Interfacial and Emulsifying Characteristics of Acid-treated Pea Protein

This work presents equilibrium and dynamic aspects for the adsorption at the oil–water interface of pea (Pisum sativum L.) protein isolate (PPI). Dynamic interfacial tension, γ, and surface viscoelasticity modulus, ε, were determined using pendant-drop method. Adsorption kinetics studies revealed that pea proteins adsorb faster at pH 7.0 than at acidic pH (pH 2.4). On the other hand, the measured ε is lower at pH 7.0. This is probably due to fast adsorption, leading to the formation of inhomogeneous film structures. In fact, compared with pHs above the isoelectric point (pI ~ 4.3), acidic conditions slow down the adsorption, but the modulus is increased. Pea-protein-stabilized emulsions are more stable to creaming at acidic pH and their particle-size distributions are more homogeneous in these conditions. Effect of pH on interfacial properties and on properties of oil-in-water emulsions stabilized by PPI was interpreted in terms of pea protein solubility, globulin dissociation, and oil-droplet surface electrostatic charge. We propose that at acidic conditions, adsorbed dissociated globulins form stronger and denser viscoelastic networks when adsorbed at oil–water interface. Consequently, the pH-dependence of pea-globulin-stabilized emulsions properties could be of great interest to tune barrier properties of oil/water interfacial membranes for several applications such as encapsulation and controlled release of lipophilic bioactive components within the food, medical, and pharmaceutical industries.     

Solid�CLiquid Transitions and Stability of HPKO-in-Water Systems Emulsified by Dairy Proteins

Stability of oil-in-water emulsions during freezing and thawing is regulated by the phase transitions occurring in the continuous and dispersed phases upon thermal treatments and by the composition of the interfacial membrane. In the present study, the impact of the water phase formulation (0–2.5–5–10–20–30–40% w/w sucrose), the interfacial composition [whey protein isolates (WPI) or sodium caseinate (NaCas) used at different concentrations], and the particle size on the stability of hydrogenated palm kernel oil (30% w/w)-in-water systems was investigated. Phase/state behaviour of the continuous and dispersed phases and emulsion destabilisation were studied by differential scanning calorimetry. System morphology was observed by particle size analysis and optical microscopy. The presence of sucrose in the aqueous phase and reduced particle size distribution significantly improved emulsion stability. WPI showed better stabilising properties than NaCas at lipid to protein ratios of 10:1, 7.5:1, 5:1 and 4:1. Increased WPI concentration significantly improved emulsion resistance to breakdown during freeze–thaw cycling. NaCas showed poor stabilising properties and was ineffective in reducing emulsion destabilisation at 0% sucrose at all the lipid to protein ratios.     

Improvement of the Surface Functional Properties of β-Lactoglobulin and α-Lactalbumin by Heating in a Dry State

Controlled heating in a dry state greatly improved the surface functional properties of whey proteins (β-lactoglobulin and α-lactalbumin). Although whey proteins were completely insolubilized by heating at 80°C in an aqueous solution, their solubility was kept even after heating at 80°C in a dry state (7.5% moisture content) for 5 days. The surface hydrophobicity of α-lactalbumin was increased during the dry-heating, while that of β-lactoglobulin was decreased. In addition, the fluorescence spectra excited at 280 nm of dry-heated whey proteins suggested the significant conformational changes. High-performance gel chromatography showed that a considerable amount of soluble aggregates was formed in the dry-heated β-lactoglobulin, while a small amount of soluble aggregate was observed in the dry-heated α-lactalbumin. The foaming properties of dry-heated whey proteins were increased to about 3 times that of untreated proteins. The emulsifying properties of dry-heated whey proteins were also increased, compared to untreated proteins, although a slight decrease in the emulsion stability was observed in dry-heated β-lactoglobulin. The improvement of the surface properties seemed to come from the partial unfolding suitable for the formation of foam film and the entrapment of oil droplets.     

Antifreeze Emulsions Produced from Linoleic Acid and Water Using Enzymatically Modified Gelatin

An enzymatically modified gelatin with covalently attached leucine dodecyl ester, referred to as EMG-12, was used as a surfactant to prepare emulsions with different properties by changing the surfactant concentration, oil volume fraction, and pH in the water phase. The emulsions generally resisted the freezing of their constituent bulk water at approximately ?10°C, but similar emulsions produced with soy protein isolate, casein, or Tween-80 as control agents were less resistant. The freezing (or unfreezing) of the bulk water in these emulsions depended on the kind of agent used, not on the emulsion properties such as average area of the oil/water interface, stability against coalescence, and stability against creaming. The emulsion produced with EMG-12, like that produced with polyglycerol stearate, tended to maintain its unfrozen state even in the presence of silver iodide crystals added as heterogeneous ice-nuclei. The significance of producing such an antifreeze emulsion is discussed from the standpoint of cryopreservation of cold-sensitive food and biological systems.     

