plant Starches

Abstract

Structures of amyloses and amylopectins of rice (japonica and indica), maize (normal, sugary-2, amylomaize) and other nine origins have been examined by the methods involving newly devised procedures, and were found to be of characteristic in the origins. Ultra-centrifugation of crude amyloses from exhaustively defatted starches was effective for purification. Purified amyloses having iodine affinities (i. a., g/100 g) of 19.4-21.7 were confirmed to be free of amylopectin by gel-permeation chromatography. Amyloses had various sizes [number-average d. p. (d. p._n) 690-5090], numbers (1.9-12.4) of chains and average chain-length (c.1. 200-525), and were composed of linear and slightly branched (4.9-19.3 chains on average) molecules in various ratios (branched molecule; 11-70% by mole). Branched molecules appeared to be larger than linear molecules. Several varieties of rice and maize had generally a small amylose (d. p._n, rice 920-1110, maize 690-960) and branched molecule with a small number (d. p._n, rice 5.7-9.7, maize 4.9-6.1) of chains compared with the other plants. Branched molecules of rice (Nihonbare) and maize (normal, unknown sp.) had side-chains with wide d. p. distribution (about 6-4000) with a peak d. p. of about 20, and the rice branched molecule was 1.6 times as large as the linear molecule. Rice and maize amylopectins had i. a. of 0.39-2.57 and 0.8-4.63, respectively, and c. 1. of 19-21 and 20-32, respectively, while amylopectins from the other origins had i. a. of 0-0.51 and c.1. of 21-24. Amylopectins with a high i. a. were found to be composed of a large amount of very long chains (d. p. >100) and a small amount of short (weight-average d. p. about 20) or long (d. p._n about 45) chains. The very long chains appeared to be poorly branched. Amylomaize starches were comprised of amylopectin components with various sizes and an unusual, short chain component having d. p._n, of about 90 and about 2 chains on average. The amylose content of starch has to be calculated by considering amylopectin i. a, since its i. a. differed in the origins. Indica rice starches had the same amylose content (about 18%) as japonica rice starches.