Hydrothermal treatment and shear synergistically modulate the starch structural and pasting properties

The change in particle surface properties can influence the hydrothermal effect of starch. To elucidate this, the synergistic effect of different hydrothermal temperatures (50 and 60 °C) and shear actions (150 and 300 rpm) on structures and pasting properties of waxy maize starch was investigated. Shear action during hydrothermal treatment significantly altered starch morphology, with cracks and erosion observed at 50 °C and more pronounced surface erosion at 60 °C. Hydrothermal treatment increased the thickness of long-range periodicity (d_L) and crystalline lamellae (dc) in the semi-crystalline lamellae. Shear action decreased d_L and dc at 50 °C but increased them at 60 °C. Shear action applied at 50 °C induced surface cracks on starch granules, promoting water plasticization and formation of the more packed crystalline structure. In contrast, shear action combined with 60 °C led to surface gelatinization of starch, facilitating water absorption into the granules, lamellar swelling and water absorption capacity. However, significant reduction in pasting temperature, peak viscosity, breakdown viscosity, and setback viscosity were observed for all shear and hydrothermally treated starches. Pearson's correlation analysis revealed no significant correlation between short-range order of starch and its pasting properties. Nevertheless, positive correlation was observed for the thickness of semi-crystalline/crystalline lamellae and pasting properties, moreover, a negative correlation existed between the thickness of semi-crystalline/crystalline lamellae and peak viscosity, breakdown viscosity, and setback viscosity. Thus, it was concluded that shear action modulated starch pasting properties mostly via cracks or erosion on starch granules and then alters the lamellar structures through hydrothermal treatment.