Investigating Hofmeister ions on rice starch gelatinization using simultaneous rheology and FTIR techniques combined with 2D correlation analysis

Abstract

Hofmeister ion-induced starch gelatinization was recognized as an efficient and simple method with low energy consumption. During the pasting process, starch was influenced by the valence of Na⁺, Mg²⁺, Cl⁻ and SO₄²⁻. The study investigated the macro functional effects of ions with different valences on starch swelling power (SP), pasting, and rheological properties, employing simultaneous rheological and FTIR techniques, along with 2D correlation spectroscopy (2D-COS). The findings revealed that Mg²⁺ and SO₄²⁻ much significantly inhibited SP of starch compared to Na⁺ and Cl⁻, resulting in reduction in pasting viscosity but an increase in pasting temperature. Small-amplitude oscillatory shear indicated that Mg²⁺ enhanced the dynamic modulus relative to Na⁺, while SO₄²⁻ exerted the opposite effect. In contrast, large-amplitude oscillatory shear experiments demonstrated that divalent ions exhibited greater stability than monovalent ions under high stress, as evidenced by the Lissajous curve. This observation aligned with the Hofmeister sequence. Notably, some starch granules containing Mg²⁺ and SO₄²⁻ retained polarized crosses, whereas the control and NaCl lost at 70 °C. For dynamic structure, high valence ions contributed to the structural ordering of water molecules, attenuated the hydration of starch, and exhibited weaker hydrogen bonding drive during the heating. 2D-COS further revealed that the C-O-H bond was particularly sensitive to bending vibrations during heating, and that divalent ions facilitated the formation of stabilized hydrogen bonding network with the hydroxyl groups of starch through water molecules in the amorphous region. These results offered valuable insights for the research and practical application of Hofmeister ion-induced gelatinization.