Performance of whey protein hydrolysate–maltodextrin conjugates as emulsifiers in model infant formula emulsions

Model infant formula emulsions containing 15.5, 35.0 and 70.0 g L⁻¹ protein, soybean oil and maltodextrin (MD), respectively, were prepared. Emulsions were stabilised by whey protein hydrolysate (WPH) + CITREM (9 g L⁻¹), WPH + lecithin (9 g L⁻¹) or WPH conjugated with MD (WPH–MD). All emulsions had mono-modal oil droplet size distributions post-homogenisation with mean oil droplet diameters (D_4,3) of <1.0 μm. No changes in the D_4,3 were observed after heat treatment (95 °C, 15 min) of the emulsions. Accelerated storage (40 °C, 10 d) of unheated emulsions resulted in an increase in D_4,3 for CITREM (2.86 μm) and lecithin (5.36 μm) containing emulsions. Heated emulsions displayed better stability to accelerated storage with no increase in D_4,3 for CITREM and an increase in D_4,3 for lecithin (2.71 μm) containing emulsions. No increase in D_4,3 over storage was observed for unheated or heated WPH–MD emulsion, indicating its superior stability.     

Disulfide-mediated Polymerization Reactions and Physical Properties of Heated WPI-stabilized Emulsions

Heating a 19 wt% corn oil-in-water emulsion stabilized by 1 wt% whey protein isolate from 30 to 70°C and then cooling to 25°C for at least 15 hr, brought about minimal changes in droplet aggregation, apparent viscosity and susceptibility to creaming. At 75°C, droplet aggregation occurred but this decreased on heating to 90°C. The apparent viscosity and susceptibility of droplets to creaming increased as the degree of droplet aggregation increased. Inclusion of the sulfhydryl blocking agent N-ethylmaleimide to inhibit thiol/disulfide interchange reactions did not affect droplet aggregation but resulted in higher apparent viscosity values and susceptibility to creaming at 85 and 90°C and not at lower temperatures. The results suggest that droplet aggregation results from noncovalent interactions between unfolded protein molecules adsorbed on different droplets and that the interactions are strengthened by disulfide bonds.     

Crosslinking of interfacial layers in multilayered oil-in-water emulsions using laccase: Characterization and pH-stability

The enzymatic crosslinking of polymer layers adsorbed at the interface of oil-in-water emulsions was investigated. A sequential two step process, based on the electrostatic deposition of pectin onto a fish gelatin interfacial membrane was used to prepare emulsions containing oil droplets stabilized by fish gelatin-beet pectin membranes (citrate buffer, 10 mM, pH 3.5). First, a fine dispersed primary emulsion (5% soybean oil (w/v), 1% (w/w) gelatin solution) (citrate buffer, 10 mM, pH 3.5) was produced using a high pressure homogenizer. Second, a series of secondary emulsions were formed by diluting the primary emulsion into pectin solutions (0 - 0.4% (w/w)) to coat the droplets. Oil droplets of stable emulsions with different oil droplet concentrations (0.1%, 0.5%, 1.0% (w/v)) were subjected to enzymatic crosslinking. Laccase was added to the fish gelatin-beet pectin emulsions and emulsions were incubated for 15 min at room temperature. The pH- and storage stability of primary, secondary and secondary, laccase-treated emulsions was determined. Results indicated that crosslinking occurred exclusively in the layers and not between droplets, since no aggregates were formed. Droplet size increased from 350 to 400 nm regardless of oil droplet concentrations within a matter of minutes after addition of laccase suggesting formation of covalent bonds between pectin adsorbed at interfaces and pectin in the aqueous phase in the vicinity of droplets. During storage, size of enzymatically treated emulsions decreased, which was found to be due to enzymatic hydrolysis. Results suggest that biopolymer-crosslinking enzymes could be used to enhance stability of multilayered emulsions.     

