Hydroxytyrosol-based natural deep eutectic solvents (NADESs): Hydrogen bond network formation, anti-freezing properties, and the regulation of starch in freeze-thaw systems.

This study employed hydroxytyrosol as a hydrogen donor to construct five natural deep eutectic solvent (NADESs) systems. A systematic investigation was conducted on the changes of functional groups within the NADESs, their freezing point depression, low-temperature rheological behavior, ice recrystallization inhibition capacity, and their applications in freeze-thaw starch systems. The hydroxyl stretching peak (3700-3000 cm-1) showed significant enhancement and broadening, indicating a hydrogen bond network formation. The freezing points of 20% NADESs ranged from -24.47 °C to -17.43 °C, demonstrating excellent antifreeze properties. As the temperature decreased, the viscosity of the NADESs increased, and the motion of 1H protons became "restricted." Different NADESs significantly altered ice crystal morphology and size. Treatment with NADESs markedly enhanced the water-holding capacity of starch. During heating, HT-LI interacted with the starch gel network, significantly reducing the content of rapidly digestible starch while increasing resistant starch content.