Effect of Sophorolipid n-Alkyl Ester Chain Length on Its Interfacial Properties at the Almond Oil–Water Interface

Abstract

Sophorolipids (SLs), produced by Candida bombicola, are of interest as potential replacements for hazardous commercial surfactants. For the first time, a series of molecularly edited SLs with ethyl (EE), n-hexyl (HE), and n-decyl (DE) esters were evaluated at an oil (almond oil)-water interface for their ability to reduce interfacial tension (IFT) and generate stable emulsions. An increase in the n-alkyl ester chain length from ethyl to hexyl resulted in a maximum % decrease in the IFT from 86.1 to 95.3, respectively. Furthermore, the critical aggregation concentrations (CACs) decreased from 0.035 to 0.011 and 0.006 mg/mL as the ester chain length was increased from ethyl to n-hexyl and n-decyl, respectively. In contrast, the CAC of natural SL, composed of 50/50 acidic and LSL, is 0.142 mg/mL. Dynamic IFT analysis showed significant differences in diffusion coefficients for all SLs studied. Almond oil emulsions with up to 200:1 (by weight) oil/SL-DE were stable against oil separation for up to 1 week with average droplet sizes below 5 μm. Emulsions of almond oil with natural SLs showed consistent oil separation 24 h after emulsification. A unique connection between IFT and emulsification was found as SL-DE has both the lowest CAC and the best emulsification performance of all natural and modified SLs studied herein. This connection between CAC and emulsification may be generally applicable, providing a tool for the prediction of optimal surfactants in other oil-water interfacial applications.

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).…”

“…None of the emulsions of this work showed oil separation or surfactant precipitation; they all show creaming (Fig. S3), which is expected due to the large particle sizes of the emulsions (Koh et al, 2016). No visual differences in the emulsification performance of SL and Triton X-100 were observed.…”

Molecular editing of sophorolipids by esterification of lipid moieties: Effects on interfacial properties at paraffin and synthetic crude oil-water interfaces

“…Upon completion, the reaction mixture was acidified to pH 4 with glacial acetic acid and purified by flash chromatography using CHCl 3 :MeOH as eluent. The structure of purified products was confirmed by Liquid Chromatography-Mass Spectrometry (LC-MS), 1 H NMR, and 13 C NMR that are identical to those previously reported [16,20].…”

A novel microbial technique for producing high‐quality sophorolipids from horse oil suitable for cosmetic applications

“…Compared with chemically synthesised surfactants that are often toxic and difficult to biodegrade, and can cause side effects in humans and the wider environment after long-term exposure, biosurfactants such as sophorolipids have lower toxicity and higher biodegradability (Lourith and Kanlayavattanakul, 2009). Sophorolipids are particularly biodegradable, and are used widely in cosmetics and personal care products as emulsifying, foaming and wetting agents, as well as solvents, due to their excellent moisture-retaining capacity (Brown, 1991;Reis et al, 2009;Ramrakhiani and Chand, 2011;Goswami et al, 2013;Koh et al, 2016). Their emulsification and antibacterial properties make sophorolipids suitable for use in antidandruff shampoos, acne removers and deodorants (Otto et al, 1999;Hardin et al, 2007;Morya et al, 2013;Borsanyiova et al, 2016), and even in kitchen supplies and detergents (Van Bogaert et al, 2013).…”