Juris Vanags

Development and application of a flexible controller in yeast fermentations using pO2 cascade control

The development and application of a flexible process controller in fed‐batch yeast fermentations using pO2 cascade control was performed. A new algorithm for fed‐batch fermentations using pO2 cascade control was developed, the concept of which could be used as a realizable solution in fermentation systems equipped according to the basic configuration. The algorithm is based on the combined influence of pO2 and pH on the substrate feeding intensity. To test and develop this algorithm, Saccharomyces cerevisiae DY 7221 and Candida tropicalis CK‐4 fermentations were carried out. As a result of the use of the combined algorithm, the specific growth rate and productivity grew in both fermentations. In this case, the effect of the use of the algorithm was most pronounced in the C. tropicalis fermentation.

The Influence of Temperature and Carbon Source on Expression of Recombinant HBcAg

Biotechnological aspects in the field of recombinant protein production are analysed in this work, which includes the investigation of factors for the production of virus like particles (VLPs) formed by recombinant Hepatitis B virus core-antigen (HBcAg) in inducible bacterial (E. coli) expression system as well as purification of these particles by gelfiltration and ion-exchange chromatography. Biomass yield and VLP production level depended on the cultivation conditions such carbon source and temperature. As inductor for protein expression lactose was used.

Model-based optimization and pO2 control of fed-batch Escherichia coli and Saccharomyces cerevisiae cultivation processes

A model‐based approach for optimization and cascade control of dissolved oxygen partial pressure (pO2) and maximization of biomass in fed‐batch cultivations is presented. The procedure is based on the off‐line model‐based optimization of the optimal feeding rate profiles and the subsequent automatic pO2 control using a proposed cascade control technique. During the model‐based optimization of the process, feeding rate profiles are optimized with respect to the imposed technological constraints (initial and maximal cultivation volume, cultivation time, feeding rate range, maximal oxygen transfer rate and pO2 level). The cascade pO2 control is implemented using activation of cascades for agitation, oxygen enrichment, and correction of the preoptimized feeding rate profiles. The proposed approach is investigated in two typical fed‐batch processes with Escherichia coli and Saccharomyces cerevisiae. The obtained results show that it was possible to achieve sufficiently high biomass levels with respect to the given technological constraints and to improve controllability of the investigated processes.