Extraction of amoxicillin and erythromycin utilising sophorolipids reversed micellar system

Abstract

Downstream processing of antibiotics conventionally involves filtration, solvent extraction, and crystallization. Formation of stable emulsion during conventional solvent extraction of antibiotics causes high solvent consumption and low product yield. Recently, reverse micelle extraction has been investigated for the extraction of proteins and dyes. Reverse micelle extraction has the advantages of easy operation, high selectivity, mild operating conditions, short extraction time, preserved protein activities, reduced emulsion formation, and safer solvents, as well as having the potential for scale up, continuous operation, and solvent recycling. Most researchers use chemical surfactants for their reverse micelle extraction. In this study, sophorolipids biosurfactant was used for the first time for formation of reverse micelles to extract antibiotics. Application of biosurfactant can further improve reverse micelle extraction in terms of sustainability and environmental friendliness. Experiments were conducted to explore the reverse micelle extraction of amoxicillin and erythromycin. Solution pH was found to be the most dominant factor during both reverse micelle extraction of amoxicillin and erythromycin. Strong attractive electrostatic interactions between antibiotics and sophorolipids at solution pH below the isoelectric point of antibiotics allow more antibiotics to be extracted during forward extraction but fewer antibiotics to be released during backward extraction. Attractive electrostatic interactions which diminished at solution pH higher than the isoelectric point of antibiotics reduced forward extraction efficiency but promoted backward extraction efficiency. Both amoxicillin and erythromycin are very sensitive to surrounding pH and will degrade at solution pH outside of their stable pH ranges. Minimum amount of KCl was needed for the reverse micelle extraction of both amoxicillin and erythromycin. High KCl concentration hindered both forward and backward extraction of antibiotics. Sophorolipids is crucial in enabling the transfer of antibiotics into the isooctane organic phase. Increasing sophorolipids concentration increases the amount of antibiotics been extracted. Mass transfer studies showed that reverse micelle extraction of amoxicillin and erythromycin can be completed in very short time. Overall mass transfer coefficients of backward extraction was lower than that of forward extraction for both amoxicillin and erythromycin indicating that backward extraction is more difficult than forward extraction process. Comparisons between amoxicillin and erythromycin showed that erythromycin has better equilibrium partitioning and larger calculated overall mass transfer coefficients compared to amoxicillin. There may be some differences on the behaviours of amoxicillin and erythromycin during the reverse micelle extraction process. This reverse micelle extraction method was found to be more efficient in extracting erythromycin compared to amoxicillin. Furthermore, the study also confirmed that the quality of palm oil based sophorolipids is comparable to those of commercial sophorolipids.