Characterization of Enzymes for Applications

In industrial food applications the usual requirement of an enzyme is that it produce the desired functionality for the minimum cost. This often implies that offerings by alternate suppliers are assayed to find the best enzyme source for the process in hand. The characterizing factors are (1) rate (activity per gram of enzyme); (2) pH optimum; (3) temperature optimum; (4) stability under conditions of use; and (5) presence (or absence) of potentially deleterious side activities.

Rate. By rate, the food processor usually means the amount of modification obtained during the time allowed for enzyme action in the process. This may be different from the initial rate of conversion of substrate to product as defined by an enzymologist. An assay that measures the latter rate may be misleading if the modification occurs during extended incubation in the process.

pH, Temperature. The pH and temperature optimum curves published by suppliers usually confound the true influence of these factors on enzyme catalytic properties with the effect on enzyme stability. Enzyme denaturation is influenced by numerous factors, is usually irreversible, and occurs with first-order kinetics. Optimum curves are constructed using assays that measure the amount of substrate modification over a period of time and represent a summation of true rate effects plus denaturation during that time. They should be used with caution.

Stability. The presence of substrate stabilizes enzyme against denaturation; thus, the real optimum of interest is the stability of enzyme under the conditions of use: time, pH, temperature, substrate concentration, inorganic ions, organic solvents, and so on. An assay used to screen enzymes for a particular application should mimic as nearly as possible the actual use conditions, to give a reliable estimate of cost benefit.

Side activities. Preparing a pure isolated enzyme is cost-prohibitive for food applications. All commercial enzymes contain some activities other than those declared on the label; for example, fungal amylase usually contains some proteolytic activity, a bacterial protease may also contain some xylanase, and so on. These side activities may present a problem when the enzyme is used in certain food processing situations, and assays should be applied that will detect them, as well as the main enzyme of interest.

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