very useful as quality control of the medium or to verify consistency between lots.

Moreover, determination of cell size/cell volume via cell counter or capacitance

probes should consider that cells do not only change in diameter due to osmolality,

but also due to cell cycle phase, metabolic state or cell lysis (virus production).

5.5.2

MONITORING CELL METABOLISM

In process development, cell growth and metabolism needs to be captured closely. High

cell concentrations can only be achieved, when nutrient supply is ample and neither

metabolites nor other toxic by-products are approaching inhibiting levels. Furthermore,

the pH of the medium should be controlled in a range of pH 7.0−7.6, and oxygen supply

should exceed 40% pO2. Moreover, agitation speed and stirrer type affects cell growth.

In small-scale cultivations offline measurement of the most important metabolites

(glucose, glutamine, lactate, ammonia), pH, and cell concentration is often enough to

optimize cell growth. When envisioning large-scale cultivation or cultivation at very

high cell concentrations, the concentration of amino acids or other media compounds

may also be monitored. In Figure 5.3, main metabolite concentrations of a typical batch

cultivation are given together with typical stoichiometric ratios.

TABLE 5.5

Non-animal substitutes of media components

Constituent

Animal source

Non-animal source

Insulin

Bovine/porcine pancreas

Bovine or human rec. from

E. coli or yeast

Transferrin

Bovine, porcine, or human plasma

fraction

Inorganic iron carriers/chelates

Serum protein fractions

(e.g., albumin, fetuin,

lipoproteins)

Bovine or animal serum

Lipid-delivery alternativesPlant-

derived hydrolysates

Protein hydrolysates

Lactalbumin, peptone, casein

Plant-derived hydrolysates

Lipids/sterols

Ovine/human cholesterol;piscine

lipids, porcine liver

Plant-derived sterols;Synthetic

and plant-derived fatty acids

Growth and attachment

factors

Murine/bovine organ digests

Rec. factorsCollagen precursors

Amino acids (e.g., tyrosine,

cyst(e)ine, hydroxyproline)

Human hair; avian feathers, bovine

collagen; bovine/porcine bone

gelatin

Synthetic (fermentation) or

plant-derived amino acids

Surfactants (e.g.,

Tween™ 80)

Bovine tallow

Plant-derived polysorbate

Dissociating enzymes

(e.g., trypsin)

Porcine pancreas

Plant-derived

enzymesMicrobial enzymes

Albumin

Bovine

Rec. from bacteria and yeast

Table from [ 33].

100

Bioprocessing of Viral Vaccines