Self-assembly of ratooning rice starch nanoparticles under debranching treatment and their effects on the texture of rice-flour gels.

Starch nanoparticles (SNPs) have a high specific surface area, small particle size, and good biocompatibility. As safe and effective texturizing ingredients, they have attracted attention for improving the texture of starch-based gel foods. In this study, SNPs were prepared by pullulanase debranching and self-assembly of ratooning rice starch (RRS), and their structural and physicochemical properties and effects on rice-flour gel texture were evaluated. As the debranching time increased from 0 to 8 h, the apparent amylose content of the debranched starch increased from 23.11% for native ratooning rice starch to 42.89%, whereas the degree of branching decreased from 8.57% to 3.04%. When the debranching time exceeded 0.5 h, the starch chains self-assembled through hydrogen bonding into nearly spherical nanoparticles with a coexisting A-type and V-type structure. The crystallinity and the R1047/1022 ratio increased up to 4 h of debranching, reaching 36.98% and 0.577 for SNPs compared with 0.504 for RRS, and then decreased slightly with further debranching. The resistant starch content increased from 21.20% to 45.42%, and the onset melting temperature increased from 68.69 to 83.20 °C, indicating enhanced resistance to digestion and improved thermal stability. When the SNPs were added at 10% of the rice-flour weight, scanning electron microscopy showed that the gel developed thickened pore walls, and its hardness and chewiness increased from 17.11 g and 9.00 for the control to 42.43 g and 17.76, respectively. These results demonstrate the potential application of SNPs in starch-based gel foods.