Modelling of the enzymatic synthesis of taste dipeptides with simultaneous extraction in a membrane phase contactor

The paper presents a model of the synthesis process of taste dipeptides carried out in a biphase water–organic phase system. An enzymatic conversion takes place within the aqueous phase where the enzyme is dissolved. The catalysis process is accompanied by the transport of reagents from/to the organic phase, which is a reservoir of hydrophobic reagents. The membrane contactor with a porous membrane holds the interface surface that serves as an interface area to the reactant mass transfer. The model was verified on the basis of the synthesis reaction of ZAlaPheOMe, a precursor of bitter dipeptide. The process was carried out in the ethyl acetate-polypropylene membrane-0.05 M Tris-HCl buffer system. Good agreement of experimental and model results was presented that enabled computer simulations of the process. That allowed us to choose the optimum parameters used in the batch and continuous process. The influence of interface surface area, phases volume and reagent concentrations on the process course, productivity and product purity was shown.

A model of the biphase membrane bioreactor where the membrane holds the interface surface through which hydrophobic reagents transfer is proposed. The aqueous phase constitutes a reaction phase because the enzyme is dissolved in it. The overall process rate is affected by the enzymatic conversion rate and mass transfer rate of the hydrophobic substrate or substrates from the organic to aqueous phase. The hydrophobic product extracts to the organic phase at a rate which would not enable exceeding of the critical concentration in the aqueous phase. The rate of these processes can be under control of process parameters, i.e., the volume of aqueous and organic phase, fluxes size, the value of interfacial area, initial concentrations of substrates and biocatalyst. A proper choice of parameters allows us to carry out the process at a relatively high productivity and output and high product purity. The proposed model of the process was verified on the basis of the synthesis of ZAlaPheOMe, a precursor of bitter dipeptide in the ethyl acetate–polypropylene membrane–water system. The enzymatic conversion carried out in the presence of thermolysin, a proteolytic enzyme, was accompanied by the transport of the hydrophobic substrate ZAlaOH from the organic phase. The reaction product characterised by very low solubility in the aqueous phase extracted to the organic phase at a rate which did not allow for its precipitation in the reaction phase. Very good agreement of experimental and model results allowed us to carry out model analysis of the discussed enzymatic conversion which ena-bled its general characteristics and determination of the range of variable parameters resulting from the process relations. It has been shown that selection of optimum values of parameters of the proposed bioreactor type is connected with the determination of criteria combining the process specific character and economy. In a general case, it is possible to obtain a product of high purity at a relatively high productivity. In this respect, a particularly interesting applicability is revealed by the reactor operating in a continuous system.