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ABSTRACT: The surface activity of β-casein, caseinate, and a whey protein isolate in aqueous solutions has been investigated over a
range of protein concentrations (1·10−5 to 5% w/w) at pH 5 and 7. The surface pressure data were determined by the Wilhelmy plate method. Surface pressure data at
low protein concentration indicate a low surface activity that rises to a plateau as the monolayer is saturated at higher
protein concentrations. The protein concentration and the surface pressure at the plateau depend on the pH and the type of
protein in the aqueous phase. Protein-monoglyceride interactions were investigated by spreading an insoluble monoglyceride
(monopalmitin, monoolein, or monolaurin) on a film of protein previously adsorbed on the interface at equilibrium. The existence
of protein-monoglyceride interactions depends on the interfacial composition and on the protein/monoglyceride ratio. The surface
activity of mixed protein-monopalmitin and protein-monoolein films is determined by the lipid as the surface pressure of the
mixed film is the same as the monoglyceride equilibrium spreading pressure, and the monolayer is not saturated by the protein.
However, the protein determines the surface activity of mixed protein-monopalmitin and protein-monoolein films as the protein
saturates the monolayer. For protein and monolaurin mixed films, protein determines the surface activity over the range of
protein-monolaurin compositions due to monolaurin dissolution in the bulk aqueous phase.
Journal of Oil & Fat Industries 04/2012; 78(9):873-879. · 1.77 Impact Factor
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ABSTRACT: Proteins and polysaccharides are widely used in food formulation. While most of the proteins are surface active, only few polysaccharides can adsorb at the air-water interface; this is the case of propylene glycol alginates (PGA). It is known that casein glycomacropeptide (CMP), a bioactive polypeptide derived from κ-casein by the action of chymosin, presents a great foaming capacity but provides unstable foams. So, the objective of this work was to analyze the impact of mixing CMP and a commercial variety of PGA, Kelcoloid O (KO), on the interfacial and foaming properties at pH 7.0. It was determined the surface pressure isotherm, the dynamics of adsorption and the foaming properties for CMP, KO and the mixed system CMP-KO. CMP dominated the surface pressure of CMP-KO mixed system. The presence of KO synergistically improved the viscoelastic properties of surface film. The foaming capacity of CMP was altered by KO. KO foam presented a higher stability than CMP foam and it controlled the stability against drainage and the initial collapse in the mixed foam.
Colloids and surfaces. B, Biointerfaces 03/2012; 95:214-21. · 2.60 Impact Factor
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ABSTRACT: The aim of this work was to study the effect of interactions between casein glycomacropeptide (CMP) and β-lactoglobulin (β-lg) at pH 6.5 and 3.5 on the foaming properties of the mixed systems with different CMP:β-lg ratios. The foaming properties were determined by the bubbling method with a Foamscan instrument. A highest overall foam capacity (OFC), foaming capacity (FC) and mainly stability of mixed foams at pH 3.5, as compared to the mixed foams at pH 6.5 or the foams of CMP and β-lg was observed. At pH 6.5, the stability of mixed foams decreased with increasing the CMP content, while OFC and FC values were similar to β-lg foam. The performance of the mixed systems was discussed in relation with the interactions between CMP and β-lg in the aqueous phase (as observed by dynamic light scattering and differential scanning calorimetry in previous works).
Colloids and surfaces. B, Biointerfaces 09/2011; 89:234-41. · 2.60 Impact Factor
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ABSTRACT: Milk whey proteins (MWP) and pectins (Ps) are biopolymer ingredients commonly used in the manufacture of colloidal food products. Therefore, knowledge of the interfacial characteristics of these biopolymers and their mixtures is very important for the design of food dispersion formulations (foams and/or emulsions). In this paper, we examine the adsorption and surface dilatational behaviour of MWP/Ps systems under conditions in which biopolymers can saturate the air-water interface on their own. Experiments were performed at constant temperature (20 °C), pH 7 and ionic strength 0.05 M. Two MWP samples, β-lactoglobulin (β-LG) and whey protein concentrate (WPC), and two Ps samples, low-methoxyl pectin (LMP) and high-methoxyl pectin (HMP) were evaluated. The contribution of biopolymers (MWP and Ps) to the interfacial properties of mixed systems was evaluated on the basis of their individual surface molecular characteristics. Biopolymer bulk concentration capable of saturating the air-water interface was estimated from surface pressure isotherms. Under conditions of interfacial saturation, dynamic adsorption behaviour (surface pressure and dilatational rheological characteristics) of MWP/Ps systems was discussed from a kinetic point of view, in terms of molecular diffusion, penetration and configurational rearrangement at the air-water interface. The main adsorption mechanism in MWP/LMP mixtures might be the MWP interfacial segregation due to the thermodynamic incompatibility between MWP and LMP (synergistic mechanism); while the interfacial adsorption in MWP/HMP mixtures could be characterized by a competitive mechanism between MWP and HMP at the air-water interface (antagonistic mechanism). The magnitude of these phenomena could be closely related to differences in molecular composition and/or aggregation state of MWP (β-LG and WPC).
