Quality deterioration of frozen dough bread during terminal freezing and thawing: From the insight of moisture and starch properties

The temperature at the terminal cold chain changes sharply, which severely affects the quality of frozen dough products. This study focused on the variations of texture, moisture distribution, starch-ordered structure, and microstructure of frozen dough bread during terminal freeze-thaw (TFT) treatment. The specific volume of the frozen dough bread after TFT-6 decreased by 45% and obvious holes appeared on the surface. Meanwhile, TFT-6 (TFT with 6 cycles) increased the bread hardness by 205 gf and chewiness by 190 gf compared to the frozen storage (FS). The maximum fermentation height of dough bread under the TFT-6 decreased by 21.19%, the gas holding rate decreased by 23%, and proportion of bound water (A21) decreased by 36.88% compared to the fresh dough bread (p<0.05). Then, the starch was reordered after TFT treatment, compared with the fresh dough bread, the relative crystallinity of TFT-6 treated bread increased by 8.7% and the R1047/1022 (proportional relationship between ordered and amorphous structures) increased by 89.33%, while scanning electron microscope (SEM) images illustrated that the internal structure of the TFT-treated bread showed obvious loose and porosity characteristics. TFT negatively affected frozen dough breads, such as bread hardening, larger empty spaces, and reduced volume, which was related to water migration and deterioration of starch structure. The above experiments provided a theoretical basis for revealing the effect of TFT in production applications.