Untitled Quiz

Study Notes

Sulfite liquors from coniferous trees are rich in hexose sugars (glucose, mannose, galactose), while deciduous trees contain mainly pentose sugars (xylose, arabinose).
Cellulose is a readily available and inexpensive substrate for sugar or alcohol production but requires hydrolysis before use by microorganisms.
Whey, a dairy byproduct, contains lactose and milk protein, which can be used for ethanol, single-cell protein, and other fermentation products.
Animal fats and oils are commonly used as supplemental substrates due to their high energy content.
Methanol is the cheapest fermentation substrate but can be metabolized by only a limited number of microorganisms.
Ethanol, derived from starch or cellulose fermentation, is readily metabolized by many microorganisms.
Hydrocarbons, particularly n-alkanes with chain lengths of C12 to C18, are readily metabolized by many microorganisms.
The use of hydrocarbons as fermentation substrates depends on the cost of petroleum.

Most industrially important microorganisms can utilize both inorganic and organic nitrogen sources.
Inorganic nitrogen is often supplied as ammonium salts (e.g., ammonium sulfate, diammonium hydrogen phosphate), ammonia, or urea.
Ammonium salts can lead to pH decrease in fermentation broth due to the release of free acid.
Organic nitrogen sources include amino acids, proteins, and urea.
Corn steep liquor is an efficiently metabolized nitrogen source rich in amino acids and is often used in fermentations.
Inducers are often required for fermentations with genetically modified microorganisms to promote the production of specific enzymes.
Fatty acids induce the production of lipase but may not be cost-effective to include in all fermentation media.
Yeast mannan induces the production of β- mannosidase by Streptomyces griseus, which converts mannosidostreptomycin into streptomycin.

Specific inhibitors can be added to fermentation media to promote the production of certain products or accumulate metabolic intermediates.
Sodium bisulphite is used as an inhibitor in glycerol production, preventing the reoxidation of NADH2 and diverting dihydroxyacetone phosphate towards glycerol production.
Other inhibitors include bromide for tetracycline production, penicillin for glutamic acid production, and alkali metals for citric acid production.

Buffers are essential for maintaining the pH of fermentation media, which is crucial for optimal productivity.
Media are commonly buffered at pH 7.0 using calcium carbonate, sodium and potassium phosphates.
Sulfuric acid or sodium hydroxide can be used for small-scale pH adjustments.
The balanced use of carbon and nitrogen sources can also help to control pH by providing buffering capacity from proteins, peptides, and amino acids.

These compounds enhance cell permeability by modifying cell walls and/or membranes, promoting the release of intracellular products into the fermentation medium.
Penicillins and surfactants are commonly added to amino acid fermentations.

Foaming in fermentation broth is a common problem that can reduce working volume, interfere with oxygen transfer, and cause cell loss.
Protein components in the medium, such as corn steep liquor and yeast extract, can contribute to foaming.
Antifoams, which are surface-active agents, can reduce surface tension in foams and destabilize protein films.
Natural antifoams include plant oils and mineral oils.
Synthetic antifoams include silicon oils, poly alcohols, and alkylated glycols.
Ideally, antifoams should be active at low concentrations, inert, cheap, heat sterilizable, nontoxic, and should not interfere with downstream processing.

Sterilization is essential to eliminate microorganisms and ensure the safety of fermentation products.
Classical sterilization techniques using saturated steam under pressure or hot air are the most reliable methods.
Other sterilization methods include filtration, ionizing radiation, and gas sterilization.
Exposure to saturated steam under pressure denatures enzymes and structural proteins, effectively killing microorganisms.
Filtration is used for thermolabile solutions, passing them through sterile bacteria-retaining filters.
Air is typically sterilized by passing it through membrane filters.

Bacterial spores are the most heat-resistant form of microorganisms.
The thermal resistance of bacterial spores varies significantly between species and even within strains.