Dough Rheology as a Function of Flour Treatment

Fig. 137: Effect of the hemicellulase Alphamalt TTC on water absorption, as shown by the Farinogram

2. Mixing Resistance
Four main wishes have been identified concerning the modification of the Farinogram curve: increased or reduced water absorption and increased or reduced stability. Enhancing the water uptake of a dough means reducing its stickiness and increasing the potential for adding more water, e.g. to achieve a longer shelf-life of the finished product. Besides adding hydrocolloids or vital wheat gluten, more elegant means exist – for instance xylanase, that only acts on water-insoluble xylan. The resulting solubilized xylan absorbs more water (Fig. 137). Xylanase preparations for improved volume yield do not only enable this activity; they also contain xylanases which degrade the pentosan fragments further, releasing water again. Although this improves the volume yield, the water uptake is reduced. Enzymes creating hydrocolloids in situ also improve water absorption; they include alternan sucrase (Popper, 2002) and dextran sucrase.

Fig. 138: Effect of glucose oxidase on the Farinogram

Farinogram stability can be improved with oxidases (Fig. 138). Oxygen is a limiting factor within a dough system. In doughs larger than those used in the Farinogram the effect will be much weaker, as the surface-to-volume ratio becomes smaller with increasing dough weight. Although one would expect oxidizing agents to result in better stability, this cannot be shown in the Farinogram. Even the opposite can happen with strong and fast oxidizing agents such as azodicarbonamide: an almost normal resistance is built up at the beginning of the mixing process, but the hard and resilient dough absorbs a lot of energy which causes its rapid breakdown (Fig. 139). Whereas the Farinograph does not take the energy input into account but keeps mixing at a constant speed, a baker would decide to stop mixing earlier, to mix at a lower speed, or to make the dough softer with additional water, etc.

Fig. 139: Effect of azodicarbonamide (ADA) on the Farinogram

Unfortunately, the very useful Farinograph sometimes creates misleading data. Another example: the instrument measures the torque caused by the resistance of the dough to kneading. The greater the torque, the greater is the assumed water absorption. The instrument does not reflect the interaction of the dough with the bowl surface, for instance a sticky dough with little water absorption adhering to the instrument and thus increasing the torque.

Fig. 140: Effect of commercial xylanase on the viscosity of a pentosan suspension, determined by capillary viscometry

Reduced water absorption can be achieved with enzymes too. Xylanases acting on the water-soluble moiety of the pentosans reduce water absorption by these polymers. This is shown by Fig. 140 using pentosans extracted from wheat. Only Trichoderma xylanase 3 reduced the viscosity of a pentosan slurry, whereas all the other xylanases tested resulted in an initial increase (caused by degradation of the insoluble pentosans into soluble pentosans absorbing more water). A low viscosity is equivalent to a low water absorption.

As we have already said, many commercial xylanase preparations contain various xylanases of different specificity. So in most cases it will only be possible to select a xylanase in which the above effect prevails. With most commercial xylanases it is also possible to increase the dosage in order to achieve a viscosity reduction in a given time (Fig. 140). Unfortunately, the Farinograph using a very viscous dough made from flour is a rather slowly reacting system compared with a viscometer using extracted pentosans.


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