Response surface methodology as optimization strategy for asymmetric bioreduction of (4S)-(+)-carvone by Cryptococcus gastricus

Response surface methodology was applied in optimizing the asymmetric bioreduction of (4S)-(+)-carvoneto dihydrocarvone (with low incidence of unsought side reactions) by using whole-cells of Cryptococcusgastricus. A factorial design (2e5) including five independent variables was performed: X1 = incubationtime; X2 = pH; X3 = amount of whole-cells; X4 = concentration of (4S)-(+)-carvone; X5 = concentration ofcofactor-recycling system. The utilization of glucose and glycerol as cofactor-recycling systems waschecked. On the basis of the results of factorial design, three independent variables (X1, X3 and X4) outof five were further selected for performing a central composite design (CCD).First and second order polynomial equations obtained by CCD were used to select the optimal values ofindependent variables in order to maximize the bioreduction yield of (4S)-(+)-carvone and, at the sametime, to minimize the occurrence of side reactions (i.e. further reduction of dihydrocarvone todihydrocarveol).