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.

Differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (NMR) and in situ Raman spectroscopy were used to explore the cryoprotective effect of enzymatic hydrolysates of flaxseed meal proteins obtained at different hydrolysis times on dough. The results showed that the thermal hysteresis activity of the 60 min hydrolysate, with a 13.62% degree of hydrolysis (DH), was highest (0.83 ℃), and the ice recrystallization inhibitory activity was also highest, minimizing the proportion of large ice crystals. It was found that addition of the hydrolysate had the most significant cryoprotective effect on dough. Compared with the control group, the proportion of strongly bound water in dough increased by 13.2%, and the proportions of weakly bound water and free water decreased by 0.7% and 7.9%, respectively. The maximum fermentation height, the final height and the onset time of CO₂ leakage increased by 18.5%, 24.4% and 34.4%, respectively. Protein structure analysis showed that the relative α-helix content of gluten proteins in dough with the hydrolysate was highest and increased by 35.3% compared with the control group, and the relative random coil content decreased by 28.9%. The intensity (I₇₆₀) of tryptophan band at 760 cm^-1 increased by 282.3%, and the ratio (I₈₅₀/I₈₃₀) between the intensities of tyrosine bands at 850 and 830 cm^-1 decreased by 59.6%. The relative contents of disulfide bond configurations g-g-g and g-g-t were increased by 8.8% and 9.8%, respectively. In conclusion, enzymatic hydrolysates of flaxseed meal proteins improved the water-holding capacity of dough, shortened dough proofing time, and weakened the damage of ice crystals to the network structure of dough, and the effect of the hydrolysate with DH of 13.62% was most pronounced.

Magnetic fields can improve the quality of foods by influencing the arrangement of water molecules, thus altering the distribution of water in foods. In this study, dough was fermented at magnetic field strengths of 0, 0.5, 1.0, 1.5, and 2.0 mT for 1 h. The effect of magnetic field treatment on the fermentation characteristics, moisture distribution, and protein molecular structure of dough was investigated by low-field nuclear magnetic resonance (NMR) and in situ Raman spectroscopy, with a view to providing a theoretical basis for the development of high-quality Chinese dough-based foods. The results showed that the fermentability of dough tended to increase first and then decrease as the magnetic field strength increased, and the most significant effect on the fermentability was observed at a magnetic field strength of 1.5 mT. The specific volume of steamed bread initially increased and then decreased. When the magnetic field strength was 1.0 mT, the specific volume was 2.24 mL/g. The hardness, stickiness, and chewiness showed a trend of initially decreasing and then increasing, but there was no obvious change in the elasticity, cohesiveness or resilience. The contents of strongly bound water and free water initially decreased and then increased, whereas the opposite trend was observed for weakly bound water. The effect of 1.0 mT magnetic field strength on the water distribution was most significant. The relative content of α-helix increased first and then declined, while the reverse trend was observed for random coil. At a magnetic field strength of 0.5 mT, the relative content of α-helix was the highest (54%) and the relative content of random coil was lowest (21%). Proper magnetic field treatment could increase the fermentability of dough, the specific volume and textural properties of steamed bread, accelerate the water distribution in dough and improve the stability of the gluten network. In conclusion, magnetic field treatment could improve the fermentability of dough and the textural properties of steamed bread by improving the distribution of water, increasing the moisture uniformity, and changing the molecular structure of gluten proteins in dough.