Steaming time effects on the moisture migration and structural properties of Chinese Northern-style steamed bread

The aim of this study was to investigate the steaming time effects on proton transverse relaxation behavior with low field 1H nuclear magnetic resonance and structural properties of Chinese Northern-style steamed bread (CNSB). Three proton populations could be distinguished at the first 4 min: T2b (0.1–1 ms) corresponded to rigid and exchangeable protons; T22 (9–21 ms) was associated with the water protons in small and large meshes of the dough microstructure; T23 (69–300 ms) was assigned to the water protons on the surface of samples. The starch gelatinization began and the water turned into the integral part of the biopolymer at 6 min, forming T21 (1–3 ms) fraction. The gelatinization effect was strengthened up to 8 min and supplied a more mobile microenvironment, resulting in the increase of T21, A21 and M21. However, the gelatinization process ended at 8 min, bringing about the stabilization of T21, A21 and M21 until 25 min. T22 fraction accounted for the largest proportion during all the steaming process. All variation trends on structural properties of CNSB and T2 relaxation parameters including Ti, Ai (relative intensity of Ti), and Mi (population abundance of Ti) indicated that 6 and 8 min were the two transitions. The gluten matrix began to be disrupted at 6 min and was quite damaged up to 8 min by scanning electron microscopy. The peaks at 15°, 18°, 20°, and 23° in X-ray diffraction patterns appeared in the first 6 min but were lost up to 8, 10, and 25 min.