Carme Güell

Membrane fouling during microfiltration of protein mixtures

Abstract Crossflow microfiltration is an efficient method for the clarification, stabilization and sterilization of fruit juices and other biological suspensions. One of the main problems with the application of this technique, however, is membrane fouling caused by the presence of proteins and polysaccharides. The fouling behavior of four 0.2 μm hydrophilic microfiltration membranes (polysulfone, polycarbonate, polyvinylidene fluoride, and cellulose acetate) is described for protein mixtures of bovine serum albumin (BSA), lysozyme (LY), and ovalbumin (OV). The study of membrane fouling was carried out using a stirred cell, and then analyzed with electron microscopy and with flux decline, total resistance and permeate concentration versus time plots. During the filtration of single protein solutions using polysulfone and polycarbonate membranes, BSA and LY displayed only internal membrane fouling for a 3-h period, whereas OV exhibited an initial phase in which internal fouling dominated, followed by external or surface membrane fouling. When different binary protein mixtures were filtered through the polysulfone and the polycarbonate membranes, the highest membrane fouling was found for those mixtures containing ovalbumin. Finally, the filtration of a ternary protein mixture showed different fouling behaviors, depending on the surface porosities of the four membranes employed; lower surface porosities exhibited more rapid external membrane fouling.

Fish Oil Microcapsules from O/W Emulsions Produced by Premix Membrane Emulsification

Fish oil microcapsules were prepared by combining a low-energy emulsification method (premix membrane emulsification) with spray drying. Oil-in-water (O/W) emulsions were prepared using a two-step emulsification method that used a rotor–stator homogenizer followed by membrane emulsification. The influence of the emulsification method (mechanical stirring or membrane emulsification), the emulsification conditions (membrane and emulsifier type), and the amount of wall material on the physicochemical characteristics of the microcapsules was studied. The results show that the emulsification method and the type and amount of emulsifier and wall material affect the final amount of encapsulated oil. Microcapsules produced by membrane emulsification and stabilized with 2xa0% Tween-20 or 10xa0% whey protein presented the highest values (higher than 50xa0%) of oil encapsulation efficiency (OEE). It has been found that the OEE increases when decreasing the droplet size of the emulsions as well as with the increase of the amount of wall material employed during drying. Morphology analysis showed that the microcapsules obtained from O/W emulsions produced by premix membrane emulsification were rounder in shape, without visible cracks on the surface and no vacuoles on the inside. Oxidation stability tests performed on some selected samples indicate that the microcapsules with higher stability are the ones produced with a higher amount of wall material and have less surface oil.

Influence of Emulsification Technique and Wall Composition on Physicochemical Properties and Oxidative Stability of Fish Oil Microcapsules Produced by Spray Drying

Encapsulation of fish oil is an effective way to protect it against oxidation and masking its fishy odor. One of the possible ways to produce fish oil microcapsules is to produce an oil-in-water (O/W) emulsion followed by spray drying. This study compares the production of the O/W emulsion by mechanical homogenization (rotor–stator) with membrane emulsification and examines the effect of the type and amount of wall material added before drying. The membrane emulsification process selected for the emulsion production is premix membrane emulsification (ME), which consists of the production of a coarse emulsion by mechanical means followed by droplet breakup when the coarse emulsion is forced through a membrane. The emulsions produced had an oil load of 10 and 20xa0% and were stabilized using whey protein (isolate and hydrolyzate at 1 or 10xa0%) and sodium caseinate with concentrations of 2 and 10xa0%. Regarding the material used to build the microcapsule wall, whey protein, maltodextrin, or combinations of them were used at three different oil/wall ratios (1:1, 1:2, 1:3). The results clearly show that premix ME is a suitable technology for producing O/W emulsions stabilized with proteins, which have a smaller droplet size and are more monodisperse than those produced by rotor–stator emulsification. However, protein concentrations of 10xa0% are required to reduce the droplet size down to 2–3xa0μm. Small and monodisperse emulsions have been found to produce microcapsules with lower surface oil content, which increases oil encapsulation efficiency and presents lower levels of oxidation during storage at 30xa0°C. Of all the possible combinations studied, the one with the highest oil encapsulation efficiency is the production of a 20xa0% O/W emulsion stabilized with 10xa0% sodium caseinate followed by the addition of 50xa0% maltodextrin and drying.

