Abstract
Extracellular polysaccharides (EPS) from Nostoc muscorum, a heterocystous, filamentous cyanobacterium isolated from a jhumland (shifting cultivation) soil of Assam, North-East India, was physico-chemically characterized to find out its potential applications and to improve its production with some stress source like ozone. Using Response Surface Methodology (RSM), EPS production was improved. Accordingly, with magnesium sulfate (MgSO4·7H2O) at 62 mg L−1, Sodium Chloride (NaCl) at 58 mg L−1 and 56 mg L−1 di-potassium hydrogen phosphate (K2HPO4), a yield of 126.73 μg mL−1 of EPS in 12 days was obtained which was four-fold higher than un-optimised control. An important finding of this study is that EPS production could be further enhanced by over 50% with a mild stress by a strong oxidizing agent ozone (O3). Physico-chemical properties of this Ozone induced EPS was evaluated and found identical to uninduced EPS. EPS was composed of the hexoses- Glucose (14.80%), Galactose (18.01%) and Mannose (12.64%), the pentoses- Arabinose (17.86%) and Xylose (11.66%), the deoxyhexose- Fucose (12.53%) and Rhamnose (12.50%). Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) analysis revealed the presence of the functional groups uronic acid and traces of sulfate group. The Zeta potential analysis revealed that the emulsions were stabilized electrosterically rather than by pure electrostatic repulsion and steric stabilization. EPS at 1% in hydrocarbons and vegetable oils was observed to be an excellent emulsifier (99%), with reasonable stability. Rheological study revealed that the EPS (1%) was a non- Newtonian weak gel, useful for emulsification activity. Unlike petroleum-based emulsifiers now in use, bio-based EPS are renewable, economical and eco-friendly. The physico-chemical characteristics suggest their utility in a wide variety of other applications including bioremediation, manufacture of paints, shear reduction in oil drilling etc.
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