29-1 |
Probing water dynamics in starch, gluten, and dough systems using time-domain NMR spectroscopy |
Y. KOU1, E. W. Ross2, and I. A. Taub2. (1) General Mills, Inc., 330 University Avenue S.E., M.S. 9941, Minneapolis, MN 55414, (2) U.S. Army Natick Soldier Center, Natick, MA 01760-5018 Most food materials are complex in composition, heterogeneous in structure, and nonuniform in reactivity. The stability of a food matrix depends strongly on its microstructure, local viscosity, and associated molecular mobility. Moisture content, constituents’ concentration, and temperature are key factors determining the structure and distribution of microstructural domains in an amorphous food matrix and controlling local viscosity and molecular mobility. The objective was to assess the influence of moisture content, constituents’ concentration, and temperature on the structure, water dynamics, and distribution of microstructural domains in starch, gluten, and dough systems. Samples with different moisture contents and starch or gluten levels were examined at different temperatures. A suite of NMR techniques was used to measure spin-spin relaxation times (T2) and spin-lattice relaxation times (T1) of protons in water. A mathematical model was developed to convert relaxation data into distinct distributions of relaxation times. T2 and T1 values were used as indicators of either water mobility or the state of water. Analysis of T2 data discerned different proton spin environments. The T2 values varied depending on the moisture and solid contents, reflecting at least three distinct populations of associated water molecules. T1 values also varied and could be correlated with the Tg of samples. Moisture content, temperature, and their effect on protein structure significantly influenced proton relaxation times and their distinct distributions. The changes in these distributions relate to changes in molecular dynamics and matrix structure and reflect changes in the distribution of microstructural domains. These results, obtained with a precise and powerful method for monitoring the various states of water in foods, provide insight into the way water binds to or associates with the constituents. Understanding microdomains and water binding in relation to structural and textural effects also provides a basis for improving food quality and extending shelf life.
Session 29, Carbohydrate
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