Aggregation Of Oil Droplets Research Articles

Synergetic interfacial adsorption of protein and low-molecular-weight emulsifiers in aerated emulsions

Whipped creams (aerated emulsions) are a complex emulsion-foam system whose oil-stabilizing potential and aeration capacity are determined by the surface activity of proteins and small surfactants. In this study, the interaction between three low-molecular-weight (LMW) emulsifiers [sodium stearoyl lactylate (SSL), phospholipid (PL), and sucrose ester (SE)] with caseinate was investigated to elucidate the mechanism of formation and stability of whipped creams. Competitive adsorption, interfacial tension, droplet aggregation, viscosity, and morphological variations of the emulsions were examined, and aeration capacity, hardness, and microstructure of whipped creams were measured. The combination of surfactants (0.05–1.0% w/w) with caseinate (0.6% w/w) produced concerted effects on the stability of emulsions. Water-soluble surfactant (SE) adsorbed more strongly than oil-soluble surfactants (SSL and PL) onto oil droplets. The lesser protein adsorption in the SE emulsion enabled a strong foaming activity in the subsequent aeration. Protrusions of triacylglycerol crystals and aggregation of oil droplets into an interactive colloidal matrix with considerable hardness and viscosity were prominently observed in SE creams. On the other hand, shear thinning followed by thickening was observed when PL was added to form the caseinate-based emulsion while no foaming was produced, and SSL, known to form α-gel at the interface, produced no stable foam. The improved emulsion stability yet the propensity to coalesce induced by cooperative actions of casein molecules and hydrophilic surfactant played a crucial role in producing aerated emulsions.

High pressure homogenization combined with pH shift treatment: A process to produce physically and oxidatively stable hemp milk

Hemp milk, an emerging beverage with high nutritional value and low allergenicity, is an attractive alternative to dairy, soy, and nut milks. To obtain a non-thermally processed, physically and oxidatively stable hemp milk, high pressure homogenization (HPH) combined with pH shift treatment was investigated. For hemp milk (4% protein, 5% fat) without pH shift, increasing the homogenization pressure (up to 60 MPa) resulted in a more uniform distribution of emulsion droplets (2.2–2.7 μm). When pH shift was applied prior to HPH, large clusters and aggregates of oil droplets (3.5–8.2 μm) were formed. Interestingly, hemp milk with such interactive structures was remarkably stable, showing negligible phase separation within 3-day storage at 4 °C. Moreover, hemp milk made by combined pH shift and HPH exhibited delayed hydroperoxides (expressed as peroxide value, PV) and malondialdehyde (expressed as thiobarbituric acid-reactive substances, TBARS) production, suggesting the resistance of such emulsion cluster structures to radicals. On the other hand, a significant reduction of microbial population was observed in hemp milk prepared by pH shift combined with HPH. The results indicate that the pH shift + HPH combination treatment may potentially be employed for the production of non-thermally processed hemp milk.

Mixtures of Quillaja saponin and beta-lactoglobulin at the oil/water-interface: Adsorption, interfacial rheology and emulsion properties

Aim of the present study was to investigate the interfacial properties of mixed films of Quillaja saponins (QS) and beta-lactoglobulin (β-LG) at the oil/water-interface. It was hypothesized that due to the differences in the physical characteristics of the dispersed phase molecular interactions and film characteristics at the oil/water interface substantially differ from the air/water-interface. Furthermore QS/β-LG-interactions will affect stability of emulsions in a concentration-dependent manner. Oscillating drop experiments were performed with subsequent analysis of raw data (Lissajous-plots) to discover non-linear behavior upon compression and expansion. Interfacial shear rheology as well as dynamic interfacial tension and two-fluid needle experiments were performed to comprehensively characterize interfacial properties of mixtures of QS/β-LG. Finally, emulsions were prepared and their stability, oil droplet size and ζ-potential were determined. It became obvious that QS dominates the interfacial film in a binary mixture as indicated by dynamic interfacial tension and dilational rheology. Strain stiffening was observed for mixed QS/β-LG interfacial layers upon dilational expansion at an amplitude above 2.8%. Intermolecular interactions increased in mixtures of QS/β-LG as indicated by shear rheology. Emulsion experiments showed extensive aggregation of oil droplets in QS/β-LG-emulsions with high content of β-LG. Aggregation of oil droplets increased velocity of creaming and after 7days a distinct creaming layer was visible. Changes in dispersity were influenced by concentration and ratio of QS and β-LG.

