Optimization and Characterization of Rhamnolipid And Sophorolipid Produced from Aspergillus Niger in a Solid-State Fermentation System using Potato Peels as Carbon Source.
ABSTRACT
This study was aimed at optimizing and characterizing rhamnolipid and sophorolipid produced by Aspergillus niger in a solid-state fermentation system using potato peels as carbon source. A two-level Plackett–Burman (PB) design was implemented to screen the medium components that significantly influence the production and response surface methodology was used for the optimization. Following the one factor at a time analysis (OFAT), a central composite design was conducted to optimize the three selected factors for rhamnolipid and sophorolipid production.
Characterization of the biosurfactants involved determination of Emulsification index, surface tension; blood hemolysis and fourier transform infrared analysis. Three vital components influencing rhamnolipid production were identified as magnesium sulphate, sodium chloride and zinc sulphate while the three vital components influencing sophorolipid productions were identified as magnesium sulphate, sodium chloride and potassium dihydrogen phosphate.
The validity of the model developed was verified, and the optimum medium containing 0.49% (w/v) magnesium sulphate, 0.2% (w/v) sodium chloride and 0.49% (w/v) zinc sulphate, 0.74%(w/v) magnesium sulphate, 0.1%(w/v) sodium chloride and 0.9%(w/v) of potassium dihydrogen phosphate led to a maximum rhamnolipid and sophorolipid production of 226.60±50.91 mg/gds and 84.41±8.73 mg/gds respectively. The analysis of variance indicated that the established models were significant (P < 0.05).
Characterization of rhamnolipid and sophorolipid showed that they were able to form clear zone with a hemolyic activity. The biosurfactants were able to emulsify petrol with an emulsification index of 54.87±1.23 and 54.86±3.64 for rhamnolipid and sophorolipid respectively. The produced rhamnolipid and sophorolipid were able to reduce surface tension of distilled water from 71mN/m to 28.09 and 30.30mN/m respectively.
INTRODUCTION
Surfactants are surface active agents that form integral part of our everyday life with a worldwide production. They are amphipathic molecules that accumulate at interfaces, decrease interfacial tensions and form aggregate structures such as micelles (Van Hamme et al., 2006). The hydrophobic portion of the molecule is long-chain fatty acids, hydroxyl fatty acids or α-alkyl-β-hydroxyl fatty acids.
The hydrophilic moiety can be a carbohydrate, amino acid, cyclic peptide, phosphate, carboxylic acid or alcohol. These compounds find applications in an extremely wide variety of industrial processes involving emulsification, foaming, detergency, wetting, dispersing or solubilization (Desai and Banat, 1997 and Banat et al., 2000). Currently, almost all the surfactants being produced are chemically derived from petroleum (Suresh et al., 2012).
However, microbial surfactants, referred to as biosurfactants which are produced by certain bacteria, filamentous fungi and a number of yeasts have gained attention in recent years because they offer several advantages over chemical surfactants, such as lower toxicity, higher degree of biodegradability, higher foaming capacity and optimal activity at extreme conditions of temperatures, pH and salinity (Chenet al., 2007).
Biosurfactants are structurally diverse and can have various chemical structures mainly consisting of glycolipids, lipopeptides, phospholipids, neutral lipids, polymeric surfactants and particulate biosurfactants, depending on the producing microorganism, raw material and process conditions (Syldatk and Hausman, 2010; Makkar et al., 2011). They can also be high molecular weight biosurfactants which are generally polyanionic heteropolysaccharides containing both polysaccharides and proteins.
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