in Bakery Foods
November 1994 -- Design Elements By: Scott Hegenbart
*April 1991-July 1996 Many food product designers consider enzyme use new and innovative. While this is true for many categories, the baking industry actually has a long history of enzyme study and application. In fact, some references to the use of added enzymes in bakery foods are over 100 years old. Even without this track record, enzymes are appealing functional ingredients for a variety of reasons. Enzymes are, for example, naturally occurring components of many bakery ingredients. If an enzyme is added, it often is destroyed by the heat of the baking process. In both cases, designers can obtain the functional benefits of the enzyme while maintaining a "clean label" image for the finished product. Enzymes also are specific to a particular function, eliminating concerns about undesired effects. Nevertheless, getting the most out of enzymes in bakery products requires some planning on the part of the designer and a better understanding of what enzymes can do.
Nature of the ingredientBecause they consist of long amino acid chains, enzymes are classified as proteins and share many protein-like qualities. An enzyme molecule, however, is folded into a specific three-dimensional globular structure. Within these contorted folds are cavities that match the external features of a substrate molecule -- a fat, protein or starch, for example -- much like a key fits into a lock. When an enzyme's active site meets with a corresponding substrate molecule, they temporarily bind to form an enzyme-substrate complex. By forming the complex, the enzyme lowers the energy required for certain reactions to take place. These reactions may either break up the substrate molecule or join it with another molecule. In addition, the complex will limit the reaction to specific bonds on the substrate molecule. Enzyme activity is highly specific. Depending on its three-dimensional structure, a particular enzyme may hydrolyze or synthesize only one type of molecule. Others are less specific to a given type of molecule, but promote a certain chemical reaction on entire classes of compounds sharing common structural elements. Whatever the reaction, the enzyme itself will remain unchanged and this is why enzymes are considered catalysts. Enzymes are named by adding the suffix "ase" to the end of the substrate. For simplicity, the substrate's name often is abbreviated. In baking applications, the general types of enzymes most commonly used are carbohydrases, proteases and lipoxygenases.
Starch segregationCarbohydrases hydrolyze glycoside linkages in carbohydrates. This linkage specifically refers to the bond between one sugar molecule's reducing functional group and the -OH (hydroxyl) group of another molecule -- usually a sugar molecule, as well. Amylases are the carbohydrases that offer the greatest number of potential functions in bakery foods. These hydrolyze amylose and amylopectin in starch, as well as starch derivatives such as dextrins and oligosaccharides. The alpha-amylase enzyme hydrolyzes starch into soluble dextrins. These dextrins may subsequently be hydrolyzed by beta-amylase to yield maltose, and/or amyloglucosidase to yield glucose. Because starch exists as a tightly packed granule, amylases must act upon starch granules that are damaged (as many are during flour milling) or on granules that have been gelatinized by moisture and heat (such as when a dough is mixed and baked). The sugars resulting from amylase activity act as food for yeast in yeast-raised products. As a result, the presence of these enzymes in the proper proportions is critical to carbon dioxide generation. Most flour naturally contains both alpha- and beta-amylase. The beta-amylase is, however, the only one naturally present in sufficient quantities. Thus, controlling the gassing power of the dough requires added alpha-amylase. Amylases also can affect the consistency of a dough. Damaged starch granules absorb more water than intact granules. This ability is reduced when the damaged granules are acted upon by amylases. With their ability to immobilize water reduced, the damaged granules release free water which softens the dough and makes it more mobile. A third function of amylases is their ability to retard staling. Over time, the crumb of baked products firms due to a complex set of changes that includes recrystallization (or retrogradation) of amylopectin in the starch. By hydrolyzing the amylopectin into smaller units, bacterial alpha-amylase can maintain softness and extend shelf life. One theory behind this suggests that amylopectin still crystallizes at the same rate with added enzymes, but that the shortened chain length maintains greater flexibility and softness when crystallized. Another theory is that the shortened amylopectin chains have a lesser tendency to retrograde. Either way, the enzyme must continue to hydrolyze starch after baking is completed. The fact that bacterial alpha-amylase is more thermally stable than other alpha-amylase sources is the reason it is used. Because the enzyme is active in the finished baked product, it is possible for the enzyme activity to go too far. Rather than maintaining softness, the crumb can actually become gummy. The starting enzyme dosage is critical to preventing this. For even greater assurance against overdosing, amyloglucosidase or pullulanase may be added along with the alpha-amylase. These enzymes don't contribute to anti-staling when used alone, but help prevent gumminess when combined with the amylase. A final use for amylases in bakery products is for