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Flour Treatment : Enzymes

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Enzymes have been in common use in the food industry for years. In contrast to most other applications in which enzymes find their way into foods, the enzymes in this case do not react at the place where they are added, namely in the mill; they do not take effect until the baker adds water. This difference in time and place is a great challenge to the flour treatment sector in general, but in the case of enzymes it is an especially complex matter. On the other hand enzymes are highly specific; that is, if they are pure enough they act on selected targets and only have to be added in small quantities. Moreover, they are entirely natural as they can only be obtained from micro-organisms by way of fermentation or from vegetable or animal tissue and fluids by means of extraction (Fig. 116).
Like all highly concentrated natural substances, enzymes have a potential for causing allergies when inhaled by workers; cases have been well documented. For this reason care must be taken during proc…

Reduction and Dough Softening

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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.

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 im…

Reduction and Dough Softening

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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 c…

Oxidation and Flour Maturation

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8. Chlorine and Chlorine Dioxide These oxidizing agents have been banned in many countries because of their possible harmful effects on health and the technical risks they involve. There is no doubt that with certain baked goods (for example cake with a high proportion of fat and sugar) chlorination of the flour – that can only be carried out at the mill – produces the best results. Products: Cl2, ClO2 (typical dosage 20 - 250 ppm), hypochlorite (NaOCl, Ca(OCl)2)
Chlorine reduces the pH because it is converted into hypochloric acid through reaction with water according to the following equation: Cl2 + H2O → HCl + HClO. The pH usually drops to 4.5 - 4.7, and in flour for certain cookie applications it even falls as low as 3.5. But the acidity is not responsible for the improving effect, since the latter is retained even after neutralization (Kulp et al., 1985).
The resulting hypochloride is a strong oxidant, reacting with flour pigments and other components. ClO2 is a green gas that di…

Oxidation and Flour Maturation

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4. Cystine
Cystine is the dimer of the amino acid cysteine in which two molecules of cysteine are linked by a disulphide bridge (Fig. 110). This sulphur bridge gives the molecule a certain oxidative effect. But at low doses it is possible that the gluten may soften, as reducing cysteine is released when cystine reacts with thiol groups of the protein. Although this has yet to be thoroughly investigated, cystine is used in spite of its high price compared to AA because it is occasionally found to have a positive effect on the properties of the dough.


5. Dehydroascorbic Acid DHAA is the oxidized form of AA (Fig. 111). This means that if DHAA were used instead of AA it would be possible to dispense with the initial step of oxidation. Tests have shown that this is quite possible. One reason why it is so rarely used, however, is its instability, but this could be improved by coating. A further problem is that it is more difficult, and thus more expensive, to synthesize.


6. Bromate The powerf…

Oxidation and Flour Maturation

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2. Enzyme-Active Soy Flour
One enzyme from soy flour, lipoxygenase, also has an oxidative effect on the protein of the gluten. During the oxidation of the lipids by lipoxygenase, peroxides are formed that have a cross-linking effect on thiol groups. However, the gluten-strengthening effect of soy flour is comparatively slight; its bleaching effect is more important. There are several types of lipoxygenases with different action patterns. While type I lipoxygenase only acts on free unsaturated fatty acids, types II and III also oxidize unsaturated fatty acid bound to the glycerol backbone. Bean flour contains mostly types II and III, which makes it an efficient agent for oxidizing all unsaturated lipids in flour. The use of lipoxygenase is limited because the enzyme creates a "green" flavour that is not desirable in this application.
3. Glucose Oxidase The enzyme glucose oxidase (GOD) is usually derived from the mould Aspergillus (in a similar manner to amylase) and sometimes …

Oxidation and Flour Maturation

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The present necessity for oxidative treatment might be regarded as a disadvantage of the fast and gentle processing of grain into flour. Natural ageing of the flour by exposure to the atmosphere alone is no longer possible, so maturation has to be speeded up with oxidative preparations. Oxidation primarily affects sulphur containing amino acids that are constituents of the gluten. The oxidation of two adjacent hydrogen sulphide (thiol) groups results in the formation of a disulphide bridge between different sections of the long gluten molecule or between different gluten molecules. This causes a hardening of the protein.

1. Ascorbic Acid By far the most important substance for this purpose is ascorbic acid (AA). Using a complex biochemical method starting with starch as the raw material it is produced in a very pure form and sold as a fine or crystalline powder in various concentrations to facilitate dosing. Less often, AA of purely biological origin is used. The most common product is…