Effect of soluble dietary fibres from Bambara groundnut varieties on the stability of orange oil beverage emulsion

Soluble dietary fibres (SDFs) [30% (w/w)] from four varieties of Bambara groundnut (BGN), viz. black-eye, brown-eye, brown and red were used to stabilize orange oil beverage emulsions at 6% (w/w) orange oil. Emulsion stability was studied using Turbiscan MA 2000 and in terms of oil-droplet size characterization. The volume-surface mean diameter (d3,2) and equivalent volume-mean diameter (d4,3) of the four emulsions ranged between 2.68–4.38 µm and 17.09–18.62 µm, respectively. Emulsions stabilized with black-eye-SDF and brown-SDF possessed the least and highest d3,2 and d4,3, respectively. The d3,2 and d4,3 of all four emulsions were significantly (p < 0.05) different. Emulsions were relatively stable to creaming and destabilized mainly by phenomenon involving oil-droplet aggregation. The backscattering flux of the emulsions ranged from 72.9% (brown-SDF stabilized emulsion) to 85.0% (black-eye-SDF stabilized emulsion). All four BGN SDFs greatly indicated their potential in stabilizing beverage emulsions.

Protein Fibrils Induce Emulsion Stabilization.

The behavior of an oil-in-water emulsion was studied in the presence of protein fibrils for a wide range of fibril concentrations by using rheology, diffusing wave spectroscopy, and confocal laser scanning microscopy. Results showed that above a minimum fibril concentration depletion flocculation occurred, leading to oil droplet aggregation and enhanced creaming of the emulsion. Upon further increasing the concentration of the protein fibrils, the emulsions were stabilized. In this stable regime both aggregates of droplets and single droplets are present, and these aggregates are smaller than the aggregates in the flocculated emulsion samples at the lower fibril concentrations. The size of the droplet aggregates in the stabilized emulsions is independent of fibril concentration. In addition, the droplet aggregation was reversible upon dilution both by a pH 2 HCl solution and by a fibril solution at the same concentration. The viscosity of the emulsions containing fibrils was comparable to that of the pure fibril solution. Neither fibril networks nor droplet gel networks were observed in our study. The stabilization mechanism of emulsions containing long protein fibrils at high protein fibril concentrations points toward the mechanism of a kinetic stabilization.

Physical characteristics of submicron emulsions upon partial displacement of whey protein by a small molecular weight surfactant and pectin addition

O/W emulsions (6wt.% olive oil) were prepared at pH3.3 using different WPI:Tween 20 weight ratios (1:0, 3:1, 1:1, 1:3, 0:1) at 1wt.% total concentration. The emulsion droplet size was found to decrease with an increase in Tween 20. A minimum droplet size of d3,2 300nm was found for Tween systems alone, similar to that found (360nm) for a 1:1 WPI:Tween 20 combination (p<0.05). This specific composition showed a value for the interfacial tension close to that of Tween 20 alone. However, the emulsions presented low stability regardless of the WPI:Tween 20 ratio. To increase their stability, pectin was added, in various concentrations (0.2, 0.4 and 0.6wt.%), using the Layer by Layer technique. In the presence of pectin, the ζ-potential of the oil droplets became negative; indicating that negatively charged pectin was absorbed onto the positively-charged droplet surface forming a secondary layer. The additional layer resulted in a wide range of emulsion stability. For all pectin concentrations, the 1:1 ratio of WPI:Tween 20 showed the highest stability. In most emulsions, extensive aggregation of oil droplets was observed, and their viscosity increased. Insufficient amounts of pectin to form the secondary layers led to bridging flocculation phenomena of oppositely charged pectin and proteins, leading to aggregation of the oil droplets. The higher the concentration of pectin, the greater the stability of the emulsion due to higher viscosity. All in all, the addition of a second layer consisting of pectin can be used to increase the stability of an emulsion containing emulsion droplets in the sub-micron range.

