Stability of oil‐in‐water emulsions as influenced by thermal treatment of whey protein dispersions or emulsions

Properties of whey protein concentrate stabilised emulsions were modified by protein and emulsion heat treatment (60–90 °C). All liquid emulsions were flocculated and the particle sizes showed bimodal size distributions. The state and surface properties of proteins and coexisting protein/aggregates in the system strongly determined the stability of heat‐modified whey protein concentrate stabilised emulsions. The whey protein particles of 122–342 nm that formed on protein heating enhanced the stability of highly concentrated emulsions. These particles stabilised protein‐heated emulsions in the way that is typical for Pickering emulsions. The emulsions heated at 80 and 90 °C gelled due to the aggregation of the protein‐coated oil droplets.     

Synergistic stabilization of heat-treated emulsions containing mixtures of milk proteins

The synergistic effect by which a very small amount of casein can confer stability to a whey protein-stabilized emulsion heated to 90 °C has been investigated. Using β-lactoglobulin (β-lg) as the main emulsifying agent, the extent of heat-induced flocculation increased with ionic strength, with commercial sodium caseinate or β-casein incorporated. The protective effect of casein was retained for a moderate concentration of ionic calcium. Casein added before heating, or shortly afterwards (i.e. before the emulsion had cooled), offered substantial synergistic protection to the heated β-lg-stabilized emulsion. With α-lactalbumin (α-la) as the primary emulsifying agent, no significant protective effect could be observed. In contrast, casein could confer significant stability to a heat-treated bovine serum albumin emulsion. Quiescent storage stability testing suggests that a combination of limited heating and casein addition could improve the long-term shelf-life of a whey protein-based emulsion.     

Oxidative stability of fish oil‐in‐water emulsions under high‐pressure treatment

Over the last decade, high‐pressure treatment has been of considerable interest as an alternative to thermal treatment for food preservation and processing. The impact of high‐pressure treatment on lipid oxidation in fish oil‐in‐water emulsions stabilised by 0.5 wt% whey protein isolate or sodium caseinate was investigated by determining thiobarbituric acid (TBA), propanal values and hydroperoxide values (PVs). The TBA value and the PV of all emulsions increased with increasing pressure at low temperature, indicating that lipid oxidation was promoted by high‐pressure treatment. The impact of high‐pressure treatment on the oxidative stability of lipids was increased when the temperature was increased as the TBA and propanal values were markedly enhanced by high pressure at high temperature. However, high‐pressure treatment did not affect the antioxidant properties of whey protein isolate and sodium caseinate in the fish oil‐in‐water emulsions, which may suggest that high‐pressure treatment does not alter the lipid oxidation pathway in emulsion systems. The promotion of lipid oxidation by high pressure is due mainly to increasing the pressure on a gas reaction shifts the position of equilibrium towards the side with fewer gas molecules.     

Physicochemical stability of egg protein‐stabilised oil‐in‐water emulsions supplemented with vegetable powders

The effect of vegetable powders on the physicochemical stability of egg protein‐stabilised oil‐in‐water emulsions was studied. Vegetable powders (beetroot, broccoli, carrot, celery, green pea, red pepper, spinach, swede, tomato and yellow pea) were added at 2.5% (w/v) to emulsions prepared with rapeseed oil. The physical stability of the emulsions was characterised using the emulsifying activity (EAI) and the emulsifying stability indices (ESI) in addition to bright field microscopy. The oxidative stability of the emulsions was monitored by means of an accelerated oxidation test (Rancimat method). The addition of most vegetable powders did not markedly affect the physical stability of the emulsions although an adverse effect of tomato was observed. The oxidative stability of the emulsions was significantly improved in most cases as indicated by the Rancimat method with broccoli exhibiting the highest increase in induction time (98.2%) compared with the control. Both polar and nonpolar antioxidants are likely to contribute to the overall chemical stability of this complex food system in a concentration‐dependent manner.     

