1.4. Other ingredients
1.4.1. Salt
Salt's main function is to bring out the flavour of the baked product. Salt tends to bring out the good flavours and mask the off-flavours. Usage levels are normally between 1,8 % and 2,2 %. Legislation may vary from country to country because the intake of too much salt is considered as a health risk. In Belgium for instance the maximum allowed is 1,8 %, while in France 2,0 % is allowed. In Scandinavia one has to pay extra taxes if the salt level in the bread is higher then 1,2 %. Bread made with less then 1,6 % salt will taste insipid and bread made with more then 2,2 % will taste too salty.
In addition to impacting flavour, salt also inhibits fermentation due to the osmotic pressure effect. Yeast cells will partially dehydrate due to the osmotic pressure. This can be illustrated easily by putting some salt on fresh yeast. After a while the yeast will liquefy due to the fact that the salt will attract the water from the yeast cell. As the cell membrane is semi permeable, water will migrate from the cell and the mixture will seem to liquefy. In reality the yeast cell undergoes a change which can be compared with the change that happens to a grape when it becomes a raisin, it just dries out.
The fact that salt influences the fermentation can be used to control the fermentation : salt can be added for instance to sponges to slow down the fermentation rate. Slowing down fermentation rate means that less sugars are metabolised into acids. The result is that the pH of the dough will be higher and the crust colour will be darker. To remember that high pH gives a darker colour, one can think about a chocolate cake. Chocolate is alkaline and to get a darker, deeper colour of a chocolate cake, one must increase the pH.
Salt toughens the gluten. Weaker flours could actually be strengthened by adding salt. Salt lengthens the mixing time so it is common to delay the addition of the salt to the mixer. Faster flour hydration is also seen with delayed salt. The reason why salt toughens the gluten must be sought in the fact that gluten is made of negatively charged proteins. Negatively charged molecules will repel and not attract each other. It is believed that the positive sodium-ions Na+ of the salt play a role in bringing the protein molecules closer to each other.
Lastly, bread with no salt will also has a crust which is lighter in colour (given the same baking time and oven temperature). This can be explained as follows. Salt will slow down fermentation, so when there is no salt, the yeast activity will increase i.e. the yeast will metabolise more sugar in a given period of time. As a result there will be less sugars left in the dough and the pH of the dough will be lower (more acids will be formed). Sugars play (together with proteins, moisture and heat) an important role in the Maillard reaction. But the Maillard reaction is also influenced by the pH : a higher pH will speed up the Maillard reaction. So in this case where the pH is lower and where there are less sugars left, the colour of the crust is lighter.
1.4.2. Sugar
Sugar's main function is to provide food for the yeast. In normal bread production, 3,0 to 3,5 % fermentable solids are required to sustain yeast activity. This food supply can come from added sugar or from the enzymatic conversion of the starch to sugar or from a combination of both. Therefore sugar is not an essential ingredient.
Starch indeed belongs chemically to the group of carbohydrates : it is a long chain of glucose units and according to its structure there are two kinds :
· amylose : linear chain of glucose units
· amylopectin : branched chain of glucose units
Glucose, fructose and galactose are monosaccharides; sucrose, lactose and maltose are disaccharides. Dextrins also contain a large number of glucose units but not as much as starch.
Secondary functions of sugar are related to sugar that is not metabolised by the yeast and which is called residual sugar. As residual sugar levels are higher, crust colour is darker, taste is sweeter, and moisture retention is improved due to the hygroscopic properties of sugar.
There are many kinds of sugar used in the industry. The most common is 42 HFCS (42 high fructose corn syrup). The 42 means that 42 % of the 71 % solids found in the corn syrup is fructose. Higher numbers mean that the fructose content of the syrup is higher and hence the syrup will taste sweeter.
