Reduction and Dough Softening

Gluten that is too short is difficult to process and results in a low volume yield, since the gas formed by the yeast is not able to expand the dough as it should. The problem can be solved by using substances with reducing properties that break down surplus disulphide bridges and thus give the protein molecules more room to move. Short gluten properties may result from the varieties used, but they are sometimes caused by the storage and processing of the grain (overheating) or the use to which the flour is put (for instance, freezing shortens the gluten). Some applications, in particular biscuits and crackers, require extensive softening of the dough for optimum processing and product properties.

1. Cysteine
A suspected "opponent" of AA is cysteine, a simple amino acid that is a constituent of all proteins and produced either by hydrolysis of extremely cysteine-rich proteins such as those from feathers or hair and complex purification procedures, or by synthetic means.

As cysteine splits disulphide bridges like other reducing agents, one would expect it to counteract the effect of AA if used at the same time. Initially it was only discovered empirically that this is not the case (Kieffer et al., 1990). In fact AA and cysteine complement each other. One makes the gluten firmer, while the other ensures adequate elasticity. This is possible – as was proved later – because the two substances act on different constituents of the gluten and attack it at different sites.

The use of these flour improvers, in frozen doughs especially, makes it necessary to add large doses of both substances, for on the one hand good fermentation stability it required (AA) and on the other hand the deep-freezing process shortens the gluten, a problem that can be solved at least in part by cysteine. The amount of cysteine added is often two-thirds of the quantity of AA.

Cysteine is usually sold as L-cysteine hydrochloride, anhydrous or monohydrate, as it is more easily synthesized and has better water solubility in the latter form. Sodium nitrocyanoferrate/ammonium hydroxide can be used for detection, for instance on the wet pekar sample, but this is an unreliable method as the blue spots are sometimes difficult to see and fade quickly.


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