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Dough Rheology as a Function of Flour Treatment

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3. Extensibility and Resistance The Extensograph and the Alveograph have many properties in common. Nevertheless it is interesting to note that most inquiries on optimization concern the Alveogram. In particular, wishes for modification include the extensibility and resistance of the Extensogram, the L-value and the P-value of the Alveogram, and also the P/L ratio of the Alveogram. Sometimes the areas beneath the curves (equivalent to the energy input) need to be modified.

Increasing the resistance of the Extensogram or the P-value of the Alveogram does not seem to be difficult, since hardly any inquiries ask for it. And in fact applying oxidizing agents effectively increases both. Fig. 141 depicts the effect of ascorbic acid and potassium bromate respectively on the resistance of the Extensogram. As potassium bromate is a rather slowly-reacting oxidizing agent, its effect can hardly be observed after only a short incubation time (Fig. 141, curve PBr 45'). Consequently, its impact…

Dough Rheology as a Function of Flour Treatment

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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.

Farinogram stability can be improved with…

Dough Rheology as a Function of Flour Treatment

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Determination of the rheological properties of a dough is part of the quality assessment of flour. The rheological properties depend to a large extent on wheat variety, crop properties and the milling process. Provided that a sufficient supply of wheat with different rheological behaviour exists, the miller will be able to adjust the desired properties by blending different lots. Nevertheless, fine tuning will require using additives such as enzymes or oxidizing agents. If raw material of adequate quality is unavailable or in short supply, more extensive flour treatment will be required. Although the author supports the idea of adjusting the rheological properties, he also insists that we should not believe in numbers only; ultimately, the properties have to suit the flour user's requirements in a chosen application.
1. Viscosity High Falling Numbers can be reduced by adding α-amylase. Since the conventional method of determining the Falling Number includes heating almost to boili…

Vital Wheat Gluten

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To describe all the aspects of gluten and its production would fill a separate book, so this section will concentrate on the issues relating to flour improvement. Information on the rheological properties of gluten is also given in The Role of Gluten Elasticity in the Baking Quality of Wheat But like many other articles, that articles only deals with native gluten, i.e. as it is extracted from wheat flour. If wheat gluten is to be used commercially as an additive, it first has to be extracted from wheat and converted into powder. This is a multiple-step process (Fig. 133), starting with the milling of the wheat grains. Milling is followed by aqueous separation of the starch and soluble substances from the aggregated gluten, disintegration of the gluten in a pin mill or the like and finally hot air drying, for example in a ring dryer.
Only about 82% of the protein of flour is insoluble in water and contributes to wet gluten formation. Furthermore, some of the watersoluble proteins a…

Flour Treatment : Bleaching Agents

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1.Benzoyl Peroxide For a long time, benzoyl peroxide was a familiar oxidative bleaching agent and it is still used to this day in many countries. In addition to its good bleaching effect it has a slight influence on the structure of the gluten, but this is not apparent when other flour improvers such as AA are used.

The dosage for benzoyl peroxide is about 5 - 10 g to 100 kg of flour (50 - 100 ppm) into the flour stream. It is usually sold as a 27 - 32% product (to enable safe transportation it is diluted with an inert carrier), and the dose is then correspondingly higher. The effect of benzoyl peroxide on the flour is already visible after 6 hours of storage and complete after 24 to 72 hours. Benzoyl peroxide decomposes to benzoic acid (Fig. 132), a substance found in various fruits and berries and used as a food preservative, e.g. in cream and fruit fillings for pastry at dosages of 0.05 - 0.15% (500 - 1,500 ppm).
2. Enzyme-Active Bean Flour and Soy Flour Enzyme-active flour made fro…

Acidulants and Acidity Regulators

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Sprouting in rye and wheat results in a high level of amylase activity in the grain itself with the usual effects on baking properties. It is generally known that even flours with very low Falling Numbers can produce good baking results if well acidified. However, not every bread consumer likes acidity and bakeries may also have less and less time and personnel available to develop acidity by sour dough fermentation. Other ways are available, and these consist in adding fruit acids, the salts of these and also carbonates and phosphates approved for use in foods. It is then possible to adjust the pH of the dough slightly so that it moves out of the range in which the enzymes of the grain have their strongest effect.
Moreover, these substances (Acidulants and Acidity Regulators) influence the swelling of the flour constituents and the protein structure, and this helps to counteract the negative effects of excessive enzyme activity (e.g. water release). The most suitable preparations ar…