Flash Thermal Conditioning of Olive Pastes during the Olive Oil Mechanical Extraction Process: Impact on the Structural Modifications of Pastes and Oil Quality

The quality of virgin olive oil (VOO) is strictly related to the concentrations of phenolic and volatile compounds, which are strongly affected by the operative conditions of the VOO mechanical extraction process. The aim of this work is to study the impact of a new technology such as flash thermal conditioning (FTC) on olive paste structural modification and on VOO quality. The evaluation of olive paste structure modification by cryo-scanning electron microscopy (cryo-SEM) showed that the application of FTC after crushing produces significant differences in terms of the breaking of the parenchyma cells and aggregation of oil droplets in comparison to the crushed pastes. The virgin olive oil flash thermal conditioning (VOO-FTC) featured a higher concentration of volatile compounds compared to that in the control, particularly of all saturated and unsaturated aldehydes and esters, whereas the phenolic concentration was higher in VOO obtained from the traditional process (VOO-C).

Golf ball-like particles fabricated by nonsolvent/solvent-induced phase separation method

Monodisperse poly(styrene-co-acrylic acid) (P(S-co-AA)) particles having a “golf ball-like” shape were prepared by nonsolvent/solvent-induced phase separation process. The method is simple and easy operation. The nonsolvent/solvent phase was mixture of butanol, n-heptane and toluene. The dimpled surface comes from the aggregation of oil droplets on the surface of polymer spheres. The dimple’s morphology can be controlled by the polymer templates, dispersion medium, reaction time, and temperature. Reverse Pickering emulsion model was suggested for the formation of golf ball-like particles.

Design of Nanoemulsions through Combination of Fixed-Volatile Oils

The aim of study was to comparatively evaluate emulsions containing volatile oils e.g. peppermint oil, optamint and tea tree oil, and those containing the combination of volatile oils with soybean oil. The emulsions were prepared and then characterized by monitoring of particle size, visual observation of creaming and cracking, and zeta potential measurement. The results showed that particle size of emulsions containing only volatile oils was in the micron range (3-10 mm). However, the particle size was decreased to less than 300 nm after incorporation with soybean oil (1:1 by weight), suggesting the formation of nanoemulsions. The nanoemulsions containing both volatile oils and soybean oil demonstrated almost 100% creaming and did not show any evidence of cracking. Additionally, percent creaming and particle size were not significantly changed even after accelerated stability testing. The results indicated the good physical stability. The stabilization of emulsion might relate with the high surface charge as observed by higher zeta potential of emulsions prepared from volatile oils combined with soybeans oil. Glycerides from soybean should give more negative charge to the oleaginous phase that help preventing aggregation of oil droplets and thus increased the stability of nanoemulsions. In conclusion, the results from this study could provide the basic guideline for preparation of stable nanoemulsions for food, cosmetic and pharmaceutical fields in the near future.

Combined microscopic and dynamic rheological methods for studying the structural breakdown properties of whey protein gels and emulsion filled gels

The microstructural and large deformation rheological properties of model food gels were studied by performing notch propagation tensile testing on the gels using a tensile stage and observing changes in the microstructure of the gels during tensile testing using confocal laser scanning microscopy (CLSM). Heat-set whey protein (WP) gels containing either added sodium caseinate (NaCN) or sunflower oil droplets emulsified with WP or NaCN as the emulsifier protein were prepared in 0 or 50 mM NaCl. The WP gel structure strengthened in the presence of added NaCl and NaCN. The rheological properties of WP gels containing sunflower oil droplets emulsified with WP or NaCN were influenced by the NaCl concentration, oil concentration and extent of oil droplet aggregation in the gel or by the type of emulsifier protein used. During tensile testing, the notch length in all gels increased above a certain critical stress, leading to fracture of the gels through the notch. Also, the microstructural changes in the oil phase of emulsion filled gels subjected to tensile testing were influenced by the structural properties of the WP gel matrix and the proximity of the oil droplet to the fracture path.

