In Situ small-angle X-ray scattering study of the gelatinization mechanism of maize starches with varying amylose content

The gelatinization behavior of starch is critically influenced by its amylose content (AC), yet the underlying mechanisms at the lamellar level remains incompletely understood, especially for starches with high AC (>50 %). In this study, we investigated the real-time structural evolution of maize starches with a wide range of AC (3.2 %–79.6 %) during gelatinization using in situ small-angle X-ray scattering (SAXS). Upon heating from 40 °C to 90 °C: (1) the lamellar thickening occurred initially but was followed by rapid disruption at low AC (3.2 % and 26.3 %); (2) the lamellar structure remained stable with minimal changes in lamellar peak intensity and lamellar thickness at high AC (58.6 %), (3) the electron density contrast between crystalline and amorphous phases increased, and both lamellar types exhibited thickening at very high AC (71.2 % and 79.6 %). Furthermore, the correlation length (ξ) decreased with increasing AC up to 60 %, suggesting a more compact viscoelastic structure due to greater chain release and entanglement. Our data provide evidence that maize starch with about 60 % amylose has especially stable crystalline lamellae. This stability likely explains why starches with moderately high amylose content tend to gelatinize at higher temperatures.