What are bread improvers and why are they used?
The term bread improver is used to embrace a wide range of materials that can be added to wheat flour and dough in order to improve some aspect of dough behaviour and final bread quality. The use of the term is common and most often applied to the addition of several ingredients at low levels blended with a 'carrier', a material that may or may not have functional properties but that aids dispersion and provides a more conveniently handled composite material. The formulation of bread improvers will be influenced by legislative control over the list of permitted ingredients that may be used in breadmaking.
Alternative names for bread improvers that may be encountered in the baking industry include:
- Dough conditioners, a specific reference to the fact that the material addition changes dough rheology.
- Processing aids, that implies a similar function to dough conditioners.
- Oxidising agents, that implies a more specific role concerned with the formation of the gluten network in the dough.
- Additives, more commonly applied to specific ingredients.
- Concentrates, similar to an improver but with a greater range of ingredients present (e.g. fat, sugar and salt) and commonly used at higher rates of addition.
Almost any material added to a flour and water dough will have some improving effect. For example, the addition of yeast improves the lightness and palatability of bread, while salt changes the handling properties of wheat flour doughs and the flavour of the baked bread. However, the term bread improver is now commonly restricted to materials that are typically added at much lower levels of addition than yeast or salt with the intention of improving gas production or gas retention in the dough, retaining bread crumb softness and obtaining a whiter crumb colour.
Some of the more common ingredients used in bread improvers are noted below. The classification used is arbitrary since the complex actions of most materials in breadmaking means that they might be classified in more than one group. For example, the addition of many enzyme preparations brings about changes in dough rheology that makes it easier to process doughs but also results in improved oven spring, a manifestation of improved gas retention.
- Aids to dough processing: enzyme-active preparations, e.g. malt flour, fungal a-amylase.
- Aids to gas production: yeast foods, such as ammonium chloride.
- Aids to gas retention: oxidising agents, such as ascorbic acid and potassium bromate.
- Aids to bread softness: e.g. glycerol monostearate (GMS).
- Aids to improving crumb colour: soya (soy) flour.
What are the functions of ascorbic acid in breadmaking?
Ascorbic acid (AA) is commonly known as vitamin C and is present in large quantities in many green vegetables and fruits. It is an essential component in the diet. Its use in breadmaking was recognised many years ago with a UK patent (BP 455,221) from 1936. It is a commonly used oxidant (improver, additive) and in many cases (e.g. within the European Union) it is the only one permitted for use in breadmaking.
In breadmaking it is used to improve dough gas retention through its effect on the gluten structure. In terms of its chemistry AA is a reducing agent (and sometimes referred to as an anti-oxidant) but during dough mixing it is readily converted to dehydroascorbic acid (DHA) (see Fig. 10) in the presence of oxygen and ascorbic oxidase enzyme (Collins, 1994). The oxygen for the conversion comes from the gas bubbles incorporated during dough mixing and the conversion is enabled by the ascorbic oxidase enzyme, which occurs naturally in wheat flour.
The chemistry of the AA oxidation process in dough mixing is complex (Williams and Pullen, 1998) but probably involves the oxidation of the —S—H (sulphydryl) groups of gluten-forming proteins and the formation of —S—S— (disulphide) bonds. The net result of the AA effect is to improve the ability of the dough to retain gas (as seen by increased oven spring) and to yield bread with a finer (smaller average cell size) crumb cell structure. These changes also result in bread crumb that is softer to the touch yet has the resiliency to recover much of its original shape after compression. This helps to convey the impression of improved freshness to the consumer.
The dependency on oxygen for the AA to DHA conversion means that the quantities of air incorporated during dough mixing play a significant role in promoting oxidation. This means that AA-assisted oxidation varies with mixer type because of the ability of different mixers to occlude different quantities of air (Marsh, 1998). Some mixing regimes have been developed that increase the total quantity of air occluded during mixing so that greater AA-assisted oxidation can be achieved; two examples are mixing in an oxygen-enriched atmosphere (Chamberlain, 1979) and the use of the so-called 'pressure-vacuum' mixer. There has been a tendency to consider that it is not possible to 'over-treat' with AA because of the limiting effect associated with oxygen availability. With the advent of the pressure-vacuum mixer such statements should be viewed with caution.
The oxidising effect of AA is mainly limited to the dough mixing period because bakers' yeast will remove any oxygen remaining in the air bubbles by the end of mixing or soon after its completion (Chamberlain, 1979). Thus, in the dough that leaves the mixer the gaseous mixture of nitrogen (from the air) and carbon dioxide (from yeast fermentation) that remains provides an environment in that AA can act as a reducing agent. If AA is used in doughmaking processes with extended periods of fermentation then the opportunity exists for the reducing effect of AA to weaken the gluten structure with subsequent loss of gas retention in the dough. Ascorbic acid is thus best suited to no-time doughmaking systems.
