The effect of addition of mixtures of α-amylase and transglutaminase (TGase) on the quality, starch multiscale structure and physicochemical properties of frozen dough and the quality of steamed bread made with starch extracted from frozen dough. The results showed that enzymatic treatment decreased the content of freezable water in the dough system (13.84%-11.56%) and induced the formation of a starch-protein interfacial interlocking structure, inhibiting phase separation caused by freeze-thaw cycles. The double-helix content (36.2%-30.5%) and short-range order (R_{1 045/1 022} = 0.93-0.79) of starch decreased, and the amorphous region content increased (59.5%-60.1%), leading to a decrease in the gelatinization temperature and gelatinization enthalpy (ΔH), an increase in peak viscosity and rheological properties, and higher elasticity and viscosity. In addition, repeated freeze and thaw of starch in dough decreased the specific volume of steamed bread (2.03-1.78 mL/g), and significantly increased the hardness and chewiness. Enzymatic treatment of starch in dough improved the specific volume and texture properties of steamed bread. The specific volume and texture properties of steamed bread made with starch from frozen dough with 900 U/kg of α-amylase were closer to the level of the unfrozen control group, the specific volume increased from 1.78 to 1.95 mL/g, and the hardness decreased from 1281.38 to 920.67 g. In conclusion, enzymatic treatment can improve the processing quality of frozen dough by affecting the structure and physicochemical properties of starch.

In order to reveal the protective mechanism of hydrocolloid on wheat dough gluten during freezing, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to investigate the secondary structure, microstructure, disulfide bond content and water-binding capacity of gluten obtained from frozen-thawed wheat dough added with different amounts of flaxseed gum (FG) or Artemisia sphaerocephala Krasch. gum (ASKG). Results showed that freezing-thawing treatment destroyed the ordered network structure of gluten, while FG and ASKG could crosslink with the gluten protein network structure to form a stable cross-linked structure. Upon the addition of FG or ASKG at 0.4%, the gluten network structure was most uniform and dense. The addition of FG and ASKG increased the content of disulfide bond and the relative content of α-helix in gluten, making the gluten structure more stable under repeated freeze-thaw cycles. In addition, the addition of FG and ASKG reduced the surface hydrophobicity and consequently led to an increase in the waterbinding capacity of wheat gluten. The highest water-binding capacity was obtained at an addition level of 0.4% for both FG and ASKG, 1.46 and 1.43 times higher than that of the control group without added hydrocolloid undergoing repeated freezethaw cycles, respectively. All these results showed that FG and ASKG could interact with gluten to form a stable cross-linked structure, thereby enhancing the water binding capacity of gluten protein and exerting a cryoprotective effect on it.