Different sugars also give a different sensation of sweetness. Take for instance glucose and fructose which chemically have exactly the same formula (C6H12O6) but the molecule has a different structure :
It is commonly known that fructose is about twice as sweet as glucose. The following table gives an overview of the relative sweetness of different sugars :
sugar |
sweetness |
| fructose | 140 |
| sucrose | 100 |
| 42 HFCS | 100 |
| glucose | 80 |
| maltose | 40 |
| lactose | 20 |
Lactose and maltose have the following molecular structure.
The main difference is however that lactose is a non-fermentable sugar : it will not be metabolised by the yeast and remain in the dough. In view of it's rather low sweetness, it will not give a sweeter product but it will influence the crust colour (Maillard reaction) and because of its hygroscopic nature delay staling.
Sugar has the same effect as salt : if too much is used, yeast activity will slow down. This effect can be seen from a 5 – 6 % sugar level. In order to compensate one can add more yeast. The sugar/yeast ratio should be 3/1. If you want to make a product that contains 15 % of sugar, the yeast level should be 5 % (baker's percentage).
Finally one should remember there are also "natural" sugars such as honey and fruit juices.
1.4.3. Fat
Fats are used in bread production to provide overall lubrication. It becomes necessary to use a small amount to facilitate slicing : 0,7 – 1,0 % will suffice to facilitate slicing.
Addition of fat helps in the handling of the dough during the make-up process. Besides lubricating the baked crumb, fat also lubricates the dough and this eases dough expansion in the proofer and in the oven. It will also tenderise the crust and improve shelf life by retarding staling.
Fats are constantly in the media with regards to health risks. Presently we have the hype around trans fatty acids. Without going into too much detail, one can divide the fats into a number of categories :
a) according to its physical state : fat or shortening is solid or semi-solid while oils are liquid at room temperature. In this context we talk about the solid fat content (SFC) which refers to the portion of solid fat at a given temperature.
b) according to its origin : vegetable fats are derived from vegetable sources only (soybeans for instance) or from animal sources such as pork (lard) or milk (butter).
c) according to its chemical structure : saturated fats (present in both animal and vegetable fats but higher in tropical oils) and unsaturated fats. In the production of margarines and fat there is a step called the "hydrogenation" and the degree of hydrogenation will affect the stability of fat and also the amount of saturated fats.
Finally cholesterol is only present in animal fats.
1.4.4. Milk solids
They primarily function as nutritional supplements. Milk is high in lysine (an essential amino acid) and calcium and the overall nutritional quality of the milk protein is excellent. European bakers prefer the use of liquid milk above the use of powder milk. Liquid milk may be less user friendly (storage, perishable), however it has the advantage that no dry matter remains in the product. Indeed, milk powder (or rather the denaturated proteins present in the milk powder) will not dissolve completely in the water and remain as dry solids in the crumb. This will give a dryer, less moist crumb. However it should be kept in mind that the milk must have been heat treated because the serum protein in milk has a weakening effect upon the gluten protein in wheat flour.
Besides improving nutritional quality, milk improves the flavour if used in a high enough amount, the dough handling and overall processing tolerance :
1.4.5. Vital wheat gluten
Vital wheat gluten is the natural wheat protein extracted from flour which still retains all of its gluten forming characteristics. It is added to the dough to help strengthen a weak flour or to obtain additional loaf volume. A 1 % addition of wheat gluten will increase the flour protein content by 0,6 % and increase the absorption by 1,5 %. By adding wheat gluten to the recipe, mixing and fermentation times are generally increased and tolerances improve. They mainly are used in systems where the gluten network is weak or where it has to carry extra ingredients such as raisins, different types of grains, extra fibres etc.
1.4.6. Bread improvers
Bread improvers (or dough conditioners as they are called in the
In earlier times, baking was a profession where appropriate time could be allocated to mixing, fermentation, proofing and the baking of bread. Adjustments could be made, as needed, for changes in flour, yeast activity, temperature, humidity, and any other environmental conditions that might occur. Today, the bread making operation is largely mechanized, and we desire to produce the same loaf of bread, roll or pizza crust every hour of every day, year after year. The use of dough conditioners has enabled the baker to overcome these challenges and produce uniform, high quality baked goods.
