From Chapter 1: Basic Food Science — Enzymes
All enzymes are proteins. They act as biological catalysts to substantially accelerate the rate of a specific chemical reaction, yet like inorganic catalysts, they remain unchanged chemically by the reaction. The action of an enzyme is highly specific to its substrate, and it continues to act until all of the substrate is converted or until the enzyme is shut down, or denatured, by heat or alterations in background chemical conditions.
Like other proteins, enzymes can be very large in size, with molecular weights ranging from about 10,000 to more than 1 million Da (Zeiger and Greer 1971), yet they are very nimble. For example, heating sucrose in acid will hydrolyze, or split, the sugar into its components, fructose and glucose. If the enzyme invertase is used instead, the conditions are much milder, with no heat or acid required, and the action much quicker, 50 billion times faster, in fact (Mathewson 1998).
Enzymes perform their jobs by bringing reactants together, rather than relying on the random motion of molecules as in conventional chemical reactions. As always, the rearrangement of bonds requires energy input. In a chemical reaction, the molecules need to collide with each other at the proper orientation and with the right amount of energy. Enzymes, however, complex with the substrate, forming reactive intermediates. This complex breaks down, releasing the altered substrate, while the enzyme remains unchanged to enter into another reaction.
Sources of enzymes
Animals and higher plants form many different kinds of enzymes in their cells to enable various life processes and were the first sources of enzymes used by bakers and other food processors. Malted cereal grains, with their natural amylase content, convert long-chain cereal starches to smaller polysaccharides. Papain and bromalain (also called bromalin), for example, can be extracted from papaya and pineapple, respectively, and are powerful proteases, breaking down proteins into smaller polypeptides. Rennet, another protease, is the complex of enzymes animals use to digest milk and that dairies employ to coagulate milk into curds during cheesemaking. These enzyme extracts were made by processing plant and muscle material, filtering, concentrating and drying the soluble and insoluble fractions. Difficult to control, the process separated the resulting enzymes more as classes than individual pure compounds. Although such extracts contain a range of compounds that act in a similar way, they also carry the risk of unwanted side activities.
Yet the industry was quick to adopt enzymes because they work at lower energy inputs and under safer conditions than many purely chemical reactions. What was needed was better isolation of individual enzymes. The greater the specificity, the better the economics.
Today, microbial fermentation is the method of choice for producing enzymes. The microorganisms involved in producing enzymes for food applications include the fungi (molds) Aspergillus niger or A. oryzae, the bacteria Bacillus subtilis and Streptomyces griseus and the yeasts Kluyveromyces fragillils and Saccharomyces cerevisae. These species consist of many families and individuals, called strains. Manufacturers are able to maintain and use pure cultures of individual strains that express their unique genetics by producing enzymes of highly specific character.
Enzyme producers develop new enzymes in several ways. They hunt microoganisms around the world. Often the environment provides a clue to the potential enzymes to be harvested: A heat-loving bacteria may carry novel heat-resistant amylases. Strains also develop spontaneous genetic mutations of their deoxyribonucleic acid (DNA), resulting in enzymes with altered properties. Others can be made to produce different enzymes by transfers of genetic material from one organism to another. Indeed, since genetic engineering first became available in the 1970s, it has opened many new doors. For example, an organism that makes a novel enzyme deemed useful may also prove to be difficult to reproduce or require complex growing conditions. The genes that code for the enzyme can be transferred to another microorganism with better production economics.
Mathewson, P.R. 1998. Enzymes. Eagan Press, St. Paul, MN.
Zeiger, E., and Greer, E.N. 1971. Principles of milling. In: What Chemistry and Technology, 2nd Ed., Pomeranz, Y., ed. American Association of Cereal Chemists: St. Paul, MN.
More on this topic can be found in “Baking Science & Technology, 4th ed., Vol. I,” Page 47, by E.J. Pyler and L.A. Gorton. Details are found in our store.