Effect of temperature and pH on droplet aggregation and phase separation characteristics of flocs formed in oil–water emulsions after coagulation

Coagulation process is used for destabilization of emulsions to promote aggregation of oil droplets on flocs which can be subsequently removed by sedimentation or flotation. The objectives of this study were to investigate the effect of temperature and pH on the effectiveness of destabilization of olive oil–water emulsions in relation to floc morphology and aggregation characteristics of oil droplets, and to quantify the ability of flocs to capture and separate oil. A cationic polyelectrolyte was used for the coagulation of oil droplets in edible olive oil–water emulsions using a jar test apparatus. The flocs formed in olive oil–water emulsions after coagulant addition were analyzed using microscopic image analysis techniques. Fractal dimension, radius of captured oil droplets on flocs, number of oil droplets aggregated on flocs, and floc size were used to quantitatively characterize and compared the effectiveness of the coagulation process at different conditions (pH and temperature) and the ability of flocs to remove oil from water. Analysis of microscopic images showed that floc size was not always the best measure of effectiveness of coagulation process in oil–water emulsions. The flocs forming at different pH levels and temperatures had significant morphological differences in their ability to aggregate different sizes and numbers of oil droplets, resulting in significant differences in their ability for separating oil. Fractal dimension did not correlate with the ability of flocs to aggregate oil droplets nor the total amount of oil captured on flocs. Temperature had a significant effect on droplet size and number of droplets captured on flocs. The differences in floc sizes at different temperatures were not significant. However, the flocs forming at 20 °C had fewer but larger droplets aggregating larger amounts of oil than flocs formed at 30 °C and 40 °C. The size of droplets at different pH levels was similar, however, there were significant differences in number of droplets aggregating on flocs and floc sizes. The amount of oil captured on flocs at pH 7 and pH 9 was significantly higher than those at pH 5 and pH 11. The calculated fractal dimensions of the flocs (all less than 1.8) indicated that the coagulation process was diffusion limited implying that there was no repulsion between the colliding particles (i.e., droplets and flocs); hence, each collision between flocs and droplets resulted in attachment.

Characteristics of submicron emulsions prepared by ultra-high pressure homogenisation: Effect of chilled or frozen storage

Model O/W pre-emulsions at an initial temperature of 24 °C and pH 6.3, and containing (w/w) 4.3% whey proteins plus 15, 30 or 45% peanut oil were processed using a ∼15 L/h homogeniser with a high pressure (HP) valve immediately followed by cooling heat exchangers. The effect of ultra-high pressure homogenisation (UHPH) between 100 and 300 MPa ( P 1) or of recycling (1–3 homogenisation passes) at 200 MPa was investigated on the droplet size distribution, size indices and viscosity. Fluid temperatures were measured at the inlet ( T 1) and outlet ( T 2) of the HP-valve, and after immediate cooling downstream of the HP-valve ( T 3) as they varied throughout UHPH. Short-life heating phenomena and mechanical energy involved in droplet processing were clearly influenced by emulsion composition. Oil droplet diameters decreased when ( P 1) increased from 100 to 300 MPa leading to submicron droplets at ≥200 MPa. Monomodal distributions with droplets well below 0.3 μm were obtained after recycling at 200 MPa for the three oil contents, with a peak at 138 nm (distribution in volume) or 60–70 nm (in number frequency). The emulsion behaviour varied from fluid (and quite Newtonian) to thick (and shear thinning) depending on the droplet size reduction and the oil volume fraction. Emulsions displayed an excellent stability vs. creaming and coalescence after 9 d storage at 5 °C. Freezing followed by 13 d storage at −24 °C then thawing, induced an increase in particle sizes depending both on the oil volume fraction and ( P 1). After UHPH at 200–225 MPa (±recycling), the freezing/thawing process maintained most of oil droplet size below 1 μm at 15% (w/w) oil, and induced mainly oil droplet aggregation through SDS-labile interactions at higher oil contents.