Dough conditioners are used:
Important dough characteristics influenced by dough conditioners include:
They can be divided into 3 main categories : enzymes, oxidising agents, reducing agents. In fact there is a 4th category : emulsifiers which will be described in a separate paragraph.
a) Enzymes
First of all it should be noted that enzymes are proteins and that they are substrate specific. This means that a given enzyme only will work on a certain substrate and only do a very particular job. Secondly it should be remembered that, although they take part in a chemical (enzymatic) reaction, they do not change during that reaction. They are what we call biological catalysts that accelerate or facilitate chemical reactions.
Because they are proteins, they are heat sensitive and all enzymes have an optimum temperature and pH for activity. Within that range, activity increases with temperature until the denaturation point is reached. At that point the enzyme will lose its functionality. Apart from temperature and pH, enzymes are also dependent upon the availability of water, amount of enzyme used, the availability of the substrate and the time allowed for the reaction.
Enzymes are biological compounds, usually proteins, which expedite the conversion of one substance into another. Their presence accelerates the rate of a chemical reaction and they are often specific and act upon only one substrate, or catalyze only one kind of reaction, in different, but related, substrates.
The activity of enzymes is dependent upon temperature. Enzymes used in baking are usually stable at room temperature and the rate of enzyme activity doubles with each 10°C increase up to the temperature of denaturation, at which the enzyme is inactivated. Most enzymes are inactivated above 60°C. An exception would be bacterial alpha-amylase, which retains its activity up to 85°C.
Enzymatic activity is pH dependent; there will be a pH optimum where maximum activity is achieved. Enzymes are usually stable at pH values between 4 and 9. Most doughs have pH values between 5 and 6. There is seldom an issue of enzyme denaturation due to pH. However, the acidity does effect the ionization of groups at the active site of the enzyme, rendering the enzyme more or less effective, depending upon the pH of the dough.
Enzymatic activity is dependent upon the concentration of the enzyme and the substrate. A higher concentration of enzyme will increase the reaction rate although not in direct proportion to substrate availability. The amount of time the enzyme and substrate are together directly affects the extent of reaction.
Many enzymes require the presence of a non-protein group, or co-enzyme, to be active. There are also compounds that act as inhibitors of enzyme activity by binding reversibly or irreversibly to the enzyme and/or substrate or in some way inhibit enzyme action. Oxidizing agents, such as bromates and iodates, and some heavy metal ions, have this effect.
There are 4 main groups of enzymes which are commonly encountered in baking : amylases, proteases pentosanases and lipoxygenases. Amylases are divided into α-amylase and β-amylase.
Two amylases are common to the baking industry, alpha-amylase and beta-amylase also known as alpha-1,4-glucan glucanohydrolase and alpha-1,4-glucan maltohydrolase.
Amylases convert starch into sugar : the α-amylase will cleave the starch randomly (the so called 1-4 bonds in the starch) while the β-amylase can only chop off two sugar units at the time at the end of the starch chain. Normally there is enough β-amylase present in the flour but sometimes addition of α-amylase is needed. The α-amylase will cut the starch into smaller units called dextrins and the more α-amylase activity there is, the better for the β-amylase because there are more extremities available. So the substrate for the β-amylase is either starch or dextrins and the product is maltose.
Alpha-amylase is an endoenzyme that attacks linkages within the molecular structure. It randomly cleaves starch chains at interior a-1,4-glycosidic linkages producing short chains of glucose molecules or dextrins. Beta-amylase is an exoenzyme and cleaves maltose units from the non-reducing end of the starch molecule. In order for these enzymes to function, the starch granule must be ruptured so that the individual starch molecules are available for enzymatic action.
Depending upon their origin, alpha- and beta-amylases show differences in pH and temperature optima, thermostability, and other chemical stability. They do not require co-enzymes for activity, although alpha-amylase activity is enhanced by the presence of calcium.