Competitive Adsorption of Lecithin and Saliva at the O/W Interface in Relation to the Oral Processing of Lipid Continuous Foods

This research is relevant to oral processing of lipid continuous foods. During this first step of food digestion, lipid continuous foods such as chocolate or margarine phase invert into oil-in-water emulsions stimulated through the mechanical action of tongue and teeth in combination with the change in temperature and the high surface activity of salivary proteins. These are hypothesised to stabilise the newly formed interface in competition with surfactants or surface active molecules released from the food if present. Here competitive adsorption between mechanically stimulated human whole saliva (HWS) and lecithin dissolved in sunflower oil freed of interfacially active contaminants was investigated in-vitro using a pendant drop tensiometer for dynamic interfacial tension and interfacial rheological measurements. Initially, it was validated that the interfacial properties of HWS samples remained unaffected by frozen storage at ?80 °C during 6 weeks. Protein concentration affected the absolute values of interfacial tension and in particular the dilatational elastic modulus. Competitive adsorption studies revealed a mixed interface and it follows that emulsion stabilisation during oral processing involves both salivary proteins and lecithin present in the oil phase.     

The Interfacial Tension of the Lipid Membrane Formed from Lipid–Amino Acid Systems

The interfacial tension of lipid membranes composed of phosphatidylcholine (lecithin, PC)–valine (Val), phosphatidylcholine–isoleucine (Ile), phosphatidylcholine–tyrosine (Tyr), and phosphatidylcholine–phenylalanine (Phe) has been studied. The membrane components formed 1:1 complexes. The interfacial tension measurements were used to determine the membrane surface concentration A ₃⁻¹, the membrane interfacial tension γ₃, and the stability constant K.     

Caseinate-Induced Competitive Displacement of Whey Protein from Interfaces

The caseinate-induced competitive displacement of whey protein from planar air-water interfaces was investigated based on atomic force microscopy (AFM) imaging and that from the surfaces of oil droplets immersed in aqueous solution based on AFM force spectroscopy. After the addition of sodium caseinate to the sub-phase, the surface pressure of planar interfacial films of pre-adsorbed whey protein increased from 8 mN/m to up to 21 mN/m. The thicknesses of interfacial films were uniform and remained to be approximately 2 nm at relatively low surface pressures up to 18 mN/m, while they became uneven at higher surface pressures and increased to up to 7.1 nm, presumably due to the compression of interfacial whey protein networks by adsorbed caseinate. The rigidity of oil droplets coated with protein adsorbed to their surfaces was then evaluated based on the slope of approximately linear force-distance curves obtained by pressing an oil droplet against another. The adsorption of whey protein to oil droplet surfaces increased droplets’ rigidity. The subsequent addition of caseinate to the bulk solution surrounding oil droplets coated with pre-adsorbed whey protein further increased droplets’ rigidity. The present results suggest that caseinate adsorbed to an interface to which whey protein had adsorbed in advance did not completely expel pre-adsorbed whey protein molecules into the aqueous phase but caused a compaction of interfacial whey protein networks and thereby strengthened the interfacial film.     

Formation of Fine Oil-in-Water Emulsions by the Gel Emulsification Method with Saccharide and Protein

An emulsification method using a gel-like phase of a saccharide and protein mixture has been developed. In the method, which is called a gel emulsification method, an oil is added to the highly concentrated saccharide solution containing protein to form a clear gel-like phase, which followed by dilution with water to form a fine oil-in-water emulsion. This emulsion was investigated as to its emulsifying activity and emulsion stability as compared with that obtained by high-shear equipment, which was called a homomixer method. The emulsifying activity of the emulsions prepared by the gel emulsification method was much higher than that of the emulsions prepared by the homomixer method.

The emulsions prepared by both methods were highly stable in terms of the stability against coalescence. On the other hand, the stability against creaming of the emulsions prepared by the gel emulsification method was much higher than that of the emulsions prepared by the homomixer method.

The surface hydrophobicity of the protein and the unfreezable water content in the highly concentrated saccharide solution containing protein were not correlated to the emulsifying properties of the emulsions prepared by the gel emulsification method, which appeared to be dependent on the viscosity of the highly concentrated saccharide solution containing protein.     

