Rice starch is the main component of the milled rice grain and the powder as the processed material. Rice starch of the non-waxy type is essentially classified into amylose and amylopectin; on the other hand the cluster structure of waxy-rice starch consists of only amylopectin. Numerous reports have demonstrated that the differences in the physico-chemical properties and functionality of rice starches are related to starch structure. 1―6) For exam- ple, there was significant correlation between amylose content and hardness of cooked rice properties 7,8) and amy- lose in non-waxy starch largely affects its physical proper- ties. 8) On the other hand, there is very little information on systematic analysis of amylopectin structure and physical properties using waxy rice amylopectin, although numer- ous investigations on the relationship between rheological properties and amylopectin structure of starches have been carried out. Structural analysis of amylopectin is one of the most important approaches to evaluate and design pal- atable rice cultivars and starches, for consumers or indus- trial uses. In this study, the chain-length distribution of amylopec- tin by high performance anion-exchange chromatography with the pulsed amperometric detection (HPAEC-PAD) method, the pasting properties of rice flour by Rapid Visco Analyser (RVA) and the physical properties of cooked rice grain by Tensipresser from several waxy-rice starches of japonica and indica types were measured in order to evaluate the relationship between the structure of amylopectin and the pasting properties of rice powder and the physical properties of cooked rice grains without the amylose effect. MATERIALS AND METHODS Materials. Thirteen kinds of waxy-rice samples were prepared in this study (Table 1). Ten japonica waxy-rice samples which were domestic cultivars in Japan, Oryza sativa L., were harvested from the experimental fields of the National Agriculture Research Center (NARC), Japan in 2001. Three kinds of endosperm mutants (EM), 9) de- signed as waxy which lacked amylose in starch, EM21 of japonica waxy type, or EM2003 and EM2009 of indica waxy types, which were deficienct in granule-bound starch synthase I (GBSS I) concerned with a kind of starch-branching enzyme during the grain developing stage 1,10) were harvested from the experimental field of Kyushu University in 2000. Preparation of milled rice and rice flour. The rice samples were milled to the milling yield of 90% by a grain testing mill (TM-05, Satake, Tokyo, Japan). The milled rice samples for determinations by rice flour were ground using a Cyclone Sample Mill (UDY Corporation, Fort Collins, USA) through a 1.0 mm sieve screen. Sample for the measurement of chain length distribu- tion of amylopectin. The samples for the measurement of the chain length distribution of amylopectin by HPAEC- PAD were prepared by the method of Umemoto et al . 11) with slightly modification. Five mg of the rice powder was suspended in 3 mL of 100% methanol and boiled for 10 min. The suspension was centrifuged at 2500 g for 10 min. The precipitated polyglucan fraction was washed twice with 5 mL of distilled water and re-suspended in 5 mL of distilled water and boiled for 60 min. After cen- J. Appl. Glycosci., 53, 227―232 (2006) ! C 2006 The Japanese Society of Applied Glycoscience Regular Paper Relationship between Chain-length Distributions of Waxy Rice Amylopectins and Physical Properties of Rice Grains (Received July 22, 2005; Accepted May 26, 2006) Keitaro Suzuki, 1,＊ Sumiko Nakamura, 1 Hikaru Satoh 2 and Ken ’ ichi Ohtsubo 1 1 National Food Research Institute (2 ―1 ―12, Kannondai, Tsukuba 305 ―8642, Japan ) 2 Faculty of Agriculture, Kyushu University (6 ―10 ―1, Hakozaki, Higashi -ku, Fukuoka 812 ―8581, Japan ) Abstract: Chain-length distributions of amylopectins by HPAEC-PAD from japonica and indica waxy-rice samples were characterized, and the relationship between the chain-length distributions and pasting proper- ties of rice flour by RVA and the physical properties of cooked rice grains by Tensipresser were studied. In comparison with jaonica and indica types, the pattern of chain-length distribution of indica amylopectin typi- cally differed, and the ratio of degree of polymerization (DP) 6―12, fa short chains of indica type was clearly lower, while the ratio of DP>13, fb1+2+3 long chains was clearly higher. The physical properties of cooked rice grains and powder pasting of the indica type showed clearly as hard type starch. There were differences in the chain-length distribution among japonica waxy-rice starches. The ratios of fb3, DP>37 for japonica waxy amylopectins were positively correlated with RVA paste viscosity parameters, such as minimum viscosity, fi- nal viscosity, pasting temperature and setback, and iodine absorbance. Iodine absorbance was negatively cor- related with properties of cooked rice grains, such as overall adhered mass, L6. The results showed the possi- bility that the long chain portion of the amylopectin structure is a factor in regulating its starch physical properties. Key words: amylopectin, chain-length distribution, physical property, waxy rice starch ＊ Corresponding author (Tel. +81―29―838―8045, Fax. +81―29―838― 8045, E-mail: ktaro@affrc.go.jp). 227