The pH optimum for alpha-amylase is 4.5 and it is inactivated at a pH of 3.3 to 4.0. This pH dependence decreases the efficacy of this enzyme in sour doughs. Beta-amylase is active across a much broader pH range, 4.5-9.2, with a pH optimum of 5.3. Alpha-amylase is relatively thermostable up to 70°C, whereas beta-amylase loses about half of its activity at this temperature. Fungal amylase is the least temperature stable, followed by cereal amylase, while bacterial amylase is stable at higher temperatures. New intermediate stability enzymes have been developed that are active above the gelatinization temperature of starch (60°C), but are totally inactivated at the later stages of baking (80-90°C). The objective is to maximize the anti-staling effect without creating a gummy, sticky product.
Amylase supplementation can occur at the flour mill or at the bakery in doughs and sponges. Malted barley flour has been used as an ingredient in bread for more than a century. Today, malted barley flour, malted wheat flour, fungal and bacterial alpha-amylases are used. The use of amylases provides a source of sugar for yeast fermentation. The increased sugars also improve flavour and enhance crust colour. Through starch modification, amylases improve moisture retention, have a crumb-softening effect and decrease staling.
Flour tends to lack α-amylase and the miller will supplement the flour with α-amylase. The diastatic activity of the flour is expressed by the falling number or the Hagberg number. A good flour has a falling number between 200 and 250 seconds. The α-amylase the miller will add can come from three different sources : cereal source (malted barley), fungal source (Aspergillius oryzae) or bacterial source (Bacillus subtilis). Bacterial amylase do denature at relatively high temperatures and some will remain in the bread after baking. The enzyme will continue to chop up starch in the baked bread. As starch is one of the main players in the staling mechanism, bacterial enzymes are used as crumb softeners because they will continue to work while the bread sits on the shelf of the supermarket. However there is a danger to it : the bread becomes softer and softer, it becomes more and more gummy and it is not uncommon that it will flatten, collapse while it sits on the shelf in case there is too much bacterial amylase left in the bread.
Malt is produced by germinating barley. During the germination the kernel will produce a lot of enzymes, mainly amylases and proteases. At a certain moment the germination process will be stopped and the enzymes will be extracted. This will lead to diastatic malt syrup i.e. a syrup which contains active enzymes. This syrup can also be dried under well controlled conditions in order to obtain malt flour. The diastatic malt is used to improve dough handling, provides more food for the yeast (as it will contain maltose), flavour, crust and crumb colour and it is a shelf life extender.
Nondiasatic malt will be treated in such a way that the enzymes will denaturate i.e. the temperatures used will be high enough to deactivate the enzymes. This product is a syrup containing about 60 % of maltose. It will aid in the fermentation of the dough, contribute to crust and crumb colour and improve the flavour of the bread.
Fungal amylases work in exactly the same way bacterial and cereal amylases work. They however are denaturated at lower temperatures.
Protease will react with proteins and weaken them. As a result mixing time will be reduced, machinability will be improved as well as pan flow (the dough will fill more easily the shape of the pan). These effects are accomplished by breaking the long protein chains, cutting peptide bonds, into smaller units.
Proteins are made up of long chains of amino acids. Proteolytic enzymes, or proteases, include proteinases and peptidases. Proteinases split proteins at the CO-NH linkages, creating polypeptides, peptides and peptones. These are then further hydrolyzed into amino acids by peptidases.
In addition to supplying amylases, malted barley flour was also once relied upon for proteolytic enzymes, but these have been replaced by proteases from plant and fungal sources. Addition of proteases enables high speed bread production by decreasing the mixing time needed to achieve pliable dough. A protease acts to decrease the size and binding ability of the gluten molecules. Their action has much the same effect as reducing agents, except their effect is permanent; it cannot be reversed by the addition of an oxidizing agent.
Pentosans are polysaccharides comprised predominantly of the five-carbon sugars xylose and arabinose. While they are present in wheat flour in very small quantities, about 2 to 3 percent, they account for as much as one-quarter of the water absorption of dough made from wheat flour. This increases the viscosity of the dough and negatively affects loaf volume. Pentosanases cleave the polysaccharide chains thereby decreasing viscosity and improving loaf volume. Pentosanases have only been available commercially in recent years.
