ABSTRACT Bio surfactants are surface active compounds produced by living microorganisms
Bio surfactants are surface active compounds produced by living microorganisms, which are either excreted extracellular or on the microbial surfaces, thus reducing the surface tension of a liquid and interfacial tension between two liquids or that between a liquid and a solid. These are amphilic compounds having both hydrophilic and hydrophobic moieties ,possessing the same mechanism as the chemical surfactants.Biosurfactants are more in demand now-a-days because of their low toxicity,biodegradable and eco-freindly in nature.
Biosurfactants are gaining more attention in recent years due to their diversity, use of agri- wastes as a substrate, possibility of large scale production, selectivity, and reduction in the wastes and their impeding applications in environmental fortification. These molecules having versatile properties including low toxicity, dropping surface tension, stabilising emulsions, enhance foaming and biodegradable in nature.
These potent molecules have vast range of applications in the different industrial sectors including pharmaceutical,cosmetics,humectants,food preservatives and detergents Presently production of biosurfactants are highly expensive method due to use of synthetic media for the production, which are highly costly and expensive which increases the cost of product and not easily purchased or utilized by the public.
Several procedures and techniques are carried out for the procurement of wide variety of wastes from agro-industrial used as a substrate like dairy wastes, vegetable oils, distillery wastes, starchy waste and animal fat. It’s the potent method of remediation technology which is used to remove the pollutants which contaminate and harmful for the environment and human being. The isolation of biosurfactants producing microorganisms have been carried out by using different methods or by using different media in order to enhance the growth of biosurfactants producing microorganisms.
For the isolation of biosurfactants producing microorganisms, soil samples were isolated from a stream polluted by industrial waste and from petroleum contaminated soil (garage).The surface tension is primarily used as criteria for the isolation of biosurfactants producing microorganisms. For the proper growth and development of microbes, mineral salt media is used with varying concentration of minerals in which yeast extract and oil samples are used as the source of carbon .Biosurfactant producing microorganisms were isolated from the cell free supernatant and then screening was done by using different tests including emulsifying test, oil drop collapse method, oil displacement method and bath assay.
KEYWORDS: Biosurfactants; Surface tension; Inter-facial Tension; Bio-remediation; Agricultural Wastes; Microbes; Pollutants
Refinery effluents comprises of wastes originating from manufacturing industries involved in refining crude oil and manufacturing lubricants, fuels and petrochemical intermediates. The pollution of landmass, water bodies and ground water reserves by industrial chemicals and drilling activities in oil fields areas is a serious problem to the environment, and the use of bioremediation for the removal of contaminants has been reported to provide a safe, efficient, versatile and economic alternative to commonly used physical and chemical treatment in several in aquatic and terrestrial ecosystems.
Surfactants are substances which can reduce the surface and interface tension in liquids and liquid systems (i.e.oil/water, air/water, or liquid/solid). These can be produced by synthetic or microbial methods. Surfactants produced by microbes are called biosurfactant.
Biosurfactants have the same amphiphilic properties like a chemical surfactant, in that they both have the character of an emulsifier (i.e. contain both hydrophobic and hydrophilic parts), which makes them useful in blending and spreading of immiscible phases .
However, being biologically degradable and displaying highly specific activity under extreme conditions of temperature, pH, and salinity, biosurfactants have advantages over chemical surfactants for industrial and environmental applications.
However, the high cost associated with the production of biosurfactants via microorganisms., is a major drawback and an area of concern.
Surfactants are amphiphilic compounds that act by replacing the bulk molecules of higher energy at an interface, thus reducing the free energy of the system. They contain a hydrophobic moiety with little affinity for the bulk medium and a hydrophilic portion that is attracted to the bulk medium. Surfactants have been used industrially as emulsifiers, lubricants and penetrants and as flocculating, wetting and foarming agents.
Because of their amphiphillic nature, surfactants tend to accumulate at interface (air-water and oil-water) and surfaces. As a result, surfactants reduce the forces of repulsion between unlike phases at interfaces or surfaces and allow the two phases to mimore easily.
