One quality parameter for yeast-raised bakery products, such as bread, rolls, and buns, is specific volume or the relative size of the finished, baked product in relation to the amount or weight of the unbaked dough piece.  To minimize ingredient costs, bakers strive to achieve the largest volume of quality product that can be produced with the least amount of dough.  Although many ingredients and processing variables contribute to acceptable volume, our discussion today will focus on dough development and the effect of added emulsifiers, or dough strengtheners.

 Wheat flour contains from 7% to 15% protein.  More than 80% of the protein is gliadin and glutenin, which are the two proteins that make up gluten.  Within the cereal grains, wheat gluten is unique in that it has the ability to form a dough with both viscous and elastic properties.  This means that it can be stretched without breaking, but it also tends to go back to its original shape.  These two characteristics make wheat gluten ideal for bread and bun production where a highly expanded finished product is desirable.  Gluten is formed when the two main flour proteins, gliadin and glutenin, are mixed together with water.  Gliadin provides dough viscosity and extensibility; whereas glutenin, and especially the higher molecular weight proteins, provides elasticity and dough strength.  A wheat dough can be defined as a dispersion of air cells, starch granules, and lipids in a continuous matrix of hydrated gluten proteins.  Therefore, proper hydration of the gluten and the energy input necessary to develop these desirable dough characteristics is essential in bread production.

To obtain optimum dough development, let's take a closer look at the mixing step.  At the beginning of mixing, the dough is a wet, sticky mass as the mixer incorporates the ingredients.  After several minutes of mixing, the outer hydrated layers of the flour particles are smeared off, and eventually all the flour particles are hydrated.  With the shearing action of the mixer, the wheat proteins are physically developed into a more cohesive mass, and the gluten network is formed.  At the end of mixing, the dough should be a homogeneous mixture with optimum dough characteristics, such as elasticity, viscous flow, and plasticity. The dough is no longer wet and sticky, and it has a smooth, dry appearance.  Mixer operators check for this optimum dough development by stretching the dough into a thin sheet.  The dough is fully developed when it can be stretched into a thin, translucent sheet, and a web-like gluten network can be seen.

 The mixing time necessary to properly develop the dough, as well as the energy requirement, can be reduced with the addition of a pre-hydration step, such as in the case of a liquid flour ferment or by using the sponge and dough processing method.  In both cases a percentage of the flour and water are mixed together very minimally and allowed to slowly hydrate over a two to four hour period.  Regardless of the method used, the final mix time should result in optimum dough consistency or machineability in order to maximize the dough's capacity for expansion.  This is largely a decision the mixer operator makes based on his own personal observations and experiences on how the dough should look and feel.

In a high speed, automated plant, over mixing the dough must be avoided because a sticky dough is difficult to handle and causes machining problems in dividing and shaping.  Even if the sticky dough pieces could be successfully panned, they will have a more fragile cell wall, or gluten network, resulting in less gas and water vapor retention and as a result, a reduction in bread volume.  To avoid machining problems caused by a sticky, difficult-to-handle dough, a common mixing practice is to slightly under mix the dough, which may then contribute to lower bread volume.

In many bakeries, the mixing time is determined by 'clean up' time and the mixing time is usually a specific number of minutes past this clean up point.  The clean up point is when the dough has been sufficiently mixed into a cohesive mass, and it no longer sticks to the sides of the mixer.  The clean up point is actually a good indicator of optimum mixing time as it takes into account all the factors that effect dough development, such as absorption, ingredients, mixing speed and efficiency, temperature and flour quality.  In an effort to quantify the optimum dough development and provide consistency between batches, newer mixers have been designed with equipment to monitor the power consumption of the mixer.

Regardless of how the optimum dough development is determined, it is important for consistent volume and product quality.  A well-developed dough provides the best cell wall structure to entrap the air incorporated during the mixing process.  It retains more of the carbon dioxide and steam vapor generated during fermentation and the initial stage of baking.  The optimum dough development can even help correct some deficiencies in flour quality; whereas improper dough development can reduce the baking potential of a good quality flour.  Therefore, mixing to achieve optimum dough development is a critical control point in bread and bun production and should be carefully monitored.