Stabilization of soybean oil body emulsions using κ, ι, λ-carrageenan at different pH values

Oil bodies, with their unique structural proteins, oleosins, are known to be useful in foods and other emulsion systems. The influence of ??, ??, and ??-carrageenans on the stability of soybean oil body emulsions at different pH values (pH 3, 4, 5 and 7) was investigated by particle electrical charge, particle size distribution, creaming stability and confocal laser scanning microscopy measurements. In acidic environment (pH 3, 4 and 5), the droplet charge of soybean oil body emulsions stabilized with carrageenan decreased with increasing carrageenan concentration for all types of carrageenan investigated, suggesting their adsorption to the oil body droplet surfaces. Extensive droplet aggregation and creaming were observed in the emulsions stabilized with ??-carrageenan at pH 3 and 5, indicating that soybean oil body droplets were bridged by carrageenan. At pH 7, there was no significant change in the droplet charge of soybean oil body emulsions stabilized with three types of carrageenan, but the emulsions stabilized with ??-carrageenan were more stable to creaming due to depletion flocculation than the emulsions stabilized with ?? or ??-carrageenan after seven days storage. The probable reason was that ??-carrageenan, which had the most densely charged helical structure, was most effective at creating highly charged interfacial membranes, thus reducing the depletion flocculation to occur.     

Influence of EDTA and citrate on thermal stability of whey protein stabilized oil-in-water emulsions containing calcium chloride

The influence of calcium ions and chelating agents on the thermal stability of model nutritional beverages was examined. Oil-in-water emulsions (6.94% (w/v) soybean oil, 0.35% (w/v) WPI, 0.02% (w/v) sodium azide, 20 mM Tris buffer, 0–10 mM CaCl₂, and 0–40 mM EDTA or citrate, pH 7.0) were stored at temperatures between 30 and 120 °C for 15 min. The particle size, particle charge, creaming stability, rheology, and free-calcium concentration of the emulsions were then measured. In the absence of chelating agents, appreciable droplet aggregation occurred in emulsions held at temperatures from 80 to 120 °C, which led to increased emulsion particle diameter, shear-thinning behavior, apparent viscosity, and creaming instability. Addition of chelating agents to the emulsions prior to heating decreased, but did not prevent, droplet aggregation in the emulsions. EDTA was more effective than citrate in decreasing droplet aggregation. Heat treatment increased the amount of chelating agents required to prevent droplet aggregation in the emulsions. Free-calcium concentration and droplet surface potential was independent of heat-treatment temperature, indicating that the performance of the chelating agents in binding calcium ions was not affected by the heat treatment. It was suggested that increased hydrophobic attractive interactions between the droplets occurred during heating, which induced droplet aggregation.     

Effects of bacteriostatic emulsifiers on stability of milk-based emulsions

For milk-based emulsion products such as canned coffee or tea, the addition of bacteriostatic emulsifiers is necessary to inhibiting the growth of heat-resistant sporeformers. Since bacteriostatic emulsifiers often cause the destabilization of emulsions, other type of emulsifiers, such as stability-enhancing ones, are necessary for the long-term stability of emulsions. Four milk-based emulsions were prepared from powdered milk combined with several types of emulsifiers. The long-term stability of emulsions, which was detected by the occurrence of a creaming layer after 3 months of storage, differed according to the composition of emulsifiers. To understand the reason for the differences in the stability of emulsions, particle size, distribution, ζ-potential, and the amount of proteins and phospholipids present in the cream layer (separated oil droplets) in the emulsions were measured. Only the amount of proteins adsorbed onto oil droplets was found to be closely related to the difference in emulsion stability, that is, the more proteins adsorbed, the higher the emulsion stability. SDS–PAGE analyses revealed that κ-casein and β-lactoglobulin play an important role in emulsion stability by adsorbing onto the oil droplet surface.     