Colloids and surfaces. B, Biointerfaces 03/2011; 85(2):306-15. · 2.60 Impact Factor
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ABSTRACT: In this contribution, we present experimental information about the effect of xanthan gum (XG) on the adsorption behaviour of two milk whey protein samples (MWP), beta-lactoglobulin (beta-LG) and whey protein concentrate (WPC), at the air-water interface. The MWP concentration studied corresponded to the protein bulk concentration which is able to saturate the air-water interface (1.0 wt%). Temperature, pH and ionic strength of aqueous systems were kept constant at 20 degrees C, pH 7 and 0.05 M, respectively, while the XG bulk concentration varied in the range 0.00-0.25 wt%. Biopolymer interactions in solution were analyzed by extrinsic fluorescence spectroscopy using 1-anilino-8-naphtalene sulphonic acid (ANS) as a protein fluorescence probe. Interfacial biopolymer interactions were evaluated by dynamic tensiometry and surface dilatational rheology. Adsorption behaviour was discussed from a rheokinetic point of view in terms of molecular diffusion, penetration and conformational rearrangement of adsorbed protein residues at the air-water interface. Differences in the interaction magnitude, both in solution and at the interface vicinity, and in the adsorption rheokinetic parameters were observed in MWP/XG mixed systems depending on the protein type (beta-LG or WPC) and biopolymer relative concentration. beta-LG adsorption in XG presence could be promoted by mechanisms based on biopolymer segregative interactions and thermodynamic incompatibility in the interface vicinity, resulting in better surface and viscoelastic properties. The same mechanism could be responsible of WPC interfacial adsorption in the presence of XG. The interfacial functionality of WPC was improved by the synergistic interactions with XG, although WPC chemical complexity might complicate the elucidation of molecular events that govern adsorption dynamics of WPC/XG mixed systems at the air-water interface.
Colloids and surfaces. B, Biointerfaces 11/2010; 81(1):50-7. · 2.60 Impact Factor
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ABSTRACT: Protein-polysaccharide (PS) interactions find many applications in food engineering and new foam formulations. In this article, we have studied the effect of anionic nonsurface active PSs [sodium alginate (SA) and lambda-carrageenan (λ-C)] in aqueous solution on interfacial and foaming characteristics of milk whey proteins [whey protein concentrate (WPC) and whey protein isolate (WPI)]. Whey protein concentration (1.0% wt), temperature (20°C), pH (7), and ionic strength (0.05 M) of the aqueous media were kept constant, while PS influence was evaluated within a 0.0–1.0% wt concentration range. The dynamic properties (dynamics of adsorption and surface dilatational properties) of WPC/PS and WPI/PS adsorbed films were considered in order to correlate the foaming characteristics of the biopolymer mixed systems. Foaming characteristics of the biopolymer mixed systems depended on the PS relative concentration in the aqueous phase and on the whey protein-PS interactions in solution and at the air–water interface. Dynamic surface properties of the adsorbed films at short adsorption time had a significant effect on foaming capacity. For a particular system, the overall foam destabilization (foam half-life time) and the individual destabilization processes (drainage, disproportionation, and bubble coalescence) depend on the nature of the PS, its relative bulk concentration, and whey protein-PS interactions in the vicinity of the air–water interface. The viscosity of the aqueous phase has an effect on the rate of drainage while the rate of disproportionation/collapse is more dependent on the interfacial characteristics of the adsorbed film. © 2009 American Institute of Chemical Engineers AIChE J, 2010
AIChE Journal 03/2010; 56(4):1107 - 1117. · 2.26 Impact Factor
