Physicochemical properties of hard wheat flour dough influenced by processing

Yong-Ro Kim, Purdue University

Abstract

Strong (sample 402) and weak (sample 401) hard wheat flour were selected and their physicochemical property changes were investigated as functions of mixing, resting and heating, especially in the aspects of rheological behavior, molecular mobility measured by NMR relaxation properties, and microstructure obtained by cry-SEM. Small deformation tests during heating agreed well with NMR relaxation times. During gelatinization, G* rapidly increased and phase angle decreased, which was correlated with the changes in three different components of T2 signal intensities and decreasing water mobility measured by NMR relaxation times. The onset temperature of the increase in G* and the decreasing rate of phase angle were different according to mixing time. Lower water mobility in the longer mixed dough, as indicated by shorter NMR relaxation times, was related to slower onset of gelatinization, which made the phase angle decrease more slowly during gelatinization. Small deformation tests showed that, during the initial resting period, G* and phase angle decreased for undermixed dough, whereas overmixed dough showed opposite trends. The G* for optimally mixed dough was stable during resting. This was more obvious for sample 402. The large deformation tests (stress growth curve) more clearly showed the differences among optimal, under and overmixed dough, and between strong and weak flour. The optimally mixed dough showed the highest peak stress and strain at the peak for both samples, and sample 402, compared to sample 401, showed much higher peak stress and stable strain at the peak during resting, suggesting that the stability of the strain at the peak, as well as the absolute value of the peak stress and the strain at the peak must be considered to evaluate the strength and the optimum mixing time of hard wheat flour dough. The initial stress in the stress growth curve had similar trends as G* in small deformation. Decreased water mobility during resting, as indicated by decreasing NMR relaxation times, was possibly attributed to increasing molecular interactions caused by prolonged hydration, which may be related to an increase in soluble compounds observed by cryo-SEM.

Degree

Ph.D.

Advisors

Cornillon, Purdue University.

Subject Area

Food science

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