| Inhibitors | Conc. ppm | Gasometric | Potentiodynamic polarization | EIS |
| Catharanthus extract | 50 | 25.8 | 41.0 | 52.0 |
| 100 | 41.9 | 46.0 | 54.3 | |
| 150 | 48.4 | 51.0 | 54.8 | |
| 200 | 56.5 | 53.0 | 6.2 | |
| 250 | 61.3 | 55.0 | 62.3 | |
| 300 | 64.5 | 66.0 | 63.0 | |
| Turmeric extract | 50 | 25.0 | 33.0 | 31.7 |
| 100 | 35.0 | 39.0 | 38.0 | |
| 150 | 41.9 | 48.0 | 47.0 | |
| 200 | 46.8 | 52.0 | 47.7 | |
| 250 | 53.2 | 58.0 | 48.9 | |
| 300 | 58.1 | 63.0 | 50.4 |