Table 1 Biosurfactant production (g L^− 1), its surface tension reduction (mN m^− 1), oil displacement test (mm), emulsification activity (% EA24) and determination of the turbidity of the emulsion (OD₆₀₀) for Rhodococcus sp. SP1d grown using different hydrophobic substrates after 10 days of incubation (n.d.) not determined. (--) Surface tension measurements were confounded by the viscousnature of butter and mineral oil and the bioemulsified cultures

n-hexadecane

Diesel

Mineral oil

Exhausted vegetable oil

Butter

Purified biosurfactant (g L ^-1 )

2.38 ± 0.51

1.86 ± 0.31

0.31 ± 0.25

1.61 ± 0.23

0.81 ± 0.29

Surface tension (mN m ^-1 )

Reference culture

Bioemulsified culture

Difference

60.9 ± 0.30

46.9 ± 1.34

14

58.6 ± 1.17

42.8 ± 2.20

15.8

34.89 ± 1.92

32.75 ± 0.44

--

53.32 ± 0.17

49.36 ± 0.33

3.96

43.35 ± 0.21

44.17 ± 0.34

--

Oil displacement test (mm)

13.6 ± 1.53

9.0 ± 1.41

2.5 ± 0.92

4.5 ± 0.71

3.2 ± 1.05

Emulsification activity (% EA24)

Diesel

56.15 ± 3.26

46.92 ± 3.26

3.84 ± 1.08

40.00 ± 2.17

40.76 ± 7.61

Olive oil

61.53 ± 4.35

44.61 ± 4.35

6.92 ± 2.17

40.76 ± 3.26

22.30 ± 5.43

Hexane

62.30 ± 2.17

46.92 ± 7.61

5.38 ± 1.08

39.23 ± 3.26

40.00 ± 2.17

Xylene

57.69 ± 1.26

51.53 ± 3.23

4.61 ± 4.35

37.69 ± 5.43

24.61 ± 2.17

Turbidity of the emulsion (OD ₆₀₀ )

Diesel

24.52 ± 4.95

12.95 ± 1.76

n.d.

5.37 ± 0.67

5.95 ± 0.35

Olive oil

14.00 ± 2.83

15.25 ± 2.47

n.d.

5.10 ± 0.84

n.d.

Hexane

23.53 ± 3.26

5.30 ± 0.14

n.d.

2.75 ± 0.49

3.80 ± 0.42

Xylene

53.50 ± 4.24

20.7 ± 2.54

n.d.

9.75 ± 3.18

n.d.