Amino acid availability is a key factor that can be controlled to optimize the productivity of fed‐batch cultures. To study amino acid limitation effects, a serum‐free chemically defined basal medium ...was formulated to exclude the amino acids that became depleted in batch culture. The effect of limiting glutamine, asparagine, and cysteine on the cell growth, metabolism, antibody productivity, and product glycosylation was investigated in three Chinese hamster ovary (CHO) cell lines (CHO‐DXB11, CHO‐K1SV, and CHO‐S). Cysteine limitation was detrimental to both cell proliferation and productivity for all three CHO cell lines. Glutamine limitation reduced growth but not cell specific productivity, whereas asparagine limitation had no significant effect on either growth or cell specific productivity. Neither glutamine nor asparagine limitation significantly affected antibody glycosylation. Replenishing the CHO‐DXB11 culture with cysteine after 1 day of cysteine limitation allowed the cells to partially recover their growth and productivity. This recovery was not observed after 2 days of cysteine limitation. Based on these findings, a fed‐batch protocol was developed using single or mixed amino acid supplementation. Although cell density and antibody concentration were lower compared to a commercial feed, the feeds based on cysteine supplementation yielded comparable cell specific productivity. Overall, this study showed that different amino acid limitations have varied effects on the performance of CHO cell cultures and that maintaining cysteine availability is a critical process parameter for the three cell lines investigated.
Schizochytrium limacinum
SR21 is an important strain for industrial production of docosahexaenoic acid (DHA), which is an important omega-3 fatty acid used in the nutraceutical and food industry. ...However, the high cost of carbon sources has limited its further application in the market with much larger volume, such as animal feed for aquaculture, poultry, and livestock. To seek low-cost carbon source, acetic acid is tested in the present study. The effect of different factors, including initial carbon source concentration, pH, aeration rate, and nitrogen sources, on biomass, lipid, and DHA production were tested. With optimized culture conditions, the biomass concentration of 146 g/L, total fatty acids (TFAs) of 82.3 g/L, and DHA content of 23.0 g/L were achieved with a pH-auxostat fed-batch cultivation. These results suggested that acetic acid is a promising feedstock for the low-cost production of DHA.
Graphical Abstract
•A majority of industrial fermentation processes are operated in fed-batch mode.•The rate of feed addition to the fed-batch process is a focus for optimising the process operation.•This review covers ...strategies for controlling the feed rate to a fed-batch fermentation process.
A majority of industrial fermentation processes are operated in fed-batch mode. In this case, the rate of feed addition to the system is a focus for optimising the process operation, as it directly impacts metabolic activity, as well as directly affecting the volume dynamics in the system. This review covers a range of strategies which have been employed to use the feed rate as a manipulated variable in a control strategy. The feed rate is chosen as the focus for this review, as it is seen that this variable may be used towards many different objectives depending on the process of interest, the characteristics of the strain, or the product being produced, which leads to different drivers for process optimisation. This review summarises the methods, as well as focusing on the different objectives for the controllers, and the choice of measured variables involved in the strategy. The discussion includes a summary of considerations for control strategy development.
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•5-Ketofructose (5-KF) is a potential low-calorie sweetener.•The sweet quality is good and without aftertaste, comparable to fructose.•Fructose dehydrogenase is overexpressed in G. ...oxydans to oxidize fructose to 5-KF.•5-KF production is characterized and a fed-batch fermentation process is developed.•Product concentrations up to 489 g/L and product yields up to 98% are reached.
Sweeteners improve the dietary properties of many foods. A candidate for a new natural sweetener is 5-ketofructose. In this study a fed-batch process for the production of 5-ketofructose was developed. A Gluconobacter oxydans strain overexpressing a fructose dehydrogenase from G. japonicus was used and the sensory properties of 5-ketofructose were analyzed. The compound showed an identical sweet taste quality as fructose and a similar intrinsic sweet threshold concentration of 16.4 mmol/L. The production of 5-ketofructose was characterized online by monitoring of the respiration activity in shake flasks. Pulsed and continuous fructose feeding was realized in 2 L stirred tank reactors and maximum fructose consumption rates were determined. 5-Ketofructose concentrations of up to 489 g/L, product yields up to 0.98 g5-KF/gfructose and space time yields up to 8.2 g/L/h were reached highlighting the potential of the presented process.
