Rhamnolipids have extensive potential applications and are the most promising biosurfactants for commercialization. The efficient and accurate identification and analysis of these are important to ...their production, application and commercialization. Accordingly, significant efforts have been made to identify and analyse rhamnolipids during screening of producing strains, fermentation and application processes. Cationic cetyltrimethylammonium bromide–methylene blue (CTAB-MB) test combines a series of indirect assays to efficiently assist in the primary screening of rhamnolipids-producing strains, while the secretion of rhamnolipids by these strains can be identified through TLC, FTIR, NMR, electrospray ionization mass spectrometry (ESI-MS) and HPLC-MS analysis. Rhamnolipids can be quantified by colorimetric methods requiring the use of concentrated acid, and this approach has the advantages of reliability, simplicity, low-cost and excellent reproducibility with very low technological requirements. HPLC-MS can also be employed as required as a more accurate quantification method. In addition, HPLC-ELSD has been established as the internationally acceptable measure of rhamnolipids for commercial purposes. The preparation of well-accepted rhamnolipids standards and modifications of analysis operations are essential to further enhance the accuracy and improve the simplicity of rhamnolipid analysis.
Key points
• Current status of R&D works on determination of rhamnolipids is listed
• Advantages and disadvantages of various types analysis are summarized
• Limitations of current rhamnolipid quantification are discussed
Graphical abstract
► Rhamnolipid showed a high demulsification activity on waste crude oil. ► The demulsification activity of rhamnolipid was confirmed on model emulsions. ► The demulsification activity of rhamnolipid ...was confirmed at pilot sale treatment. ► The recovered crude oil can enter into refinery process. ► Rhamnolipid showed great prospects in industry as a biodemulsifier.
Waste crude oil emulsion was inevitably produced in the petroleum industrial process, causing harmful impact on the ecological and social environment. In this study, rhamnolipid was for the first time investigated for demulsification of waste crude oil. As found in this paper, rhamnolipid treatment could obtain over 90% of dewatering efficiency on refractory waste crude oil and such efficient demulsification was confirmed on model emulsions. As further demonstrated on the pilot scale (100L), rhamnolipid treatment could recover over 98% of crude oil from the wastes. The recovered oil contained less than 0.3% of water and thus can directly re-enter into refinery process while the aqueous phase can be disposed into dischargeable water due to largely reduced soluble COD after subjected to 5days of active sludge treatment. It seems that rhamnolipids as biodemulsifiers were of great prospects in the industrial demulsification of waste crude oil.
Biosurfactant rhamnolipids have been claimed to show biological activities of inhibiting the proliferation of cancer cells. In this study, the cytotoxicity of rhamnolipids was examined on four cancer ...cells (HepG2, Caco-2, Hela, MCF-7 cells) and two normal cells (HK-2 cell, primary hepatocyte). Interestingly, both cancer cells and normal cells exhibited similar sensitivities to the addition of rhamnolipids in culture medium, and the cytotoxicity was largely attenuated by the presence of fetal bovine serum (FBS) in culture medium. In correlation of the mono-/di-rhamnolipid cytotoxicity with the surface tension of culture medium, it was found that rhamnolipids triggered cytotoxicity whenever the surface tension of culture medium decreased below 41 mN/m irrespective of the FBS content in culture medium, cell line, or rhamnolipid congener. Similarly, each chemical surfactant (Tween-80, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate) could cause cytotoxicity on HepG2 cells whenever its addition made the surface tension under 41 mN/m in culture medium with or without the presence of FBS. It seems that rhamnolipids, like chemical surfactants, exhibited cytotoxicity by reducing the surface tension of culture medium rather than by changing its specific molecular structure, which had no selection on tumor cells. This study could offer helps to correct the misleading biological activity of rhamnolipids and to avoid the possible large wastes of time and expenses on developing the applications in antitumor drugs.