Spray dried double emulsions containing procyanidin-rich extracts produced by premix membrane emulsification: Effect of interfacial composition

Spray drying of procyanidin-loaded W1/O/W2 emulsions produced by premix membrane emulsification (ME) enabled to produce microcapsules containing procyanidins. The interface of the emulsion droplets prior to spray drying was stabilized with several hydrophilic emulsifiers (whey protein (WPI), WPI-carboxylmethyl cellulose, WPI-gum Arabic, and WPI-chitosan). Their effect on procyanidin encapsulation efficiency, water activity, moisture and oil content, and microcapsule size distribution was investigated. Furthermore, the microstructure and droplet size distribution of redispersed microcapsules were analyzed. Although premix ME produced W1/O/W2 emulsions with a narrow droplet size distribution regardless the hydrophilic emulsifier (main peak of droplet size distribution around 9 μm), microcapsules after spray drying and double emulsions after redispersion showed profound differences in sizes depending on the interfacial composition. WPI-CMC stabilized microcapsules not only showed the highest procyanidin content (5.3 g kg(-1)) but also gave the narrowest particle size distribution with the lowest particle size for both microcapsules and the corresponding emulsions after rehydration (7.7 and 9.9 μm respectively).

Encapsulation of grape seed phenolic-rich extract within W/O/W emulsions stabilized with complexed biopolymers: Evaluation of their stability and release

The ability of electrostatic complexes made up of sodium caseinate (NaCAS) and a polysaccharide, carboxymethyl cellulose (CMC) or gum Arabic (GA), to retain polyphenols from grape seed extract when encapsulated in W1/O/W2 emulsions was compared to that of the single NaCAS (1%). Both electrostatic complexes (0.5% NaCAS - 0.375% CMC and 0.5% NaCAS - 0.5%GA at pH 5.6) used as hydrophilic emulsifiers in W1/O/W2 were able to stabilize the O/W2 interface for 14u202fdays, even though their protein content was reduced by a 50% regarding that of the emulsions only stabilized with NaCAS. Moreover, interfacial adsorption did not show significant differences between NaCAS-polysaccharide electrostatic complexes and the single NaCAS. In terms of interfacial barrier properties, the rate of polyphenol release during storage was not affected by the type of hydrophilic emulsifier. Since polyphenol transport in W1/O/W2 emulsions was diffusion controlled, interfacial adsorption was considered the main factor limiting polyphenol retention.

Apparent Interfacial Tension Effects in Protein Stabilized Emulsions Prepared with Microstructured Systems

Proteins are mostly used to stabilize food emulsions; however, production of protein containing emulsions is notoriously difficult to capture in scaling relations due to the complex behavior of proteins in interfaces, in combination with the dynamic nature of the emulsification process. Here, we investigate premix membrane emulsification and use the Ohnesorge number to derive a scaling relation for emulsions prepared with whey protein, bovine serum albumin (BSA), and a standard emulsifier Tween 20, at various concentrations (0.1%, 0.5%, 1.25% and 2%). In the Ohnesorge number, viscous, inertia, and interfacial tension forces are captured, and most of the parameters can be measured with great accuracy, with the exception of the interfacial tension. We used microfluidic Y-junctions to estimate the apparent interfacial tension at throughputs comparable to those in premix emulsification, and found a unifying relation. We next used this relation to plot the Ohnesorge number versus P-ratio defined as the applied pressure over the Laplace pressure of the premix droplet. The measured values all showed a decreasing Ohnesorge number at increasing P-ratio; the differences between regular surfactants and proteins being systematic. The surfactants were more efficient in droplet size reduction, and it is expected that the differences were caused by the complex behavior of proteins in the interface (visco-elastic film formation). The differences between BSA and whey protein were relatively small, and their behavior coincided with that of low Tween concentration (0.1%), which deviated from the behavior at higher concentrations.