One challenge the mixer operator has each year is the changeover from flour produced with the previous year's wheat to flour milled from the new wheat crop.  Until the possible differences in both the mixing time and absorption can be established for the flour from the new wheat crop, a close working relationship with your flour miller is important.  The bakery's specific flour requirements should be communicated to the miller and continual feedback, both positive and negative, should be provided during this period in order to minimize production problems and to identify the flour requirements for producing the best quality bakery products.

Another challenge in determining the optimum dough development is in the production of variety breads and diet or high fiber breads.  In these products the amount of white flour, and therefore the gluten content, is diluted.  The gluten network must be well developed to carry the additional weight of these non-white flour components.  The addition of coarse fibers and grains, as well as wheat bran, competes with the gluten proteins for hydration and typically the absorption must be adjusted to compensate.  The mixing time may need to be adjusted to adequately hydrate and develop the gluten network.  It may be advantageous to mix the dough for a couple of minutes in low speed before changing to high speed due to the delayed hydration of the coarser particles.  Often these variety and fiber doughs are more fragile.  Therefore, they are less tolerant to over mixing and abuse.   Compared to white bread, many variety and diet bread formulations require higher oxidation levels and higher levels of emulsifiers to strengthen the dough.

In determining the amount of mechanical energy necessary to achieve a well-developed dough, all dough handling equipment, including the dough divider, should be taken into consideration.  This is especially evident when equipment changes are made in the dough make up areas that increase the amount of dough handling or put more energy into the dough.  The mixing time must be adjusted to compensate for the additional work put into the dough, or the dough will be developed past the optimum point resulting in difficulties in handling and processing.  The new developments in equipment design, especially dividing and conveying equipment, has resulted in more mechanical abuse to the dough.  This abuse affects both the bread volume and product quality.  Maintaining the viscoelastic gluten network, which was so carefully developed in the mixing and make up steps, is critical to providing the structure and expanded volume that is desirable in the North American market.

The delicate nature of a well-developed dough can cause serious production challenges, especially when the industry trend continues to move towards larger, faster production lines while also trying to reduce production costs.  For many years, bakers have added emulsifiers to help strengthen the dough, to improve volume and to provide more processing tolerance.  These emulsifiers, or dough strengtheners, function by interacting with the flour components. This category of emulsifiers includes calcium and sodium stearoyl lactylate, DATEM, ethoxylated monoglycerides, succinylated monoglycerides, and polysorbate 60.

For example, in this graph of baked bread volume, comparing two different quality flours, DATEM, a dough strengthening emulsifier, was added at two different use levels: 0.2% and 0.4%, flour weight basis.  The addition of 0.2% DATEM to the weaker flour provided comparable volume to the medium quality flour with no added emulsifier.  When the emulsifier use level was increased to 0.4%, there was only a slight difference in bread volume between the two quality flours.  With both quality flours, the addition of a dough strengthening emulsifier improved the bread volume.

The key characteristic of emulsifiers is that they have a love/hate relationship with water, which is typically illustrated with the matchstick model shown here.  The head, or hydrophilic part of the molecule prefers to be in an aqueous or polar environment; whereas the tail, or hydrophobic part, prefers to be in a lipid environment.  If an emulsifier is dissolved in a mixture of oil and water, it will migrate to the interface between the oil and water in order to place its hydrophilic head in the water phase and its hydrophobic tail in the oil phase.  To better understand how these emulsifiers function, let's investigate what a well-developed dough might look like at the molecular level.

 All of the flour components, the protein, damaged starch, intact starch granules, pentosans and flour lipids, play a significant role in dough formation.  Under magnification, the gluten looks like a continuous, three-dimensional film of thin, hydrated strands of proteins.  Imbedded in these gluten protein strands are starch granules, other flour particles, and air that was incorporated during mixing.  Scientists studying how these protein strands are held together have identified several types of bonds or cross-linking, both within the protein molecule and between protein molecules, that are responsible for the formation of this network.

