ETHANOL PRODUCTION
Ethanol is an organic acid. It is widely used as a solvent. Ethanol is produced from carbohydrates (sucrose and starch). Ethanol is used as fuel.
Microorganisms producing ethanol
Both bacteria and fungi produce ethanol. Bacteria used for ethanol production are Zymomonas mobilis. The yeasts used for ethanol production are Saccharomyces cerevisiae, and Kluyveromyces fragilis.
Factors affecting ethanol production
Ethanol is inhibitory in higher concentrations. So, the microorganisms used in industrial production must be tolerant to the high concentrations of ethanol.
Pure sugar solution can increase the yield of ethanol. Osmotic tolerance of microorganisms is also important for ethanol production.
Organisms must have a high specific growth rate.
pH for ethanol production is 5-7.
The temperature for ethanol production is 30ºC.
PRODUCTION OF ETHANOL
The process of ethanol production involves the following steps1) Preparation of nutrient medium
2) Fermentation
3) Distillation of ethanol.
Preparation of medium
Substrates used for ethanol production are-
Starch-containing roots, tubers, or grains
Molasses
Wood waste
Starch used in ethanol production has a low yield.
The substrate is heated to soften the substrate. It is liquefaction.
It is enzymatically metabolized into sugars
Molasse is also used as a source of sugar for ethanol production.
Continuous culture is used to increase ethanol production.
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| BIOSYNTHESIS OF ETHANOL |
Product recovery
Product recovery of ethanol involves two main steps.
1) Separation of biomass, which involves centrifugation.
2) Distillation of ethanol, this step of product recovery for ethanol production is the most energy demanding. It increases the cost of production of ethanol.
So, the cheap source of sucrose is beneficial for ethanol production.
Lactic acid production
Lactic acid was the first
organic acid that was produced in 1880. Lactic acid can be produced through
chemical methods or through fermentation. There is a competition between the chemical production of lactic acid and fermentation.
Lactic acid production by the chemical method is cheaper. The production of lactic acid through fermentation should be from a cheaper feedstock.
Making it more economical through fermentation technology, it is challenging for lactic acid production.
The organisms that produce lactic acid are classified as homofermentative organisms or Hetero fermentative organisms. The homofermentative organisms produce especially the lactic acid only. However, Heterofermentative organisms produce lactic acid as well as other acids.
BIOSYNTHESIS OF LACTIC ACID
Bio-synthesis of lactic acid occurs from glucose when oxygen is insufficient. As we know that glucose is metabolized to pyruvate through glycolysis. Pyruvate is a feeder molecule of the Kreb cycle, where it is oxidatively metabolized into carbon dioxide and water. However, when oxygen is limiting Pyruvate is converted into lactic acid by the enzyme lactate dehydrogenase. Lactic acid is produced maybe Levo or dextrorotatory.
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| BIOSYNTHESIS OF LACTIC ACID |
MICROORGANISMS USED FOR LACTIC ACID PRODUCTION
Organisms those produced
lactic acids are Lactobacillus brueckii
and Lactobacillus leichmannii, Lactobacillus pentosus. These
organisms are facultative anaerobes. Thus only reducing the presence of oxygen
can induce the production of lactic acid.
Lactic acid production
does not require the complete exclusion of oxygen from the fermentation vessel.
The process of lactic acid production
It requires the preparation of medium, inoculation, and extraction of product. Preparation of the medium requires calibrating the medium according to the needs of the organism. For
bacterial culture, the medium contains containing 12 to 13% Glucose, Ammonium
Phosphate 0.25%, Vitamin B, and calcium carbonate are used.
The vessel size can be 25
to 120 m3.
The temperature of the culture is 45 to 50ºC. The maximum production of
lactic acid occurs within 72 hours. So, the product is extracted after 72 hours.
The higher concentration of lactic acid in the medium is poisonous to the bacteria.
The concentration of lactic acid in the culture medium becomes up to 80 grams per liter
per hour.
Amylase Production
Amylase is a starch liquefaction enzyme. There are two types of amylase, α-amylase, and β-amylase. These enzymes are used in the sweetener industry for the conversion of starch into dextrins, maltose, or glucose. The conversion of starch into these products is called starch saccharification.
Both α-amylase and β-amylase are extracellular enzymes. These are produced by bacteria as well as fungi both the amylases attack on 1-4 α glycosidic bond of starch thus producing the product of different lengths. The products include dextrins which are oligosaccharides, maltose which are disaccharides, and glucose which are monosaccharides.
All these
products are sweet in taste so amylase found its application in the sweetener
industry, baking industry, beverage industry, paper and pulp industry, and cloth
industry. The enzymes that cause starch saccharification are α- amylase, β-
amylase, and o- glucoamylase. Other enzymes
are isoamylase and x-pullulanase. These can metabolize amylopectin as well
because they can attack 1-6 α- glycosidic bonds as well.
The microorganisms that are used for amylase production
Bacterial species used in fermentation Technology for the production of amylase are
Bacillus subtilis,
Bacillus cereus,
Bacillus amyloliquefaciens,
Pseudomonas and Thermofactor
The thermophilic species used for amylase production is Thermobacter.
It can be cultured at 53ºC.
Fungi used in amylase production are
Aspergillus,
Penicillium,
Aspergillus oryzae,
Mucor,
Candida,
and Rhizopus.
Medium for amylase production by fungi has
8% starch,
1.2% NaNO3,
0.1 MgSO4,
2.0% Malt extract,
0.05%KCl,
0.003% FeSO4,
0.08% Mg(NO3)2.
Medium used for amylase production by bacteria has
0.5% starch
0.56% NH4NO3
0.28% sodium citrate
0.13%KH2PO4
0.05% MgSO4.7H2O
0.01%CaCl2
0.05% peptone
0.2% yeast extract
Amylase is an extracellular enzyme. It is produced in the cytoplasm. It has a signal sequence that targets the
enzyme to the cell membrane of the organism, where it is folded into three-dimensional structures which is the functional form of the enzyme. The enzyme is
released into the extracellular matrix, where it converts starch into different
sweeteners.
Glucose present in the culture medium increases the growth of the bacteria but decreases amylase
production.
When nitrogen is a limiting factor in the medium, amylase production decreases. The maximum production
occurs at 45ºC in 18 hours for bacterial species. Up to 3000 units/ml is
produced at 27 ºC to 37 ºC.
Amylase is a heat-tolerant protein that can tolerate up to 70°C temperature.
Purification of
amylase is done through protein purification Technology.
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