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ABSTRACT: The aim of this research is to quantify the competitive adsorption of a whey protein concentrate (WPC) and hydroxypropyl-methyl-cellulose (HPMC so called E4M, E50LV and F4M) at the air-water interface by means of dynamic surface tensiometry and Brewster angle microscopy (BAM). These biopolymers are often used together in many food applications. The concentration of both protein and HPMC, and the WPC/HPMC ratio in the aqueous bulk phase were variables, while pH (7), the ionic strength (0.05 M) and temperature (20 degrees C) were kept constant. The differences observed between mixed systems were in accordance with the relative bulk concentration of these biopolymers (C(HPMC) and C(WPC)) and the molecular structure of HPMC. At short adsorption times, the results show that under conditions where both WPC and HPMC could saturate the air-water interface on their own or when C(HPMC) > or = C(WPC), the polysaccharide dominates the surface. At concentrations where none of the biopolymers was able to saturate the interface, a synergistic behavior was observed for HPMC with lower surface activity (E50LV and F4M), while a competitive adsorption was observed for E4M (the HPMC with the highest surface activity). At long-term adsorption the rate of penetration controls the adsorption of mixed components. The results reflect complex competitive/synergistic phenomena under conditions of thermodynamic compatibility or in the presence of a "depletion mechanism". Finally, the order in which the different components reach the interface will influence the surface composition and the film properties.
Journal of Colloid and Interface Science 05/2009; 336(2):485-96. · 3.07 Impact Factor
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ABSTRACT: Caseinoglycomacropeptide (GMP) is a hydrophilic glycopeptide released from milk kappa-casein by chymosin hydrolysis during cheese making. GMP is thought to be a potential ingredient for specific dietary applications with several health benefits. In this study GMP was characterized at the air-water interface and its behaviour was related with the self-assembly of GMP in solution as affected by pH. This GMP self-assembly was investigated by dynamic light scattering and the interfacial properties were determined by tensiometry and surface dilatational measurements at pH 4, 5 and 7. At pH 5 GMP exhibited higher surface pressure at equilibrium than at pH 7. At pH 4 the behaviour was more complex due to self-assembly close to GMP pI. Dynamic measurement showed that the adsorption/penetration rate constant (K(ads)) is facilitated at higher GMP bulk concentrations, while the rate constant of rearrangement (K(r)) decreased at higher GMP concentrations which could be attributed to the existence of a steric restriction due to the higher GMP load at the interface. K(r) was higher at pH 5 because of lower electrostatic interactions close to the pI. The viscoelastic properties showed a complex behaviour due to the existence of protein-protein interactions depending on the GMP concentration, on the pH of the bulk and on the rates of diffusion, adsorption and rearrangement of GMP at the air-water interface.
Colloids and surfaces. B, Biointerfaces 03/2009; 71(2):230-7. · 2.60 Impact Factor
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ABSTRACT: The surface pressure (pi)-area (A) isotherms and Brewster angle microscopy (BAM) images of beta-casein-dioleoyl phosphatidylcholine (DOPC) mixed films spread on buffered water at pH 7 and 9 and at 20 degrees C were determined as a function of the mass fraction of DOPC in the mixture (X(DOPC)). The structural characteristics, miscibility, and topography (morphology and reflectivity) of DOPC-beta-casein mixed films were very dependent on surface pressure and monolayer composition. The structure in DOPC-beta-casein mixed monolayers was liquid-expanded-like, as for pure components. The monolayer structure was more expanded as the pH and the DOPC concentration in the mixture were increased. From the concentration and surface pressure dependence on excess area and elasticity (E) it was deduced that DOPC and beta-casein form a practically immiscible monolayer at the air-water interface. The BAM images and the evolution with the surface pressure of the reflectivity of BAM images give complementary information on the interactions and structural characteristics of DOPC-beta-casein mixed monolayers, which corroborate the conclusions derived from the pi-A isotherm. After the spreading or just after the expansion at pi approximately 0 we have observed the presence of 2D-foams, typical topography of DOPC monolayers at low pi. The 2D-foams disappear after the compression of the monolayer and the topography is homogenous and isotropic. From the reflectivity of BAM images it is possible to distinguish between the coexistence of DOPC and beta-casein or beta-casein displacement by DOPC, depending on the surface pressure. The surface dilatational properties of the mixed films corroborate the coexistence of DOPC and beta-casein at pi lower than the equilibrium spreading pressure (pi(e)) of beta-casein and beta-casein displacement by DOPC at pi>pi(e) of beta-casein. The phenomena observed appear to be generic for protein and polar (monoglycerides) and ionizable (phospholipid) mixed monolayers.
