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. 2021 Jun 16;44(10):2003–2034. doi: 10.1007/s00449-021-02597-5

Fig. 9.

Fig. 9

The double diffusion agar test occurs with the addition of biosurfactant samples in wells in a row regularly spaced against another row of wells filled with a known cationic or anionic element. The appearance of precipitation lines (48 h) between the wells indicates the ionic character of the biosurfactants