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

摘要

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 4min: T-2b (0.1-1ms) corresponded to rigid and exchangeable protons; T-22 (9-21ms) was associated with the water protons in small and large meshes of the dough microstructure; T-23 (69-300ms) 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 6min, forming T-21 (1-3ms) fraction. The gelatinization effect was strengthened up to 8min and supplied a more mobile microenvironment, resulting in the increase of T-21, A(21) and M-21. However, the gelatinization process ended at 8min, bringing about the stabilization of T-21, A(21) and M-21 until 25min. T-22 fraction accounted for the largest proportion during all the steaming process. All variation trends on structural properties of CNSB and T-2 relaxation parameters including T-i, A(i) (relative intensity of T-i), and M-i (population abundance of T-i) indicated that 6 and 8min were the two transitions. The gluten matrix began to be disrupted at 6min and was quite damaged up to 8min by scanning electron microscopy. The peaks at 15 degrees, 18 degrees, 20 degrees, and 23 degrees in X-ray diffraction patterns appeared in the first 6min but were lost up to 8, 10, and 25min.