Colloids and surfaces. B, Biointerfaces 12/2008; 69(1):15-25. · 2.60 Impact Factor
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ABSTRACT: The aim of this work was to study the interactions and adsorption of caseinoglycomacropeptide (GMP) and GMP:beta-lactoglobulin (beta-lg) mixed system in the aqueous phase and at the air-water interface. The existence of associative interactions between GMP and beta-lg in the aqueous phase was investigated by dynamic light scattering, differential scanning calorimetry (DSC), fluorometry and native PAGE-electrophoresis. The surface pressure isotherm and the static and dynamic surface pressure were determined by tensiometry and surface dilatational properties. The results showed that GMP presented higher surface activity than beta-lg at a concentration of 4%wt but beta-lg showed higher film forming ability. In the mixed systems beta-lg dominated the static and dynamic surface pressure and the rheological properties of interfacial films suggesting that beta-lg hinders GMP adsorption because, in simple competition, GMP should dominate because of its higher surface activity. The surface predominance of beta-lg can be attributed to binding of GMP to beta-lg in the aqueous phase that prevents GMP adsorption on its own.
Colloids and surfaces. B, Biointerfaces 10/2008; 68(1):39-47. · 2.60 Impact Factor
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ABSTRACT: The manufacture of food dispersions (emulsions and foams) with specific quality attributes depends on the selection of the most appropriate raw materials and processing conditions. These dispersions being thermodynamically unstable require the use of emulsifiers (proteins, lipids, phospholipids, surfactants etc.). Emulsifiers typically coexist in the interfacial layer with specific functions in the processing and properties of the final product. The optimum use of emulsifiers depends on our knowledge of their interfacial physico-chemical characteristics - such as surface activity, amount adsorbed, structure, thickness, topography, ability to desorb (stability), lateral mobility, interactions between adsorbed molecules, ability to change conformation, interfacial rheological properties, etc. -, the kinetics of film formation and other associated physico-chemical properties at fluid interfaces. These monolayers constitute well defined systems for the analysis of food colloids at the micro- and nano-scale level, with several advantages for fundamental studies. In the present review we are concerned with the analysis of physico-chemical properties of emulsifier films at fluid interfaces in relation to foaming. Information about the above properties would be very helpful in the prediction of optimised formulations for food foams. We concluded that at surface pressures lower than that of monolayer saturation the foaming capacity is low, or even zero. A close relationship was observed between foaming capacity and the rate of diffusion of the foaming agent to the air-water interface. However, the foam stability correlates with the properties of the film at long-term adsorption.
Advances in Colloid and Interface Science 09/2008; 140(2):95-113. · 8.12 Impact Factor
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ABSTRACT: In this contribution, we have analyzed the effect of sucrose on dynamic interfacial (dynamic surface pressure and surface dilatational properties) and foaming (foam capacity and foam stability) characteristics of soy globulins (7S and 11S). The protein (at 1 x 10(-3), 1 x 10(-2), 0.1, and 1 wt %) and sucrose (at 0, 0.25, 0.5, and 1.0 M) concentrations in aqueous solution and the pH (at 5 and 7), and ionic strength (at 0.05 and 0.5 M) were analyzed as variables. The temperature was maintained constant at 20 degrees C. We have observed the following. (i) The dynamics of adsorption (presence of a lag period, diffusion, and penetration at the air-water interface) of soy globulins depend on the peculiar molecular features of proteins (7S or 11S soy globulin) and the level of association/dissociation of these proteins by varying the pH and ionic strength, as well as the effect of sucrose in the aqueous phase on the unfolding of the protein. The rate of adsorption increases with the protein concentration in solution, at pH 7 compared to pH 5, at high ionic strength, and in the absence of sucrose. (ii) The surface dilatational properties reflect the fact that soy globulin adsorbed films exhibit viscoelastic behavior. The surface dilatational modulus increases at pH 7 compared to pH 5, but decreases with the addition of sucrose into the aqueous phase. (iii) The rate of adsorption and surface dilatational properties (surface dilatational modulus and phase angle) during adsorption at the air-water interface play an important role in the formation of foams generated from aqueous solutions of soy globulins. (iv) The increased interfacial adsorption (at high surface pressures) and the combined effects of interfacial adsorption and interfacial interactions between adsorbed soy globulin molecules (at high surface dilatational modulus) can explain the higher stability of the foam, with few exceptions.
