Gelatinization property is one of the most important rheological indicators of cooking quality and processing characteristic of rice starch. Amylopectin side chains length affects the gelatinization of rice endosperm starch granules in urea solution as well as in alkali solution (Nishi et al., 2001, Umemoto et al., 2002). Hanashiro et al., (1996) reported that the amylopectin chain with DP <= 12, 13 <= DP <= 24, 25 <= DP <= 36 and DP >= 37 correspond to A chains, B₁ chains, B₂ chains and long chains of amylopectin, respectively. Variations of the amylopectin chains length structure have been observed in dull, ae, sbe1, sbe2, sug1, sug2 and flo2 endosperm of rice mutant lines (Okuno et al., 1983, Nishi et al., 2001, Kubo et al., 1999, and Satoh et al., 2003). However, no report on the amylopectin chains length structure of opaque endosperm in rice has been done. This is the first report dealing with the amylopectin chains length distribution of opaque endosperm type in Myanmar local rice cultivar.

The rice cultivar with opaque endosperm type, MMR310, collected from mountain areas in Myanmar shows chalky endosperms, as seem in waxy, but contains amylose (Fig. 1 and Table 1). The gelatinization properties of MMR310 and two controls such as IR36 and Kinmaze were characterized by alkali digestibility test (Little et al., 1958). Their amylopectin chains length distribution patterns were determined by HPAEC-PAD as described by Nishi et al., (2001). Standard cultivars, IR36 and Kinmaze, exhibited low (score 1) and high (score 7) alkali digestibility, respectively (Table 1). Significant differences were also observed in the proportion of amylopectin chain length between IR36 and Kinmaze (Fig. 2 A). MMR310 showed intermediate score 5 compared with those of IR36 and Kinmaze. The amylopectin structure of MMR310 (wx^op) was characterized by the significant decrease in A chains with DP 12- 21 and slightly decrease in long chains DP >= 37, and the remarkable increase in A chain with DP 7- 11, and slightly increase in B₁ chains with DP 22- 29, compared to IR36 (Fig. 2 B and D). Compared to Kinmaze, MMR310 had significantly decrease in A chains with DP 4-

11, and slightly increase in B₁ chain with DP 19- 36 and in long chains with DP >= 37 (Fig. 2 C and D). The A chains proportion fa (DP <= 12) of MMR310 showed lower than that of Kinmaze and higher than that of IR36, while B₁ chains fb₁ (13 <= DP <= 24) had higher than that of Kinmaze and lower than that of IR36. The difference in the proportion of fb₂ (25 <= DP <= 36) was not significant among three varieties. On the other hand, the differences in the proportions of fb₃ in IR36 and MMR310 showed higher than that of Kinmaze (Table 1). The activity of starch synthase IIa affects the proportion of short chains (Umemoto et al., 2002). This shows the higher proportion of short chains, therefore the activity levels of SSIIa in MMR310 are estimated lower than that of IR36 and higher than that of Kinmaze. MMR310 had significantly increase in short chains compared with that of IR36, while remarkably decrease in short chains compared with that of Kinmaze, suggesting that the amylopectin structure of MMR310 was different between IR36 and Kinmaze. The B₁ chains and long chains amylopectin structure of MMR310 were distinct from that of Kinmaze and IR36 and the proportion of A chains of MMR310 showed between IR36 and Kinmaze. The amylopectin fine structure of opaque endosperm type was different from that of Kinmaze and IR36, suggesting that the different physicochemical properties of starch and amylopectin fine structures of opaque starches depended on the value of alkali digestibility. Therefore, the value of alkali digestibility or gela-

tinization temperature in rice is very important for determining of physicochemical starch properties and the fine structure of amylopectin.

This study was partly supported by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan.

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