Article

Physical Properties of Olive Oil in Water Model Emulsion: Effect of Aqueous and Oil Phase Concentration and Homogenization Types

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Abstract

In this study, olive oil in water emulsions with different oil contents (30, 40 and 50% w/w on dry matter basis) were prepared for further encapsulation processes. Whey protein isolate and maltodextrin were used as encapsulating agents at different dry matter contents (30, 40 and 50%), and Tween 20 was used at 1% as a stabilizer. Emulsions were produced by a rotor-stator (classic) or an ultrasonic homogenizer. The effect of dry matter content, composition of aqueous phase containing encapsulating agents and oil content on the emulsion stability, rheological properties, droplet size, and microscopy images were determined. The water phase of emulsions containing maltodextrin was more viscous that resulted in better emulsion stability. Moreover the viscosity of emulsions increased with increasing dry matter content and decreasing oil content. The droplet size of emulsions (D[4,3]) prepared by ultrasonic homogenization were lower (0.390-1.974 μm) than that by classic homogenization (1.003-5.205 μm).

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... Emulsion stability was determined by the measurement of the extent of gravitational phase separation through the estimation of the percentage of the height of the cream phase over the height of the total system sample [42][43][44]. The emulsion creaming index ( ) was determined based on the following equation: ...
... The droplet flocculation could be adjusted via the increase of the surface-active components at the oil/water interface to regulate the attractive and repulsive interactions between the droplets [71,72]. The results agree with the reported by Zungur et al. [42]. ...
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This paper focuses on the development of an effective methodology to determine the optimum levels of three independent variables leading to (a) maximize turbidity, (b) minimize polydispersity index (PDI) and (c) obtain the target value for average particle size and density of orange beverage emulsion. A three-factor central composite design (CCD) was employed to determine the effect of Arabic gum content (7–13% w/w), xanthan gum content (0.1–0.3% w/w) and orange oil content (6–10% w/w). The emulsion properties studied as response variables were: turbidity (Y1), average particle size (Y2), PDI (Y3) and density (Y4). The response surface analysis was carried out to create efficient empirical models for predicting the changes of response variables. In general, analysis of variance (ANOVA) showed high coefficients of determination values (R2) in the range of 0.922–0.975 for the response surface models, thus ensuring a satisfactory adjustment of the polynomial regression models with the experimental data. The results of regression analysis indicated that more than 92% the response variation could be explained by the models. The results also indicated that the linear term of xanthan gum was the most significant (p<0.05) variable affecting the overall responses. The multiple optimization results showed that the overall optimum region with high total desirability (D=0.92) was found to be at the combined level of 13.88% w/w Arabic gum content, 0.27% w/w xanthan gum content and 11.27% w/w orange oil content. Under the optimum condition, the corresponding predicted response values for turbidity, average particle size, PDI and density of the desirable orange beverage emulsion were 129.55, 988, 0.261 and 1.03, respectively. For validation of the models, the experimental values were compared with predicted values to check the adequacy of the models. The experimental values were found to be in agreement with those predicted, thus indicating suitability of the models employed using response surface methodology (RSM) for optimizing the physical properties of the orange beverage emulsion.
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Article
Effective use of expressed human milk in infant feeding requires proper handling, processing, storage, and administration in order to maintain its unique nutritional properties. One of the problems with expressed human milk is the separation of fat during processing, storage, and administration to the infant. Administration by continuous nasogastric infusion, either by intermittent gravity flow or by continuous mechanical pump, resulted in significant loss of fat and variation in the constitution of the milk delivered. Homogenization by ultrasonic treatment prevented changes in fat concentration during infusion and essentially eliminated loss of this nutrient during administration. The conditions necessary to achieve fat dispersion and stabilization of fat particles in human milk by ultrasonic treatment are described.
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We report on shear rheological measurements at 30°C of fine oil-in-water emulsions (volume-surface average diameter < 0.5 &mgr;m) prepared at pH 6.8 with sodium caseinate as the sole emulsifier (1-6 wt%) and n -tetradecane as the dispersed phase (10, 35, or 45 vol%). Strong sensitivity of rheological behavior to total protein concentration was indicated by both steady-state viscometry and small-deformation oscillatory experiments. The behavior can be classified into three types, depending on the protein/oil ratio. (1) Emulsions containing insufficient protein for (near-) saturation protein surface coverage develop a time-dependent increase in low-stress apparent viscosity and associated shear-thinning behavior; this can be attributed to bridging flocculation. (2) Emulsions having full protein surface coverage but relatively little excess unadsorbed protein in the continuous phase are stable Newtonian liquids. (3) Emulsions containing a substantial excess of unadsorbed sodium caseinate exhibit considerable pseudoplasticity which can be attributed to depletion flocculation. Taken as a whole, the time-dependent rheological properties for this set of emulsions as a function of protein content and oil volume fraction are largely consistent with our previous results on the creaming stability and the particle gel microstructure for these same emulsion systems. In particular, the reversible flocculation of emulsion samples of high protein content is readily explicable in terms of depletion flocculation of droplets by unadsorbed protein existing in the form of approximately spherical caseinate submicelles.
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Development of stable dry emulsions being able to reform the original o/w-emulsion by reconstitution in water is presented. Dry emulsions were prepared by spray drying liquid o/w-emulsions in a laboratory spray dryer. Three hydroxypropylmethylcellulose (HPMC) types were applied as solid carrier and emulsifier. The lipid phase was fractionated coconut oil. The ratio of solid carrier to lipid phase influenced the reconstitution properties. It was possible to prepare redispersible dry emulsions of a lipid content up to 40% dry powder mass. The different HPMC types had no noticeable effect on the reconstitution properties, but too viscous liquid o/w-emulsions were difficult to atomise. The type of rotary atomizer, or the rate of rotation did not affect the technical properties of the dry emulsions containing 40% lipid. It was concluded that low viscosity HPMC was a useful solid carrier. The dry emulsions remained physically stable for at least 6 months.
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The aim of this work is to compare the oil-in-water emulsions produced by mechanical agitation (Ultra-Turrax, 10,000 rpm, P = 170 W) or power ultrasound (ultrasound horn, 20 kHz, 130 W) using the same model system: water/kerosene/polyethoxylated (20 EO) sorbitan monostearate. The following parameters were varied: emulsification time, surfactant concentration, consumed power and volume fraction of oil. With ultrasound, the drop size (Sauter diameter, d32) is much smaller than that given by mechanical agitation under the same conditions, which makes insonated emulsions more stable. For a given drop size (d32), less surfactant is required.
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This review deals with the use of rheology for assessment and prediction of the long-term physical stability of emulsions. It starts with an introduction, highlighting the importance of having accelerated test to predict emulsion stability. This is followed by a section on the stability/instability of emulsion systems, giving a brief summary of the driving force of each instability process and its prevention. The classical techniques that can be applied for assessment of creaming or sedimentation, flocculation, Ostwald ripening, coalescence and phase inversion are briefly described. This is followed by several sections on the application of rheological techniques to assess and predict each of these instabilities. This involves the use of steady state shear stress-shear rate measurements, constant stress (creep) measurements and dynamic (oscillatory) techniques. The last section gives an example of model emulsions to illustrate the correlation between the various break-down processes with the rheological characteristics of the system.
Applications in the food industry
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