Native starch chain-length distributions shape structural reorganization and functionality in rice–chestnut flour systems following ultra-high-pressure homogenization pretreatment and spray drying

Abstract The effects of ultra-high-pressure homogenization (UHPH) pretreatment on starch structural reorganization during spray drying (SD) and the consequences of these structural modifications on hydration and viscoelastic behaviour remain unclear. Rice flour, chestnut flour, and rice–chestnut blends (10%, 20%, and 30% chestnut substitution) were spray-dried with or without UHPH pretreatment at 400 MPa. In rice flour, combined UHPH–SD treatment shifted amylopectin-region size-exclusion chromatography (SEC) peaks to a lower apparent degree of polymerization (DP), accompanied by higher apparent relative crystallinity and a numerically greater gelatinization enthalpy than SD alone (39.6% vs. 36.4% and 10.0 J/g vs. 8.7 J/g). Chestnut starch contained a larger long amylopectin-chain (AP2) fraction and higher amylose-region fractions, together with more uniformly thermostable ordered structure. Upon UHPH–SD treatment, its SEC peaks shifted to larger apparent chain sizes, whereas its relative crystallinity and gelatinization enthalpy remained largely unchanged, showing that the SEC changes did not parallel changes in double-helical or crystalline organization. These contrasting responses were consistent with the native chain distribution and thermal organization modulating glucan-chain mobility and thereby the extent of structural rearrangement during UHPH–SD. In the 20% blend, UHPH reduced compact aggregation and increased swelling, yet the resulting dispersion developed the lowest peak storage modulus during heating. Thus, native starch structural organization shaped how UHPH redirected reorganization during SD, while blend-specific particle organization modified the hydration performance and elastic-network development. These findings provide a basis for UHPH parameter optimization and chestnut flour proportion selection when designing composite powders with targeted hydration and heating-induced rheological properties.