Design and performance of a milliliter range bioreactor prototype for bioprocess operation

Abstract

This study aimed to design a mililiter range bioreactor (MRS) prototype and evaluate the performance of this MRB using lactose (milk) hydrolysis enzymatic reaction. A scaling down approach was used in performing biocatalysis experiments using immobilized enzymes in a stirred MRB system, due to uneven distribution in packed bed reactor and cost effective way in enzyme application. Poly-methyl methacrylate polymer was utilized as raw material for fabrication of MRS vessel. Impellers were designed using computer-aided design software and fabricated using 3D printer. Online monitoring system of MRS was set-up via LabVIEW software. The MRB was integrated with agitation motor, heating element, inlet and outlet control system. The feasibility of MRS was evaluated through lactose hydrolysis reaction using immobilized ~-gal actosidase. The enzyme was immobilized on alginate beads and stirred in MRB system with a working volume between 12 tol5 mL. The effects of temperatu re (27°C and 40°C), agitation speed (150, 250 and 300 rpm) and different types of impellers (T-shape, five-bladed turbine, paddle and edge beater blade impeller) on the glucose yield and rate of reaction were investigated to obtain an optimum lactose hydrolysis. The rate of reaction was calculated by measuring glucose production throughout the reaction. The sample was analyzed using glucose analyzer and high performance liquid chromatography. Performance of MRS was benchmarkedwith a bench-top stirred tank bioreactor (STR) system (volume of 250-450 mL). The bench-top STR used different types of impeller namely pitch blade turbine, Rushton turbine, marine propeller and pitch paddle. Kinetics study of the lactose hydrolysis was performed using Michaelis Menten model while kinetic adsorption model was used for immobilized ~-galacto sidase . Results showed that MRS with T-shape impeller system at temperature of 40°C and agitation speed of 150 rpm under batch operating mode was the best condition in achieving high yield of glucose. The rate of reaction increased about 25% w/vas the agitation speed increased from 150 rpm to 250 rpm. At constant agitation speed (250 rpm), rate of reaction increased double from 27°C to 400C. MRB with T-shape impeller at 40°C and250 rpm was the best condition that resulted in the highest enzymatic rate of reaction of 0.23±0.03 mg/rnin, The result obtained showed that MRS can be utilized for lactose hydrolysis with 6% w/v more glucose production compared to bench-top STR. The kinetic adsorption models showed that all the samples were following Pseudo second order model. The Michaelis-Menten constants K; and Vm for the immobilized enzyme have been determined at 0.07 mM and 3.22 mol ONP min'! mg enzyme, respectively . From this study, it can be concluded that the MRS has improved liquidphase mass transfer and it is feasible to be used for lactose hydrolysis using stirred immobilizedenzyme beads system.