Membrane fouling was inevitable in the ultrafiltration process in dairy industry, causing harsh reduction of the membrane performance. The current cleaning agents like acid/base and chemical ...surfactants would be limitedly used in future due to their detrimental effect on membrane or/and environment/health. In this study, the environmental-friendly biosurfactant rhamnolipid was for the first time applied to clean the ultrafiltration membrane fouled by protein. The cleaning by rhamnolipid under pH 9 could largely remove the foulant from the PSU, PAN and PEG-g-PSU membranes and restore the water flux to about 94% of the initial level, performing much better than the flux recovery of 50–70% for Tween 20 and SDS, the most extensively used surfactants in membrane cleaning. Moreover, rhamnolipid exhibited superior properties over the commonly used cleaner of sodium hydrate (NaOH) and even the commercial membrane cleaner in view of cleaning efficiency and operation mildness. Finally, rhamnolipid was demonstrated to be effective in cleaning the long-term fouling membrane. Taken together, rhamnolipid as an economical product of lowly costive cell-free broth shows great potential in industrial application as membrane cleaner.
•Rhamnolipid manifested excellent cleaning activity on fouled membrane.•Rhamnolipid showed superior properties over typically cleaners on cleaning.•Rhamnolipid cleaning would not affect the membrane performance.•Rhamnolipid presented great potential on industrial membrane cleaning.
Oily sludge dewatering is practically needed prior to sludge treatments. However, the conventional use of physical treatments with or without chemical conditionings presented poor feasibility in ...industrial applications due to either poor cost-efficiency or lacking environmental friendliness. In this paper, biosurfactant rhamnolipid was for the first time applied for dewatering of oily sludge. Rhamnolipid treatments under the concentration of 300–1000 mg/L, pH of 5–7 and temperature of 10–60 °C could directly separate 50–80% of water from the stable oily sludge. And both mono-rhamnolipid and di-rhamnolipid were identified to be of equivalent dewatering ability, which is closely related to their equivalent performance in breaking the emulsified oil droplets. Demulsification was found to be involved in settling water from oily sludge. Furthermore, the effectiveness of rhamnolipid was further demonstrated at pilot scale (1000 L) treatment of oily sludge. After pilot treatment, the settled water with residual oil of 10 mg/L and soluble COD of about 800 mg/L could be directly effluxed into the biotreatment system while the concentrated oil sludge with a reduced volume by 60–80% can be pumped into coking tower, achieving completely harmless treatment. It seems that rhamnolipid as dewatering agent was of great prospects in the industrial dewatering of oily sludge.
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•Rhamnolipid treatment could directly separate water from oily sludge.•Demulsification of oily droplets by rhamnolipids mediated the dewatering.•Mono/di-rhamnolipid showed the same demulsifying and dewatering activity.•The dewatering activity of rhamnolipid was confirmed at pilot scale treatment.
•Current status of R&D works on efficient rhamnolipids fermentation is listed.•Advantages and disadvantages of various types cultivations are summarized.•Limitations of chemical antifoam in ...rhamnolipid fermentation are discussed.•Prospects for foam-control in large-scale of rhamnolipids fermentation are discussed.
The global market for rhamnolipids production holds great promise, and is in need of an economically viable mass-production scheme. Accordingly, several strategies have been employed to improve the efficiency of rhamnolipid production in the past few decades. Currently, rhamnolipids can be produced by Pseudomonas aeruginosa at a high yield (over 70 g/L) when vegetable oil is used as the carbon source under optimized fed-batch cultivations. However, severe foaming during rhamnolipid fermentation inhibits scaling-up and production efficiency. Stop valve was found to effective break the extremely stable rhamnolipids foams during fermentation, and production efficiency of rhamnolipids was highly improved, while its scale-up mechanism needs further study. In addition, the combination of both chemical and mechanical approaches is likely to be more efficiently resolving the foam problem existed in rhamnolipids fermentation than either chemical or mechanical methods alone.
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•Surfactin has a pH-regulated emulsification activity.•Surfactin precipitated and lost emulsification activity under acidic pH.•Surfactin can be readily reused after oil ...separation.•Surfactin has great application feasibility in EOR.
