Volume 56, Issue 5

The economically viable large-scale production of the pure isoforms of the surfactin biosurfactants, involving bacterial – Bacillus subtilis – fermentation of biomass hydrolysate feedstock, relies on the types of bacterial strains, optimization of the fermentation processing parameters, differences in the composition of the carbon and nitrogen in the bacterial media, and the chromatography techniques used for isolation of the isoforms. Here, we biosynthesized the surfactin isoforms in their mixture forms through fermentation of biomass hydrolysates at 2 wt.% carbohydrate content. The surfactin isoforms were assessed for their surface-active properties and toxicity. The enzyme hydrolysates considered were from switchgrass, soyhull (fiber), alfalfa, and bagasse. The isoform mixtures obtained after fermentation of the hydrolysates and, glucose as a control, were concentrated using chromatography columns, and characterized for molecular weights (MWs) and relative distribution using LCMS. The isoform mixtures, obtained in different fermenters (5- and 15-L) and, for different hydrolysates, invariably constituted 5 isoforms with MWs as 992.6, 1006.6, 1020.6, 1034.6, 1048.6, 1062.6 m/z amu, with their relative proportions as 6, 24, 35, 24, and 10 weight % respectively. The surface tension values of all these isoforms, in the absence of electrolytes and at 12 ppt salinity, were similar: 37 (pH 6.5) and 31 (pH 9.5) mN/m. Furthermore, the emulsification index values for the isoforms were also similar: Dispersant-to-Oil ratio as 1:20. The LC 50 for Gulf killifish, Fundulus grandis for these surfactin isoforms ranged between 10 and 20 mg/L; a microbially-produced surfactin variant FA-Glu (Fatty acid Glutamate) was least toxic with LC 50 at ∼100 mg/L. Thus, the surfactin synthesis approach adopted here suggested that pure (>95 wt.%) non-toxic isoforms of surfactin biosurfactants can be produced in the forms of their mixtures with surface-active properties similar to those of the pure forms of the surfactin isoforms.

Starmerella bombicola and Candida kuoi are known to secrete structurally divergent sophorolipid type glycolipids (SLs) under nitrogen limitation. In the present work SLs were produced in titers of 3.9–78.6 g L −1 with the two yeast strains utilizing stearic, oleic and linoleic acid as substrates. HPLC-ELSD combined with HPLC-MS and NMR spectroscopy was used for qualitative and quantitative analysis of the SL mixtures. While S. bombicola almost exclusively produced lactonic diacetylated SLs with a preference for subterminal fatty acid hydroxylation, C. kuoi synthesized diacetylated, terminally hydroxylated open chain SLs with up to 25% of dimeric and trimeric products. Surface tension measurements showed a higher surface and interface activity of the lactonic products from S. bombicola in comparison to open chain C. kuoi based SLs. The lowest CMC of 5.4 mg L −1 and minimum surface tension at the CMC of 35.9 mN m −1 were obtained for the stearic acid based lactones. Similar tendencies were observed in interfacial tension analysis with 3.6 mN m −1 for oleic acid based lactonic SLs at the interface water/paraffin oil in comparison to 9.4 mN m −1 for the corresponding open-chain SL. The acidic C. kuoi SL mixtures directly exhibited foaming properties whereas the S. bombicola SLs needed alkaline deacetylation and ring opening to display foaming comparable to that of the structurally related alkyl polyglycosides.

The consumer demand for greener, sustainable and skin friendly chemicals is driving the use of amino-acid based surfactants in the personal care area. Acyl glutamates and glycinates are already being used in commercial products. Available literature clearly shows that the amino acid based surfactants are generally milder than their corresponding alkyl sulfates and carboxylates. However, they do offer some interesting challenges in the area of structuring and consumer desired lather properties. Furthermore, the amino acid surfactants, unlike alkyl sulfates, have pH as an interesting variable for fine-tuning their functional properties. In this paper, the solution, interfacial and skin mildness properties of commercially relevant amino acid surfactants are reviewed and the opportunities and challenges for their wider application are outlined.

We report a novel Raman technique that allows fast and reliable ex vivo assessment of the irritability of personal care cleansing products to the skin in terms of the molecular-level effects such as retention of water by corneocytes, change in the packing order and content of intercellular lipids, and the structure of keratin. We test this technique for the single surfactants (dodecyl glucoside, sodium dodecyl sulfate, sodium cocoyl glycinate, lauramidopropyl betaine) that are typically used in personal care, as well as on three types of commercial soap bars (“superfat”, “syndet”, and “combar”). We find that soaking of the skin for prolonged time in pure water can cause unfolding of keratin, which is commonly considered as a signature of “harshness” when dealing with the surfactant formulations. Moreover, molecular-level signatures of irritability of the test surfactants and soaps at brief (10 min) exposure times do not follow the trend expected from their critical micelle concentrations (CMC) and collagen swelling. In particular, dodecyl glucoside has positive impact on the barrier properties of the stratum corneum (SC) and apparent detergency properties (solubilizes lipids without affecting their packing order). We also find that two qualitatively different soap bars (“superfat” and “syndet”) are similarly mild under the conditions studied, while the “combar” soap has detergency properties. These results demonstrate that to improve methodology of predicting irritability of a surfactant-based formulation, we need to study more systematically the molecular-level responses of the SC to exposure.

