In Situ Characterization and Analysis of Molecular Structure of Gluten Proteins and Moisture Distribution in Dough during Freezing

In this experiment, confocal laser Raman spectroscopy and low-field nuclear magnetic resonance imaging were used to in situ characterize and analyze the molecular structure changes of gluten proteins and water migration during the freezing process of dough. The results showed that the disulfide bond configuration of gluten proteins in dough with 45% water content was the most stable, and the relative percentage of the gauche-gauche-gauche (g-g-g) configuration decreased by 4.33% after freezing. During the freezing process, the relatively stable g-g-g configuration was transformed to unstable gauche-gauche-trans (g-g-t) and trans-gauche-trans (t-g-t) configuration. The ratio between the intensities of the absorption peaks at 740 and 1004 cm^-1 (I_740/1004) in the Raman spectrum, which represents the microenvironment around the side chains of amino acids, reached the maximum when 45% water was added to dough, and decreased continuously during freezing. At the end of freeze, there was no significant difference in the relative percentage of α-helix in the secondary structure of gluten proteins with water addition, but the relative percentage of α-helix decreased by 3.63% during the freezing process. The results of water distribution and migration showed that the quality deterioration caused by ice crystal growth appeared earlier with the increase of water addition during the freezing process of dough. The results of this study will help to clarify the mechanism of dough quality deterioration during freezing.