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Ingredient Characterization and Hardening of High-Protein Food Bars: an NMR State Diagram Approach

¹Department of Bioproducts and Biosystems Engineering and Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN. ²Solae, St. Louis, MO. ³MOE Key Laboratory of Food Science, Nanchang University. ⁴Yangtze Scholar Distinguished Guest Professor, Nanchang University, and Professor, University of Minnesota, St. Paul, MN 55108. ⁵Corresponding author. E-mail: ruanx001@umn.edu

A second-degree simplex lattice mixture design was used to study the effects of soy, dairy, and soy-dairy blends of powdered proteins in three high-protein food bar models (sugar syrup, polyol syrup, and reduced-sugar syrup). Overall protein performance was evaluated based on textural changes during accelerated storage, bar integrity, and dough stickiness and was a strong function of the syrup model used (R² = 92.33%). Nuclear magnetic resonance (NMR) relaxometry was used to measure relaxation times (T₂, T₂*, and T₁) at 20°C and to create state diagrams (temperature, T₂* curves) for the individual powdered proteins and syrups over a temperature range of –35 to 50°C. Increases in relaxation times for powdered protein samples were indicative of better overall protein performance, whereas increases in relaxation times for syrup samples were associated with increases in moisture content and concentration of polyols. Increases in water activity (a_w) of the bars during accelerated storage suggested an elevated rate of hardening for polyol-containing bars that was caused by a decrease in the amount of water capable of acting as a plasticizer in the product. Proteins were separated into four types (A, B, C, and D) based on the shape of the state diagram curve. Predicted to be the most stable, type D proteins (SUPRO 313 and SUPRO 430) offered the most versatility and, when blended with other proteins, often induced synergistic softening effects in the nutrition bars which led to an extended product shelf life. The NMR state diagram technique appears to be a valuable tool for predicting overall performance of powdered proteins in sugar-, polyol-, and reduced-sugar syrup based food bars.