Four stages of multi-scale structural changes in rice starch during the entire high hydrostatic pressure treatment

The degree of gelatinization (DG) was used as the variable to describe changes in the multi-scale structure of rice starch during the entire high hydrostatic pressure treatment (HHP-treatment), and four stages were identified. (1) Energy accumulation (100-400 MPa, DG<10%): water molecules were pressed into the amorphous lamellae and starch continued to receive energy with the increasing pressure, which resulted in the loosening of hier-archical structures. (2) Disruption of low-level structures (400-600 MPa, 10% < DG<30%): more water mole-cules entered the crystalline lamellae, leading to the disruption of the molecular and helical structures. The lowest Mw, Mn and Rz and the highest rho values were observed and the content of helical structure decreased significantly. (3) Destruction of high-level structures (400-600 MPa, 30% < DG<50%): both the entry of water molecules and the alteration of low-level structures reduced the amount of short-ordered structure and crys-talline structure, as well as the thickness of lamellar structure. The starch granules were deformed, and the particle size increased significantly. (4) Disintegration of all hierarchical structures (400-600 MPa, 50% < DG<100%): all hierarchical starch structures were progressively destroyed and the "broken gel fragments" were formed. This study reveals four stages of structural changes in the HHP-treated rice starch, which provides theoretical guidance for obtaining modified starch with different properties under the HHP-treatment.