Examination of the Interaction of Chitosan and Oil-in-Water Emulsions Under Conditions Simulating the Digestive System Using Confocal Microscopy

ABSTRACT Chitosan is a cationic biopolymer that has been used extensively in dietary supplements to reduce fat absorption in the fight against obesity. The mechanism of fat binding of chitosan is still not fully understood and has been the subject of controversy. This study was designed to improve the understanding of the underlying mechanism by investigating the interaction of chitosan with oil-in-water emulsion droplets. Our results indicated that (0.1% w/w) chitosan adsorbed to a 20% w/w phosphatidylcholine-stabilized anionic primary emulsion to form a secondary cationic emulsion by electrostatic attraction forces under conditions resembling the stomach (pH 2). Bile salts (6 mM) were added to simulate secretion in the small intestine and pH increase. Bile salts adsorbed to the chitosan secondary emulsion, which resulted in aggregation of oil droplets followed by coalescence due to close packing of droplets. Increased viscosity (267–2531 cp) and increased degree of deacetylation (40–92% DDA) of chitosan enhanced emulsion breakdown. Increasing the pH to 7.5 without addition of bile salts yielded little aggregation. Pronounced aggregation is thought to decrease the accessibility of lipase to the oil resulting in lower bioavailability and reduced caloric intake. Understanding how chitosan interacts with oil droplets in the digestive tract is vital to developing a comprehensive model of the influence of chitosan on the bioavailability of dietary lipids. The information gained in this study may be useful for the interpretation and experimental design of animal and human feeding studies and for the rational design of chitosan-based functional foods for fat reduction.

Physicochemical and rheological properties of soybean protein emulsions processed with a combined temperature/high-pressure treatment

Processing treatments such as temperature or high pressure (T/HP) can modify the structure and emulsifying properties of soybean protein isolates (SPIs). Few studies concern the processing of previously prepared oil-in-water emulsions stabilized with SPIs. Furthermore, the combined effects of T and HP were not assessed. Consequently, the aim of this study was to better understand the impact of the combined T/HP (T 20–60 °C/HP 0.1–600 MPa) treatment on physicochemical and rheological properties of emulsions prepared with native SPIs at 7% (w/v). Our results show that the size and aggregation of oil droplets of emulsions prepared with SPI 7% (w/v) solutions are not altered by the combined T/HP treatment. Such emulsions did not flocculate or coalesce. Simultaneously, we observed a significant increase of the apparent viscosity with the intensification of pressure, which was reinforced by temperature. This phenomenon can be attributed to gelation of non-adsorbed soybean proteins facilitated by their high concentration. Furthermore, temperature seems to improve this gelation process but only until 400 MPa. For higher pressure, the combined effect of temperature and pressure conduced to dissociation of the protein aggregates, lowering gelation. This distinct behavior could be used to obtain SPI emulsions with modulated rheological properties.

Characterisation of fish oil emulsions stabilised by sodium caseinate

Fish oil emulsions varying in sodium caseinate concentration (25% w/w oil and 0.1–1.0% w/w protein, giving oil-to-protein ratios of 250–25) were investigated in terms of their creaming stability, rheological properties, the mobility of oil droplets and the oil/protein interaction at the interface. The presence of excessive protein in an emulsion (i.e., at 1% w/w) caused the aggregation of oil droplets through depletion flocculation, resulting in low creaming stability and high low-shear viscosity. At a lower protein concentration (0.1% w/w), when protein was limited, the emulsion droplets were stabilised by bridging flocculation and showed good stability to creaming. Shear-thinning behaviour was observed for both flocculated emulsions. A reduction in the low-shear viscosity and a Newtonian flow was obtained for the emulsion containing an intermediate concentration of protein (0.25% w/w). At this concentration, there was relatively little excess unadsorbed protein in the continuous phase; thus the emulsion was most stable to creaming. NMR was used to characterise these emulsion systems without dilution. Shorter T 2 values (by low-field 1H NMR), for the emulsions containing both high (1% w/w) and low (0.1% w/w) amounts of protein, indicated increased restricted mobility of oils, caused by depletion or bridging flocculation. The line broadening in oil signals in the high-field NMR spectra ( 1H, 13C) indicated increased interaction between oil molecules and proteins at the interface with increasing protein concentration in emulsions. In addition, 31P NMR spectra, which reflect the mobility of the casein component only, showed increased line broadening, with reduction in protein content due to the relatively higher proportion of the protein being adsorbed to the interface of the oil droplets, compared to that in the continuous phase (i.e., as the oil-to-protein ratio was increased). The T 2 values of resonances of the individual groups on oil molecules, obtained using high-field 1H NMR, reflected their different environments within the oil droplet.