Journal of Agricultural and Food Chemistry 05/2008; 56(7):2512-21. · 2.82 Impact Factor
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ABSTRACT: The structural and shear characteristics of mixed monolayers formed by an adsorbed Na-caseinate film and a spread monoglyceride (monopalmitin or monoolein) on the previously adsorbed protein film have been analyzed. Measurements of the surface pressure (pi)-area (A) isotherm and surface shear viscosity (eta(s)) were obtained at 20 degrees C and at pH 7 in a modified Wilhelmy-type film balance. The structural and shear characteristics of the mixed films depend on the surface pressure and on the composition of the mixed film. At surface pressures lower than the equilibrium surface pressure of Na-caseinate (at pi<pi(e)(CS)), both Na-caseinate and monoglyceride coexist at the interface, with a structural polymorphism or a liquid expanded structure due to the presence of monopalmitin or monoolein in the mixture, respectively. At higher surface pressures, collapsed Na-caseinate residues may be displaced from the interface by monoglyceride molecules. For a Na-caseinate-monopalmitin mixed film the eta(s) value varies greatly with the surface pressure (or surface density) of the mixed monolayer at the interface. In general, the greater the surface pressure, the greater are the values of eta(s). However, the values of eta(s) for a Na-caseinate-monoolein mixed monolayer are very low and practically do not depend on the surface pressure. The collapsed Na-caseinate residues displaced from the interface by monoglyceride molecules at pi>pi(e)(CS) have important repercussions on the shear characteristics of the mixed films.
Journal of Colloid and Interface Science 09/2007; 313(1):141-51. · 3.07 Impact Factor
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ABSTRACT: In this contribution, we have analyzed the effect of different strategies, such as change of pH (5 or 7) or ionic strength (at 0.05 and 0.5 M), and addition of sucrose (at 1 M) and Tween 20 (at 1 x 10(-4) M) on interfacial characteristics (adsorption, structure, dynamics of adsorption, and surface dilatational properties) and foam properties (foam capacity and stability) of soy globulins (7S and 11S at 0.1 wt %). We have observed that (1) the adsorption (presence of a lag period, diffusion, and penetration at the air-water interface) of soy globulins depends on the modification in the 11S/7S ratio and on the level of association/dissociation of these proteins by varying the pH and ionic strength (I), the effect of sucrose on the unfolding of the protein, and the competitive adsorption between protein and Tween 20 in the aqueous phase. The rate of adsorption increases at pH 7, at high ionic strength, and in the presence of sucrose. (2) The surface dilatational properties reflect the fact that soy globulin adsorbed films exhibit viscoelastic behavior but do not have the capacity to form a gel-like elastic film. The surface dilatational modulus increases at pH 7 and at high ionic strength but decreases with the addition of sucrose or Tween 20 into the aqueous phase. (3) The rate of adsorption and surface dilatational properties (surface dilatational modulus and phase angle) during adsorption at the air-water interface plays an important role in the formation of foams generated from aqueous solutions of soy globulins. However, the dynamic surface pressure and dilatational modulus are not enough to explain the stability of the foam.
