| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 591506 | Colloids and Surfaces A: Physicochemical and Engineering Aspects | 2016 | 12 Pages |
•Sophorolipids (SLs) are safe, scalable biosurfactants with promising surface activity.•Modified SLs outperform natural SLs with low CACs and low IFT with lemon oil.•By tuning the surfactant structure, adsorption and emulsification can be optimized.•Modified SLs cause depletion flocculation in lemon oil emulsion systems.•Emulsion and interfacial data can be used to form a predictive model.
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 SL-esters 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 0.026 mg/mL while SL-hexyl ester (SL-HE) had a lower CAC, 0.02 mg/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 1 wt% SL 20 wt% 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 acidic SLs (LSL + ASL). LSL + ASL has similar emulsion properties to SL-EE at low SL concentrations while emulsions collapsed at higher SL concentrations.
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