Industrial Media Flashcards
What are the advantages of defined media?
Control of medium composition- the amount of each ingredient is known and can omit/substitute individual components- can modify medium to enhance yield.
Reproducibility- each batch is similar and there is very little variation in fermentation performance.
Foaming
Recovery- easier to recover the product from a defined medium (fewer interfering molecules)
Availability- not subject to seasonal availability
What’s the difference between defined and crude media?
Defined: composition of media is known and made using relatively pure ingredients
Crude: made from agricultural and food industry waste products. Exact composition is unknown and can vary between batches.
What are the advantages of crude media?
Cheaper
Growth rates and yield- generally hire in crude media because it supplied many preformed molecules (eg carbs, amino acids, nucleotides) which can be used directly (saves the cell the energy of synthesising them from basic C skeletons).
Nutritional value- more complex condition and usually more complete (growth factors and trace elements are present in higher concentrations).
List the constituents of crude media
Molasses Cornsteep liquor Sulphite waste liquor Whey Starch Cellulose Hydrocarbons Supplementary N sources Water
Describe three types of molasses
Blackstrap molasses: cheapest kind and obtained from the final stage of sugar crystallisation. 80% dry matter (50% sugar, 10% inorganic, 20% non-sugars). It contains large amounts of vitamins but extra N might be needed
High-test/invert molasses: contains 70-75% sucrose. It’s not a waste product- is produced especially for fermentation media. Partial acid hydrolysis of whole cane juice converts some sucrose to D-glucose and D-fructose. Hydrolysate is then neutralised and concentrated.
Corn molasses: by-product of the production of glucose from maize starch. Is 60% glucose (may have a higher salt content)
Describe cornsteep liquor.
A by-product of starch production from maize. The corn kernels are steeped in warm water with a little SO2 for 2 days. His leads to dissolution of a large amount of soluble material (concentrated then to 50% solids). Approx half is lactic acid and the rest is protein, amino acids, sugars, salts and vitamins. Is valuable as an N supplement.
What is sulphite waste liquor?
A byproduct of the paper and wood pulp industry. The wood chips are digested to cellulose pulp by heating with calcium bisulphate under pressure. It can be used to constitute a dilute fermentation medium if first detoxifier using steam stripping to drive off the SO2 and the addition of lime (to neutralise sulphurous acid).
Contains 10-12% solids (of which 20-39% are sugars) and is used primarily for the cultivation of yeasts (eg. Saccharomyces cerevisiae and Candida utilis)
What is whey?
A byproduct of the dairy industry (the liquid portion left after the coagulated solids have been removed during cheese making). The lactose (4-5%) is a low- value substrate but is used widely for the production of ethanol, single cell proteins and other fermentations.
What is starch?
A glucose polymer consisting of soluble amylose (20-30%) and insoluble amylopectin. It is not readily used by microorganisms and ha to be broken down to glucose and short-chain glucose oligosaccharides before it can be assimilated.
What is amylose and amylopectin?
Amylose: straight chain a-1,4 linked glucose polymer (usually 100-100000 glucose units long).
Amylopectin: consists of branched amylose chains with a-1,6 linked branch points (generally 17-23 glucose units long)
Name some starch degrading enzymes
a-Amylase: only hydrolyses starch at a-1,4 linkages where there are at least three linked glucose units. It is unable to hydrolyse a-1,6 linkages. It breaks down starch into glucose, oligosaccharides and a-limit dextrins.
B-Amylase: hydrolyses a-1,4 linkages from non-reducing end of amylose. The glucose subunits are removed in pairs to form B-limit dextrins. Less stable than a-amylase.
Glucoamylase: removes glucose from the ends of the shorter a-1,4 glucan chains and is able to cleave a-1,4 linkages of the limit dextrins. This combined with the above two enzymes allow for a complete conversion of starch to glucose.
Isoamylase and pollulanase: cleave a-1,6 bonds and function as amylopectin hydrolysing enzymes. They debranch amylopectin
Explain starch hydrolysis
To facilitate enzyme attack, starch is cooked and liquified (mashing). A small amount of heat-resistant a-amylase is added to help dissolve the starch by degrading it into smaller molecules. Complete saccharification to glucose usually only occurs during fermentation. Glucose is consume day microorganisms during fermentation and the equilibrium shifts in favour to further starch hydrolysis
What special considerations should be taken into account when dealing with hydrocarbons as crude media?
Solubility: alkalis with chain length C10- C28 are soluble at 6-16mg/l and are readily utilised by many microorganisms.
Yields: very high cell yields are obtained
Availability: not subject to seasonal availability
Price: subject to competitive pressures (also used in chemical industry)
Fermentation constraints: hydrocarbons are broken down in highly aerobic fermentations that consume large volumes of oxygen and generate a lot of heat. Large amounts of energy are needed to provide the oxygen and cooling is essential.
Why is the inoculum medium important?
Is formulated to yield large numbers of microbial cells in the required physiological state (usually differs in composition from production media). Must also supply log-phase cells adapted to the C source they will encounter in the production medium (so cell growth for production can start immediately after inoculation).
What economic considerations are there?
Costs associated with production media are considerable.
The high C and N content of these media makes it NB to use the cheapest possible source.
The cost associated ei the recovery of the soluble products is directly related to the physical and chemical characteristics of the medium.
Simple downstream processing procedures keep costs low.
