Production and Optimization of Biosurfactants from Citrullus lanatus Seeds and Activity Determination with Pseudomonas aeruginosa Isolate

Aims: To produce and optimize biosurfactants from Citrullus lanatus seeds.

Study Design: Randomized design.

Place and Duration of Study: Department of Biochemistry Lab. and Department of Microbiology lab. University of Nigeria, Nsukka, between April and August, 2017.

Methodology: Biosurfactants were produced in two fermentation media consisting of basal mineral medium+ watermelon (C. lanatus) seed (BMM+WMS), and Nutrient broth (NB). Optimization of production process was carried out with respect to time/duration of fermentation and pH of production which indicated 7 days fermentation period at pH 8.0. The Pseudomonas aeruginosa used was isolated from soil. The biosurfactants stability under some environmental conditions were studied using; Thermostability test at 30°C, 60°C, and 100°C; Halostability test with %w/v concentration of NaCl in; 2%NaCl, 5%NaCl, 7%NaCl, and 10%NaCl; pH stability test was conducted with pH 2.0, pH 4.0, pH 6.0, pH 8.0, pH 10.0, and pH 12.0.

Results: Proximate analysis(%) showed; protein (0.317­ ± 0.02), lipid (17.66 ± 0.17), carbohydrate (62.77 ± 0.21), ash (2.33 ± 0.24), fibre (4.84 ± 0.79), and moisture (12.06 ± 0.17).The Emulsification index (E24) for the crude biosurfactant solutions (supernatants) that resulted from the two production media, and sodium dodecyl sulfate 1% SDS in distilled water (control) using palm oil (PO), olive oil (OO), engine oil (EO), kerosene (KR), and petrol (PT) for BMM+WMS biosurfactant gave PO (79.66±1.52%), OO (64.66±7.23%), EO (15.33±4.93%), KR (12.66±6.50%), and PT (0.00±0.00%). Also, the NB biosurfactant resulted in; PO (71.00±2.00), OO (54.33±3.78), EO (42.66±6.42), KR (22.66±7.57), and PT (0.00 ± 0.00) E24 values. There were significant decreases (p<0.05) in biosurfactants activities in all vegetable oils and hydrocarbons when compared to the SDS surfactant. However, there was no significant decrease (p>0.05) in WMS biosurfactant activity in palm oil compared to SDS surfactant activity in palm oil.

Conclusion: The biosurfactants were shown to have high thermostablity as their E24 values increased with rise in temperature.