Heat-Induced Whey Protein Gels: Effects of pH and the Addition of Sodium Caseinate

The effects of pH (6.7 or 5.8), protein concentration and the heat treatment conditions (70 or 90 °C) on the physical properties of heat-induced milk protein gels were studied using uniaxial compression, scanning electron microscopy, differential scanning calorimetry, and water-holding capacity measurements. The systems were formed from whey protein isolate (10–15% w/v) with (5% w/v) or without the addition of caseinate. The reduction in pH from 6.7 to 5.8 increased the denaturation temperature of the whey proteins, which directly affected the gel structure and mechanical properties. Due to this increase in the denaturation temperature of the β-lactoglobulin and α-lactalbumin, a heat treatment of 70 °C/30 min did not provide sufficient protein unfolding to form self-supporting gels. However, the presence of 5% (w/v) sodium caseinate decreased the whey protein thermo stability and was essential for the formation of self-supporting gels at pH 6.7 with heat treatment at 70 °C/30 min. The gels formed at pH 6.7 showed a fine-stranded structure, with great rigidity and deformability as compared to those formed at pH 5.8. The latter had a particulate structure and exuded water, which did not occur with the gels formed at pH 6.7. The addition of sodium caseinate led to less porous networks with increased gel deformability and strength but decreased water exudation. The same tendencies were observed with increasing whey protein concentration.     

Emulsions Based on the Interactions Between Lactoferrin and Chitosans

In this work, purification of lactoferrin from whey was performed with high recovery rate. Lactoferrin was then exploited in the preparation of food emulsions. Two tertiary emulsions, formed by olive oil, lecithin, chitosan, and lactoferrin, were compared: both the emulsions showed similar turbidity and stability. In the secondary emulsion formed by oil/lecithin/chitosan, the pH was increased to 9 before addition of lactoferrin. Then, lactoferrin was added, and the pH was stabilized above pH 9. Lactoferrin was found in amounts of 1 to 2.5 mg/ml in the multiple experiments. A fraction of the added lactoferrin was also present in a milky layer above the emulsion layer. This was, to our knowledge, the first study of emulsions made exploiting the interactions between lactoferrin and chitosan. It was noted that chitosan droplets remained soluble, although the hydrocolloid solubility occurs at pH lower than 5.9. These results showed the feasibility of manufacturing lactoferrin-based emulsions as functional foods.     

Biosurfactant production by Mucor circinelloides: Environmental applications and surface‐active properties

Biosurfactants are structurally a diverse group of surface‐active molecules widely used for various purposes in industry. In this study, among 120 fungal isolates, M‐06 was selected as a superior biosurfactant producer, based on different standard methods, and was identified as Mucor circinelloides on the basis of its nucleotide sequence of the internal transcribed spacer (ITS) gene. M. circinelloides reduced the surface tension to 26 mN/m and its EI₂₄ index was determined to be 66.6%. The produced biosurfactant exhibited a high degree of stability at a high temperature (121°C), salinity (40 g/L), and acidic pH (2–8). The fermentation broth's ability to recover oil from contaminated sand was 2 and 1.8 times higher than those of water and Tween 80, respectively. The ability of biosurfactant to emulsify crude oil in the sea and fresh water was 64.9 and 48% respectively. This strain could remove 87.6% of crude oil in the Minimal Salt Medium (MSM) crude oil as the sole carbon source. The results from a primary chemical characterization of crude biosurfactant suggest that it is of a glycolipid nature. The strain and its biosurfactant could be used as a potent candidate in bioremediation of oil‐contaminated water, soil, and for oil recovery processes.     

Modulation of pH Sensitivity of Surface Charge and Aggregation Stability of Protein-Coated Lipid Droplets by Chitosan Addition

The impact of a cationic polyelectrolyte on the pH sensitivity of the electrical charge and aggregation stability of protein-coated lipid droplets was examined. One percent (w/w) corn oil-in-water emulsions containing lipid droplets coated by β-lactoglobulin [0.05% (w/w) β-Lg, 10 mM acetate buffer, pH 3] were prepared in the absence (“primary” emulsions) and presence (“secondary” emulsions) of chitosan (0 to 0.05 wt%). The pH (3 to 8) of these emulsions was adjusted, and the particle charge, particle size, creaming stability, and microstructure were measured. Chitosan adsorbed to the β-Lg-coated droplets from pH 4.5 to 7.5, which was attributed to electrostatic attraction between the cationic polyelectrolyte and anionic patches on the droplet surfaces. Droplets coated by β-Lg–chitosan had better stability to flocculation than those coated by β-Lg alone around the isoelectric point of the adsorbed proteins (pH 4.5 to 5.5), which was attributed to increased electrostatic and steric repulsion between the droplets. We have shown that chitosan may be used to modulate the electrical characteristics and stability of protein-coated lipid droplets, which may be useful in the design and formation of delivery systems for use in the food, pharmaceutical, and other industries.     

