Assessment of Rheological Behaviour of Water-in-Oil Emulsions Mediated by Glycolipid Biosurfactant Produced by Bacillus megaterium SPSW1001

A screening programme using mineral salt medium supplemented with n-hexadecane resulted in isolating a Bacillus megaterium SPSW1001 which was capable of producing surface active molecules lowering culture medium surface tension to 27.43 +/- 0.029 mN/m and interfacial tension to 0.38 +/- 0.03 mN/m at 72 h and an emulsification index (E-24) (85.63%). The biosurfactant product was further used to assess its effects on the rheological characteristics of water-in-oil emulsion prepared with engine oil. Structural characterization of the biosurfactant product by FTIR revealed a C-O-C stretch in sugar moiety and ester carbonyl linkage group between sugar and fatty acids, respectively, while mass spectral analysis revealed its glycolipid nature, with an m/z value of 662.44. The fluid behaviour of water-in-oil emulsion showed a non-Newtonian viscoelastic dilatant flow after yielding exemplified appropriately by Herschel-Bulkley model with 100% confidence of fit. The present study is significant in formulation and handling, processing, and transport of emulsion and in understanding flocculation characteristics.

Automated summary

In this study, a screening programme successfully isolated a Bacillus megaterium capable of producing surface active molecules that significantly lower surface tension and interfacial tension. The biosurfactant product was then used to evaluate its effects on rheological characteristics of water-in-oil emulsion. Structural and mass spectral analysis revealed the glycolipid nature of the biosurfactant. The water-in-oil emulsion showed non-Newtonian viscoelastic dilatant flow, fitting appropriately with the Herschel-Bulkley model.