NAD+ regeneration in a microreactor using permeabilized baker’s yeast cells

NAD(P)-dependent oxidoreductases represent a great interest in the field of biotechnology and biotransformation. Although they have many advantages, the biggest drawback and limitation of oxidoreductase usage is the price of the coenzymes. In order to solve this problem, many in situ methods for regeneration of coenzymes have been studied and developed. Unfortunately, although results indicate that those methods are suitable for regeneration procedure, most of the processes need additional optimization to make them more sustainable. As an alternative, microreactor technology could be used as a new technique for coenzyme regeneration processes due to many advantages.In this study regeneration of coenzyme NAD⁺ was carried out in a microreactor by acetaldehyde reduction to ethanol using enzyme alcohol dehydrogenase (ADH). Suspended and immobilized whole permeabilized baker’s yeast cells were used as the source of the ADH enzyme. A 65.3% conversion of NADH was achieved with suspended permeabilized baker’s yeast cells for a residence time of τ = 36 s and equimolar concentration of substrates (c_i,NADH = 5.5 mmol/dm³, c_{i,acetaldehyde} = 5.5 mmol/dm³). When working with immobilized cells, conversion achieved for the same residence time was 10 fold lower. When permeabilized baker’s yeast cells were used for coenzyme regeneration process was stabile for 6 days of continuous operation which makes this system a good alternative for coenzyme regeneration.