Enzymes

Abstract

The history of enzymes is closely connected with the knowledge obtained in the fields of foodstuff chemistry and technology (1,2). It started around 1526 with Paracelsus’ studies of fermentation products.The enzyme levels of a certain food are ascertained to determine its degree of freshness (as in the case of oxidative enzymes in vegetables), to detect particular treatments, such as pasteurization (easily monitored in milk by measuring the levels of phosphatase and lactoperoxidase), or to see whether decay or microbial contamination has started. Enzyme levels can be measured easily by observing how they act on their substrates, since most of these enzyme-catalyzed reactions have an absolute specificity. The first satis-factory mathematical analysis of the course of an enzyme-catalyzed reaction was made by Michaelis and Menten in 1913, who suggested that the rate of transformation of a substrate (v) is a function, over a certain range, of the substrate [S] and enzyme [E] concentration:v ¼ kcat½E½S KM ü ½S ð1ð where kcat and KM are constants. Assuming that this equation is valid for most enzyme-catalyzed reactions, the enzymeconcentration (or activity) is proportional to the rate of appearance of a product or disappear-ance of a substrate, and independent of substrate concentration, only when [S ] KM for which the above expression may be reduced to: v ¼ kcat½E ð2ü For this reason, it is desirable to know the Km (Michaelisconstant) of an enzyme for a particular substrate in a particular food. This can easily be calculated through the Lineweaver-Burk (doublereciprocal) plot of Eq. (1). The variability in the Km value makes it difficult to describe a universal method of analysis for a certain enzyme, since KM values vary greatly for the same enzyme, depending on the substrate used and the food analyzed. This means that ifenzyme activity/concentration is tobe accu-rately estimated, prior knowledge of the KM value is necessary.