Differences in starch structure, thermal properties, and texture characteristics of rice from main stem and tiller panicles

Abstract

The physicochemical properties of grains from main stem and tiller panicles are primarily responsible for the overall quality of rice. Thus, in this study, we report our findings on the starch structure, thermal properties, and cooked rice texture of main stem and tiller panicles from three Japonica rice varieties. Compared to main stem panicle, rice grains from tiller panicles had inferior processing and appearance qualities. Starch from tiller panicles had a lower apparent amylose content (AAC), lower average degree of polymerization (DP) and long-chain (DP ≥ 37) content in amylopectin, while the proportion of amylopectin fractions, fa (DP 6–12) and fb2 (DP 25–36), increased; this resulted in a higher swelling power, water solubility, lower gelatinization temperature and retrogradation. Although there was no change in starch crystal type between the main stem and tiller panicles, grains from tiller panicles had a higher relative crystallinity. While grains from tiller panicles had a lower hardness after cooking, stickiness conversely increased. Overall, the results suggest that grains from tiller particles, particularly late-initiated panicles, have lower grain processing and appearance qualities; however, the resultant physicochemical properties of the starch lead to improved thermal properties and higher quality of cooked rice. The results from this study will aid in efforts directed towards improving cooked rice quality.