Flour Treatment : Emulsifiers

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3. Emulsifier Complexes
In many cases it is possible to enhance the properties of an emulsifier by combining it with another emulsifier. An example of this is the mono- and diglycerides, that achieve their optimum suitability for use in flour treatment through combination with lecithin. The lecithin improves their solubility and dispersion, and clearly their interaction with constituents of the flour as well. Well-known and widely used organic flour improvers fall into this category. The combination makes it possible to reduce the dose necessary for optimum effect to 100 - 300 g with 50% emulsifier in the complex.
Diacetyl tartaric esters of mono- and diglycerides are also receptive to enhancement with lecithin: the addition of as little as 10% lecithin improves their emulsifying effect and also reduces the vinegar smell. The above combinations are only effective if the emulsifiers are mixed before being converted into their powdered form. Interestingly, it is not sufficient just to m…

Flour Treatment : Emulsifiers

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Due to their polar character, emulsifiers have interactions with most ingredients of wheat flour. Fig. 128 summarizes the effects of emulsifiers in baking. It has been shown that the flour's own polar lipids – mainly phospholipids (lecithin) and galactolipids already have a positive effect on the volume yield (MacRitchie and Gras, 1973).

Flour from which all lipids had been extracted only showed an improvement in volume yield when the polar lipids (or all lipids) were readded, but not with non-polar lipids (i.e. oil) alone (Fig. 129).

It is probable that all emulsifiers build complexes with gluten, as shown in Fig. 130 for lecithin. On the one hand they increase the binding forces between the protein chains, but on the other hand they act as a kind of lubricant, improving the gliding of the protein layers over each other.
Some emulsifiers with long non-polar, linear chains, such as monoglycerides, form complexes with starch, preventing the recrystallization of the gelatinized star…

Flour Treatment : Enzymes

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5. Transglutaminase
Transglutaminase (TG) is able to crosslink protein chains either with adjacent loops of the same protein or with other proteins of the same or a different type. It requires lysine and glutamine groups as a target. Although lysine is a limited amino acid in wheat flour, there is sufficient lysine for the action of TG to take place. The result is a strengthening effect on the dough, similar to that of AA.
Since it is much more expensive than AA, TG is little-used. Its main use is in prolonged or retarded fermentation, when the enzyme has enough time to achieve its function even at a low dosage. Bauer et al. (2003) provide more detailed information on the function of TG.
6. Other Enzymes Cellulase and β-glucanase are present as natural side activities in many enzyme preparations, e.g. xylanases. They do have some effect on the water-binding behaviour of dough, particularly from whole meal or rye flour containing larger amounts of fibrous components than standard bread …

Flour Treatment : Enzymes

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3. Protease Protease (also known as proteinase or peptidase) splits the protein strands of the gluten molecule (Fig. 123) and thus leads first to a softening and then to a complete collapse of the structure. Sometimes a rather surprising initial increase in viscosity or dough stability is observed. Although the causes are not clear, this may be due to improved water solubility at an early stage of hydrolysis when the main structure is still intact.
With short gluten structures a slight softening may well be desirable; in this case it has a similar significance to the use of cysteine. But unlike the amino acid, protease does not stop acting when the additive is used up. As a result, its effects increase with the fermentation time of the dough. That is why there is a considerable demand for enzyme preparations that do not contain even traces of protease. This fear may be exaggerated, at least if purified, single proteases are available: a single protease only acts on a few specific amin…

Flour Treatment : Enzymes

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2. Hemicellulase, Pentosanase and Xylanase Wheat flour with an ash content of about 0.5% contains about 2.5% pentosans (typical rye flour about 7%) that can bind up to ten times their weight of water. These pentosans belong to the category of the hemicelluloses, "relatives" of cellulose (Fig. 119), and are made up of different sugar molecules (including glucose, xylose and arabinose). The prevailing polymer consists of a xylose backbone with arabinose side chains (Fig. 120) and is therefore called xylan or arabinoxylan, and the enzymes accordingly xylanases or arabinoxylanases, or – less specifically – pentosanases. Approximately one third of these pentosans are soluble in water, while two thirds are larger molecules that are water-insoluble.

Xylanases break these substances down. This process initially leads to the formation of more soluble molecules from the water-insoluble pentosan, and this increases the binding of water and thus viscosity. These molecules are broken dow…

Flour Treatment : Enzymes

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1. Amylases
1.1. Enzyme-Active Malt Flour Like all other living material, grain needs enzymes for its vital functions. As it does not come back to life, so to speak, until germination, this is the phase when enzymes are produced in large quantities. Bakers have long put this characteristic to use by germinating cereals before processing them further.
Malt flour is the dried product made from germinated barley, wheat or rye. The functions of the three of them are largely identical. Malt flour contains primarily α- and β-amylase, but it also contains protease, glucanase and many other enzymes. Some of these may have a positive effect on the baking process (amylases and glucanases), but some can also cause damage (proteases). Like the flour's own amylases, the amylase of the malt flour has a pronounced effect on the Falling Number. If this is very high (i.e., the flour's own enzymatic activity is very low), anything up to 150 g or more of malt flour to 100 kg of flour may be neede…