Finally also lipoxygenase is used in the bakery which is found in soy flour. This enzyme will bleach the flour. Flour contains a yellowish pigment that will be broken down by lipoxygenase. As a result one will obtain a whiter crumb.
b) Oxidising agents
Oxidising agents are used by the baker to improve dough strength. Due to the oxidising action SH-groups in the gluten network will be transformed into –S-S- bonds between the protein chains rendering a stronger gluten network. They will improve dough handling for better machining and contribute to improved gas retention, giving better volume and a more regular grain of the crumb. Some oxidants are fast acting, working in the mixer and early make-up stage. Bromates, which are cancerogenous and which are only allowed in the
One oxidant with which good results were obtained in the
Calcium peroxide is an oxidant but is used for its dough drying capabilities. It tends to take away the stickiness without stiffening the dough. It reacts immediately on contact with water.
The most widely used oxidising agent is ascorbic acid or vitamin C. No need to say it is safe to use. However one needs oxygen to be present because ascorbic acid as such is a reducing agent. In the presence of oxygen however it will become dehydroxyascorbic acid and it is actually the dehydroxyascorbic acid reacting as an oxidising agent.
c) Reducing agents
Reducing agents are used to weaken the protein and have the same effect as proteases. The difference being however that the proteases will be destructed by the high temperatures in the oven while reducing agents will remain in tact of course. Reducing agents will reduce mixing time and improve dough machinability i.e. moulding will be facilitated. Reducing agents break bonds between the proteins during mixing. They have the opposite effect of oxidising agents. The most commonly used reducing agent is L-cysteine.
The functional characteristics of a protein are determined by its amino acid content. About 2 percent of the amino acid content of wheat gluten is cysteine. The amino acid cysteine contains a sulhydryl group (-SH) which can be oxidized to cystine and form a disulfide (-S-S-) bridge between two adjacent polypeptide chains or within one molecule. This is a relatively strong bond and results in an intricate and rigid network of protein molecules. The dough resulting from this oxidation will have increased gas retention, but will also be very elastic and resist flow. These doughs are often described as "bucky."
Addition of a reducing agent to dough "relaxes" the dough and gives it increased extensibility. This occurs by reducing or breaking the disulfide bonds formed between or within gluten molecules. This action serves to reduce the mixing time and less total energy is required to reach peak dough development. The time required for hydration of the starch and gluten molecules is shortened so that dough development starts earlier in the mix cycle. The rate of energy input during mixing is increased and dough development times are shortened.
Reducing agents act quickly in dough and each molecule reacts only once. The amount of gluten relaxation can be controlled by the amount of reducing agent added. Overuse of a reducing agent results in poor quality bread products. Characteristics observed include low volume, a coarse crumb texture, poor crumb colour, and a generally poor appearance.
Reducing agents common to the baking industry include L-cysteine and glutathione. L-cysteine is an amino acid and glutathione a tri-peptide.
The action of a reducing agent can be reversed and the disulfide bonds renewed through addition of an oxidant. Combination of a reducing agent with a slow-acting oxidant, such as ascorbic acid, reduces the mixing time of straight dough to be more in line with that of a sponge or liquid pre-ferment without the need for any extra equipment and space required. However, addition of a reducing agent may require an increase in floor time to achieve machinable dough, thus offsetting the gain from a decreased mixing time. Many combinations of reducing agents with oxidants are offered commercially, enabling optimization for specific situations in a bakery.
1.4.7. Emulsifiers
A surfactant is an amphipilic molecule. That is, one portion of the molecule has no charge (non-polar) and associates with the lipid or air phase, while another portion of the molecule is charged (polar) and associates with the water or aqueous phase of a system. These molecules migrate to the interfaces between two physical phases, with each end of the molecule associating with the preferred medium. In bread products, surfactants function less as a true emulsifier than as a surface-active agent that modifies the behaviour of the proteins and starches with which they interact. Gluten protein contains about 40% hydrophobic amino acids and interacts with the non-polar portion of surfactants.
