Starch structures of high amylose progeny (IR5 x IR8) in relation to differences in gel consistency

Amylose is the key determinant of the cooking and eating quality of cooked rice. High amylose rice are characterized by flaky, dry, hard, and separated cooked grains while low amylose rices are sticky, soft and glossy. However, rice varieties with similar amylose content can have very different functional properties. Gel consistency (GC) test discriminate high amylose rices in terms of textural quality after cooling. Previous studies have shown that the fine structure of starch significantly influences rice characteristics like gelatinization and pasting properties. It can also be assumed that the structure of rice starch at its various levels could explain the observed variation in gel consistency among high amylose varieties. Thus, this study was conducted to evaluate starch physicochemical properties and structure of progeny derived from a cross between two high amylose varieties with different gel consistency. Physicochemical analyses indicated that GC, gelatinization temperature (GT) and CTsub n repeats varied in all high amylose progeny evaluated. Soft GC progeny were predominantly higher than hard and medium GC. GT of the progeny was classified into high and low. CT repeats analyses revealed that majority of hard GC (91%) carried CT11 and 69% of soft GC inherited CT10 allele. Pasting properties of the progeny showed significant differences on the mean pasting viscosities of the progeny. Moreover, GC correlated significantly with pasting viscosities. Hard GC had higher properties of hot-water insoluble starch and lower amounts of hot-water soluble starch, whereas the opposite was observed for the soft GC progeny. GC correlated positively and negatively with hot-water insoluble and soluble fractions, respectively. Significant differences were observed on the long chains insoluble amylopectin (DP 35-100) of the progeny. This study also confirmed that the proportions of hot-water soluble and hot-water insoluble starch fractions contribute to the differences in the cooked rice texture of high amylose rices.