The development of digital bioprocessing technologies is critical to operate modern industrial bioprocesses. This study conducted the first investigation on the efficiency of using physics‐based and ...data‐driven models for the dynamic optimisation of long‐term bioprocess. More specifically, this study exploits a predictive kinetic model and a cutting‐edge data‐driven model to compute open‐loop optimisation strategies for the production of microalgal lutein during a fed‐batch operation. Light intensity and nitrate inflow rate are used as control variables given their key impact on biomass growth and lutein synthesis. By employing different optimisation algorithms, several optimal control sequences were computed. Due to the distinct model construction principles and sophisticated process mechanisms, the physics‐based and the data‐driven models yielded contradictory optimisation strategies. The experimental verification confirms that the data‐driven model predicted a closer result to the experiments than the physics‐based model. Both models succeeded in improving lutein intracellular content by over 40% compared to the highest previous record; however, the data‐driven model outperformed the kinetic model when optimising total lutein production and achieved an increase of 40–50%. This indicates the possible advantages of using data‐driven modelling for optimisation and prediction of complex dynamic bioprocesses, and its potential in industrial bio‐manufacturing systems.
This study investigates the efficiency of different digital techniques for long‐term bioprocess optimal control and visualisation. Cutting‐edge physics‐based and data‐driven models are exploited to identify the optimal light intensity and nitrate inflow rate for a fed‐batch microalgal lutein photo‐production system. Significant increases in lutein intercellular content and total production are achieved compared to the previous studies, and consumption of nitrogen source is greatly reduced, demonstrating the potential of current modelling strategies for bioprocess optimisation and design.
•Waste cooking oil is a good sustainable feedstock for sophorolipid production.•Use of ultrasound benefits the productivity.•Fed batch operation is better as compared to conventional batch ...mode.•Kinetic analysis for product yield and substrate consumption.
Waste cooking oil (WCO) has been used as a sustainable and economical raw material for the production of sophorolipids using Starmerella bombicola. Initially, pretreatment of waste cooking oil has been carried out using activated earth for reduction of the peroxide value to less than 5. Fermentation experiments were carried out in a fermentor of capacity 2.5L and the effect of stirring speed, presence of ultrasound and mode of operation (i.e. batch or fed batch) on the sophorolipid yield has been investigated. Batch fermentation in the presence of ultrasound gave higher yield of sophorolipids as 24.7gL−1 at a stirring speed of 300rpm as compared to the operation involving only stirring. The better results can be attributed to cavitational effects which increase the cell permeability, improve the substrate intake and increase the metabolism of microbial cells leading to an overall increase in the sophorolipid yield. Fermentation kinetic models have been developed for cell growth, product yield and substrate consumption. Sophorolipid yield was observed to be the maximum as 55.6g/L in the fed-batch mode of fermentation assisted with ultrasound. The obtained sophorolipid was found to contain major component as lactonic sophorolipid, which has been confirmed by FTIR analysis. The surface active properties of the final product have also been confirmed based on the fact that the use of sophorolipid reduced the surface tension of water from 72 to 32.6mN/m and interfacial tension at the water and n-heptane interface in the presence of sophorolipid was 1.4mN/m.
This paper considers optimal control of glycerol producing 1,3-propanediol (1,3-PD) via microbial fed-batch fermentation. The fed-batch process is formulated as a nonlinear switched time-delay ...system. In general, the time-delay in the fed-batch process cannot be exactly estimated. Our goal is to design an optimal switching control scheme to simultaneously maximize 1,3-PD productivity and 1,3-PD yield under time-delay uncertainty. Accordingly, we propose a robust multi-objective optimal switching control model, in which two objectives, i.e., 1,3-PD productivity and 1,3-PD yield, and their sensitivities with respect to uncertain time-delay are considered in the objective vector. The control variables in this problem are the feeding rate of glycerol, the switching instants and the terminal time of the process. By introducing an auxiliary dynamic system to calculate the objective sensitivities and performing a time-scaling transformation, we obtain an equivalent multi-objective optimal switching control problem in standard form. We then convert the equivalent multi-objective optimal control problem into a sequence of single-objective optimal switching control problems by using a modified normal boundary intersection method. A novel gradient-based single-objective solver combining control parameterization with constraint transcription technique is developed to solve these resulting single-objective optimal control problems. Finally, numerical results are provided to verify the effectiveness of the proposed solution approach.
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