The recovery and purification of fermented products involves the following major procedures:
a) Removal of microbial cells and other solid matter: these include the use of electrophoresis and dielectrophoresis to exploit the charged properties of microbial cells, ultrasonic treatment to improve flocculation characteristics and magnetic separations.
b) Foam separation: foam separation depends on using methods which exploits differences in surface activity of materials. The material may be whole cells or molecular such as a protein or a colloid, and is selectively adsorbed or attached to the surface of gas bubbles rising through a liquid, to be concentrated or separated and finally removed by skimming.
c) Precipitation: precipitation may be conducted at various stages of the product recovery process. Typical agents used in precipitation are acids and bases, salts such as sodium and ammonium sulphates, organic solvents such as methanol, chilled ethanol and acetone, non-ionic polymers such as polyethylene glycol (PEG), and some protein binding dyes such as triazine dyes.
d) Filtration: it is commonly used to separate suspended particles from liquid or gas, using a porous medium which retains the particles but allows the liquid or gas to pass through.
e) Centrifugation: the various types of centrifuges which are used in bioprocess technology are the basket centrifuge, the tubular-bowl centrifuge, the solid-bowl scroll centrifuge, the multichamber centrifuge, the disc-bowl centrifuge.
f) Cell disruption: in order to release the cellular contents of the cells from their extremely tough cell wall a number of methods have been developed for cell disintegration. These include: physico mechanical methods such as liquid shear, solid shear, agitation with abrasives, freeze thawing, and ultrasonication. The chemical methods include usage of detergents, osmotic shock, alkali treatment, and enzyme treatment.
g) Liquid- liquid extraction: the separation of components from liquid mixture by treatment by a solvent in which the desired component is preferentially soluble is known as liquid-liquid extraction.
h) Solvent recovery: solvent recovery is usually done by distillation which occurs in three stages evaporation, vapour-liquid separation in a column and condensation.
i) Two-phase aqueous extraction: Liquid-liquid extraction is well established technology in chemical processing and in certain sectors of biochemical processing. Organic solvents and natural and synthetic hydrophilic polymers are used in two –phase aqueous extraction.
j) Supercritical fluid extraction: It utilizes the dissolution power of supercritical fluids that is fluids above their critical temperature and pressure. They are used in the extraction of hop oils, caffeine, vanilla, vegetables oils, and ĂŸ-carotene.
k) Chromatography: the different types of chromatography techniques are adsorption chromatography, ion-exchange chromatography, gel permeation chromatography, affinity chromatography, reverse-phase chromatography and high-performance liquid chromatography. It is used to isolate and purify relatively low concentrations of metabolic products.
l) Membrane processes: The major membrane processes are ultrafitration, reverse osmosis and liquid membranes. Both ultrafitration and reverse osmosis utilize semi-permeable membranes to separate molecules of different sizes and liquid membranes are liquids which are selective for a given solute and separate two other liquid phases.
m) Drying: It is the last stage of manufacturing process. It involves final removal of water from a heat-sensitive material insuring that there is a minimum loss in viability and activity and nutritional value.
n) Crystallization: It is used in the initial recovery of organic acids and amino acids and more widely used for final purification of a diverse range of compounds.
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