Enzymes' role in milling

by World Grain Staff
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by Lutz Popper

For a long time, - and ß-amylase were thought to be the only enzymes that could be used in the milling industry. This view has changed dramatically since the introduction of hemicellulases two decades ago and recently through the success of lipolytic enzymes. As shown in table 1, there are many more enzymes that still play only niche roles for certain applications but which may turn out one day to be just as versatile.

HEMICELLULASE The term hemicellulase designates a family of enzymes. All the members shown in figure 1 are able to break down the pentosans, but their impact on dough and baking properties varies widely.

It is assumed that pentosans form a network with gluten; the more pentosans are involved, the firmer the network. That is why darker wheat flours and mixtures containing rye flour have a lower volume yield than white flours. The volume yield of all flours can be increased considerably by adding hemicellulases.

Most of these enzymes are derived from Aspergillus mold strains selected for, or specializing in, the production of hemicellulases.

Hemicellulases are mostly sold in compounds with amylase. It is not possible to give a general dosage recommendation as there is no standard method of determining hemicellulase activity. The available methods are usually based on determining the release of reducing sugars, the reduction of viscosity or the breakdown of synthetic or colored molecules and are very difficult to relate to each other. Moreover, even the use of a standard method for different hemicellulases does not necessarily permit conclusions in respect of baking properties, presumably because the points at which hemicel- lulases of different origin attack the pentosan molecules are too varied. PROTEASE As shown in Figure 2, proteases (also known as proteinases or peptidases) split the protein strands of the gluten molecule and thus lead first to a softening and then to a complete collapse of the structure. A purified single and very specific protease would only be able to break down a few of the peptide bonds, resulting in only limited softening.

With short gluten structures a slight softening may well be desirable; in this case it has a similar significance to the use of cysteine. The proteolytic action is more time dependant than the function of cysteine. As a result, its activity level increases 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.

The use of protease is less crucial with flours that are rich in gluten. The enzyme is very common in the production of pan (toast) bread, where soft dough that precisely fills the tin is required. Proteases are also very useful in the production of cracker, biscuit or wafer flours where elasticity of the gluten is not desirable.

ENZYMES FOR BISCUITS, CRACKERS AND WAFERS

Whereas a high protein content and strong gluten are desired properties in many bread processes, flours with little and weak gluten are preferable for more durable baked goods. The tendency of dough to spring back after rolling and the undesired formation of gluten lumps in wafer batter are the reasons for this requirement.

Whether a flour with low and weak protein is available or not, the use of elasticity-reducing agents will have benefits in all stages of the process: the lamination will be more uniform; reduction of the thickness of the dough sheet can be performed faster and with more reproducibly; relaxation periods for the dough sheet can be shortened or even omitted; the dough pieces will keep their cut shape; shrinkage and bending in the oven as well as the formation of hairline cracks (checking) are prevented. With suitable amylases, expensive recipe components such as milk solids otherwise necessary for sufficient browning can be omitted. Furthermore, the whole process will be less dependent on flour quality. BISCUIT AND CRACKER APPLICATIONS Table 2 shows the recipes for simple hard biscuits made without and with protease (Alphamalt BK 5020). The last row compares the dimensions of the biscuits. As the length:width ratio shows (average of 25 biscuits), there is almost no difference between the length and width of biscuits with enzyme addition, while those without enzyme showed shrinkage in one direction.

Since the protease takes away most of the internal tension, the products are less inclined to bend during baking.

WAFER APPLICATIONS Batters for wafer production contain a large amount of water. Low viscosity as well as uniform dispersion of all ingredients is essential to produce wafers with a homogeneous structure. The use of low protein flour is desirable but may not be sufficient to prevent the formation of gluten lumps during mixing that can result in downtime due to blocked feed tubes and sieves, non-uniform browning and reduced stability of the baked goods.

Liquefyied hydrolytic enzyme complexes are able to decompose any gluten present in a liquid batter, resulting in a uniform mixture with optimum flow properties. Due to the viscosity reduction, the amount of water used in the recipe can be lowered, which results in a lower energy consumption for baking and a higher oven throughput. Wa- fers of higher density are crisper and remain crisp longer because of reduced water absorption.

Such enzymes are most suitable for semi-continuous processes with batch times of at least 10 minutes because the enzyme reaction needs some minutes to take effect. SODIUM METABISULPHITE REPLACER Sodium metabisulphite (SMB) is a strong reducing agent that splits the inter-chain and intra-chain disulphide bonds of the gluten, causing an immediate fall in dough resistance or batter viscosity. SMB is very cheap and easy to use; therefore many countries still use SMB in wafer and cracker production. Unfortunately, SMB destroys vitamin B1, and can cause health problems in sensitive people. Furthermore, it inhibits the browning reaction and causes a sulfurous off-taste. Not only do enzymes offer a healthy alternative to SMB but also they have decisive technical advantages, such as stable dough properties once the reaction is accomplished, including a comparable texture of return dough and fresh dough; the reduction of water addition to wafer batters and control of wafer density and stability.

When tested in the Farinograph, both SMB and enzymes show a decline in kneading resistance. The reaction of SMB occurs much faster but probably due to the presence of atmospheric oxygen, some of the resistance is restored upon continued mixing when disulphide bonds broken by SMB recover. The slower but persistent reaction of the enzymes results in a minimum resistance, when all the substrate of the enzymes has been degraded. GLUCOSE OXIDASE The enzyme glucose oxidase is usually derived from the mold Aspergillus, sometimes from Penecillium species. Honey is also a rich source of glucose oxidase. The enzyme stems from the pharyngeal glands of the bees. However, its suitability is rather restricted by the taste of its carrier.

