Study on the Water State and Distribution of Noodle Dough Using NMR and DSC
Y. M. WEI (1), R. Liu (1), L. Wu (1), Y. Zhang (1), B. Zhang (1). (1) Institute of Agro- Products Processing Science and Technology, CAAS, Beijing, China
Three wheat flours milled from 3 cultivars with different quality were used as materials, the noodle doughs were made by vacuum mixing at different vacuum degrees and mixing times with the moisture content of 35%. The state and distribution of water in sheeted dough were determined by <sup>1</sup>H nuclear magnetic resonance (NMR) and differential scanning calorimetric (DSC). The correlation between results of water state detected by the two techniques was also analyzed. The results showed that three spin-spin relaxation time constants, namely T<sub>21</sub>, T<sub>22</sub> and T<sub>23</sub>, were identified by the NMR experiments using the Carr-Purcell-Meiboom-Gill pulse sequences. The second categories of water (T<sub>22</sub>, 0.49～21.54 ms), represented the less tightly bound water, make up for almost 80% of the total moisture. Vacuum mixing at 0.06 MPa may promote the interaction of water and gluten protein, resulting in a decrease in the molecular mobility of water in noodle dough, retarding water migration and texture deterioration during storage, as evidenced by NMR, MRI and DSC. And non-vacuum or excessive vacuum (0.09 MPa) could either increase the molecular mobility of water in dough. For cultivar Jimai20 and Jimai22, the mobility of water was low in noodle dough mixed for 8 min, and deficiency (4 min) or excess (12 min) of mixing time could lead to significantly higher water mobility. While for cultivar Ningchun4 flour with low protein and gluten content, the water mobility was low in dough mixed for 4 min; with mixing time prolonging, the less mobile fraction of water decreased and the more mobile fraction increased. The results of water state in noodle dough measured by NMR and DSC were consistent. The change tendency for less tightly bound water detected by NMR was same to that for freezable water detected by DSC, and the change tendency for tightly bound water was same to that for non-freezable water.
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