Influence of Ultrasonication Parameters on Physical Characteristics of Olive Oil Model Emulsions Containing Xanthan

Ultrasonic emulsification of 20-wt.% o/w emulsions (pH 3.8) containing a food-grade emulsifier (whey protein isolate, WPI, 2.7 wt.%) and xanthan gum (XG, 0.25 wt.%) was performed. Time and amplitude of ultrasonic treatment changed in order to evaluate their influence on emulsion droplet size, viscosity, and stability (by multiple light scattering (MLS) profiles) during cold storage (10 days at 5 °C). Ultrasonic treatment duration changed from 1 to 4 min at constant amplitude of 70 %. Considering the amplitude, intervals of 40, 60, 80, and 100 % were chosen, for a constant time of 1 min. Similarly, time and amplitude conditions were used to treat solutions of XG of 1 wt.% and evaluate their influence on viscosity and how that was related to the stability of the emulsion. Increase in sonication time from 1 to 4 min led to a significant oil droplet size decrease from 1.14 to 0.89 μm (median droplet diameter). The viscosity of emulsions and XG solutions was highly influenced and considerably decreased with sonication time applied. At those conditions, an increase of backscattering was observed from 58.9 to 72.7 % after 10 days of storage, meaning that more stable emulsions, thinner and of smaller oil droplet size were produced. A similar trend was observed when the amplitude was increased, but droplet size and creaming were always greater than those noticed by changing the sonication time. However, the rate of viscosity, droplet size, and stability change was greater by increasing the amplitude rather than by changing the sonication time.     

Enhancement of gel strength by application of thermal treatments in highly flocculated emulsions

Thermal-induced changes of the rheological behavior of flocculated emulsions through the optimization of in situ thermorheological treatments, as well as the effect that several compositional variables (oil fraction, egg yolk concentration or cholesterol reduction level) exert on the enhancement of gel strength, were investigated. With this aim, oil-in-water emulsions were prepared using a spray-dried egg product. Different temperature ramps under oscillatory shear and droplet size distribution measurements were carried out. An increase in temperature produces, first of all, an increase in the storage modulus up to a critical temperature, which depends on heating rate. Subsequently, a dramatic decrease in the viscoelastic functions occurs, due to emulsion breakdown. However, the application of upward/downward temperature cycles, setting the maximum temperature at 67 °C, avoids emulsion breakdown and yield significantly higher values of the rheological functions in comparison to those found with fresh emulsions, in spite of the thermal-induced droplet coalescence observed. The final values of linear viscoelastic functions and droplet size depend on the type of cycles applied, which are based on different heating rates or times at the maximum temperature, and emulsion composition.     

Stability and rheology of concentrated O/W emulsions based on soybean oil/palm kernel olein blends

Droplet size distribution and rheological properties of egg yolk-stabilized emulsions were studied before and after storage (25 °C, 30 days). The dispersed phase (70%) of the emulsions was based on soybean oil (SBO) and 10–40% palm kernel olein (PKO) replacements of SBO. Replacement of PKO resulted in a significant increase in droplet mean diameters and a decrease in rheological properties of the emulsions. All emulsion exhibited a gel-like characteristic with storage modulus higher than loss modulus and tan δ greater than 0.3. Significant increase (p < 0.05) was found for droplet mean diameters and rheological properties of the emulsions after storage. Emulsion with fully SBO and the highest PKO replacement (40%) were found to be the most unstable, which was ascribed to a strong flocculation. With 10–30% PKO replacements, the emulsions displayed a better stability after storage, most probably promoted by significant content of short-medium chain fatty acids in PKO.     

Droplet characterization and stability of soybean oil/palm kernel olein O/W emulsions with the presence of selected polysaccharides

Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water (O/W) emulsions as affected by the presence of xanthan gum (XG), carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The dispersed phase (40%) of the emulsions was based on soybean oil/palm kernel olein blend (70:30) that partially crystallized during extended storage at 5 °C. In freshly prepared emulsions, the presence of XG, CMC, GG and LBG had significantly decreased the droplet mean diameters. XG, LBG, GG and CMC emulsions exhibited a shear-thinning behavior but AG emulsion exhibited a Bingham plastic behavior and control (without gum) emulsion almost exhibited a Newtonian behavior. Both control and AG emulsions exhibited a severe phase separation after storage (30 days, 5 °C). The microstructure of stored XG emulsion showed the presence of partially coalesced droplets, explaining a large increase in its droplet mean diameters. Increases in droplet mean diameters and decreases in flow properties found for stored GG and LBG emulsions were attributed to droplet coalescence. Nevertheless, the occurrence of droplet coalescence in these emulsions was considered to be small as no free oil could be separated under centrifugation force. Increases in flow properties and excellent stability towards phase separation found for stored CMC emulsion suggested that CMC could retard partial coalescence. Thus, the results support the ability of CMC, GG and LBG in reducing partial coalescence either by providing a sufficiently thick continuous phase or by acting as a protective coating for oil droplets.     

Tannic acid enhanced the emulsion stability,rheology and interface characteristics of Clanis Bilineata Tingtauica Mell protein stabilised oil-in-water emulsion

Clanis Bilineata Tingtauica Mell Protein (CBTMP) was one of the new natural insect protein resources. However, due to its strong surface hydrophobicity and poor emulsion stability, its application has greatly been limited. In this study, Pickering emulsions were prepared by CBTMP–Tannic acid (CBTMP–TA) particles and soybean oil (φ = 50%). The presence of TA significantly increased the zeta-potential (from −23.5 ± 0.73 to −29.23 ± 0.58 mV) and three-phase contact angle (from 129.9 ± 4.53° to 87.27 ± 3.20°) of complex, especially the concentration of TA was 0.4 mm . Besides, the stability of emulsions was significantly improved according to the results of the droplet size and static multiple light scattering. Furthermore, rheological properties including viscosity, thixotropy and creep recovery were significantly enhanced, which indicated the formation of a more stable network structure. Interfacial behaviour (Interfacial tension, interfacial film viscoelasticity and diffusion rate) of emulsions was significantly changed, forming a more stable interfacial layer as TA content increased. The CBTMP–TA complex was adsorbed at the interface and the adsorption rate was also mainly affected by the content of TA. The study indicated CBTMP–TA compositions to enhance stability, rheological behaviours and interfacial characteristics, and demonstrated the potential applications of insect protein resources in food emulsion systems.     

球磨-酯化复合改性槟榔芋淀粉对Pickering乳液形成的影响

为了提高淀粉颗粒的乳化能力,以球磨-酯化复合改性槟榔芋淀粉为颗粒乳化剂,大豆油为油相,制备水包油型Pickering乳液.采用激光粒度仪、研究级正置显微镜、流变仪等对Pickering乳液外观、液滴粒径、显微形态及动态流变特性进行表征,考察淀粉颗粒质量浓度(1、5、10、20、30 mg/mL)和油相体积分数(10％、...     

Secondary adsorption of milk proteins from the continuous phase to the oil–water interface in dairy emulsions

Low protein surface concentration emulsions are susceptible to secondary protein adsorption where protein moves from the continuous phase to the existing, oil–water interface. The resulting increase in protein surface concentration can greatly alter emulsion properties. Butteroil was emulsified with whey proteins and the emulsion was combined with a solution of dissolved skim milk powder (SMP), producing mixes with fat and protein levels representative of ice cream. The primary adsorbed layer was modified by heating the whey protein solution prior to emulsion formation (70°C, 80°C, 90°C), by heating the emulsion (70°C, 80°C, 90°C) or by pH adjustment of the emulsion (6–8). Modifications of the SMP solution included heat treatment (80°C, 95°C) or sugar addition with or without κ-carrageenan. The effect of addition of SMP solution on the protein surface concentration and shear stability of the diluted emulsions was determined. Addition of untreated solution to the control, heated or pH adjusted emulsions greatly reduced shear destabilization and increased the protein surface concentration. Addition of heat treated or sugar containing SMP solution to the control emulsion produced the same result. However, sugar and carrageenan in the mix maintained the susceptibility to partial coalescence and reduced the secondary adsorption of caseins and whey proteins.     