The effect of tapioca maltodextrins on the stability of oil‐in‐water emulsions

The effect of concentration of tapioca maltodextrin with three different DE values on the viscosity, depletion attraction potential (W_dep), rate of coalescence (K_c), and creaming rate of oil‐in‐water emulsion have been investigated. The relative viscosity and W_dep increased with increasing maltodextrin concentration. Critical flocculation concentration (CFC) of emulsions containing maltodextrin with DE of 16 (DE16), 12 (DE12), and 9 (DE9) were 11, 7, and 5.5 wt%, respectively. At maltodextrin concentrations below CFC, there was no change in K_c and no creaming was observed. At maltodextrin concentrations above CFC, an increase in the concentration of DE9 and DE12 resulted in an increase in K_c until it reached a constant value. K_c values remained to be constant in the concentration range between 30 and 40 wt% for DE9 and that between 35 and 45 wt% for DE12. Further increasing in concentration of DE9 and 12 decreased K_c. K_c of DE16 monotonically increased with increasing concentration from CFC to 50 wt%. The rate of creaming decreased with increasing maltodextrin concentration over CFC until it reached zero. Creaming was not observed at maltodextrin concentrations more than 35 wt% for DE9 and 40 wt% for DE12 whereas DE16 showed creaming at all concentrations above CFC. A maltodextrin with a lower DE inhibited creaming more efficiently than maltodextrin with a higher DE because of higher viscosities. The K_c tended to increase with decreasing DE because the strength of interaction between oil droplets increased.     

Influence of composition and structure of oil‐in‐water emulsions on retention of aroma compounds

The influence of the composition and structure of oil‐in‐water emulsions on aroma retention was examined for 20 volatile compounds. Compositional and structural parameters included the fraction of emulsifier phase, the fraction of lipid phase and the particle size distribution of the dispersed lipid phase in the emulsion. Air/liquid partition coefficients of dimethyl sulphide, 1‐propanol, diacetyl, 2‐butanone, ethyl acetate, 1‐butanol, 2‐pentanol, propyl acetate, 3‐methyl‐1‐butanol, ethyl butyrate, hexanal, butyl acetate, 1‐hexanol, 2‐heptanone, heptanal, α‐pinene, 2‐octanone, octanal, 2‐nonanol and 2‐decanone were determined by static headspace gas chromatography. The hydrophobicity of the compounds determined the influence of the compositional and structural parameters of the emulsions on air/liquid partitioning. Increase of the emulsifier fraction increased the retention of mainly hydrophilic aroma compounds and decreased the retention of hydrophobic compounds. Higher lipid levels led to increased retention of hydrophobic compounds and release of hydrophilic compounds. Emulsions with larger particles showed increased aroma retention, which was independent of the lipid fraction and the polarity of the aroma compounds. The data demonstrated a profound effect of both composition and structure of oil‐in‐water emulsions on the air/liquid partitioning of the 20 aroma compounds under equilibrium conditions. © 2002 Society of Chemical Industry     

Effect of emulsifier type on physicochemical properties of water‐in‐oil emulsions for confectionery applications

In a first step of designing tailored confectionery masses using water‐in‐oil emulsions, a parameter screening on emulsion rheology and stability was carried out. The experimental set‐up included cocoa butter as continuous phase and the variation of the disperse phase (water, or 50% sucrose in water), two volume fraction levels and the type of emulsifier (lecithin, polyglycerol polyricinoleate (PGPR), ammonium phosphatide (YN) and blends of lecithin or YN with PGPR). Emulsions were characterised by microscopy, laser diffraction, analytical centrifugation and shear rheology. Results show multimodal droplet size distributions in lecithin‐ or YN‐stabilised emulsions, and droplets which tend to form aggregates and an internal network responsible for shear thinning. PGPR emulsions are characterised by monomodal droplet size distributions and smaller droplets without networking tendency. They exhibit Newtonian flow behaviour and a much higher stability against phase separation. In emulsifier blends, PGPR is mainly responsible for the modulation of physical properties of the emulsions.     

Effects of residual phospholipids on surface properties of a soft-refined sunflower oil: Application to stabilization of sauce-types’ emulsions

Vinegar sauces’ type emulsions were prepared from water–alcohol mixture (90:10) and three different sunflower oil samples (Reference oil, SUN1 and SUN3) at 20 wt% with sunflower lecithin as O/W emulsifier. Besides the addition of lecithins at 0–2 wt%, the oil composition varied based on the minor components present in each oil due to the different crushing and refining process. Reference oil sample was nutrient-free while SUN oil contained nutrient component sterols, tocopherols, phosphorus and phenols. Interfacial tension of the different systems was monitored using an automated tensiometer. The vinegar sauces’ type oil-in-water emulsions were prepared by a two-step homogenization procedure (10,000 rpm for 10 min, followed by a passage through an homogenizer at 400 bar pressure), the lipid droplets’ stability against aggregation/coalescence was monitored using integrated light scattering (particle size distribution) and multiple light scattering (creaming) measurements for two-month storage at 4 °C. In the absence of added lecithins, SUN oil sample containing phospholipids presented lower interfacial tension values than the Reference oil. Equilibrium values obtained are ∼4.4 mN m⁻¹ for SUN3, ∼10.5 mN m⁻¹ for SUN1, instead of 13.7 mN m⁻¹ for Reference sample. Addition of phospholipids (lecithin) to the Reference sample led to a similar trend of adsorption kinetics observed in the SUN sample (nutrient rich oil). SUN3 showed the best ability to form elastic film and Reference oil showed lowest ability, which could be attributed to concentration and the composition of phospholipids.     