Pea,Chickpea and Lentil Protein Isolates: Physicochemical Characterization and Emulsifying Properties

This work is focused on physicochemical and emulsifying properties of pea (PP), chickpea (CP) and lentil (LP) proteins. We evaluated the molecular weight distributions, surface net charge, free sulfhydryl group (SH) and disulfide bond (SS) contents, protein solubility and thermal stability of the protein isolates. Their emulsifying properties (droplet size distribution, flocculation, coalescence and creaming) were also determined as function of pH values. The three protein isolates exhibit similar physicochemical properties, including good solubility and high thermal stability despite a high degree of denaturation. In addition, we analysed the influence of pH on stability of oil-in-water (O/W; 10 wt%/90 wt%) emulsions stabilized by the legume protein isolates. Concerning emulsifying ability and stability, the most unfavourable results for all three protein isolates relate to their isoelectric point (pI?=?4.5). A significant improvement in emulsion stability takes place as the pH value departs from the pI. Overall, this study indicates that pea, chickpea and lentil proteins have great potential as food emulsifiers.     

Comparison of Emulsifying Properties of Plant and Animal Proteins in Oil-in-Water Emulsions: Whey,Soy, and RuBisCo Proteins

There is increasing interest within the food industry in replacing animal-derived ingredients with plant-derived alternatives. In this study, we compared the emulsifying properties of an emerging plant protein (RuBisCo protein) with those of a well-established plant (soy protein) and animal (whey protein) protein. The RuBisCo protein (ribulose 1,5-bisphosphate carboxylase) was isolated from duckweed (lemna minor), which is an abundant plant material with a higher protein yield and biomass per unit area than most other plant protein sources. The ability of the three proteins to form and stabilize 10 wt% soybean oil-in-water emulsions was examined. The minimum amount of protein required to produce small droplets (d <?350 nm) decreased in the following order: RuBisCo > soy > whey protein. This effect was mainly attributed to the fact that the molar mass of the proteins decreased in the same order. Even so, the RuBisCo proteins were able to form stable emulsions when used at sufficiently high concentrations (≥ 1%). All three types of protein-coated oil droplets aggregated at pH values near their isoelectric points and at high ionic strengths but there were differences between them. In the absence of added salt, extensive droplet aggregation occurred from pH 4 to 5 for whey protein, from pH 2 to 5 for soy protein, and from pH 2 to 6 for RuBisCo protein. The isoelectric points of all three protein-coated droplets were around pH 5, but the magnitude of the surface potential at low and high pH values was higher for whey protein than for the two plant proteins. At pH 7, extensive droplet aggregation occurred at ≥100 mM NaCl for RuBisCo- and soy protein-coated droplets, but only at ≥400 mM NaCl for whey protein-coated ones. The RuBisCo-coated oil droplets were more prone to flocculation when heated, especially in the presence of salt (100 mM NaCl). Overall, these results show that RuBisCo protein can be used to form and stabilize oil-in-water emulsions, but the pH, salt, and temperature conditions must be carefully controlled to avoid droplet aggregation. We should note that droplet aggregation is advantageous in some applications because it leads to an increase in emulsion viscosity or gelation.

     

Biosurfactant production by two isolates ofPseudomonas aeruginosa

Two strains of biosurfactant-producing bacteria, identified asPseudomonas aeruginosa, were isolated from injection water and crude oil-associated water in Venezuelan oil fields. Both biosurfactants resembled rhamnolipids and produced stable emulsions of heavy and extra-heavy crude oils, reducing the surface tension of water from 72 to 28 dynes/cm. Tenso-active properties of the biosurfactants were not affected by pH, temperature, salinity or Ca²⁺ or Mg²⁺ at concentrations in excess of those found in many oil reservoirs in Venezuela.     

