40
C h a p ter 2
human insulin, it is important that the production costs are kept low, which requires an expression
system with a high productivity,
i. e. E. coli
or 5.
cerevisiae.
For very complex molecules like tissue
plasminogen activator (tPA) and erythropoietin (EPO) it is, however, not possible to obtain
sufficiently active compounds in microbial systems, and here a higher eukaryotic expression system
is required.
2.2.2
Fermentation Media
An important aspect in design of a fermentation process is the choice of fermentation medium,
which represents the raw material for the process. The fermentation medium should fulfill the
following criteria:
It should contain a carbon, nitrogen and energy source.
It should contain all essential minerals required for growth.
*
It should contain all necessary growth factors to ensure rapid growth and high yield of the
desired product.
*
It should be of a consistent quality and be readily available throughout the year.
It causes a minimum of problems in the downstream processing.
*
It causes a minimum of problems in other aspects related to the fermentation process, i.e.,
it has no negative effect on the gas-liquid mass transfer.
Traditionally complex media from the agricultural sector were used, as these were present in
large quantities and were relatively cheap. Table 2.9 lists some typical complex media
components used in the fermentation industry together with some typical products produced
using the different media.
The advantages of applying complex media are that they often contain an organic nitrogen
source, essential minerals and different growth factors. Thus, two frequently applied complex
media, com steep liquor and pharmamedia; both contain a large variety of amino acids, many
different minerals and many different vitamins. The disadvantages of complex media are that: 1)
there may be a seasonal variation in the composition, 2) the composition changes with storage,
Table 2.9 Complex fermentation media often applied in the fermentation industry.
Medium
Contents
Oriffin
Tvnical annlication
Com steep liquor
Lactate, amino acids, minerals,
vitamins
Starch processing from
com
Antibiotics
Com starch
Starch, glucose
Com
Ethanol, industrial
enzymes
Barley malt
Starch, sucrose
Barley
Beer, whiskey
Molasses
Sucrose, raffinose, glucose,
fructose, betain
Sugar cane or sugar beet
Bakers yeast, ethanol
Pharmamedia
Carbohydrates, minerals, amino
acids, vitamins, fats
Cotton seed
Antibiotics
Serum
Amino acids, growth factors
Serum
Recombinant
proteins
Whey
Lactose, proteins
Milk
Lactic acid
Yeast extract
Pentides. amino acids, vitamins
Yeast_________________ Enzymes___________
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