The action of AA during mixing also brings about changes in the rheology of the dough, making it more resistant to deformation (Cauvain et al., 1992) by comparison with doughs treated with an addition of potassium bromate. Potassium bromate does not exert its full effect until the dough reaches the late stages of proving and the early stages of baking.
We have heard that soya flour is added in breadmaking to make the bread whiter. Is this true, and if so how does it work?
Full-fat, enzyme active soya flour has commonly been used as a functional ingredient (improver) in breadmaking since the 1930s. It is often described as a 'carrier' for other functional ingredients, e.g. oxidants, to facilitate the addition of the small quantities that are commonly used but it does contribute functionality of its own. The soya bean contains a high percentage of natural oil and has a distinctive 'beany' flavour that can be unpleasant if used at high levels of addition but not at the 1 or 2% level normally used with bread improvers.
Soya flour has three basic functions: it gives a white bread crumb, it contributes to gas retention through oxidation and it increases the level of water that needs to be added to the dough. The first two functions are caused by the actions of the natural enzyme systems that are present and so it is important that the enzyme-active form of soya flour is used.
Soya flour is rich in the enzyme lipoxygenase, that plays a major role in its bleaching action. With the help of the enzyme the intermediate oxidation compounds formed during dough mixing transfer oxygen from the atmosphere to bleach the yellow-coloured carotinoid pigments present in the flour. By this mechanism the flour is bleached and the bread crumb becomes whiter. The greater the availability of oxygen, the greater the bleaching effect.
The oxidation effect appears to come from freeing bound lipids from specific sections of the gluten proteins, thereby allowing the proteins to become hydrophilic and helping to form the viscoelastic surface of the air bubbles in the dough.
Soya flour and its derivatives have found other uses in baking, for example as an egg replacer and in 'gluten-free' breads.
We are using a bread improver that contains enzyme-active malt flour and find that doughs are becoming too soft and that the sidewalls of loaves collapse inwards to give a 'keyhole' shape. Is the malt flour to blame?
The 'keyhole' shape that you describe (see Fig. 11) occurs because you are adding too much cereal a-amylase to your dough via the addition of malt flour. In addition to the dough softening and the loss of shape you may also observe some dark, dense patches in the crumb near to the areas of collapse. These are often referred to as ' bone' by bakers and derive from the same source, namely the excess of cereal a-amylase.
Malted wheat or barley flours are good sources of enzymic activity that can be used to improve gas retention in the dough. This improvement in dough gas retention comes from the high level of cereal a-amylase present but because of continued yeast action in the oven the centre of the dough piece continues to expand for a considerable period after the outer crusts have formed. This expanding centre crumb then compresses more crumb against the crust, squeezes the air out of the cells and that causes the dark colour. You can see this effect if you squeeze a portion of normal crumb firmly between your fingers.
The excessive expansion of the centre crumb lowers the density to such an extent that as the bread cools and the effects of external pressure are manifest, the loaf is unable to support itself and it collapses. This will be exacerbated when the loaf is handled, such as during slicing.
Keyholing in bread
The softening of the dough you observed is most probably due to the presence of proteolytic enzymes which are also present in the malt flour. Malting encourages and raises levels of all of the enzymes present in the grain. The proteolytic enzymes weaken the protein structure, causing it to lose its rigidity and become soft. The a-amylase also contributes to the dough softening through the breakdown of the starch from the flour and the subsequent release of 'free' water into the dough.
Dough softening because of enzymic action is usually a much greater problem when using doughmaking processes with a period of bulk fermentation because the length of time available for enzymic action is considerable. In no-time doughs, dough softening may not be obvious but the 'keyhole' effect can be readily observed when high levels of malt flour are used.
We understand that an enzyme called a-amylase can be added to flour or dough to improve bread quality but that there are several different forms. We have tried several and get different effects on bread softness. Which one(s) should be used?
The a-amylases are a group of enzymes that facilitate the breaking down of the hydrated starch granules, both amylose and amylopectin, in flour doughs to shorter chained, unbranched molecules known as dextrins. This action creates sites for any ^-amylase present to convert the starch to individual maltose molecules. Wheat flours usually contain sufficient ^-amylase but levels of a-amylase vary and in many cases may be so low that the starch to maltose conversion is limited.
Maltose is fermented by bakers' yeast to provide carbon dioxide gas in the dough and thus a key role for a-amylase is to support gas production. While this was the original reason behind the addition of sources of a-amylase to wheat flour doughs, in many cases its addition also leads to improvements in gas retention, bread volume and softness (Cauvain and Chamberlain, 1988) and this has now become the main reason for its addition.