replacing potassium bromate, an oxidizing agent that strengthens gluten strands. Strengthened gluten produces a dough with improved gas retention and, consequently, higher volume in the finished product. Based on various health studies, bromate use is on a sharp decline. Other oxidants -- such as ascorbic acid -- can promote comparable volume, but they don't provide a direct match for bromate. To compensate, alpha-amylase can be added with ascorbic acid to improve the volume and increase the quality of the crumb. Bakeries may either add alpha-amylase and ascorbic acid separately or select a custom blend featuring an optimized mixture of the two components. Amylases are not the only carbohydrases useful in bakery products. Pentosanases also can be added to improve quality. Both wheat and rye flour contain pentosans. These non-starch polysaccharides are highly hydrophilic and contribute significantly to the water absorption properties of a dough. In wheat flour-based products, pentosans also interfere with volume development. Adding pentosanase to a wheat flour-based product can improve product volume by hydrolyzing the pentosans present. At the same time, though, hydrolyzed pentosan will release water, making the dough very slack. When using pentosanase, the water absorption of the dough must be adjusted to compensate. If the dough is too slack, not only will it be difficult to machine, but the volume-building benefits of the pentosanase will not occur. In rye bread, the pentosans in the rye flour are critical to building structure since rye flour's gluten content isn't sufficient. If pentosan content is too high, though, it will compete for water with the starch and prevent it from swelling and gelatinizing properly. Pentosanase will help control the pentosan content so there is enough to build structure, but not so much as to interfere with the starch functionality. Pentosanases that hydrolyze cellulose also are available. These may be added to high-fiber bakery products to help improve their eating qualities by breaking up the long cellulose chains that contribute to gritty mouthfeel.
Harnessing protein pruningProteases hydrolyze the peptide bond between the amino group of one amino acid and the carboxyl group of the next amino acid in a protein. In dough, this serves to weaken the gluten chains. This can affect the dough in two ways, depending on when the protease is added. If the protease is allowed to hydrolyze a portion of a dough early in the process -- added to the sponge of white pan bread, for example -- it will reduce the mixing time necessary to develop the dough. Early addition of a protease to a complete dough, however, will cause the gluten to become too weak to build structure properly, resulting in a course, uneven crumb. Nevertheless, protease could be added to an entire dough later, at the mixing stage. This won't reduce the mixing time because the enzyme will not have had enough time to hydrolyze much gluten. Still, as hydrolysis occurs through shaping, floor time and proofing, the protease will help improve the flow of the dough. This procedure might be used to eliminate short pan fills in a straight (non-sponge) dough system or to help the pan flow of buns and English muffins. Another application for proteases is in replacing sodium sulfites in cracker doughs. Cracker doughs contain low levels of fat and water, making them rather stiff. This stiffness makes it difficult to laminate the dough into layers and to sheet it to cracker thinness. Sodium sulfites hydrolyze the disulfide bridges on the gluten molecule, reducing its resistance to extension and making the resulting dough more plastic. Sulfites have undesirable side effects, however. They break down vitamin B2, inhibit browning reactions that are desirable in baked products, and are a marketing no-no because some consumers exhibit allergic reactions to the substance. In fact, many countries have banned or are considering banning sulfite's use in bakery products. Adding a protease to the formula and allowing sufficient time for the enzyme to act (sulfites, by comparison, react more rapidly) can achieve the desired workability in the dough without the negative side effects.
Bond-building catalystWhile proteases help make dough more slack, lipoxygenases can help do the opposite. Lipoxygenases catalyze the addition of an oxygen molecule to polyunsaturated fatty acids to form peroxides such as hydroperoxy-linoleic acid. These then will interact with a gluten side chain, making the gluten more hydrophobic and, subsequently, stronger. With stronger gluten, the dough will have better gas-retention properties and increased tolerance to mixing. In a way, lipoxygenases offer results similar to those obtained with dough strengtheners such as sodium stearoyl-2-lactylate, but they also offer additional benefits. Although the exact mechanism behind it is not fully understood, lipoxygenase can bleach fat-soluble flour pigments to produce a whiter crumb in finished bread and rolls.
Application intricaciesUnderstanding what different types of enzymes do to bakery products is the first step in enzyme selection. Considering how specific enzyme action is, once the desired results are determined, the enzyme to use will be a straightforward decision. Other factors in enzyme selection and use aren't so easy. These include the enzyme source and form, the strength of the enzyme activity and how much to use, and the conditions under which the enzyme will be used and handled. Amylases used in bakery foods come from three primary sources.
Understanding Enzyme Function in Bakery Foods