Reduction and Dough Softening

2. Reducing Yeast Preparations
Yeast also produces reducing substances, but these are only released when the cells die. There are now preparations made of inactivated, killed yeast on the market that have a softening effect similar to that of cysteine (Fig. 114). But as the dose required is about 100 times higher (100 - 1,000 g to 100 kg of flour), even the lower price (about 1/10 or even less) cannot make up for it. This is true even of so-called glutathione yeast, a variant with a very high reductive potential. So one might say that the main advantages of inactivated yeast are in the field of labelling.

Fig. 114: The effect of reducing agents (L-cysteine or inactivated, glutathione-rich yeast) on the Extensogram (45 min)

3. Sodium Metabisulphite and Sulphur Dioxide
These powerful reducing agents are especially good at breaking down the gluten fast and reliably (Fig. 115), which greatly simplifies the production of biscuits, crackers and wafers. But as these substances are known to destroy vitamin B1 (thiamine) and to cause health problems in sensitive persons, their use should be avoided. They also impart a sulphur taste which can only be tolerated as long as no comparison to products without sodium metabisulphite (SMB) can be drawn. The dosage of SMB varies from 10 ppm to more than 1,000 ppm. Whereas 10 ppm are hardly effective, concentrations above 100 ppm are detectable sensorily, and concentrations larger than 500 ppm even cause a clear off flavour. Alternatives based on enzymes are now available; they achieve the same results but react rather more slowly and often require some process adjustment and hence knowledge on the part of the user. On the other hand, certain enzyme preparations based on proteases and amylases permit the reduction or omission of expensive ingredients, e.g. sugar, milk or whey powder, and therefore offer economic advantages.

Fig. 115: Farinographs of German soft wheat flour without (left) and with 500 ppm SMB (right)

Furthermore, sulphites are often not permitted, or they are restricted to low dosages or have to be declared in the labelling. Enzymes, on the other hand – natural proteins classified as processing aids – are not subject to restrictions and do not have to be declared in most countries.

Tab. 87: Reducing substances used in baking applications

4. Other Substances
with Reductive Potential Tab. 87 lists substances commonly used in bread production which have a certain potential for reducing disulphide bonds to thiol groups. Even malt flour has been found to have a softening effect through its reductive potential (Tab. 88). Ascorbic acid acts as a reducing agent at elevated levels which cannot be completely oxidized by ascorbate oxidase because of limited oxygen in the dough. The threshold depends largely on the processing conditions.

Tab. 88: Reducing potential of malt flour a


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