On the conceptual design of a partitioning technology for the bioconversion of (+)-valencene to (+)-nootkatone on whole cells: Experimentation and modelling

Abstract

The conceptual design of a four-phase partitioning bioreactor to produce (+)-nootkatone out of (+)-valencene on whole cells of Yarrowia lipolytica 2.2ab requires yet from the proper modelling and analysis of those phenomena limiting the bioconversion in this reaction system. This work is aimed at modelling this partitioning bioreactor. In this sense, a pseudo heterogeneous model is, particularly, developed by using experiments under biotic and abiotic conditions. First, in a two-phase abiotic reactor, interfacial mass transfer in absence of reaction is characterized by determining the effective interfacial coefficients for sequiterpenes (kiAdp) and for oxygen (KLa). Then, kinetics and cell deactivation are characterized by developing the corresponding models in a three-phase biotic reactor; two types of whole cells are evaluated here, namely Yarrowia lipolytica 2.2ab untreated and treated with cetyl trimethylammonium bromite (CTAB) to expel possible reaction intermediate out of the cell and with niacin (vitamin B3) to favour the regeneration of the cofactor nicotinamide adenine dinucleotide phosphate (NADPH+). It is worth stressing that kinetic and cell deactivation models account for (+)-valencene inhibition, (+)-nootkatone inhibition and oxygen inactivation. To this end, the partitioning four-phase reactor model, making use of the calculated mass transport, kinetic and deactivation parameters, is able to describe observations and predict enzyme coverage profiles at different cell activity scenarios. A parametric sensitivity study allows the identification of volume disperse phase fraction (ϕ=0.2–0.5), agitation rate (200–400rpm) and airflow rate (0.5–1vvm) as the main operational variables influencing the biological conversion of (+)-valencene. At studied conditions, the highest production rate of (+)-nootkatone is obtained at 300rpm, 1vvm and, essentially, at ϕ=0.35.