Viscoelastic Properties of Heat-Set Whey Protein-Stabilized Emulsion Gels with Added Lecithin

Our objective was to determine how lecithin affects the small-deformation shear rheology of heat-set emulsion gels made from whey protein concentrate (WPC). Fine oil-in-water emulsions were prepared with WPC, lecithin or WPC + lecithin present during homogenization. Storage and loss moduli were measured in situ during thermal processing at temperatures up to 90°C and afterwards at 30°C. The positive influence of pure egg lecithin added after emulsification on the elastic modulus of the WPC emulsion gel was attributed to lecithin-protein complexation. Crude egg lecithin gave a broadly similar increase in gel strength, but pure soybean lecithin was not so effective in reinforcing the network, and crude soybean lecithin was ineffective. Using lecithin as sole emulsifier, with WPC added after homogenization, gave a lower modulus for the heat-set WPC emulsion gel. With protein + lecithin present during emulsification, the considerable loss of gel strength was attributable to some WPC displacement from the emulsion droplet surface.     

Monitoring air/liquid partition of mastic gum oil volatiles in model alcoholic beverage emulsions: Effect of emulsion composition and oil droplet size

The purpose of this work was to study the impact of the structure and composition of hydroalcoholic emulsions on the air–liquid partition of aroma compounds of the essential oil of Pistacia lentiscus var. chia, commonly known as mastic gum oil (mainly consists of terpenes). Oil-in-water emulsions (φ = 0.17), containing 15% (v/v) ethanol, stabilized by three different emulsifiers (sodium caseinate, whey protein isolate and Tween 40), were prepared by using two different lipid phases (sunflower oil and anhydrous butter fat). The homogenization conditions were varied to obtain emulsions with different volume–surface mean diameters. The partition of the volatile compounds between air phase and emulsions at three different temperatures (25, 37 and 50 °C) was monitored by applying the Headspace Solid Phase Microextraction technique, followed by gas chromatography–mass spectrometry (GC–MS) analysis. In general, the results obtained showed that sodium caseinate was the most effective in retaining mastic aroma compounds, while WPI was the least effective. This could partly be explained by the different structure of the two proteins which, when adsorbed at the interface, form a membrane that acts as a barrier and influences the partition of the aroma compounds between the air and the liquid. At the same time interactions of aroma compounds with the two proteins in the bulk phase may also play a role. The retention of the aroma compounds depended on the oil droplet size only in the case of sodium caseinate containing emulsions at 37 and 50 °C. This behaviour could be due to the substantial increase in the thickness of the adsorbed casein layer when moving from a fine sized emulsion to one with a much larger size as well as to differences in the ratio of free to adsorbed emulsifier. The composition of the lipid phase also appeared to have a significant impact on the concentration of volatile compounds in the headspace of mastic gum oil containing emulsions stabilized by proteins. This was lower in the case of butter fat probably due to differences in composition with regard to fatty acid degree of saturation as well as to volatile absorption by the liquid lipid at 40 °C and subsequent entrapment in the semisolid fat at 25 °C.     

A study of stability of O/W emulsions stabilized by soybean and pea globulins

Flotation stability of O/W emulsions, stabilized by total globulins of soybean and peas increases with an increase in protein concentration and diminishes with NaCI concentration. Stability increases significantly as a result of long emulsion storage (24 h and 72 h) at room temperature, that is most likely caused by the flocculation process. Heating of emulsions, stabilized by soybean globulins at 100 °C and 120 °C results in an increase in their flotation stability. Emulsion heating during the first 10 min is associated with diminishing in stability to coalescence, that becomes more pronounced as protein concentration decreases. At further heating the resistance to coalescence remains unchanged apparently because of interface adsorption layers gelation.     

