Effect of concentrated flaxseed protein on the stability and rheological properties of soybean oil-in-water emulsions

Flaxseed protein concentrate containing-mucilage (FPCCM) was used to stabilize soybean oil-in-water emulsions. The effects of FPCCM concentration (0.5, 1.0, 1.5% w/v) and oil-phase volume fraction (5, 10, 20% v/v) on emulsion stability and rheological properties of the soybean oil-in-water emulsions were investigated. Z-average diameter, zeta-potential, creaming index and rheological properties of emulsions were determined. The result showed that FPCCM concentration significantly affected zeta-potential, creaming rate and emulsion viscosity. The increasing of FPCCM concentration led to a more negative charged droplet and a lower creaming rate. Oil-phase volume fraction significantly affected Z-average diameter, rheological properties, creaming index and creaming rate. With the increase of oil-phase volume fraction, both Z-average diameter and emulsion viscosity increased, while creaming index and creaming rate decreased. The rheological curve suggested that the emulsions were shear-thinning non-Newtonian fluids.     

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).     

Flocculation of Whey Protein Stabilized Emulsions as Influenced by Dextran Sulfate and Electrolyte

The creaming stability and viscosity of oil-in-water emulsions stabilized by whey protein isolate were monitored as functions of dextran sulfate (DS) and electrolyte (NaCl) concentration. At a specific DS concentration (the critical flocculation concentration, CFC), the droplets became flocculated, which promoted creaming. Addition of electrolyte caused an increase in CFC. At NaCl concentrations <0.5 wt%, addition of electrolyte decreased emulsion viscosity, but at concentrations >0.5 wt% it caused an increase in viscosity due to increased flocculation. The results were due to the influence of electrostatic screening on the effective volume of DS molecules and colloidal interactions between droplets.     

Ability of flaxseed and soybean protein concentrates to stabilize oil-in-water emulsions

The ability of flaxseed protein concentrate (FPC) to stabilize soybean oil-in-water emulsion was compared with that of soybean protein concentrate (SPC). The stability of emulsions increased with increase in protein concentration. The FPC-stabilized emulsions had smaller droplet size and higher surface charge, but worse stability at the same protein concentration compared to SPC-stabilized emulsions. Oil-in-water emulsions stabilized by both proteins were diluted and compared at different pH values (3–7), ionic strength (0–200 mM NaCl) and thermal treatment regimes (25–95 °C for 20 min). Considerable emulsion droplet flocculation occurred around iso-electric point of both proteins: FPC (pH 4.2) and SPC (pH 4.5). FPC and SPC-stabilized emulsions remained relatively stable against droplet aggregation and creaming at NaCl concentration below 100 and 50 mM, respectively. The emulsions stabilized by both proteins were fairly stable within these thermal processing regimes. FPC appears to be less effective as an emulsifier compared to SPC due to its lower emulsion viscosity. Hence, FPC could be more effective in emulsions that are fairly viscous.     

ENHANCING EFFECT OF AN OIL PHASE ON THE SENSORY INTENSITY OF SALT TASTE OF NACL IN OIL/WATER EMULSIONS

The effect of an oil phase on the sensory intensity of the salt taste of NaCl in an oil/water emulsion was studied using the magnitude estimation technique. The perceived intensity of the salt taste of 0.9 wt % NaCl in emulsions containing 10 wt % egg yolk, 70 wt % oil and 20 wt % water was much higher than that of the aqueous solution without oil droplets at the same NaCl concentration. The salt taste of low-fat emulsion (35 wt % oil) was less intense than that of the high-fat emulsion (70 wt % oil) at the same NaCl concentration, suggesting that the sensory score depends on the oil content. The NaCl concentration measured in the water phase of the high-fat emulsion, containing 0.9 wt % NaCl, was 2.66 wt %. The sensory score of the high-fat emulsion, containing 0.9 wt % NaCl, was much lower than that of an aqueous solution of 2.66 wt % NaCl without oil droplets. These results suggest that the enhancing effect of an oil phase on the perceived intensity of the salt taste in an oil/water emulsion might be due to a combination of the concentrated NaCl in the water phase and the suppressed contact of NaCl to gustatory cells by the oil droplets.     

Fatty Acid Compositions of Oil Species Affect the 5 Basic Taste Perceptions

ABSTRACT: To elucidate the effects of oils, particularly tuna oil, on taste perception, we conducted sensory analysis employing an oil-in-water emulsion prepared with basic taste substances and 3 oil species. Each type of oil extended perception retention, and did not affect sweetness or saltiness, but suppressed sourness and bitterness. Bitterness suppression was highest in tuna oil. Tuna oil also enhanced umami intensity. The results of individual fatty acid addition test were in good agreement with these effects of tuna oil. Thus, we proposed that tuna oil's specific fatty acid composition resulted in the specific taste effects of tuna oil.     

