2.6. Surface tension measurement

In order to determine the main surfactant‐producing strains, surface tension test was performed by tensiometer (FTM‐TN‐556, Toos Nano). The surface tension was measured by Du Nouy Ring Method. In this method, the device ring, made of platinum alloy, is immersed in the liquid, the force applied to the immersed ring is adjusted to zero and the ring is slowly pulled out of the fluid. The maximum force recorded by the device to remove the ring from the liquid surface is considered as the surface tension of the liquid. A total of 25 mL of 48‐h culture of each sample was poured into the apparatus. The sample temperature was set to 25°C before measuring the surface tension [³⁹]. This test was done in three repetitions and the average of the replicates is listed.