Journal of Agricultural and Food Chemistry 08/2007; 55(15):6339-48. · 2.82 Impact Factor
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ABSTRACT: In this work we have used different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial shear rheology), to analyze the static (structure, topography, reflectivity, miscibility, and interactions) and flow characteristics (surface shear characteristics) of milk protein (beta-casein, caseinate, and beta-lactoglobulin) and monoglyceride (monopalmitin and monoolein) mixed films spread and adsorbed on the air-water interface. The structural, topographical, and shear characteristics of the mixed films depend on the surface pressure and on the composition of the mixed film. The surface shear viscosity (eta(s)) varies greatly with the surface pressure (pi). In general, the greater the pi values, the greater were the values of eta(s). Moreover, the eta(s) value is also sensitive to the miscibility and/or displacement of film-forming components at the interface. At surface pressures lower than that for protein collapse, protein and monoglyceride coexist at the air-water interface. At surface pressures higher than that for the protein collapse, a squeezing of collapsed protein domains by monoglycerides was deduced. Near to the collapse point, the mixed film is dominated by the presence of the monoglyceride. Different proteins and monoglycerides show different interfacial structure, topography, and shear viscosity values, confirming the importance of protein and monoglyceride structure in determining the interfacial characteristics (interactions) of mixed films. The values of eta(s) are lower for disordered (beta-casein or caseinate) than for globular (beta-lactoglobulin) proteins and for unsaturated (monoolein) than for saturated (monopalmitin) monoglycerides in the mixed film. The displacement of the protein by the monoglycerides is facilitated under shear conditions.
The Journal of Physical Chemistry B 08/2007; 111(28):8305-13. · 3.70 Impact Factor
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ABSTRACT: In this work we have analyzed the structural, topographical, and shear characteristics of mixed monolayers formed by adsorbed beta-lactoglobulin (beta-lg) and spread monoglyceride (monopalmitin or monoolein) on a previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm, Brewster angle microscopy (BAM), and surface shear characteristics were obtained at 20 degrees C and at pH 7 in a modified Wilhelmy-type film balance. The pi-A isotherm and BAM images deduced for adsorbed beta-lactoglobulin-monoglyceride mixed films at pi lower than the equilibrium surface pressure of beta-lactoglobulin (pi(e)(beta-lg)) indicate that beta-lactoglobulin and monoglyceride coexist at the interface. However, the interactions between protein and monoglyceride are somewhat weak. At higher surface pressures (at pi > or = pi(e)(beta-lg)) a protein displacement by the monoglyceride from the interface takes place. The surface shear viscosity (eta(s)) of mixed films is very sensitive to protein-monoglyceride interactions and displacement as a function of monolayer composition (protein/monoglyceride fraction) and surface pressure. Shear can induce change in the morphology of monoglyceride and beta-lactoglobulin domains, on the one hand, and segregation between domains of the film-forming components on the other hand. In addition, the displacement of beta-lactoglobulin by the monoglycerides is facilitated under shear conditions.
Langmuir 06/2007; 23(13):7178-88. · 4.19 Impact Factor
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ABSTRACT: The dynamic surface pressure (π) and surface viscoelastic properties (surface dilatational modulus, E, its elastic, Ed, and viscous, Ev, components, and loss angle tangent, tan φ) of lipids (diglycerol-monostearate and diglycerol-monolaurate) and proteins (sodium caseinate and β-lactoglobulin) at different concentrations in the aqueous phase were measured using a dynamic drop tensiometer. Temperature, pH, and, ionic strength were maintained constant at 20 °C, 7, and 0.05 M, respectively. The surface dilatational properties depend on the chemistry of the molecule (length of the hydrocarbon chain in lipids and disordered or globular characteristics of the protein). Lipid films are essentially elastic, but protein films are viscoelastic. The values of Ed increase with the emulsifier (lipid or protein) concentration in solution and were higher at the critical micellar concentration (CMC) for lipids or at the adsorption efficiency (AE) for proteins. The values of E reflect not only the amount of emulsifier adsorbed at the interface but also the degree of interaction between adsorbed emulsifier molecules. E increases with the van der Waals interactions between lipid hydrocarbon chains, which are higher for diglycerol-monostearate than for diglycerol-monolaurate. The values of E for caseinate adsorbed films were lower than those for β-lactoglobulin adsorbed films. These differences are due mainly to differences in the looping of amino acid residues for adsorbed films of random coil (caseinate) and globular (β-lactoglobulin) proteins at the air−water interface. The values of E are lower for protein compare to lipid adsorbed films. The role of surface dynamic properties of lipid and protein adsorbed films on foam formation and stabilization is discussed.