Effect of xanthan and guar gums on the formation and stability of soy soluble polysaccharide oil-in-water emulsions

The incorporation of relevant amounts of non-adsorbing hydrocolloids to oil-in-water (O/W) emulsions is a suitable alternative to reduce creaming. The effect of incorporating xanthan gum (XG) or guar gum (GG) in soy soluble polysaccharide (SSPS) stabilized oil-in-water (O/W) emulsions was studied. The emulsions contained 6 wt.% of SSPS, 20 wt.% Perilla seed oil (PSO), an omega-3 vegetable oil, and variable amounts of XG or GG ranging from 0.03 to 0.3 wt.%. The presence of minute amounts of XG or GG in fresh emulsions significantly decreased the emulsion droplet size (EDS) although such low concentrations did not provide enough continuous phase viscosity to arrest creaming. Emulsion microstructure indicated the presence of flocculation even at high concentrations of XG or GG caused by a depletion mechanism. All emulsions with XG or GG exhibited pseudoplastic behavior while the control emulsions showed an almost Newtonian behavior. Emulsion droplet polydispersion generally decreased with increase in the continuous phase viscosity indicating the importance of continuous phase viscosity in the dissipation of shear energy throughout the emulsion during homogenization. The characteristics of the emulsions were closely related to the rheological changes of the continuous phase.     

Effect of pH and Ionic Strength on the Physicochemical Properties of Coconut Milk Emulsions

ABSTRACT:  Coconut milk (16% to 17% fat, 1.8% to 2% protein) was extracted from coconut ( Cocos nucifera L.) endosperm and diluted in buffer to produce natural oil-in-water emulsions (10 wt% oil). The effect of pH (3 to 7) and NaCl (0 to 200 mM) on the properties and stability, namely, mean particle size, ζ-potential, viscosity, microstructure, and creaming stability, of the natural coconut milk emulsions was investigated. At pH values close to the isoelectric point (IEP) of the coconut proteins (pH 3.5 to 4) and in the absence of NaCl, coconut milk flocculated, but did not coalesce. Flocculation corresponded to low surface charges and was accompanied by an increase in emulsion viscosity. Adding up to 200 mM NaCl to those flocculated emulsions did not change the apparent degree of flocculation. Coconut milk emulsion at pH 6 was negatively charged and not flocculated. Upon addition of salt, the ζ-potential decreased from –16 to –6 mV (at 200 mM NaCl) but this was not sufficient to induce flocculation in coconut milk emulsions. At low pH (< IEP), the positively charged droplets of coconut milk emulsions only flocculated when the NaCl concentration exceeded 50 mM, as the ζ-potential approached zero.     

EFFECT OF HYDROCOLLOIDS ON ORAL VISCOSITY AND BASIC TASTE INTENSITIES *

Abstract. This study determined the effects of low concentrations of five food hydrocolloids on the taste intensities of aqueous solutions of sucrose, citric acid, sodium chloride, saccharin, and caffeine. The effects of the taste compounds on both oral and Brookfield viscosities were also measured. In general, sourness of citric acid and bitterness of caffeine were suppressed, while sweetness of saccharin was enhanced. Among the basic tastes, sourness was affected the most and saltiness the least. Except for sucrose, modification of taste intensity was independent of viscosity, and appeared to be related to the physicochemical properties of the hydrocolloid and the taste compound. About 16 cps were needed to reduce significantly the sweetness of sucrose. The taste compounds altered oral and physical viscosities differentially depending on the specific gum/taste combination. Generally, viscosity was reduced by the addition of all taste compounds except sucrose which increased the physical viscosity.     

Physicochemical Properties of Whey Protein-Stabilized Emulsions as affected by Heating and Ionic Strength

Corn oil-in-water emulsions (19.6 wt%; d₃₂～ 0.6 μm) stabilized by 2 wt% whey protein isolate (WPI) were prepared with a range of pH (3–7) and salt concentrations (0–100 mM NaCl). These emulsions were heated between 30 and 90°C and their particle size distribution, rheological properties and susceptibility to creaming measured. Emulsions had a paste-like texture around the isoelectric point of WPI (～φ 5) at all temperatures, but tended to remain fluid-like at pH >6 or <4. Heating caused flocculation in pH 7 emulsions between 70 and 80°C (especially at high salt concentrations), but had little effect on pH 3 emulsions. Flocculation increased emulsion viscosity and creaming. Results were interpreted in terms of colloidal interactions between droplets.     

