A versatile family of sophorolipid esters: Engineering surfactant structure for stabilization of lemon oil-water interfaces

Abstract

Sophorolipids (SLs) are biosurfactants produced by Candida bombicola from renewable feedstocks in yields > 400 g/L. Molecular editing of natural SLs gave a series of n-alkyl SLesters that, along with natural SLs, were interrogated to determine how structural changes alter SL interfacial tension (IFT), diffusion, adsorption, and emulsification at the lemon oil/water interface. SL-ethyl ester (SL-EE) reduced the IFT by 95.1% and has a critical aggregation concentration (CAC) of 0.026mg/mL while SL-hexyl ester (SL-HE) had a lower CAC, 0.02mg/mL, but a lower IFT reduction (87.5%). Adsorption behavior further highlighted differences between the SL-esters as SL-decyl ester (SL-DE) had the lowest surface excess concentration while SL-HE had the highest adsorption coefficient. The competing effects of these interfacial parameters were manifested in the relative performance of SL-esters in forming lemon oil-in-water emulsions. SL-EE had the largest average emulsion droplet size but showed no oil separation up to 200:1 wt/wt oil/surfactant. Microscopy provided information on macroscopic emulsion morphologies. For example, flocculation was observed for all 1wt% SL 20wt% lemon oil emulsions. These results were corroborated by shear thinning rheological behavior. Studies were conducted with a natural SL mixture consisting of 1:1 wt/wt lactonic and

Biosurfactants from Waste: Structures and Interfacial Properties of Sophorolipids Produced from a Residual Oil Cake

“…The average droplet sizes of SL emulsions increase with the increment in the percentage of almond oil for a given time, with mean values ranging from 500 to 5000 nm. Similar trends have recently been reported for SL emulsions using almond oil (Koh et al, 2016), lemon oil (Koh and Gross, 2016a), and paraffin oil (Koh and Gross, 2016b).…”

Asymmetrical, Symmetrical, Divalent, and Y-Shaped (Bola)amphiphiles: The Relationship between the Molecular Structure and Self-Assembly in Amino Derivatives of Sophorolipid Biosurfactants

“…14,18,19 This short survey shows that, despite the rich phase behavior of this class of compounds, the diversity in terms of molecular structure remains very limited and generally confined to the general formula sugar-spacer-COOH, where the spacer is commonly a C18:1 or C18:0 hydrocarbon, although more complexity can be found in rhamnolipids and cellobioselipids. 20,21 To explore new properties and broaden the application potential of the natural sophorolipids, several chemical derivatives including alkyl esters (better emulsifiers) [22][23][24][25] and polymers 26 have been recently developed, just to cite some. 27 One possible approach consists in modifying the double bond in the C18:1 backbone.…”

Microbial Synthesis of Nonionic Long‐Chain Sophorolipid Emulsifiers Obtained from Fatty Alcohol and Mixed Lipid Feeding

“…While most publications reported the emulsification behavior of SLs with high energy input (shear homogenizer), [19][20][21] we already observed an excellent emulsification ability during the purification steps of the long-chain SL esters. Therefore the stabilization of a paraffin oil/water mixture with oleyl alcohol based SL ester from S. bombicola was tested in a system with low energy input.…”

“…[17][18][19] The CMC values of the esters decreased with increasing chain length [18] and the long-chain esters exhibited good emulsifying properties of several oil/water mixtures. [19][20][21] Upon enzymatic re-acetylation of the sophorose, diacetylated long-chain esters with a structure closer to that of the native SLs were obtained. [17,22] These esters behaved differently than the corresponding non-acetylated SLs exhibiting increased CMCs at lipid tail lengths of >C22.…”