Emulsion stabilization mechanism of combination of esterified maltodextrin and Tween 80 in oil-in-water emulsions

Food Science and Biotechnology - Esterified maltodextrins (EMs) were prepared using enzyme-catalyzed reaction of maltodextrin (DE of 16 and 9) and palmitic acid. The emulsion stabilization...     

水酶法乳状液的稳定性及其破乳方法研究进展

从液滴和界面膜性质等方面介绍了影响乳状液稳定性的因素,同时介绍了破坏乳状液稳定性的最新研究,并展望了今后破乳方法的研究方向。     

Pea protein exhibits a novel Pickering stabilization for oil-in-water emulsions at pH 3.0

In this paper we reported that pea protein isolate (PPI) at pH 3.0 exhibits a novel Pickering stabilization for oil-in-water emulsions. At pH 3.0, most of the proteins in PPI were present in the nanoparticle form, with the hydrodynamic diameter of 134–165 nm depending on the concentration (c; 0.25–3.0 g/100 mL). For the emulsions formed at a specific oil fraction of 0.2, increasing the c from 0.25 to 3.0 g/100 mL resulted in a considerable reduction in the emulsion size, while their creaming stability progressively increased, and especially at c values higher than 2 g/100 mL, no creaming occurred even after storage of 20 days. Confocal laser scanning microscopy observations showed that increasing the c resulted in a progressive increase in extent of droplet flocculation, and at higher c values, a network consisting of flocculated droplets could be formed. The emulsions formed at c values above 1.0 g/100 mL exhibited extraordinary stability against coalescence. The flocculated droplet network formation was closely associated with the increased amount of adsorbed proteins at the interface. The results suggest that pea proteins exhibit a good potential to act as a kind of Pickering stabilizers for oil-in-water emulsions at acidic pHs.     

Construction of cold‐triggered/heat‐destroyed emulsions for use as a practical cold‐storage thermal history indicator

BACKGROUND: To provide a record of the occurrence of a high‐temperature event during a cold‐chain system in the range from 1 to 10 °C, an indicator material that undergoes an irreversible temperature‐related visual change in response to high temperatures is needed. RESULTS: In order to obtain the required indicator, we attempted to construct highly thermo‐sensitive cold‐triggering and heat‐destructive emulsions that could start monitoring a high‐temperature event just by cooling, and after triggering provide an irreversible visual change over the upper limitation of the monitoring temperature. Emulsions composed of oil mixtures of triacylglycerols and fatty acid esters provided a 1 °C triggering and 10 °C destructive emulsion. The effect of the oil‐phase composition was studied by differential scanning calorimetry, nuclear magnetic resonance and microscopy with a cooling/heating system. CONCLUSION: The emulsion was triggered by cooling at 1 °C and was immediately destroyed by heating to 10 °C, with clear visible phase separation. For cold‐triggering, crystalline structures of frozen oils should work to destroy the interfaces of the emulsion droplets. This could be used as a thermal indicator that would trigger in cold‐chain distribution systems and be destroyed in these systems. Copyright © 2009 Society of Chemical Industry     

Iron‐mediated lipid oxidation in 70% fish oil‐in‐water emulsions: effect of emulsifier type and pH

The objective of this study was to investigate the protective effect of five different emulsifiers on iron‐mediated lipid oxidation in 70% fish oil‐in‐water emulsions. The emulsifiers were either based on protein (whey protein isolate and sodium caseinate) or based on phospholipid (soy lecithin and two milk phospholipids with different phospholipid contents, MPL20 and MPL75). Lipid oxidation was studied at pH 4.5 and 7.0, and results were compared to lipid oxidation in neat fish oil. Results showed that all emulsions oxidised more than neat oil. Furthermore, emulsions prepared with proteins oxidised more at low pH than at high pH, and casein emulsions oxidised the least (Peroxide value (PV) at day 7 was 0.5–0.7 meq kg^?1). Among emulsions prepared with phospholipids, emulsions with MPL75 were the most oxidised followed by emulsions prepared with lecithin and MPL20. Thus, PV in MPL75 emulsions was 5.0–5.5 meq kg^?1 at day 7 compared with 0.9–1.9 meq kg^?1 in MPL20 emulsions.