Physical Properties of Whey Protein Stabilized Emulsions as Related to pH and NaCl

Corn oil-in-water emulsions (20 wt%, d₃₂～ 0.6 μm) stabilized by 2 wt% whey protein isolate were prepared with a range of pH (3–7) and salt concentrations (0–100 mM NaCl), and particle size, rheology and creaming were measured at 30°C. Appreciable droplet flocculation occurred near the isoelectric point of whey protein (pH 4–6), especially at higher NaCl concentrations. Droplet flocculation increased emulsion viscosity and decreased stability to creaming. Results are related to the influence of environmental conditions on electrostatic and other interactions between droplets.     

Destabilization of protein-based emulsions by diglycerol esters of fatty acids – The importance of chain length similarity between dispersed oil molecules and fatty acid residues of the emulsifier

Destabilizing effects of diglycerol mono-esters of different saturated or one mono-unsaturated fatty acids (DF) on protein-based emulsions prepared with various types of oil were examined by visual observations and particle size analyses. By diglycerol esters of oleic acid (DO), a hexadecane-in-water emulsion was more obviously destabilized than an octadecane-in-water emulsion or food oil-in-water emulsions. Interfacial tension measurements indicated that the adsorbed protein on oil droplet surfaces of hydrocarbon emulsions can be more easily displaced by DO compared to the case of food oil emulsions. The degree of hydrocarbon emulsion destabilization by DO varied with the chain length of hydrocarbon molecules. From the results of combination tests of five hydrocarbons varying in chain length in oil phase and five DF having different mono-fatty acid residue, we described a possibility that DF could effectively destabilize the hydrocarbon emulsion when the chain length of fatty acid residue of DF was similar to that of hydrocarbon molecules.     

Emulsifying properties of β-lactoglobulin and Quillaja bark saponin mixtures: Effects of number of homogenization passes,pH, and NaCl concentration

The effects of number of homogenization passes, pH, and NaCl concentration on the formation and stability of oil-in-water emulsions comprising a mixture of a biosurfactant (Quillaja bark saponin) and a globular protein (β-lactoglobulin) were investigated. The emulsions were characterized as to visual appearance, droplet size, droplet surface charge, and rheology. The emulsions obtained by different conditions (4, 6, or 8 passes; pH 7, 8, or 9; and 0, 100, or 200 mmol L^?1 of NaCl) were polydisperse, presented relatively small average droplet sizes (z-average < 323 nm) as well as negative droplet charge (between –20 and –79.6 mV) in all evaluated conditions. Regardless of the number of homogenization passes, the emulsions exhibited low apparent viscosity and pseudoplastic behavior with small yield stress. Viscoelastic behavior was also observed, thus the emulsions were characterized as weak gels. Four homogenization passes were enough to obtain small droplets in the evaluated conditions. Droplet size was not significantly affected by NaCl concentration and pH (p > 0.05). On the other hand, the absolute ζ-potential values significantly decreased and increased upon increased NaCl content and pH, respectively. Regardless of the tested conditions, all emulsions had good stability against phase separation and droplet aggregation, since no significant changes in average droplet size were observed throughout storage (p > 0.05). In the presence of NaCl, in which droplet charge significantly decreased, emulsion was also stable. Thus, we can conclude that electrostatic repulsion as well as steric repulsion was responsible for stabilization.     

Viscosity ratio: A key factor for control of oil drop size distribution in effervescent atomization of oil-in-water emulsions

The present study focused on the effervescent atomization of oil-in-water emulsions and its influence on the internal emulsion structure. The impact of atomization conditions and nozzle geometry on an oil-in-water emulsion with varied viscosity ratio of disperse phase to emulsion was determined. The viscosity ratio is known as a key factor for the drop breakup in emulsification processes. The results depict that oil drops are broken up according to emulsification mechanisms during atomization. A maximum breakup was found for a viscosity ratio between 0.5 and 1. The expected stress dependency of the drop size change was observed for high viscosity ratios only. Relevance of elongational stress on the drop breakup was proven with significant drop size change at high viscosity ratios. The viscosity ratio thus allows for an efficient control of oil drop size change in effervescent atomization as the spray characteristics are invariant to viscosity changes within certain limits.     