Matrix properties affect the sensory perception of emulsion-filled gels

The breakdown properties and sensory perception of emulsion-filled gels with different matrices were studied at varying emulsion concentrations. The gel matrices used were cold-set whey protein isolate (WPI), gelatin, κ-carrageenan and a mixture of κ-carrageenan and ι-carrageenan. The oil-in-water emulsions added to the gels were either stabilised by native WPI or WPI aggregates. The emulsion droplets were homogeneously distributed in WPI gels, slightly aggregated in mixed κ/ ι-carrageenan and extensively aggregated in κ-carrageenan gels. For gelatin, gels with equal composition but with either non-aggregated or aggregated emulsion droplets could be prepared by changes in processing conditions. The gel modulus as determined by large deformation experiments increased at increasing emulsion concentration for WPI and gelatin gels, but decreased for κ-carrageenan gels. For mixed κ/ ι-carrageenan no effect of emulsion concentration on gel modulus was observed. Based on these observations, we concluded that the emulsion droplets were bound to the matrix in WPI and gelatin gels and unbound in carrageenan gels. Most of the mouthfeel attributes generated by a quantitative descriptive analysis (QDA) sensory panel discriminated between emulsion concentrations and different types of gel matrix. At increasing emulsion concentration the perceived creaminess of the samples increased. For gelatin, κ-carrageenan and mixed κ/ ι-carrageenan gels, i.e., for gels melting at the oral processing temperature or containing unbound oil droplets, the creaminess scores were consistently higher than for WPI gels, which were perceived as more rough. For gelatin gels, no effect of oil droplet aggregation on sensory perception was found.

Emulsifying properties of soybean soluble polysaccharide

Soybean soluble polysaccharide (SSPS) is an ingredient extracted from the by-product of the isolation of soybean protein. The objective of this work was not only to study the emulsifying properties of SSPS, but also to determine if different extraction conditions would affect the behavior of the polysaccharide when adsorbed at oil/water interfaces. For this reason, three types of soy polysaccharide, SSPS-L, SSPS-H, and SSPS-M were investigated. Emulsions prepared at pH 3.5–5.0, containing 20% soybean oil and concentrations of SSPS above 4% were stable to creaming for 30 days, for all the SSPS tested. In spite of the presence of galacturonic acid in SSPS, the emulsions were not affected by changes in pH or by addition of CaCl 2 (5–25 mM) or NaCl (5–25 mM). Among the three SSPS tested, SSPS-L extracted at 120 °C and pH 3 for 2 h showed the best emulsifying properties forming stable emulsions at a concentration of 4% and up to 50% oil. Differences in the thickness of the adsorbed layer were found depending on the type of SSPS. The thickness of SSPS calculated after hemicellulase or pectinase treatment was estimated to be about 17 nm (SSPS-L), 21–24 nm (SSPS-H), and 30–36 nm (SSPS-M), respectively. The enzymatic degradation of SSPS resulted in oil droplet aggregation, indicating that oil droplet stabilization occurred mainly via steric repulsion.

