Determining elasticity of dough in the micro-doughLAB

Jennifer M.C. Dang and Mark L. Bason
Perten Instruments, Australia

The micro-doughLAB’s novel torque measurement system and high speed data acquisition enables the instrument to perform stress-relaxation (stress-decay) tests. In these tests, the mixing blades are forced to dead-stop, while still measuring the residual torque as the dough relaxes. The relaxation of the dough gives an indication of its elasticity, allowing evaluation of both the viscous and elastic properties of dough throughout a single mixing test. Generally, the more elastic a material, the slower the decay will proceed (Fig. 1, Steffe, 1996).


Figure 1. Stress-relaxation (stress-decay) curves. Source: Steffe, 1996.

Stress-relaxation tests

Blade positioning

For elasticity experiments, the blade position is controlled and set in the ‘home’ position using the ‘Set Home Position’ wizard in the software (DLW).

Test configuration

A strong and a weak flour were obtained from local sources. The optimum water absorption (WA) and dough development time (DDT) were predetermined for elasticity tests on the micro-doughLAB. In the elasticity configuration mixing was stopped at two stages during the test: peak consistency and after 18.3 minutes of mixing (overmixed dough). At each stage, three replicate dead-stop steps were introduced. Torque data was obtained at high speed and averaged over the three dead-stop intervals to monitor the viscoelastic properties of the optimum and overmixed dough.

Analysis of stress-relaxation curves

The area under the stress-relaxation curve gives an indication of the elasticity of the dough.

Generally, the more elastic the dough, the slower the decay, and the larger the area under the curve. The software (DLW) calculated the average area under the triplicate stress-decay curves for optimum and overmixed dough (Table 1, Fig. 3).

Table 1. Dead-stop times and duration for stress-relaxation tests of strong and weak flours.

Parameter

Strong

Weak

Optimum dead-stop time point (min.)

8.0

3.0

Overmixed dead-stop time point (min.)

18.3

18.3

Dead-stop duration (min.)

0.3

0.3

Number of dead-stops per stage

3

3

The baseline corrected area under the torque curve (Fig. 4) is calculated as:

Baseline corrected area = Total area under torque curve – Baseline Area


Figure 3. Stress-relaxation curves of strong (blue) and weak (red) flours, in duplicate, showing dead-stops (3 replicates at 20-s intervals) for optimum and overmixed dough. The boxed area is shown in more detail in Fig. 4.


Figure 4. Detailed stress-relaxation curve, from Fig. 3, of the strong flour sample, showing triplicate dead-stop steps at optimum consistency.

Results

The micro-doughLAB differentiated between the strong and weak flours (Fig. 3, Table 2). The strong flour showed larger areas under the stress-relaxation curve (slower stress-decay) for both optimum and overmixed dough compared to the weak flour (Table 2). This indicates that the strong flour was stronger and more elastic than the weak flour. For each type of flour, the overmixed dough had a smaller area (faster decay) than the dough at peak consistency, indicating that overmixing dough had reduced elasticity.

Table 2. Area under stress-relaxation curves of strong and weak flours.

Parameter

Test

Strong

Weak

Average optimum dead-stop area in mNm.s (gm2s-1)

1

34.4

25.5

Average optimum dead-stop area in mNm.s (gm2s-1)

2

31.1

26.5

Mean

 

32.8

26.0

 

 

 

 

Average overmixed dead-stop area in mNm.s (gm2s-1)

1

23.5

19.9

Average overmixed dead-stop area in mNm.s (gm2s-1)

2

24.1

19.9

Mean

 

23.8

19.9

The blade positioning capability of the micro-doughLAB, high speed data acquisition (100 Hz), and torque synchronization with blade dead-stop ensure that results are repeatable and accurate.

The ability of the micro-doughLAB to provide mixing characteristics and viscoelastic properties of a dough, as well as its small-scale capabilities, makes it a potentially useful one-stop instrument for bakers, breeders, and researchers.

References

  1. Steffe, J.F. 1996. Rheological methods in food process engineering. 2nd edn. East Lansing, MI: Freeman Press.