Bio surfactants are surface active compounds with widely varied structures. They correspond to amphiphilic molecules with a hydrophilic (amino-acids, peptides, anionic or cationic, di or polysaccharides) and a hydrophobic (saturated or unsaturated fatty acids) moieties, which are synthesised by a wide spectrum of microorganisms.
They are categorised mainly by their chemical composition and their microbial origin. The major classes of biosurfactants include lipopeptides, glycolipids, lipoproteins, phospholipids and fatty acids, particulate surfactants and polymeric surfactants..
Wide range of microbes are able to produce different types of biosurfactants viz. low molecular weight glycolipids, lipopeptides and high molecular weight polymers like lipoproteins , lipopolysaccharide , protein complexes and complexes of polysaccharide –protein –fatty acid.
It is well known that several strains of Pseudomonas can accumulate surface –active compounds characterized as rhamnolipids when grown on different carbon sources. Biosurfactants can play vital role in environment friendly remediation and other industrial applications.
.All surfactants have two ends namely, a hydrocarbon part which is less soluble in water (hydrophobic end). The hydrophobic part of the molecule is a long-chain of fatty acids or alpha-alkyl-beta-hydroxy fatty acids. The water soluble end (hydrophilic) can be a carbohydrate, amino acid, cyclic peptide, phosphate, carboxylic acid or alcohol 4.
Additionally, the hydrophobic moiety is usually a C8 to C22 alkyl chain or alkylaryl that may be linear or branched 5. The unique properties of biosurfactants allow their use and possible replacement of chemically synthesised surfactants in a number of industrial operations 6. Biosurfactants reduces surface tension, Critical Micelle Concentration (CMC) and interfacial tension in both aqueous solutions and hydrocarbon mixture 7.
3. Economic factors of biosurfactant production
In order to overcome the high cost constraints associated with production of biosurfactants, two basic strategies are adopted:
• The use of inexpensive and waste substrates for the formlation of fermentation media which lower the intial raw material costs involved in the process.
• Development of efficient and successfully optimized bioprocess, including optimization of the culture conditions and cost effective recovery processes for maximum Biosurfactant production and recovery 72.
.The residues from tropical agronomic crops such as cassava (peels), soybean(hull) 73, sugarbeet 74 , sweet potato (peet and stalks), potato(peel and stalks), sweet sorghum 75, rice and wheat (bran and straw) 76; rice , hull soy, bagasse of sugarcane and cassava. In addition residues from the coffee processing industry such as coffee pulp, coffee husks, spent coffee grounds; residues of the fruit processing industries such as pomace and grape ,waste from pineapple and carrot processing, banana waste ;waste from oil processing mill waste; saw dust ,corn cobs, carob pods, tea waste ,chicory roots etc. have been reported as substrates for Biosurfactant production 77.
Additional, substrates used for biosurfatant production include waste-miscible wastes, molasses, whey milk or distillery wastes 78.
4. Advantages of bio surfactants
Biosurfactants have number of advantages.
1 Biodegradability: Biological surfactants are easily degraded by microorganism 136.
2 Low toxicity: Biosurfactant demonstrate higher toxicity than the chemical- derived surfactants .It was also reported that biosurfactants showed higher EC 50 (effective concentrations to decrease 50% of test population) values than synthetic dispersants 137.
3 Availability of raw materials: Biosurfactants can be from very cheap raw materials which are available in large quantities. The carbon source may come from hydrocarbons, carbohydrates and lipids, which may be used separately or in combination with each other 138.
4 Physical factors: Many biosurfactants are not affected by environmental factors such as temperature, pH and ionic strength tolerances. Lichenysin produced by Bacillus licheniformis strain was not affected by temperature ranges of up to 50 degree celcius, a pH range of 4.5-9, and NaCl concentration of 50g/l and Ca concentration of 25g/l 139.
5 Surface and Interface activity: Mulligan 140 stated that a good surfactant can lower surface tension of water from 75 to 35mN/m and the interfacial tension water/hexadecane from 40 to 1mN/m. Surfactins possess the ability to reduce the surface tension of water to 25mN/m and the interfacial tension of water/hexadecane to