Surface properties of textiles play an essential role in their functionalization with micro/nanometer-sized polymeric capsules containing active agents that can provide controlled release. The attached capsules provide additional functionalities such as deodorizing, anti-microbial, or insect repellant properties. The efficiency of capsule attachment depends on the interaction between the selected textile material and the type of capsules. In this study, surface characteristics of the textiles were modified systematically to enhance the attachment of polyethyleneglycol based polymeric capsules. In the first phase of textile selection, four different textile materials, composed of 100% single fiber, were analyzed. Among the analyzed textile samples, cotton and polyester blends were investigated in detail due to their higher hydrophobicity, less negative zeta potential after treatment with finishing solution and broad applicability in sports outfits. In the second phase, statistical design of experiment (DoE) approach was used to have a deeper understanding of the processing factors such as the silicon (hydrophobic component) concentration in the finishing solution and the cotton/polyester blend ratio. An optimal textile was designed based on maximizing the capsule attachment on the cotton fibers woven on top and polyester at the bottom for providing strength and ease of ironing. The selected blend, treated with the required silicon concentration in the finishing solution, retained the highest amount of polymeric capsules containing eucalyptus oil for tick/insect repellency.

Novel biosurfactants with high performance are always needed in the petroleum industry for environmental sustainability. Herein, we developed a series of biosurfactants to enhance the heavy oil recovery from Canadian oil sands. Pseudo-Gemini biosurfactants were designed to be interfacially active and CO 2 switchable. The strong interfacial activity of biosurfactants promotes the liberation of heavy oil from solid substrates, which was demonstrated by the liberation visualization cell. On the other hand, the separation of heavy oil from extraction fluid was also facilitated by activating the CO 2 switchability of biosurfactants. Since the efficiencies in both the heavy oil liberation and the oil-water separation were improved, the total heavy oil recovery could be significantly enhanced. Therefore, these biosurfactants are believed to be promising in the application of enhanced oil recovery from oil sands ore.

The large-scale use of dispersants during the BP Horizon spill revealed various risks associated with these formulations, particularly the use of volatile organic compound (VOC) solvents linked to respiratory illnesses, and the poor biodegradability of surfactants. Previous attempts at solving these issues involved formulations of lecithin and polyethylene glycol ester of sorbitan monooleate (Tween ® 80) that still required the use of a volatile solvent, ethanol. In this work, the Hydrophilic-Lipophilic Difference (HLD) framework was used to develop a lecithin formulation containing food-grade lipophilic (Glycerol MonoOleate – GMO- and sorbitan monooleate – Span ® 80) and hydrophilic (polyglycerol caprylate) linkers in combination with a nonvolatile and mineral oil solvent with food additive status. The HLD parameters for lecithin, linkers, and oils were used to determine the lecithin-linker formulas that yielded HLD ∼0 (the surfactant phase inversion point), reaching interfacial tensions of 10 −2 mN/m, and high emulsification effectiveness with diluted bitumen. This effectiveness was close to that obtained with a simulated dispersant, and superior to the lecithin-Tween ® 80-ethanol formula. The lecithin-linker system produced 4–11 μm emulsified drops, sufficiently small to enhance the biodegradability of the dispersion.

To reduce environmental and occupational impact of flotation reagents, there is an emerging need to find greener reagents for sulphide mineral flotation. This study presents a comparison of the interactions of chalcopyrite with three glycolipid biosurfactants (sophorolipid, glucolipid and glucoside) and three traditional thiol surfactants (collectors) to assess the potential of the biosurfactants as collectors. The mineral-surfactant interactions are studied using adsorption isotherm, zeta potential, FTIR spectroscopy and flotation tests. We find that glycolipid biosurfactants hold high potential as collectors for flotation of copper sulphides.

Two novel biosurfactants – surfactin and its variant fatty acyl glutamic acid (FA-glu) – were compared with two commercial emulsifiers – lecithin, and a mixture of Tween 80 and lauric „arginate (TLA) – for formation and stability of emulsions and nano„emulsions containing cinnamaldehyde (CM). The nano„emulsions’/emulsions’ antimicrobial performance against two common foodborne pathogens Escherichia coli O157:H7 and Listeria monocytogenes was also compared. Two emulsifier concentrations (0.5% w/w and 1% w/w) and two homogenizing pressures (62.05 MPa and 124.10 MPa) were compared for emulsions droplet stability during storage for 46 days at 4°C, 25°C, and 37°C. Surfactin, FA-glu, and TLA resulted in formation of nanoemulsions at both concentrations, but lecithin did not. Droplet sizes did not change significantly during 38 days at stored temperatures for surfactin- and TLA- stabilized nano„emulsions. However, FA-glu and lecithin stabilized emulsions coalesced after Day 13 at 37°C; also, FA-glu stabilized emulsion thickened on the 38 th day at 4°C. The incorporation of CM in nanoemulsions or emulsions did not lower the minimum inhibitory concentration (MIC) for two bacteria tested in broths. However, the CM nanoemulsions and emulsions showed enhanced effects in inhibiting bacterial growths at concentrations lower than MICs compared to non-emulfied CM, with more inhibition from nanoemulsions.