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1Biochemical Engineering
Biochemical engineering is a branch of chemical engineering
thatmainly deals with the design and construction of unit processes
that involve biological organisms of molecules.
Applications of biochemical engineering are used in the food,
feed, pharmaceutical, biotechnology and water treatment industries.
Will include a study of bioreactors including bioreactor
design.
Marta HenriquesESAC-IPC
Cells & nutrients
Biochemical Engineering13-14
Marta HenriquesESAC-IPC
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2Cells composition
Water (80%) Dry weight (10-20%) Protein (50%) ex. enzymes Lipids
(5-15%) ex. some cells accumulate PHB up to
90%
Others (35-45%) ex. carbohydrates, minerals
Intracellular composition depends on the type and age of the
cells and the composition of the nutrients media.
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3 The qualitative and quantitative nutritional requirements of
cells need to be determined to optimize growth and products
formation
Cell Nutrients
Nutrients required by cells can be classified in two
categories:
- are needed in concentrations larger than 10-4 M.
C, N, O, H, S, P, Mg 2+, and K+.
- are needed in concentrations less than 10-4 M.
Mo, Zn, Cu, Mn, Ca, Na, vitamins, growth hormones and metabolic
precursors.
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4Cell Nutrients- Macronutrientscompounds are the major sources
of cellular
carbon and energy.
Heterotrophs use organic carbon sources such as carbohydrates,
lipid, hydrocarbon as a carbon source.
Autotrophs can use CO2 as a carbon source. They can form
carbohydrate through light or chemical oxidation.
In aerobic fermentations, about 50% of substrate carbon is
incorporated into cell mass and about 50% of it is used as energy
sources.
In anaerobic fermentation, a large fraction of substrate carbon
is converted to products and a smaller fraction is converted to
cell mass (less than 30%).
Cell Nutrients- Macronutrients
Carbon sources:- In industrial fermentation, the most common
carbon sources are molasses (sucrose), starch (glucose, dextrin),
corn syrup, and waste sulfite liquor (glucose).
- In laboratory fermentations, glucose, sucrose and fructose are
the most common carbon sources. Ethanol, methanol and methane also
constitute cheap carbon sources.
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5Cell Nutrients- Macronutrients
compounds are important sources for synthesizing protein,
nucleic acid.
Nitrogen constitutes 10% to 14% of cell dry weight.
Is incorporated into cell in the form of proteins and nucleic
acids.
The most commonly used nitrogen sources are ammonia or ammonium
salts such as ammonium chloride, sulfate and nitrate, protein,
peptides, and amino acids. Urea can be cheap source.
Some m.o. such as Azotobacter sp. and cyanobacteriafix nitrogen
from atmosphere to form ammonium.
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6Cell Nutrients- Macronutrients
constitutes about 20% of the cell dry weight.
- Molecular oxygen is required as terminal electron acceptor in
the aerobic metabolism of carbon compounds.
- Gaseous oxygen is introduced into growth media by sparging air
or by surface aeration.
- Improving the mass transfer of oxygen in a bioreactor is a
challenge in reactor control.
Cell Nutrients- Macronutrients
: 8% of dry cell weight
major source: carbohydrates.
- methanogen bacteria can utilize hydrogen as an energy
source
: 3% of cell dry weight
- present in nucleic acids and in the cell wall of some
gram-positive bacteria.
- a key element in the regulation of cell metabolism.
- sources: Inorganic phosphates.
The phosphate level should be less than 1 mM for the formation
of many secondary metabolites such as antibiotics.
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7Cell Nutrients- Macronutrients
: 1% of cell dry weight- present in protein and some coenzymes.
- source: ammonium sulfate, Sulfur containing aminoacids, cysteine-
some autotrophs can use S0 and S2+ as energy sources.
: a cofactor for some enzyme and is required in carbohydrate
metabolism. cofactor: any of various organic or inorganic
substances necessary to the function of an enzyme. - source:
potassium phosphates.
: a cofactor for some enzyme and is present in cell walls and
membranes. Ribosomes specifically requires Mg2+ .- sources:
Magnesium sulfate or chloride
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8Cell Nutrients- Micronutrients
Micronutrients could be classified into the following categories
(required less than 10-4 M):
Cell Nutrients- Micronutrients
1. most widely needed elements are Fe, Zn and Mn. Such elements
are cofactors for some enzyme and regulate the metabolism.
2. trace elements needed under specific growth conditions are
Cu, Co, Mo, Ca, Na, Cl, Ni, and Se. For example, copper is present
in certain respiratory-chain components and enzymes.
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9Cell Nutrients- Micronutrients
3 Trace elements rarely required are B, Al, Si, Cr, V, Sn, Be,
F, Ti, Ga, Ge, Br, Zr, W, Li and I. These elements are required in
concentrations of less than 10-6M and are toxic at high
concentration.
4 Growth factor is also a micronutrient. Stimulatesthe growth
and synthesis of some metabolites. e.g. vitamin, hormones and amino
acids. They are required less than 10-6M.
Growth Media
There are two types of growth medium: defined medium and complex
medium.
contains specific amounts of pure chemical compounds with known
chemical compositions.
Glucose (30g/L), (NH4)2HPO4 (6g/L), NH4Cl (1.32 g/L), MgS04.7H2O
(0.6 g/L), CaCl2 (0.05 g/L), KH2PO4 (10.0 g/L).
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Defined Media
- Results are more reproducible and the operator has better
control of the fermentation.
- Recovery and purification processes are easier.
Growth Media
contains natural compounds whose chemical composition is not
exactly known.- yeast extract, peptone, molasses or corn steep.-
high yields: providing necessary growth factor.- cheaper than
defined medium- more complex separation
Glucose (30g/L), yeast extract, NH4Cl (1.32 g/L), MgS04.7H2O
(0.11 g/L), CaCl2.2H2O (0.08 g/L), K2HPO4 (2.0 g/L)for ethanol
production by S. cerevisiae.
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Summary of Cell Nutrients
Nutrients required by cell living can be categorized into
macronutrient that are required higher than 10-4M, micronutrients
that less than 10-4M.
Macronutrients include N, C, O, H, S, P, K and Mg. They are
major components in cell dry weight.
Micronutrients are classified into most widely needed elements,
needed under specific conditions and rarely needed ones.
Growth medium can be either defined or complex.
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Stoichiometry of microbial growthand product formation
Microbial growth
Product formation
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