It is believed that the formation of the gluten network in wheat dough is due to the formation and excellent mobility of disulfide bonds between and within the gluten proteins.  However, recent investigations into the protein chemistry involved in the development of the gluten network suggest that the cross-linking of tyrosine amino acids might also be important.  Dough is a very complex system and although we have yet to determine precisely how the gluten network is formed, cereal chemists continue to try to determine the exact mechanism.

Several theories exist to explain how emulsifiers or surfactants improve dough strength.  These theories involve different flour components such as proteins, lipids and starch.  As is the case with the formation of the gluten network, the exact mechanism is poorly understood.  One theory on how emulsifiers improve dough strength focuses on how they interact with gluten proteins.  The emulsifiers form hydrophobic bonds with amino acids.

Amino acids are the building blocks of proteins.  Over 40% of the amino acids that make up the gluten proteins are hydrophobic, which means that they do not like a water environment.  These proteins interact strongly with the lipid or fat-type substances.  In a dough system, these proteins bind to the carbon chain end of the emulsifier since they prefer this environment.

A second explanation involves the electrostatic charge of some ionic emulsifiers.  These emulsifiers have a net negative electrical charge and include emulsifiers such as calcium and sodium stearoyl lactylate, DATEM, and succinylated monoglycerides.  Positively charged proteins repel each other similar to the effect of positively charged magnets when they are placed together.  When the negative charged emulsifiers are added to the dough, they effectively neutralize the positive charge of the proteins which allows the gluten proteins to aggregate or bond together.  This results in a stronger gluten network and increased dough strength.

Investigations into emulsifier functionality have studied the effect of various emulsifiers on the soluble proteins in dough.  In these tests, flour and an excess amount of water were mixed together in order to fully hydrate the flour.  Then the mixture was centrifuged to separate the insoluble gluten matrix from the aqueous phase.  This liquid was analyzed for the amount of soluble proteins without emulsifiers and then tested with the addition of different dough strengthening emulsifiers.  All of the emulsifiers were added at a use level of 0.5%, flour weight basis.

As shown in this graph of the test results, all of the emulsifiers reduced the amount of soluble proteins remaining in the aqueous phase.  The addition of these emulsifiers increased the amount of proteins bound within the gluten structure.  Of the emulsifiers tested, DATEM and sodium stearoyl lactylate were the most effective.  Additional tests involving fat that is extracted from the dough have also demonstrated this protein binding effect.  In these tests, even though DATEM is a lipid or fat, it is not extracted with the lipids.  The DATEM is bound to the gluten protein.

Another theory on the functionality of emulsifiers involves how they interact with the native flour lipids.  For many years, scientists have known that the formation and development of dough involves the binding of specific polar flour lipids to the gluten protein.  Several studies have shown that these polar lipids are a key factor in achieving a dough with the appropriate rheological properties for producing bread.  It is believed that polar lipids are incorporated into the interfacial film in the gluten network.  With increased pressure, the gluten protein layers are ruptured but the lipid film is still intact.  When the protein layers are ruptured, they are replaced at the interface, or bubble surface, with lipids.  When testing combinations of gluten proteins and emulsifiers, such calcium and sodium stearoyl lactylate and DATEM, the pressure could be increased about 50% before the bubble was ruptured.

Another lipid-lipid interaction theory suggests that these dough strengtheners are able to form aqueous films with a lamellar structure between the gluten strands and the starch molecules while they are bound to the gluten.  A dough model was developed by T. Carlsson to illustrate what this may look like.  It shows a cross section of dough under four levels of magnification.  Beginning with the frame on the left, with the least amount of magnification, each frame to the right has increased levels of magnification.  The first illustration on the left shows the larger, oval-shaped spheres as the starch molecules and the light circles as air cells; both of which are imbedded within the gluten matrix.  The dispersed lipids are shown as the small, dark circles.

