Effect of dilution on particle size analysis of w/o emulsions by dynamic light scattering

Dynamic Light Scattering (DLS) is a well-known (sub)micron particle size analysis technique. As such, it should be a valuable technique for water droplet size determination in (sub)micron water-in-oil emulsions. In this study, the sample pretreatment conditions were optimized in order to enable accurate droplet size determination by DLS. Whereas DLS was indeed capable of detecting differences between differently produced (sub)micron sized w/o emulsions, it was observed that the estimated droplet size was highly influenced by the measurement conditions used. First of all, the experimentally determined diffusion coefficient decreased with increasing water droplet concentration, which is thought to be due to interaction effects between the water droplets. To minimize this effect, the used concentration should be as low as possible. However, in doing so, the water droplets were frequently observed to disappear during storage or even during analysis, due to their dissolution in the dilution medium. The latter disturbing effect could be avoided by (sufficient) water saturation of the dilution medium and preventing water evaporation by closing the diluted sample and by restricting the head space. Summarizing, (sub)micron water droplets can be characterized using DLS. However, careful selection of the sample preparation and measurement conditions is necessary to obtain reliable data

Influence of non-ionic surfactant type on the salt sensitivity of oregano oil-in-water emulsions

During the last decade, there has been a growing interest for more "label-friendly" ingredients in food industry, as well as in pharmaceuticals, and cosmetics. Thus, a lot of research has been developed to the antimicrobial and/or antioxidant characteristics of essential oils. We, therefore, examined the influence of environmental stress conditions (i.e. salt addition and acidification) on the stability of oregano essential oil emulsions that were stabilized by either Tween 80 or Inutec SP1. Whereas Tween 80 is a non-ionic, food-grade ethoxylated sorbitan ester, Inutec SP1 is a biodegradable and renewable hydrophobically modified inulin. Whereas the emulsions prepared with Tween 80 exhibited phase separation (oiling off) at all salt concentrations studied, the emulsions stabilized with Inutec SP1 remained stable for several days; pH variation on the other hand exhibited no significant effect on the stability. Diffusion ordered spectroscopy measurements by nuclear magnetic resonance (DOSY NMR) as well as viscosity measurements suggested the dehydration of the polyoxyethylene (POE) head groups of Tween 80 upon NaCl addition. Measurements by a Quartz crystal microbalance with dissipation, on the other hand, presented no NaCl effect on the thickness of the adsorbed Tween 80 layer to a hydrophobic surface. Besides the effect of NaCl addition or pH variation, the influence of the ripening inhibitor concentration in the lipid phase and/or temperature variation on the Ostwald ripening levels were also investigated. Emulsions containing a 50:50 ratio of oregano essential oil to sunflower oil stored at 4 degrees C exhibited a significant reduction in Ostwald ripening rate. This study has implications for the development of essential oil emulsions to be used as antimicrobial agent when exposed to environmental stress conditions

Transport of uncharged organics in ion-exchange membranes : experimental validation of the solution-diffusion model

The concentration-gradient transport of uncharged organics in ion-exchange membranes (IEMs) and the experimental validation of the solution-diffusion model were investigated. Free interaction energies between organics (paracetamol, theophylline, phenazone) and IEMs were above 0, indicating potential solute resistance against partitioning into the membrane phase. Experiments performed in diffusion cells showed a linear increase in the organics concentration in the receiving solution as a function of time, suggesting a purely diffusion-driven transport. A higher organics transport was observed in anion-EMs (AEMs) than in cation-EMs (CEMs), possibly due to the higher cross-linking and lower affinity to organics of CEMs. A correlation between transport and molecular weight was observed in all IEMs following the trend: paracetamol > theophylline > phenazone. The experimental validation of the solution-diffusion model showed that the model underestimated the solutes transport in IEMs. Monte Carlo analysis indicated that the discrepancy between modeled and measured fluxes could not be eliminated even after considering experimental errors. The method for determining contact angle would influence the modeled fluxes. Moreover, the definition of diffusive hindrance factor may lead to these discrepancies, requiring further investigation. This study contributes to the field of selective organics/inorganics separation in the treatment and resource recovery of organics-rich industrial wastewater

Fat crystallization and melting in W/O/W double emulsions : comparison between bulk and emulsified state

Water-in-oil-in-water (W/O/W) technology enables the development of an emulsion-based delivery system for functional food applications. The functionality of this system depends on the oil barrier of the double emulsion, whereby the fat matrix properties (e.g. solid fat content) play an important role. First, the effect of W/O/W emulsification on fat crystallization and melting behavior was studied and compared to bulk fat. Second, the effect of fat composition was investigated. As such, W/O/W emulsions were produced with a slow and fast crystallizing fat, i.e. soft palm mid fraction (sPMF) and partially hydrogenated sunflower oil, respectively, upon cooling and subsequent isothermal crystallization. Low resolution NMR and DSC techniques were applied, and indications about the polymorphic behavior were verified by real-time synchrotron XRD measurements. Except from increased supercooling, the overall fat crystallization dynamics in the W/O/W emulsions were similar to bulk, irrespective of the used fat. Yet, broadening of the long spacing peaks in the W/O/W emulsions indicated less ordered triacylglycerol longitudinal stacking compared to bulk. This effect was more pronounced in case of alpha-crystals than beta'-crystals. With respect to W/O/W functionality, the melting behavior of the W/O/W-sPMF emulsion showed promise as a possible carrier system with a thermo-responsive release mechanism for functional foods

Quantification of counterion binding to and its effects on aqueous dispersions of dialkyl cationic surfactants

Dialkyl cationic surfactants, such as dioctadecyl dimethyl ammonium bromide (DODAB) form vesicles upon dispersion in water. In order to study the influence of the surfactant's counterion, the same dialkyl surfactant was prepared with a fluoride counterion (DODAF). Visually, quite transparent dispersions were prepared when fluoride was selected as counterion, whereas more turbid dispersions were obtained using the bromide surfactant. LR-NMR revealed that the permeability of the DODAF dispersions for water was much larger, which indicated that these rather contained uni-or oligolamellar vesicles, whereas the DODAB dispersions were multilamellar. These observations seemed to indicate an increasing degree of surface charge neutralization by the heavier anions, in line with the Hofmeister series, which was indeed confirmed by electrophoretic light scattering measurements. In order to further quantify the surfactant-counterion interaction, HR-NMR diffusometry measurements were performed on dispersions of a dialkyl cationic surfactant with methyl sulphate counterion in deuterated water. The diffusion data showed that the mobility of this organic anion increased when adding different sodium halides, with a stronger effect from fluoride over chloride and bromide to iodide, which clearly indicated the gradual displacement of the methyl sulphate counterion from the vesicular surface by the stronger binding anions