Causal relations among starch chain-length distributions, short-term retrogradation and cooked rice texture

Rice is cooked and consumed after a short-term cooling which is associated with the short-term starch retrogradation. The two most important textural attributes (hardness & stickiness) of 28 cooked rice varieties were investigated in this study, based on the causal relations between starch chain-length distributions (CLD) and short-term retrogradation properties. Size-exclusion chromatography (SEC) was used to characterize the starch CLD, while the setback viscosity (SBV) from rapid visco-analyzer and hydrogel firmness (HF) from textural profile analyzer were represented as characteristics of the short-term retrogradation process. Pearson correlations showed that regardless of amylose content, rice starches containing relatively shorter amylose molecules with short to long chains, and more amylopectin medium and long chains with the degree of polymerization (DP) > 69 can all promote the short-term retrogradation rate, resulting in cooked rice with a hard and non-sticky texture. It also suggests that both SBV and HF could be utilized to predict the final cooked rice texture such as the hardness and stickiness. Furthermore, rice starches with a relatively higher amount of medium chains but less short chains within the amylopectin molecules are related to a less sticky texture of the cooked rice. The current study provides important information for rice industry and breeding programs to develop new varieties with targeted eating qualities.