One effect of glucose oxidase in the dough is to oxidize glucose to form gluconic acid with the aid of atmospheric oxygen, but the slight souring that occurs in the process is negligible. Its other effect is to transform water into hydrogen peroxide. This oxidizing agent acts on the thiol groups of the gluten, directly or via several pathways, inducing formation of disulphide bonds and thus tightening of the protein. The limiting factor in this process is the availability of oxygen. Besides other chemical reactions that consume oxygen, yeast needs oxygen before starting the actual fermentation, as it initially breathes instead of fermenting. This means that the conditions for glucose oxidase are only good on the surface of the dough where plenty of oxygen is always available. This limitation can be solved by technical measures during dough preparation. For example, overpressure or the supply of additional oxygen through the mixing tool. LIPOLYTIC ENZYMES Lipase is yet another enzyme that has been underestimated for a long time. The enzyme converts non-polar lipids into diglycerides and monoglycerides, (i.e. emulsifiers). There are also polar lipids in wheat flour, such as phospholipids and glycolipids (Figure 3, see page 30) that can be converted into more hydrophilic lyso-forms by some special lipases or phospholipases.

The in situ formation of emulsifiers results in dough strengthening and larger volume yield but not improved shelf life. This is in contrast to the effect of monoand diglycerides, which are added to a bread formula. Due to interaction with starch they are able to reduce the stal- ing rate. On the other hand, their effect on volume yield is very limited. Most probably, the action of enzymatically formed emulsifiers on volume yield is pronounced because they are already located at the right sites of the dough for improving the protein properties; but for anti-staling effects, not enough emulsifier is formed to interfere with starch retrogradation. Interestingly, it is being disputed whether dough has to contain additional fat, and if so, what kind of fat, for lipase to work satisfactorily. According to Mühlenchemie’s findings, fat reduces the efficacy of lipase, probably by "distracting" the lipase from the "right target." (i.e. the flour lipids).

There is also the problem of potential taste impairment caused by the release of flavor-active fatty acids. This becomes a particular issue if butter is involved. However, there are certain applications where lipases are of considerable use. STEAMED BREAD Chinese steamed bread is often made from a wheat flour of low or medium protein, depending on the type of steamed bread. The preparation process is sometimes quite similar to western style pan bread, but the final product is cured in a steam chamber or basket, not baked in an oven. Therefore, there are some differences in appearance. Steamed bread is white in color and has a soft and shiny surface. The common types of steamed bread weigh 30 – 120 g, with shapes either pillow-like or round.

Enzymes such as amylases or hemicellulases improve the overall appearance of steamed bread. Some kinds of steamed bread seem to be ideal playing grounds for lipases. Particularly after extensive kneading or long fermentation processes, a dramatic effect on dough stability and volume yield can be seen. However, this effect cannot be reproduced with all dough preparation methods.

Development of the dough by sheet- ing favors the beneficial effect of lipase. This is probably due to a more extensive exposure to atmospheric oxygen. Lipolyse exposes the fatty acids to the action of wheat lipoxygenase, which – in the presence of sufficient oxygen – is converted into hydroperoxides. These in turn will react with flour components. In addition to dough strengthening, a bleaching effect occurs due to the oxidation of flour carotenoids. Since lipases are specific for the type of fatty acid present in the triglyceride, not all lipases are suitable for the improvement of steamed bread. NOODLES The effect of lipase is also visible with noodles. Pastazym is a compound based on lipase that contains a selection of other enzymes as well. The lipase is responsible for a brightening and firming effect. Both effects are not only detectable in the laboratory but also by the consumer. There are certain limitations, of course. Pasta made from durum wheat only cannot be improved, and the use of eggs also masks the effect of enzymes. The greatest efficacy is achieved in noodles made from hard or soft wheat only. The bleaching effect is not always required, as some consumers prefer yellowish noodles. Nevertheless, it can be useful in this case too. If for instance a speckled or grayish flour is used, the enzyme reduces both the speckles and the dark color and therefore provides a bright background for permissible yellow food colorants (Figure 4). REPLACEMENT OF POTASSIUM BROMATE Less spectacular but probably even more important from a global point of view is the replacement of potassium bromate in bread-making processes. This very efficient and cheap bread improver is being banned in more and more countries for health reasons. Apart from alternative oxidizing agents, using oxidative enzymes was a very early approach to tackling this challenge. Surprisingly, these enzymes turned out to be of limited use. Amylase, xylanases and nowadays lipases proved to be far more efficient if combined with safe oxidizing agents such as ascorbic acid. Oxidases can nevertheless support their function. Figure 5 shows an early test for replacing bromate in ‘no-time’ bread-making processes. Figure 6 represents the effect of the bromate-replacing enzyme compound Alphamalt BX, which can be used for short processes as well and is most suitable for long fermentation (3 – 24 h). WG Dr. Lutz Popper is director of research and development, Mühlenchemie GmbH, Ahrensburg, Germany. For further information, E-mail: lpopper@muehlenchemie.com We want to hear from you — Send comments and inquiries to worldgrain@sosland.com. For reprints of WG articles, e-mail reprints@sosland.com.

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