In the second level of magnification from the left, it can be seen that both the starch and air cells are covered with lipid bilayers or emulsifier film.  Upon increased magnification, the lamellar structure of the emulsifier is easier to see.  In this structure, the hydrophilic, or water-loving head of the emulsifier is aligned with the hydrated protein matrix while the fatty acid carbon chain, or the hydrophobic end of the emulsifier is aligned together with other lipid bilayers.  The presence of these bilayers or lamellar structures explains the extensibility of the gluten network, because they are very easy to deform or stretch.  This improved film forming ability of the gluten results in increased gas retention during fermentation and provides improved dough tolerance to mechanical abuse and over fermentation.  Ultimately, the dough strengtheners increase the baking performance of the flour and result in increased bread volume.

A final theory involves how emulsifiers interact with starch.  Triglycerides, such as shortening, and emulsifiers modify the gelatinization behavior of wheat starch.  In studies evaluating the effect of  various emulsifiers on bread volume, emulsifiers were ten times more effective in increasing volume than the addition of shortening.  A low level of emulsifier such as 0.2% to 0.4% provided a similar effect to adding 3% shortening to the dough.  DATEM interacts with starch by raising the swelling temperature and thereby allowing more time for dough expansion in the oven prior to the starch gelatinization.  New investigations also suggest that most of the water-soluble proteins are not in the gluten fraction after the addition of emulsifiers, but they are connected to the starch phase.

Emulsifiers/dough conditioners that are approved in the United States for use in standardized and non-standardized bakery products include:

  Calcium Stearoyl Lactylate & Sodium Stearoyl Lactylate
  DATEM
Ethoxylated Monoglycerides
Polysorbate 60
Succinylated Monoglycerides

Calcium stearoyl lactylate and sodium stearoyl lactylate, DATEM, and succinylated monoglycerides are available in powder form for direct addition to the dough.

Due to the low melting point of ethoxylated monoglycerides, they are not available in a pure powder form.  Ethoxylated monoglycerides are typically available in a plastic form mixed with monoglycerides to increase the melting point high enough so the mixture can be sprayed into a beaded form.  Another form is a powder where the ethoxylated monoglycerides have been plated onto a carrier.  Both forms contain between 60% and 70% ethoxylated monoglycerides.

In addition to a powder form, succinylated monoglycerides are also available blended with monoglycerides and sprayed into a powder that contains approximately 60% succinylated monoglycerides.  It is also available in a paste form, which is a hydrated dispersion containing about 30% monoglycerides.

Polysorbate 60 is available in a semi-liquid or paste form at room temperature.

With the exception of DATEM, these emulsifiers/dough conditioners maybe used alone, or in combination, in bakery products at a use level not to exceed a total of 0.5% based on flour weight.  In contrast, DATEM is a GRAS food ingredient and its use level in bakery products is dictated by good manufacturing practice or GMP.

In Mexico, bakery product regulations for calcium stearoyl lactylate, sodium stearoyl lactylate, DATEM, and succinylated monoglycerides are similar to the US regulations.  The maximum allowable polysorbate 60 application level is 0.46% for the product.  Ethoxylated monoglycerides are not permitted.

The Canadian regulations do not permit the use of ethoxylated monoglycerides or succinylated monoglycerides.  Calcium stearoyl lactylate and sodium stearoyl lactylate are permitted at 0.375%, flour weight basis, in both bread and unstandardized bakery products and at 0.5% on a dry weight basis for cake mixes.  The maximum use level for DATEM is 0.6%, flour weight basis, for breads and at good manufacturing practice or GMP levels for non-standardized foods.  Polysorbate 60 is only permitted in cakes and cake mixes at 0.5% on a dry weight basis.

In summary, the key to producing quality, highly expanded bakery products is gas retention; all beginning with optimum dough development.  A well-developed dough is essential to maximizing the baking quality of your flour and to help minimize ingredient costs.  The addition of special emulsifiers, or dough conditioners, can improve the gas retention of a properly mixed dough resulting in improved processing tolerance, increased bread volume, and excellent grain and texture.  It's all about gas retention!  Thank you for your attention.