Efficient isolation of rhamnolipids from fermentation broth via an advanced acid-induced precipitation process with heat treatment

Acid-induced precipitation (AIP) is the most efficient approach for isolation of rhamnolipids (RLs), while it does not work at certain cases. Therefore, for certain specific fermentation processes, efficient and low-cost separation of RLs remains a challenge. In this study, an advanced AIP process based on heat treatment was developed to efficiently isolate RLs from a fermentation broth where RLs were unable to precipitate. Over 97 % of RLs with purity of 90.8 % were recovered after treatment at 120 °C for 10 min at a pH below 4. The involved mechanism might be related to that heat treatment at pH below 4 results in the degradation of certain components in broth that interfere with the RLs precipitation, thus no longer affecting the precipitation performance of RLs at acidic conditions. Moreover, the obtained RLs manifested well-maintained surface and emulsification activities. It can reduce the surface tension of water to approximately 29 mN/m at concentration of 65 mg/L, and the emulsification index was 72–80 % against varied types of oil. The approach exhibited superior performance compared to regular AIP processes, demonstrating excellent universality in real applications. However, more systematic research needs to focus on clarifying the interfering component which should be the main limitation of the present study.