Changes of water status and proportion during wheat flour dough mixing

The purpose of this study was to investigate the changes of water state, proportion and structure during dough mixing and resting in order to establish a relationship between those changes and dough quality properties during dough mixing and resting using Farinograph and Extensograph, which helps to understand the dough development mechanism for flour with different gluten strength. Two wheat varieties (Ningchun4 and Shiluan02-1) with different gluten strength were selected as experimental materials. Water state (T2) and relative proportion (A2) in dough were investigated at different time during dough mixing, and dough resting and stretching by Low-Field Nuclear Magnetic Resonance (LF-NMR). Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance micro (FTIR-ATR) was used to analyze the distribution of starch and protein and the structural changes of protein at different sampling points during the dough mixing. The results showed that water in raw flour were mainly less tightly bound water (T22). While flour was mixed with water in Farinograph to dough development time, three types of water, tightly bound water (T21), less tightly bound water (T22) and free water (T23) were found in the dough. With longer mixing time, the relative proportion of tightly bound water (A21) in Yongliang 4 significantly decreased; transverse relaxation time of tightly bound water (T21) in Shiluan 02-1 did not show by the end of the mixing, transverse relaxation time of less tightly bound water (T22) was significantly prolonged, while the relative proportion of free water (A23) was significantly increased (P<0.05). Water states and proportion for dough mixed with salt or without salt showed no significant changes during dough resting and stretching (P<0.05). After resting, the transverse relaxation time of free water (T23) in Yongliang4 was significantly shortened (P<0.05). The network of dough with higher gluten content was more compact in dough structure. The changes of the relaxation time and proportion of tightly bound water and less tightly bound water during mixing were related to the gluten content and strength. During dough mixing, the relaxation time of strongly bound water (T21), extended or disappeared by the end of mixing. The relative proportion of free water (A23) increased significantly. Strong gluten wheat flour had a longer retention time of strongly bound water. The changes of relaxation time and ratio of strongly bound water and weakly bound water were related to the gluten content and strength. The essences of flour quality characterized by Farinograph were the change of gluten network structure and the tolerance degree of kneading during dough mixing. The changes of water binding state and proportion during dough formation could be effectively characterized by LF-NMR technology. The results can provide some theoretical basis for the selection and optimization of mixing processing. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.