Biocatalysis can be defined as the application of a biocatalyst to achieve a desired conversion under controlled conditions in a bioreactor. A biocatalyst can be an enzyme, an enzyme complex, a cell organelle or a whole cell. Over recent years there has been an exponential increase in the production of high-value specialty chemicals using either isolated enzymes, especially hydrolases, to catalyze single-step transformations or whole cells to catalyze multi-step
reactions. This increase is motivated by the fact that enzymes, whether isolated or contained within whole cells, can catalyze a broad range of reactions, at times with high levels of chemoselectivity, regioselectivity and stereoselectivity. In fact, biocatalysts in the form of isolated enzymes, or enzymes contained in whole cells, can often catalyze reactions with a specificity that is difficult to obtain by classical chemical routes. Further, they act under mild conditions of pH and temperature and biocatalytic processes generate fewer residues than chemical processes do, such that biocatalysis is often referred to as »green chemistry«.