Effect of Freeze-Thaw Cycles at Different Temperatures on the Properties of Gluten Proteins in Unfermented Dough

The effects of freeze-thaw cycles (from 1 to 5 cycles) at different temperatures (-6 °C, -12 °C, -18 °C, -24 °C, and -30 °C) on the properties of gluten isolated from dough were investigated. The results showed that after the same number of freeze-thaw cycle, the water-holding capacity of gluten protein was higher at lower temperatures, and the viscoelasticity and bound water content increased slightly with decreasing temperature. The microstructure of gluten protein was more uniform and relatively complete at -30 °C and -24 °C compared with other temperature conditions. Lower temperatures led to a significant decrease in the proportion of α-helices and β-turns and a notable increase in that of β-sheets. At the same temperature, the water-holding capacity, bound water content and viscoelasticity decreased with increasing number of freeze-thaw cycles. Compared with the first freeze-thaw cycle (F1), the cavity in the gluten microstructure of the fifth freeze-thaw cycle (F5) was larger and even exhibited fracture. In short, the increase in the number of freeze-thaw cycles damages the properties of gluten protein, and lower temperatures are more conducive to maintaining the stability of gluten properties.