Impact of long-term storage on multi-scale structures and physicochemical properties of starch isolated from rice grains

Rice short-term (less than 12 months) storage significantly affected starch structures and physicochemical properties, and in turn, influenced rice functionalities. However, effects of rice long-term (more than 12 months) storage on starch structures and functionalities have been not resolved yet. This study revealed the changes in structures and physicochemical properties of starch during rice long-term storage (12–36 months). Rice storage resulted in degradation of starch molecules, which increased amylose content and reduced the content of long branch-chains of amylopectin, double helices, short-range ordered structures, crystalline structures, and lamellar ordering degree along with apparent erosion of starch granules. Those structural changes significantly increased starch thermostability, favored starch short-term reassociation, and promoted starch enzymatic digestion. Comparing with the short-term storage (1 year of storage), the long-term storage (2 or 3 years of storage) yielded a more serious degradation on starch multi-scale structures, and in turn, resulted in a higher thermostability, and better-defined gel structures and higher starch digestion extent after cooking and cooling. Compared with the short-term aged rice, the long-term aged rice is a better candidate to prepare rice-based gel-like foods such as noodles. This study provided a promising pathway to control structures and physicochemical properties of rice starch and even rice-based foods via simply controlling rice-storage time.