Effect of hydroxypropyl starch on the multiscale structure and pasting properties of starch in γ-irradiated fresh rice noodles

Fresh rice noodles (FRNs) are widely consumed starch based foods whose quality and shelf life depend strongly on the structural stability of the starch matrix. γ-Irradiation can effectively extend the shelf life of FRNs but induces starch depolymerization, altering starch structure and functionality. This study investigated the effects of hydroxypropyl starch (HPS) incorporation on the molecular characteristics, ordered structure, and thermal and pasting properties of starch in γ-irradiated FRNs. The results showed that 6% HPS incorporation produced the most balanced structural and functional characteristics. Overall, HPS increased molecular size parameters, apparent α-1,6 linkage ratio, short range molecular order, relative crystallinity, and peak viscosity, while decreasing the long B3 chains proportion and gelatinization enthalpy. Correlation analysis showed that A chains were positively correlated with short-range order, relative crystallinity, and swelling power, and negatively correlated with peak viscosity, whereas B3 chains showed the opposite trend, suggesting that the superior pasting behavior at 6% HPS was associated with a more balanced amylopectin chain architecture. HPS incorporation altered the relative amylopectin chain length distribution of the starch system, with 6% addition increasing the proportion of A and B1 chains relative to B2 and B3 chains, thereby favoring granule swelling and paste viscosity development. However, excessive HPS addition over-enriched short chains and weakened paste stability. These findings clarify the structure–function relationships in γ-irradiated starch systems and provide a scientific basis for optimizing the quality of irradiated rice-based products.