Characterization and optimization of biosurfactants produced by Acinetobacter baylyi ZJ2 isolated from crude oil-contaminated soil sample toward microbial enhanced oil recovery applications

The present work aims to investigate the surface activity of the biosurfactant produced by Acinetobacter baylyi ZJ2 isolated from crude oil-contaminated soil sample in China and evaluate its potential application in microbial enhanced oil recovery. The biosurfactant produced by A. baylyi ZJ2 was identified as lipopeptide based on thin-layer chromatography, Fourier transform infrared spectroscopy and nuclear magnetic resonance techniques. This biosurfactant could reduce the surface tension of water from 65 mN/m to 35 mN/m, and interfacial tension against oil from 45 mN/m to 15 mN/m. Moreover, surface activity stability results showed that this biosurfactant was effective when the salinity was lower than 8% and the pH value was 4–9, and it was especially stable when the salinity was lower than 4% and pH was 6–7. Based on the result of gas chromatography, there was a decrease in heavy components and an increase in light components, which indicated that A. baylyi ZJ2 exhibited the biodegradability on the heavy components of crude oil. Furthermore, the ability of recovering oil from oil-saturated core showed that nearly 28% additional residual oil was displaced after water flooding. The lipopeptide biosurfactant produced by A. baylyi ZJ2 presented a great potential application in microbial enhanced oil recovery process, owing its good surface activity and satisfying degradation ability to crude oil.     

Legume Protein Isolates for Stable Acidic Emulsions Prepared by Premix Membrane Emulsification

Proteins originating from dry legumes are not that much used in food formulations, yet, they are interesting components from a sustainability point of view, and could have interesting functional properties, e.g. for emulsion preparation. Therefore, this work focuses on the potential of the water soluble part of pea, chickpea and lentil protein isolates under acidic emulsions (pH 3.0) using a novel mild technique: premix membrane emulsification. Pea proteins (PP) and chickpea proteins (CP) lower the interfacial tension in the same way as whey protein isolate (WPI), which suggests that they could facilitate emulsion droplet formation similarly as WPI, while lentil proteins (LP) are slightly less effective. It is possible to make oil-in-water (O/W) emulsions with an average droplet diameter (d _4,3 ) of ~5 μm after 5 cycles in the premix system. The droplet size distribution of the emulsions remained constant during one day of storage, indicating that legume proteins are able to form and kinetically stabilize O/W emulsions. CP and PP exhibited emulsifying properties comparable to those of WPI, whereas LP is slightly less efficient, therewith indicating the great potential and that pea and chickpea protein isolates hold as emulsifiers in acidic food formulations.     

Purification of lysozyme by affinity-based reversed micellar two-phase extraction

A dye-affinity reversed micellar system was used for lysozyme purification from a crude solution of chicken egg white. The dye-affinity reversed micelles consisted of Cibacron Blue F-3GA (CB; 0.1 mM) modified lecithin (50 g/l) in n-hexane. Starting with a crude egg white solution containing lysozyme of 0.0381 mg/mg protein, lysozyme purity was increased by 16 to 20 times, reached 0.62 to 0.76 mg/mg protein. The affinity micellar system was recycled and used three times. Addition of polyoxyethylene (20) sorbitan trioleate (Tween 85) as a cosurfactant could increase the capacity of the affinity-based reversed micelles. A lysozyme recovery yield of over 70% was obtained at a forward aqueous phase pH of 9.16 using the reversed micelles additionally containing 20 g/l of Tween 85.     

A Model Representing a Physiological Role of CO2 at the Cell Membrane

A model is presented suggesting the interaction of CO₂ and bicarbonate on lipids of the cell membrane. The interfacial tensions between water and oil (benzene) phases were measured using the stalagmometer and the sessile drop methods. Effects of electrolyte solutions and of CO₂ on molecular arrangement at the interface were calculated. Chloride solutions against oleic acid in benzene produced little decrease in interfacial tension from that measured for pure water against the oil phase. Presence or absence of CO₂ caused no change in interfacial tension of water or chloride solutions against the oil phase. Bicarbonate salts in the absence of CO₂ caused marked decreases in interfacial tension from that measured for water or chloride solutions. Concomitant with this decrease in interfacial tension were an increase in hydration of the interface and changes in molecular spacings of the lipid. This hydration may be considered as reflecting a more ionic-permeable cell membrane. The addition of CO₂ to the bicarbonates caused an increase in interfacial tension of the model, approaching that of the chlorides, with decreased hydration of the interface. Viewed as occurring at the cell membrane this would make the lipid more continuous and decrease the ease of ionic penetration. In this way the action of bicarbonates and CO₂ at the interface suggests an explanation of the action of CO₂ on the cell.