Effect of chitosan on the stability and properties of modified lecithin stabilized oil-in-water monodisperse emulsion prepared by microchannel emulsification

The effect of chitosan (CHI) on the stability of monodisperse modified lecithin (ML) stabilized soybean oil-in-water (O/W) emulsion was investigated. Monodisperse emulsion droplets with particle size of 24.4 ± 0.7 μm and coefficient of variation below 12% were prepared by microchannel (MC) emulsification using a hydrophilic asymmetric straight-through MC silicon 24 × 24 mm microchip consisting of 23,348 microchannels. The stability of the ML stabilized monodisperse emulsion droplets was investigated as a function of CHI addition at various concentration, pH, ionic strength, thermal treatment and freezing-thawing treatment by means of particle size and ζ-potential measurements as well as microscopic observation. The monodisperse O/W emulsions were diluted with CHI solution at various concentrations to a final droplet concentration of 1 wt% soybean oil, 0.25 wt% ML and 0–0.5 wt% CHI at pH 3. Pronounced droplet aggregation was observed when CHI was present at a concentration range of between 0.01 and 0.04 wt%. Above this concentration range, flocculations were less extensive, indicating some restabilization. ML stabilized emulsions were stable at a wide range of NaCl concentrations (0–1000 mM) and pH (3–8). On the contrary, in the presence of CHI, aggregation of the emulsion droplets was observed when NaCl concentration was above 200 mM and when the pH started to approach the pKa of CHI (i.e. ∼6.2–7.0). Emulsions containing CHI were found to have better stability at high temperature (>70 °C) in comparison to the emulsion stabilized only by ML. With sucrose/sorbitol as cryoprotectant aids, emulsions with the addition of CHI were found to be more resistant to droplet coalescence as compared to those without CHI after freezing at −20 °C for 22 h and thawing at 30 °C for 2 h. The use of CHI may potentially destabilize ML-stabilized O/W emulsions but its stability can be enhanced by selectively choosing the appropriate CHI concentrations and conditions of preparation.     

Mangosteen Oil-In-Water Emulsions: Rheology, Creaming, and Microstructural Characteristics during Storage

The rheological properties and physical stability of mangosteen (Garcinia mangostana L.) extract in oil-in-water (MIO/W) emulsions were investigated. Rheological study on the emulsions exhibited Newtonian flow behavior. The 20?wt.% emulsion showed higher apparent viscosity than 10?wt.% MIO/W sample. The effects of salt (NaCl) concentration (0, 50, 100, and 200?mM) and heat treatment (70?°C) on the stability of the emulsions were also examined. Heat (70?°C)- and NaCl (100 and 200?mM)-treated emulsions showed creaming and droplet aggregation on storage for a period of 60?days. The 10?wt.% MIO/W emulsions stored at 4?°C showed a homogeneous distribution of oil droplets with good stability to creaming and viscosity independent of shear stress (i.e., a Newtonian liquid).     

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 20 % and were stabilized using whey protein (isolate and hydrolyzate at 1 or 10 %) and sodium caseinate with concentrations of 2 and 10 %. 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 10 % are required to reduce the droplet size down to 2–3 μm. 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 30 °C. Of all the possible combinations studied, the one with the highest oil encapsulation efficiency is the production of a 20 % O/W emulsion stabilized with 10 % sodium caseinate followed by the addition of 50 % maltodextrin and drying.     

高压均质对大豆蛋白乳液性质影响的研究进展

大豆蛋白作为一种高分子蛋白质,具有良好双亲性和表面活性,可通过在油水界面形成粘弹性蛋白层的方式在乳液中起到乳化作用,从而提高乳液体系的稳定性。高压均质技术是一种通过静高压和均质阀产生的综合效应从而改变蛋白质的结构和加工特性的新型非热加工技术,可以制备纳米级的大豆蛋白乳液。本文聚焦大豆蛋白乳液,阐述了高压均质制备大豆蛋白乳液的过程以及均质条件的影响,分析总结了高压均质处理对大豆蛋白乳液结构（粒径、ζ-电位、空间结构）和功能特性（流变特性、乳化性能和凝胶性能）影响的国内外研究进展及作用机理。最后,针对目前研究进展对高压均质在大豆蛋白乳液的加工应用做出展望,以期为大豆蛋白乳液的研究提供一定的帮助。