Biosurfactant by Serratia sp. BR13816: Fermentation Optimization and Nanoemulsion Formation

Abstract

The main objective of this study was to optimize the fermentation process using Serratia sp. BR13816, a bacterial isolate from Amazonian soil, and to evaluate the formation of nanoemulsions. Submerged fermentation was carried out with different carbon and nitrogen sources. Based on the emulsification index and surface tension results, we selected a hydrophobic (corn oil) and a hydrophilic (glycerol) carbon source, and a nitrogen one (urea). For fermentation using corn oil/urea greater emulsification indexes and lower surface tensions were verified at pH 8, 25 °C, and 48 h, whereas for glycerol/urea-supplemented medium the best conditions were attained at pH 7, 30 °C, and 96 h. These preselected factors (pH, temperature, and time) were used in a central composite rotatable design (CCRD) for an additional fermentation optimization of the two carbon/nitrogen mediums, corn oil/urea and glycerol/urea. The two best nutritional systems based on corn oil/urea and glycerol/urea were selected using a central composite rotatable design (CCRD). The mathematical models using the response surface methodology showed adequate adjustment. The best run of the experimental design for corn oil/urea (6.00% /0.60%) and glycerol/urea (3.00% /1.40%) systems presented surface tension values of 35.70 mN/m and 37.10 mN/m, respectively. The nanoemulsions produced by a low-energy method presented average sizes by dynamic light scattering varying from 453.1 nm to 667.3 nm when 0.1% of the oil was employed. Therefore, Serratia sp. BR13816 showed promising biosurfactant-producing potential for future industrial applications.