The baking industry has made use of yeasts and enzymes for hundreds of years to manufacture a wide range of high-quality products. It is now well accepted that wheat endogenous enzyme systems and yeast enzymes playa major role in the baking process. Wheat and consequently wheat flour contain a wide range of enzyme activities; these different endogenous activities can vary greatly depending for example, on growing/harvesting and storage conditions. A well-known example is wheat a-amylase. Too high activities render a wheat unfit for bread-making. Conversely, a too low activity results in a sub-optimal product.
Malt is one source of enzymes widely used in the baking industry. It contains a whole range of enzymes including the enzyme diastase, which can be used to compensate for too low endogenous a-amylase levels. Malt is used in breads and rolls to give these products a higher volume, a better color and a softer crumb. These effects are mainly attributed to the enzyme diastase. Malt, however, contains a whole range of enzymes, including proteases and pentosanases. The enzyme profile of malt can vary depending on the variety used and the malting conditions. The main enzyme activities found in these commercial enzyme preparations are starch-degrading enzymes (amylases), proteases and pentosanases.
Amylases
Amylases can be used in three steps of bread-making process: dough mixing, dough fermentation, and baking. Since starch granules are only degraded at a slow rate by a-amylases, damaged starch and solubilised amylose are the main substrates for this enzyme in a dough. The amount of damaged starch can vary, depending on the type of flour and milling conditions. Grists used for bread-making purposes generally contain 5-9% damaged starch. The hydrolysis of damaged starch plays an important role in rheological properties of dough since a considerable amount of water in the dough is bound by damaged starch.
Depending on the types of amylases or glucoamylases used, different amounts of maltose, glucose and dextrins are formed during dough fermentation. Malto and glucose are important for yeast metabolism. Production of maltose by β-amylase in a dough is dependent primarily on the action of α-amylase on damaged starch. Levels of β-amylase are usually sufficient in wheat but levels of α-amylase vary considerably. Production of sufficient quantities of glucose can be achieved by adding a glucoamylase, which is advantageous since glucose is fermented at a higher rate than maltose. Glucoamylases can therefore be used to activate fermentation and to reduce the fermentation time.
In the oven, dough viscosity initially decreases enabling higher enzyme action, and from 56°C onwards, starch gelatinises and becomes highly susceptible to amylolysis. Temperature optima and thermo stability of the enzymes used are therefore of great importance.
Proteases
Small amounts of proteases can have large effects on gluten physical properties. It is demonstrated that cleavage of a few peptide bonds resulted in a rapid decrease in the viscosity of glutenin dispersions. Also, evidence to support the hypothesis that gluten softening is the direct result of peptide bond scission catalysed by proteases has been reported. Extensive softening was observed although very few peptide bonds were broken. Proteases can be used to assure bread dough uniformity and help control bread texture and improve flavor. Alkaline proteases have a rather weak action on gluten. However, the neutral proteases have a very strong action on gluten.
With the increased use of vital wheat gluten as a partial substitute for high-protein, high-quality hard wheats in European bread flours, another application of proteases is possible. Quality variations in gluten pose an important problem and are thought to result from heat damage. The damaged gluten gives a less elastic and stiffer dough and therefore an inferior product. Since heat damage makes the gluten far more susceptible to proteolysis, proteases can be used to alleviate this problem by specifically modifying these damaged structures in a dough.
Pentosanases
Hemicellulases are able to destroy the water-binding capacity of wheat flour pentosanases and release water. This causes dough softening. When this only occurs to a limited extent it may result in an increased volume. This effect can be regarded as quite nonspecific and, in many cases, is not an objective since it is difficult to control compared with other enzyme activities that cause dough softening. In this respect a clear distinction must be made between exo- and endo-xylanases. The use of early enzyme formulations containing exo-xylanases could easily lead to sticky doughs. Endo-1,3-beta-xylosidases have a limited activity on wheat soluble and insoluble pentosans and are less likely to cause an overdose effect. Therefore, these endoxylanases are the preferred enzyme. Another possible effect of pentosanases is that they could offset the negative effects of insoluble pentosans present in the flour.
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