乳状液成分对O/W乳状液性质的影响

采用单因素实验设计,通过机械搅拌方法制备O/W乳状液。通过乳状液的离心稳定性、粘度和乳状液的显微结构,研究不同HLB值的复合乳化剂及含量、脱脂乳粉溶液的浓度以及油和水比例对乳状液性质的影响,最终确定较佳的乳状液成分。实验结果表明:当以Span-80和Tween-80为复合乳化剂,其HLB值为9.6、复合乳化剂含量为16%(w/w)、脱脂乳粉溶液浓度为25%(w/v)、油与水比为1∶1(w/w)时,可以获得状态较好的乳状液,此时乳状液的离心稳定性最高,可以达到97.5%。     

A PRELIMINARY STUDY OF W/O/W EMULSIONS WITH A VIEW TO POSSIBLE FOOD APPLICATIONS

A study was made of the influence of various additives on the stability and low shear viscosity of water-in-olive oil-in-water emulsions. The additives were glucose, sucrose, acetic acid, citric acid, ascorbic acid, sodium chloride and sodium acetate, Glucose and sucrose increased viscosity for some time until a constant value was reached. With the other additives an initial increase in viscosity was followed by a decrease and a corresponding decrease in stability. These observations are explained in terms of the osmotic pressure gradient between the inner and outer water compartments, and the effect of additives on the physical state of the emulsifier films adsorbed at the interfaces between the two water compartments and the oil phase.     

Iron-catalyzed lipid oxidation in emulsion as affected by surfactant,pH and NaCl

Corn oil-in-water emulsions stabilized by sodium dodecyl sulfate (SDS), Brij 35 or dodecyltrimethylammonium bromide (DTAB) were prepared to determine the influence of surface charge on iron-catalyzed lipid oxidation. Oxidation was measured using lipid peroxides, conjugated dienes, and thiobarbituric reactive substances. At pH 6.5, initial oxidation rates were in the order of SDS> Brij>DTAB. As pH was decreased from 8 to 3, oxidation of SDS-stabilized emulsions increased, while oxidation of Brij and DTAB emulsions were unaffected. NaCl (1.0%) decreased oxidation of the SDS-stabilized emulsion by 20% but had minimal influence on oxidation of Brij and DTAB emulsions. These results indicate that the surface charge of emulsion droplets plays an important role in their oxidative stability.     

pH对玉米胚芽蛋白Pickering乳液稳定性及流变学性质的影响

以玉米胚芽蛋白为原料,制备玉米胚芽蛋白Pickering乳液。研究不同pH(3、5、7、9、11)下乳液的粒径、电位、贮藏稳定性、离心稳定性及流变学性质。结果表明:乳液类型为水包油型;随着pH的增加,乳液粒径先增大后减小,电位绝对值先减小后增大;离心后,pH为5的乳液出现分层现象,离心稳定性最差,其他pH下的乳液离心稳定性均较好; p H为11的乳液在贮藏时间为1、3、7 d时均未出现分层,贮藏稳定性最好;乳液表观黏度随着剪切速率的增加而逐渐下降,呈剪切稀释现象,随着pH的增加,乳液的表观黏度先增大后减小。     

Chemical and physical stability of protein and gum arabic-stabilized oil-in-water emulsions containing limonene

ABSTRACT:  An important flavor component of citrus oils is limonene. Since limonene is lipid soluble, it is often added to foods as an oil-in-water emulsion. However, limonene-containing oil-in-water emulsions are susceptible to both physical instability and oxidative degradation, leading to loss of aroma and formation of off-flavors. Proteins have been found to produce both oxidatively and physically stable emulsions containing triacylglycerols. The objective of this research was to determine if whey protein isolate (WPI) could protect limonene in oil-in-water emulsion droplets more effectively than gum arabic (GA). Limonene degradation and formation of the limonene oxidation products, limonene oxide and carvone, were less in the WPI- than GA-stabilized emulsions at both pHs 3.0 and 7.0. These data suggest that WPI was able to inhibit the oxidative deterioration of limonene in oil-in-water emulsions. The ability of WPI to decrease oxidative reactions could be due to the formation of a cationic emulsion droplet interface at pH 3.0, which can repel prooxidative metals, and/or the ability of amino acids in WPI to scavenge free radical and chelate prooxidative metals.     

Oral behaviour of food hydrocolloids and emulsions. Part 1. Lubrication and deposition considerations

Physico-chemical and physiological factors that affect aroma and taste release in the mouth are discussed in relation to hydrocolloid levels and o/w emulsion phase volumes. Changes in viscosity introduced through the use of biopolymer solutions only have a small effect on aroma and taste release, while changes in the fat levels have a marked effect on both aroma and taste. Based on an understanding of the inter-relationship between microstructure, in-mouth processing and oral physiology, microstructures were specifically designed to control the delivery and release of aroma and taste during consumption. Gelled emulsion particles (microstructured emulsions) have been designed to control aroma delivery in low fat foods and duplex emulsions have been designed to control sour taste perception in low pH foods.