03/2007;
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ABSTRACT: The surface pressure (π) at equilibrium (surface pressure isotherm) and surface dynamic properties (dynamic surface pressure and surface dilatational characteristics) of diglycerol ester (diglycerol-monocaprinate, diglycerol-monolaurate, diglycerol-monostearate, and diglycerol-monooleate) and protein (sodium caseinate) as emulsifiers, at different concentrations in the aqueous phase, were measured using tensiometry and a dynamic drop tensiometer, respectively. We have observed that (1) at equilibrium the value of critical micelle concentration (CMC) decreases and the maximum surface excess (Γmax) increases as the hydrocarbon chain increases because the hydrophobic character of the lipid also increases. The presence of a double bond in the hydrocarbon chain also increases the value of CMC and decreases those of Γmax. Caseinate presents higher adsorption efficiency but the surface activity is between those for lipids. The surface pressure isotherm of mixed systems is dependent on the emulsifier concentration and the protein/lipid ratio in the mixture. (2) The adsorption of pure emulsifiers at the air−water interface increases with emulsifier concentration in the aqueous phase via diffusion and penetration of the emulsifier at the interface. For mixed films, the rate of adsorption depends on the concentration and composition of the mixture. Competitive or cooperative phenomena were observed during the adsorption of both emulsifiers at the interface. (3) The surface dilatational characteristics of mixed films are viscoelastic. The surface dilatational modulus reflects the amount of emulsifier adsorbed at the interface and confirms the idea that the protein−lipid interactions at the air−water interface are somewhat weak, there even being the possibility of phase separation.
03/2007;
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ABSTRACT: In this contribution, we have determined the effect of limited enzymatic hydrolysis on the interfacial (dynamics of adsorption and surface dilatational properties) and foaming (foam formation and stabilization) characteristics of a soy globulin (beta-conglycinin, fraction 7S). The degree of hydrolysis (DH = 0, 2, and 5%), the pH of the aqueous solution (pH = 5 and 7), and the protein concentration in solution (at 0.1, 0.5, and 1 wt %) were the variables studied. The temperature and the ionic strength were maintained constant at 20 degrees C and 0.05 M, respectively. The rate of adsorption and surface dilatational properties (surface dilatational modulus, E, and loss angle) of beta-conglycinin at the air-water interface depend on the pH and DH. The adsorption decreased drastically at pH 5.0, close to the isoelectric point of beta-conglycinin, because of the existence of a lag period and a low rate of diffusion. The interfacial characteristics of beta-conglycinin are much improved by enzymatic treatment, especially in the case of acidic aqueous solutions. Hydrolysates with a low DH have improved functional properties (mainly foaming capacity and foam stability), especially at pH values close to the isoelectric point (pI), because the protein is more difficult to convert into a film at fluid interfaces at pH approximately equal to pI.
Journal of Agricultural and Food Chemistry 03/2007; 55(4):1536-45. · 2.82 Impact Factor
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ABSTRACT: In this contribution, we have determined the effect of limited enzymatic hydrolysis on the interfacial (dynamics of adsorption and surface dilatational properties) and foaming (foam formation and stabilization) characteristics of a soy globulin (β-conglycinin, fraction 7S). The degree of hydrolysis (DH = 0, 2, and 5%), the pH of the aqueous solution (pH = 5 and 7), and the protein concentration in solution (at 0.1, 0.5, and 1 wt %) were the variables studied. The temperature and the ionic strength were maintained constant at 20 °C and 0.05 M, respectively. The rate of adsorption and surface dilatational properties (surface dilatational modulus, E, and loss angle) of β-conglycinin at the air−water interface depend on the pH and DH. The adsorption decreased drastically at pH 5.0, close to the isoelectric point of β-conglycinin, because of the existence of a lag period and a low rate of diffusion. The interfacial characteristics of β-conglycinin are much improved by enzymatic treatment, especially in the case of acidic aqueous solutions. Hydrolysates with a low DH have improved functional properties (mainly foaming capacity and foam stability), especially at pH values close to the isoelectric point (pI), because the protein is more difficult to convert into a film at fluid interfaces at pH ≈ pI. Keywords: Food dispersion; foam; emulsifier; soy protein; β-conglycinin; adsorption; surface tension; surface dilatational rheology; air−water interface
01/2007;