The traditional source of a-amylase for breadmaking was from malted barley or wheat flour but today it is more common to use amylases derived from the fermentation of microscopic fungi (Aspergillus oryzae) or a bacterial source. The main difference between the amylases lies with their heat stabilities (Williams and Pullen, 1998). The more heat stable the amylase, the greater the breakdown of the starch during baking. In general terms fungal a-amylase is inactivated before cereal (malt) which, in turn, is inactivated before bacterial. The so-called maltogenic amylases are derived from modified bacterial sources and have a profile more similar to that of the fungal source.
The heat stability of the amylase source is important in providing a balance between good and bad effects in baking. In the dough the amylase attacks the damaged starch granules and breaks down the starch molecules. As heating proceeds, especially during baking, the swelling and later gelatinising starch provides a larger quantity of available substrate for the amylase enzymes that are now working at a faster rate because of the higher temperature. The positive benefits are the improvements in gas retention through a more extensible gluten network while the disadvantages are related to the formation of sticky dextrins.
To maximise the benefits you should use the fungal source. The maltogenic form can be used because of its greater anti-staling effect which gives softer bread. However, if used at too high a level you may find difficulties in slicing the bread because of its enhanced initial softness. Avoid using the traditional bacterial form as this may survive the baking process and lead to unwanted liquefication of the product crumb during storage.
Effect of temperature on a-amylase activity
Why are emulsifiers used in bread improvers? How do we decide which one we should be using?
Emulsifiers are used in bread improvers for a number of different reasons including:
- to help control gas bubble size;
- to improve gas retention;
- to improve dough stability;
- to improve crumb softness.
Each of the emulsifiers permitted for use in breadmaking contributes something to all of the above dough and bread properties to greater or lesser degrees depending on the particular emulsifier.
The most commonly used emulsifiers and their likely contribution to dough character and bread quality are as follows:
- Diacetylated tartaric acid esters of mono- and diglycerides of fatty acids (DATA esters, DATEM) are thought to reduce the average gas bubble size in bread doughs, which leads to a finer cell structure. They are known to improve dough gas retention, which contributes to improved bread volume and crumb softness. Levels of use are usually up to 0.3% flour weight in a variety of bread and fermented products.
- Sodium steoryl-2-lactylate (SSL) improves dough gas retention, bread volume and crumb softness but weight for weight is less effective than DATA esters. It is commonly preferred in the production of sweeter fermented products, e.g. buns and doughnuts.
- Glycerol mono-stearate (GMS) is best used in the hydrated form but can be added as a powder. It does not greatly contribute to dough gas retention of bread volume but does act as a crumb softener through its proven anti-staling effect.
- Lecithins are a group of naturally occurring, complex phospholipids commonly derived from soya. They are used in baguette and other crusty breads to improve dough gas retention to a degree and contribute to crust formation.
Since no single emulsifier will equally perform all of the tasks required in breadmaking it becomes a case of choosing a given emulsifier to fit with the main product and process requirements. A blend of emulsifiers could be used. Price may also influence your final choice.
What is L-cysteine hydrochloride and what is it used for in bread improvers?
Cysteine is a naturally occurring amino acid that, because of its sulphydryl group (—S—H), is able to act as a reducing agent on the disulphide (—S—S—) bonds present in the gluten structure of wheat flour doughs. It is most commonly used in the hydrochloride form to improve its solubility.
It came into common use in breadmaking in the 1960s when it was a key component of the breadmaking process known as Activated Dough Development (ADD) (Cauvain, 1998). In ADD L-cysteine hydrochloride was combined with potassium bromate and ascorbic acid to give an improver capable of delivering both chemical reduction and oxidation processes during doughmak-ing. ADD was designed to allow bakers to obtain the benefits of making no-time doughs without the need for the high-speed mixers associated with the Chorleywood Breadmaking Process (CBP). ADD remained very popular with smaller bakers until superseded by the use of spiral mixers (Cauvain, 1998).
In some ways the chemical reduction of gluten disulphide bonds by L-cysteine hydrochloride can be equated to the mechanical disruption of such bonds in the CBP. This view has led to the consideration that one of the benefits derived from the use of L-cysteine hydrochloride is that work levels can be reduced in the CBP.
More certain is that the reducing effects of L-cysteine hydrochloride beneficially modify dough rheology and improve its processing. For example, its addition to so-called 'bucky' doughs in the USA (i.e. doughs having high resistance and lacking extensibility) improves dough moulding, and in the CBP ' steaks and swirls' in the crumb may be reduced, but not eliminated (Williams and Pullen, 1998).
Additions of L-cysteine hydrochloride may be made to fermented products that are sheeted, e.g. pizza base, and to laminated and short pastry to reduce dough and product shrinkage.
Continue reading here: Other bakery ingredients
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