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Study of Water in Dough Using Nuclear Magnetic Resonance

¹Department of Biosystems and Agricultural Engineering, University of Minnesota, 1390 Eckles Ave., St. Paul, MN 55108. ²Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Ave., St. Paul, MN 55108. ³Corresponding author. Phone: (612) 625-1710. Fax: (612) 624-3005. E-mail: ruanx001@tc.umn.edu ⁴Pillsbury Technology Center, 330 University Ave., Minneapolis, MN 55414.

The amount and state of water play an important role in the preparation and properties of wheat flour doughs and their products. A new method for presentation and analysis of relaxation time measurements of protons in dough is described in this article. This new method acknowledges a continuous probability distribution of protons having different relaxation times in heterogeneous systems such as dough, which is dramatically different from the conventional discrete methods that rely on prior assumptions of a number of discrete relaxation components. In the present study, pulsed proton nuclear magnetic resonance was used to study the relaxation characteristics of dough systems at moisture levels of 12–45%. The relaxation curves obtained using a 90-degree pulse (Onepulse) sequence and the Carr-Purcell-Meiboom-Gill pulse sequence were analyzed using a multiexponential discrete model and a continuum model. The discrete model produced three fractions of protons relaxing in three different time domains. The continuum model produced spectra of spin-spin relaxation time vs. amplitude, from which two to five peaks, depending on the moisture content, could be identified. At moisture contents of 23 and 35%, dramatic changes in relaxation time and amplitude were observed with both models. The continuum model provided additional information about the homogeneity of the morphology and physical state of the dough systems.