In yeast-leavened baked goods, surfactants have been shown to strengthen the viscoelastic gluten-starch film, delay setting of the dough during baking, and to interact with starch molecules to inhibit starch retrogradation and staling.
The most commonly used emulsifiers in baking are:
The use of surfactants can increase product volume, create a fine, uniform crumb, produce a more tender crumb and crust, improve moisture retention, improve sheeting properties, and reduce staling. This paper will review a few of the more commonly used surfactants.
Some emulsifiers form complexes with the starch and slow down the retrogradation process during storage stages. Glycerol mono-stearate (GMS) is one such emulsifier possessing this property and has been used extensively in the past as a bread improver. GMS may come in a number of forms and with varying monoglyceride contents and is at its most effective against bread staling when used as a hydrate in the alpha gel form. This condition is achieved over a limited range of GMS concentrations and preparation temperatures, and careful preparation is required to ensure most effective use of this emulsifier.
Other emulsifiers that may be included for their anti-staling properties are DATA esters, and CSL or SSL. These too, have the ability to form complexes with flour components and to influence the rate at which gelatinized starch retrogrades during storage and can have an impact on reducing the staling rate.
DATA esters, CSL, and to a lesser extent, GMS, are able to play a similar role to that of fat in bread making with respect to maintaining freshness in bread.
Mono- and diglycerides are the surfactants most widely used in baking. They are esters of glycerol and one or two fatty acids. When one fatty acid is bound to glycerol it can be in either the first or the second position. The fatty acid is depicted by an "R" in the slide. These are also referred to as alpha- and beta- monoglycerides, respectively. In the production of mono- and diglycerides for commercial use, approximately 40-60% of the finished product will be monoglycerides, 30-40% diglycerides and the balance a mixture of triglycerides, glycerol and fatty acids. The alpha-monoglycerides have been described as the functionally important components and interact with amylose to inhibit recrystallisation of the starch to bring about a crumb softening effect. Propylene glycol esters of fatty acids function in much the same manner as mono- and diglycerides.
Lecithin is a naturally occurring surfactant comprised of a glycerol backbone and two fatty acids, phosphoric acid and choline. Lecithin is used in bread dough at 0.15-0.20% of the flour weight. Lecithin functions in bread dough to reduce mixing time, increase water absorption, improve machinability, yield a more uniform crust colour, a more tender crust, and to produce a softer crumb with a decreased rate of staling.
Ethoxylated mono- and diglycerides are strongly hydrophilic surfactants and function as dough strengtheners by forming strong hydrogen bonding with dough components. Use of this conditioner improves the tolerance of dough to shock in mechanized bread production.
There are no restrictions in the amount of mono- and diglycerides, propylene glycol esters of fatty acids, lecithin, and ethoxylated mono-and diglycerides that can be used in yeast-leavened baked goods, as overuse causes detrimental changes, such as an open and irregular cell structure.
Diacetylltartaric acid esters of mono- and diglycerides (DATEM) are both hydrophilic and lipophilic. They function well in dispersing shortening evenly throughout the dough, thereby improving the elasticity and extensibility of the gluten, dough handling characteristics, tolerance to mechanical shock, and improved gas retention, to yield products with greater loaf volume and a finer crumb. Diacetylltartaric acid esters of mono- and diglycerides function in a manner similar to monoglycerides to complex with starch and retard crumb staling.
Sodium and calcium stearoyl-2-lactylates are multifunctional surfactants that complex with gluten proteins and the amylose fraction of wheat starch to increase dough absorption, improve mixing tolerance and dough machinability, increase loaf volume, improve the texture of the crumb, create a more tender crust and improve shelf life. Both conditioners are limited in usage levels to less than 0.5% of the weight of flour used.
Noël Haegens
