Reheating-Induced Matrix Reorganisation Modulates the In Vitro Digestibility of a Retrograded Normal/High-Amylose Maize Starch Blend

Reheating alters residual molecular order and matrix architecture in retrograded starch, but these changes do not necessarily produce parallel changes in enzymic digestion. Gels of normal maize starch (NM), high-amylose maize starch (HM), and a 50/50 (w/w) NM/HM blend were stored at 4 °C for 7 d and steam-reheated to core temperatures of 50 or 80 °C. HM was less hydrolysed than NM at either temperature. At 300 min, hydrolysis reached 51.3% and 61.4% for HM at 50 and 80 °C, respectively, versus approximately 81% for NM. DSC and XRD showed that HM-containing gels retained more thermally stable ordered structures. The 50/50 blend responded differently: reheating to 80 °C lowered hydrolysis from 72.6% to 65.6% despite no corresponding increase in residual order. This inverse response coincided with lower pore area (12.8 to 4.6 m2/g), larger 4 V/A pore diameter (966 to 2623 nm), and a more continuous freeze-dried morphology, consistent with fewer fine mercury-accessible pores and internal interfaces. Overall, starch structural composition established the broad ranking of hydrolysis after reheating, whereas matrix reorganisation modified the relationship between residual order and enzymic susceptibility in the 50/50 blend. Residual molecular order alone was therefore insufficient to predict the digestion response after reheating.