Yong Yang, Shuaishuai Zheng, Zhen Li, Zhili Pan, Zhongmin Huang, Jianzhong Zhao, Zhilu Ai
Three types of freezing methods, namely, spiral tunnel freezing method (SF), cryogenic refrigerator freezing method (RF) and liquid nitrogen spray freezing method (LF), were applied to frozen unfermented dough. The particle size distribution and SEM results showed freezing methods reduced the average particle size of starch granules and destroyed the surface microstructure, especially RF, and the damaged starch content and swelling power of starch after treatment increased. Gelatinization and pasting properties of starches changed to varying degrees, indicating freezing methods caused the internal rearrangement of starch molecules. This view could also be inferred from X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FT-IR) data. The relative crystallinity (35.51%–38.56%) and the R1047/1022 (0.562–0.590) were increased, compared with the control (32.44%, 0.559, respectively). Meanwhile, freezing treatment improved the digestibility of starch by promoting the combination of enzymes and starch, especially RF. Larger ice crystals formed by RF with slower freezing rate produced larger damage to starch structure, more likely to promote the binding with enzymes. LF with faster freezing rate had less effect on the starch composition than RF and SF with slower freezing rate. The data obtained clarified the influence of freezing methods on the structure and properties of starch in a yeast-free dough system, and enriched the knowledge regarding the effect of freezing technology on food components.
Freezing methods, Frozen unfermented dough, Starch digestibility, Ordered structure, Relative crystallinity