ABSTRACT
Of the estimated 25,000 enzymes present in nature, 2800 have been classified and 400 have been commercialized. On a larger industrial scale, in particular for detergent and food processing, only 50 enzymes are used. The main impetus for the use of enzymes is the continuous growth in the demand for enantiomerically pure compounds. This trend plays an important role in the use of chiral drugs, but is also essential in the flavor industry where, besides microbial fermentation, enzyme technology is an alternative for the biotechnological production of flavor compounds (1). For example, acetaldehyde is an important low-molecular-weight flavor compound that plays a significant role in the flavor of yogurt and certain fruits, such as orange. Figure 1 shows the conversion of ethanol to acetaldehyde using alcohol dehydrogenase. This process suffers from the same drawbacks as all enzymatic oxidation reactions that rely on cofactor regeneration. Specifically, the process involves the use of alcohol dehydrogenase and its cofactor NADþ, which during the reaction is reduced and subsequently regenerated by light-catalyzed oxidation with flavin mononucleotide (FMN). The reduced flavin mononucleotide (FMNH2) is reconverted to FMN by oxidation with molecular oxygen. The byproduct of this reaction is hydrogen peroxide, which is in turn decomposed by the action of the enzyme catalase to oxygen and
water. Conversion rates in the range of 10-20% are typically obtained, and in a continuous batch reactor system the concentration of acetaldehyde is 2:5 g=L after a period of 9 h (2).
