18A-24

I. PARK¹, A. M. Ibanez², K. S. McKenzie², and C. F. Shoemaker³. (1) Dept. of Food Science and Technology, Univ. of California at Davis, 1 Shields Ave, Davis, CA 95616, (2) California Cooperative Rice Experiment Station, Biggs, CA 95617, (3) Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616

Rice is one of the most important crops in terms of its contribution of calories to the human diet. The relationship between rice starch molecular structure and its functionality is important for the development of new rice varieties for improved quality. The objective of this research was to measure molecular structure and thermal properties of isolated rice starch from 10 different rice varieties belonging to 4 different grain types (long, medium, short, waxy) which were grown in California (CA) and Texas (TX) in consecutive crop years (2002 and 2003). Amylose content of two crop years was waxy °Ö 1.0%, low-amylose 7.8~12.8%, short and medium 12.0~16.5%, and long grain 17.0~23% respectively as measured with the Concanavalin A method. This study showed that higher molecular weights correlated to lower amylose content. Weight-averaged molecular weights (Mw) of starch were between 0.52 and 1.96x108 g/mol in both crop years and Mws of amylopectin were between 0.46 and 2.50x108 g/mol in both crop years. Waxy starch had the highest Mw of both the starches and amylopectins. No significant differences were observed in amylose content, Mw of starch or amylopectin between crop years and growing locations (p < 0.001). However, for short and medium grains, CA grown samples had higher amylose contents than the TX samples. The onset temperature (To), peak temperature (Tp), and enthalpy (DH) were measured for gelatinization and retrogradation. The onset temperature (To) and enthalpy (DH) of gelatinization were negatively correlated with amylose content both crop years except for some short and medium grain types. Amylose content correlated with retrogradation onset (To) and peak temperature (Tp) in 2003 but did not show this correlation in 2002. This study shows that amylose content is important factor related to molecular structure and thermal properties of different rice starch.

Session 18A, Carbohydrate: General
2:00 PM - 5:30 PM, Sunday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana