Extraction Separation of Rhamnolipids by n‐Hexane via Forming Reverse Micelles

Abstract

Rhamnolipids (RL) have been regarded to be insoluble in n‐hexane. Unexpectedly, we have noticed that RL could be extracted together with vegetable oil by n‐hexane at analyzing oil content of fermentation broth. This paradoxic phenomenon was assumed to be due to the formation of reverse micelles. As found in this paper, the micelle size as well as conductivity increased due to water solubilization, illustrating the formation of reverse micelles of RL in n‐hexane. In this reverse micellar system, the maximal water solubility was detected to be 6.26 mol H2O/mol RL while the reverse critical micelle concentration of RL was around 3% (w/w). Hence, it seems that the presence of water could increase the dissolution of RL in n‐hexane via forming the reverse micelles of RL/n‐hexane/water. Lastly, the formation of reverse micelles was further applied for extraction of RL by n‐hexane. Using this method, over 99.0% of RL was extracted under the appropriate pH of 4.5. This extraction separation using n‐hexane instead of chloroform proposed a much cleaner and safer strategy in RL manufacture. Moreover, the capability of RL in forming reverse micelle system could benefit the future application on improving enzymatic reactions, stabilizing nanoparticles, environmental treatment, and protein folding, etc.

Food Waste Digestate-Based Biorefinery Approach for Rhamnolipids Production: A Techno-Economic Analysis

“…The method of extracting rhamnolipids using n-hexane used in the present study deviates from the previous literature reports by Müller et al and El-Housseiny et al who reported the use of n-hexane to determine the oil content in the fermentation media but not for rhamnolipids extraction from this oil-containing medium [16,17]. On the contrary, a recent report by Zhou et al suggested that rhamnolipids could be extracted from the fermentation broth using n-hexane in the presence of oil due to the formation of reverse micelles [18]. Zhou et al first performed acid precipitation of rhamnolipids produced in an oil-containing fermentation medium followed by its extraction with n-hexane.…”

Glycolipid Biosurfactant Production from Waste Cooking Oils by Yeast: Review of Substrates, Producers and Products

“…The BS product obtained from solvent extraction and/or acid precipitation is often described as being completely pure, but this is not the case, since the product usually still contains up to 60% water and a number of other contaminants [55]. Ethyl acetate is the most common extracting solvent that is used either alone or in combination with other solvents, such as methanol and chloroform [76,80,97,[102][103][104][105][106][107]. The use of ethyl acetate and chloroform in the production of environmentally sustainable products is not advisable, since these solvents are toxic and must be used in large amounts for these extraction procedures [98].…”

“…The use of ethyl acetate and chloroform in the production of environmentally sustainable products is not advisable, since these solvents are toxic and must be used in large amounts for these extraction procedures [98]. Zhou et al (2020) suggest that these unfavorable solvents could be replaced by n-hexane, a less-harmful solvent [97].…”