Fed-batch processes

S. cerevisiae is produced by fed-batch processes in which molasses supplemented with sources of nitrogen and phosphoms, such as ammonia, ammonium sulfate, ammonium phosphate, and phosphoric acid, are fed incrementally to meet nutritional requirements of the yeast during growth. Large (150 to 300 m ) total volume aerated fermentors provided with internal coils for cooling water are employed in these processes (5). Substrates and nutrients ate sterilized in a heat exchanger and then fed to a cleaned—sanitized fermentor to minimize contamination problems. 

Figure 4.19 Continuous feed of substrate and removal of products synthesis of 3-phenylcatechol from 2-phenylphenol applying a fed batch process with fluidized bed adsorption followed recrystallization...

Similarly, whole-cell Lactobacillus kefir DSM 20587, which possesses two alcohol dehydrogenases for both asymmetric reduction steps, was applied in the reduction of tert-butyl 6-chloro-3,5-dioxohexanoate for asymmetric synthesis of ft rf-butyl-(31 ,5S)-6-chloro-dihydroxyhexanoate (Figure 7.5), a chiral building block for the HMG-CoA reductase inhibitor [ 17]. A final product concentration of 120 him and a specific product capacity of 2.4 mmol per gram dry cell were achieved in an optimized fed-batch process. Ado 99% was obtained for (3R,5S)- and (3.S, 55)-te/ f-butyl-6-chloro-dihydroxyhexanoate with the space-time yield being 4.7 mmolL-1 h-1. 

Generally, poly(3HB) can be produced discontinuously or continuously. To reach high biomass concentrations fed-batch processes are the method of choice. Continuous methods have only been occasionally used, but unfounded, as shown below. Comprehensive reviews on the current state of technical procedures have been given by Lee and Chang [103], Lee [99], Braunegg et al. [37], and Madison and Huisman [104]. Special conditions and approaches to maximize the exploitation of bacterial potentials with the two types of process regime are discussed below. 

Batch and fed-batch processes are the usual regimes for the production of poly(3HB). It seems they meet well the physiological requirements for synthe-... 

The medium composition used in the fed-batch process was optimized, resulting in cell densities near 100 g l-1. By using an exponential feed rate resulting in a growth rate of 0.05 h-1, a maximum biomass concentration of 112 g 1 1 was attained, with a biomass productivity of 1.8 g 1 1 h. The poly(3HAMCL) productivity however was low, 0.34 g 1 1 h, caused by a steady decrease of the poly(3HAMCL) content during the last part of the fermentation [51]. When this optimized medium composition was used in the continuous culture system described above, a maximum biomass concentration of 18 g 1 1 was reached. The PHA content however remained low at approximately 10% [51]. It is still unclear what causes these low PHA contents. 

C. M. Watteeuw, W. B. Armiger, D. L. Ristroph, and A. E. Humphreys, Production of single cell protein from ethanol by fed-batch process. Biotechnol. Bioeng. 21, 1221-1237 (1979). 

Crowley et al. performed some interesting work with Pichia pastoris in a fed-batch process.19 The complex mixture was measured using a multibounce attenuated total reflectance (HATR) cell. The authors developed models for glycerol, methanol, and the product, a heterologous protein. The results are reported somewhat differently from normal chemometric results. The authors used root-mean square error (RMSE) for the product as a performance index and measured a percent difference for the methanol and glycerol. 

One interesting paper addresses amino acid production.37 The authors describe a fed-batch process for production of amino acids, such as L-lysine (from Corynebacterium glutamicium) and L-threonine (from Escherichia coli). For the fermentation broth of the L-lysine, the optical density, ammonium, and L-lys were measured. For L-threonine, OD, ammonium, and L-thr were measured. For all materials, the values were deemed acceptable and comparable with the reference methods. 

The synthesis of 6-hydroxy fluvastatin with M. rammaniana DSM 62752 gave high conversion (>95 %) in shake flask culture on 400 mL scale with 0.1 g L of fluvastatin as well as on 22 L scale in a Wave bioreactor-fed batch process at a final substrate concentration of 0.4 g L Instead of the partial purification by a second solid-phase extraction described above, 6-hydroxy fluvastatin can be obtained in high purity ( 95 %) by, for example, preparative medium-pressure liquid chromatography (MPLC) on RP18 silica gel. ... 

C. Cannizzaro, M. Rhiel, 1. Marison and U. von Stockar, On-line monitoring of Phaffia rhodozyma fed-batch process with in situ dispersive Raman spectroscopy, Biotechnol. Bioeng., 83, 668-680 (2003). 

One of the most important developments in the history of large scale fermentations is the fed-batch process. Again, this derives from the work of Marvin Johnson at the University of Wisconsin during development of the penicillin fermentation over 50 years ago. Soltero and Johnson wrote Glucose, intermittently fed to fermentations, has given penicillin yields on synthetic medium equal to, or even better than, those obtained with lactose. Penicillin yields of twice those of lactose controls have been obtained when glucose or sucrose is continuously added to the fermentations . 

Fermentation and alternative production techniques, such as roller bottles, can be carried out in four different ways. They are (1) batch process, (2) fed-batch process, (3) chemostat process, and (4) perfusion process. Batch and fed-batch processes require termination of cell growth while chemostat and perfusion processes allow continuous cell cultivation. 

Liquid concentrate medium has emerged recently as an alternative to powdered medium (33,34). For liquid concentrate preparation, medium components are grouped according to solubility criteria. Liquid medium concentrates allow for the preparation of medium in-line, by automated dilution of the concentrates with water of the appropriate quality (35). This would be particularly useful in continuous or perfused processes that require constant preparation of medium. Medium cost and component stability make it a secondary option for batch or fed-batch processes. 

The physiological state and concentration of microorganisms in a batch or a fed-batch process change as a fermentation progresses therefore, it is desirable to determine current control strategy (set-point) in real time based on current process variables. However, the limited availability of online sensors to measure... 

Cannizzaro, C. Rhiel, M. Marison, I. 8c von Stockar, U. On-Line Monitoring of Phaffia Rhodozyma Fed-Batch Process with In Situ Dispersive Raman Spectroscopy Biotech. Bioeng. 2003, 83, 668-680. 

Maass, D., Gerigk, M.R., Kreutzer, A., Weuster-Botz, D., Wubbolts, M. and Takors, R. (2002) Integrated L-phenylalanine separation in an E-coli fed-batch process from laboratory to pilot scale. Bioprocess and Biosystems Engineering, 25, 85. 

A simple mathematical model is used for quantitative description of the process and consists of a set of equations relating inputs, outputs, and key parameters of the system. The model for an alcoholic fermentation fed-batch process developed by Mayer (10) and adapted with the Ghose and Tyagi (11) linear inhibition term by the product was used as the starting point for the development of a model-based substrate sensor with product (ethanol) and biomass on-line measurements. 

The following equations describe a general form of the model for the fed-batch process and total medium, having only substrate as feed flow, and include mass balances for substrate, product, biomass, and kinetic relations, respectively. 

Bibila T, Robinson DK (1995), In pursuit of optimal fed-batch process for monoclonal antibody production, Biotechnol. Progr. 11 1-13. 

As can be observed in Figure 10.1, information from the process (value of the temperature measured by the sensor) arrives at the control loop, which defines it as a closed loop. This is the case for most controllers installed in bioreactors. If the decisions of a controller do not take into account any of the monitored information of the process, it is called an open loop. An example of an open loop is a fed-batch process, where it... 

---