Effects of heat on physicochemical properties of whey protein-stabilised emulsions

The effect of heating has been studied for whey protein-stabilised oil-in-water emulsions (25.0% (w/w) soybean oil, 3.0% (w/w) whey protein isolate, pH 7.0). These emulsions were heated between 55 and 95 °C as a function of time and the effect on particle size distribution, adsorbed protein amount, protein conformation and rheological properties was determined. Heating the emulsions as a function of temperature for 25 min resulted in an increase of the mean diameter ( d 32) and shear viscosity with a maximum at 75 °C. Heating of the emulsions at different temperatures as a function of time in all cases resulted in a curve with a maximum for d 32. A maximum increase of d 32 was observed after about 45 min at 75 °C and after 6–8 min at 90 °C. Similar trends were observed with viscosity measurements. Confocal scanning laser micrographs showed that after 8 min of heating at 90 °C large, loose aggregates of oil droplets were formed, while after 20 min of heating compact aggregates of two or three emulsion droplets remained. An increase of the adsorbed amount of protein was found with increasing heating temperature. Plateau values were reached after 10 min of heating at 75 °C and after 5 min of heating at 90 °C. Based on these results we concluded that in the whole process of aggregation of whey protein-stabilised emulsions an essential role is played by the non-adsorbed protein fraction, that the kinetics of the aggregation of whey protein-stabilised emulsions follow similar trends as those for heated whey protein solutions and that upon prolonged heating rearrangements take place leading to deaggregation of initially formed large, loose aggregates of emulsion droplets into smaller, more compact ones.

Physico-chemical characteristics of oil-in-water emulsions based on whey protein–phospholipid mixtures

Emulsions prepared with whey proteins, phospholipids and 10% of vegetable oil were used for a model typifying dressings, coffee whitener and balanced diets. For the present study, two whey proteins (partial heat-denatured whey protein concentrate (WPC) and undenatured whey protein isolate (WPI)) in combination with different phospholipids (hydrolysed and unmodified deoiled lecithin) were chosen to investigate the interactions between proteins, phospholipids and salt (sodium chloride) in such emulsion systems. Oil-in-water (o/w) emulsions (10 wt.% sunflower oil) containing various concentrations of commercial whey proteins (1–2%), phospholipids (0.39–0.78%) and salt (0.5–1.5%) were prepared using a laboratory high pressure homogeniser under various preparation conditions. Each emulsion was characterised by droplet size, creaming rate, flow behaviour and protein load. The dynamic surface activity of the whey proteins and lecithins at the oil–water interface was determined using the drop volume method. The properties of emulsions were significantly influenced by the content of whey protein. Higher protein levels improved the emulsion behaviour (smaller oil droplets and increased stability) independent of the protein or lecithin samples used. An increase of the protein content resulted in a lower tendency for oil droplet aggregation of emulsions with WPC to occur and emulsions tending towards a Newtonian flow behaviour. The emulsification temperature was especially important using the partial heat-denatured WPC in combination with the deoiled lecithin. A higher emulsification temperature (60°C) promoted oil droplet aggregation, as well as an increased emulsion consistency. Emulsions with the WPC were significantly influenced by the NaCl content, as well as the protein–salt ratio. Increasing the NaCl content led to an increase of the droplet size, higher oil droplet aggregation, as well as to a higher creaming rate of the emulsions. An increase of the lecithin content from 0.39 to 0.78% in the emulsion system resulted in a small reduction of the single droplet size. This effect was more pronounced when using the hydrolysed lecithins.

Effects of fat crystallization on the behavior of proteins and lipids at oil droplet surfaces

AbstractThe effects of fat crystallization induced by thermal treatment on the rheological properties of creams and physical phenomena at the oil droplet surfaces were investigated. Creams A or B were prepared from commercial proprietary fats A or B (vegetable oils with different triaclyglycerol composition) and aqueous solution containing proteins. Thermal treatment of the creams at the “critical temperatures” (temperatures inducing a small percentage of solid fats in the oil droplets) caused a rapid increase of solid fat contents in the following cooling process. The thermal treatment of cream B at the “critical temperature” caused an increase of viscosity of the cream and an increase of protein surface coverage during the subsequent cooling process. These results suggest that the oil droplet aggregation induced by the thermal treatment at the “critical temperature” and the subsequent cooling occurred via further adsorption of proteins. Electron spin resonance measurement demonstrated the dramatic reduction of fluidity of triacylglycerol molecules at the oil droplet surface in cream B during the cooling process after thermal treatment at temperatures below “critical”. Based on these results, we speculated on the mechanism for the destabilization of thermally treated creams during the cooling process.