Effect of heat treatment on physical, structural, thermal and morphological characteristics of zein in ethanol-water solution

• Thermal treatment modified the size distribution and secondary structure of zein.
• Denaturation of zein was dependent on both of the heating temperature and the time.
• The morphology of zein was changed to the dumbbell-like shape after heat treatment.
• A three-step mechanism was proposed, including folding, unfolding and aggregating.

The effects of different heat-treated temperatures (75, 85 and 95 °C) and times (15, 30 and 45 min) on physical, structural, thermal and morphological characteristics of zein in ethanol-water solution were investigated. The result of particle size distribution suggested that the volume percentage of small zein colloidal nanoparticles (d < 200 nm) was increased from 87.9% to 98.2% after heat treatment at 75 °C for 15 min. Both of the fluorescence intensity and ultraviolet absorption of zein approached to the maximum value when zein solution was heated at 95 °C for 30 min. Differential scanning calorimetry thermograms implied that heat treatment enhanced the thermal stability of zein with the rise of denaturation temperature. The secondary structure changes of zein induced by heat treatment might be explained by a potential mechanism of three-step process, including partial protein folding, a larger extent unfolding and the formation of partial protein aggregates. In addition, heat treatment significantly modified the morphology of zein from the typical sphericity to distinct oval at 75 and 85 °C, as well as obvious dumbbell-like shape at 95 °C for 30 min.

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