In the present study, the pH-regulated emulsification activity of surfactin was studied and its potential application in oil separation towards enhanced oil recovery (EOR) was investigated. As demonstrated, surfactin can stabilize emulsions quite well beyond pH 7.4. An oil emulsification ratio of about 98% was obtained at pH 11.0; while this emulsification activity was rapidly and completely lost when pH decreased to below 3.0, having an oil separation ratio of over 98%. This pH-sensitive property is probably due to surfactin dissolution-precipitation induced by the ionization-protonation of a carboxyl group in its structure under alkaline or acidic conditions. This property allows oil emulsification or oil separation to be readily achieved via simple pH adjustments when surfactin is used as an emulsifier. Furthermore, surfactin sustained its activity after demulsification and can be readily reused many times. The above obtained results indicated surfactin-based EOR processes have great application feasibility.
Discovering new antibacterial agents is crucial to addressing the increasing risk of bacterial infections induced by antimicrobial resistance in food and agricultural industries. Here, biocompatible ...acidic-type sophorolipids (ASLs) and glucolipids (GLs) prepared via chemical modification of natural sophorolipids from fermentation were functionalized via amide modification for use as potential antibacterial agents. It was found that the arginine methyl ester derivative of GLs (GLs-d-Arg-OMe) showed excellent antibacterial activity, killing more than 99.99% of Escherichia coli at 200 mg/L. The sterilization dosage of the GLs against Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus was 16–64 mg/L, in contrast to 32–64 mg/L for the fungus Candida albicans. In particular, GLs-d-Arg-OMe showed the best biocompatibility with a therapeutic index of up to 18. It was shown that amide modification of glycolipids can effectively improve antibacterial activity while maintaining biocompatibility, which can be exploited for the development of novel antibiotics in food and agricultural fields.
The development of new preservatives is an ongoing investigation in the food industry, especially those which are safe and environmentally friendly. In this study, biosurfactant sophorolipids (SLs) ...functionalized with amino acids were developed as efficient preservative agents. SLs were first isolated from fermentation broth by Candida bombicola ATCC 22214, hydrolyzed, and purified by extraction. The typical recovery is around 70%, while the extracted material consists of over 90% deacetylated acidic SLs (SL-COOH). Four types of SL derivatives were then synthesized via dicyclohexylcarbodiimide amidation reactions from prepared SL-COOH. Among the derivatives produced, the arginine SL conjugates (SL-d-Arg) displayed the highest activity against Gram-positive bacteria and fungi and even inhibited the cell growth of Gram-negative bacteria and mildew. Furthermore, the arginine conjugates performed the broadest antimicrobial activity among the derivatives evaluated. The sterilization dosage of the arginine conjugates against the food-spoilage pathogen Bacillus spp. was 63–125 mg/L, in contrast to 250 mg/L for the enterotoxin producer Staphylococcus aureus and 500 mg/L for fungi. More importantly, SL-d-Arg displayed excellent biocompatibility, with a therapeutic index of over 7.94. SL-d-Arg has excellent potential as an alternative to traditional chemical preservatives.
Rhamnolipids are glycolipid biosurfactants that have extensive applications as cleaner alternatives to chemically synthesized surfactants. The cost of producing rhamnolipids is typically high due to ...the poor yields realized. This cost has limited their use in commercial applications. In this study, an advanced sequential fed-batch fermentation process with high cell densities was developed for the efficient fermentative production of rhamnolipids. With this approach, the total produced rhamnolipids reached over 665 g/L by Pseudomonas aeruginosa PAO1 during the fermentation period of 18 days, with an extremely high productivity of 1.54 g/L·h. This represents a more than a 5-time improvement over the regular fed-batch fermentation. The present advanced sequential fed-batch fermentation process is extremely efficient due to the high cell density and the presence of 18 g/L NaNO3 and 2 mg/L FeSO4·7H2O with enhanced mass-transfer efficiency, presenting a new strategy to improve the fermentation level of rhamnolipids.
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•An extremely efficient process to produce rhamnolipids was developed.•The rhamnolipids productivity was significantly improved 1.54 g/L·h.•Nitrate and Fe2+ under enhanced mass-transfer are crucial to improve RLs production.•This advanced process possesses of great potential in real fermentation of RLs.
