Search

The article examines the effect of anionic non-surface active protein-polysaccharides (PS) on the foaming and interfacial characteristics of milk whey proteins (MWP) and whey protein isolate (WPI). The influence of the PS is evaluated while the ionic strength of the aqueous media is stabilized. The dynamic properties of the adsorbed films of the WPI and MWP are correlated to the foaming characteristics of the biopolymer systems.

Abstract: The foaming and emulsifying characteristics of proteins are important attributes during the production stage, storage, transport, and consumer perception of quality (appearance) of food dispersions (emulsions and foams). In this contribution, we are concerned with the analysis of interfacial, foaming, and emulsifying characteristics of a typical milk protein (sodium caseinate) as a function of protein concentration in aqueous solution (C, % w/w). We have observed that there exists close relationships between foaming (power of foaming, foam capacity, foam density, and foam conductivity) and the rate of diffusion (slope of π vs. t1/2) of caseinate to the air–water interface. The foam stability (quantified by the relaxation time (t) due to drainage and disproportionation/collapse) correlates linearly with the equilibrium surface pressure (πe) of aqueous solutions of caseinate. At surface pressures lower than that of monolayer saturation (at C<1×10-3%, w/w) the foaming is zero. The emulsifying capacity (quantified by the droplet size and the specific surface area) was correlated with the protein concentration in solution (surface pressure at equilibrium). Coalescence was observed only at the lower caseinate concentration in solution (C<0.1%, w/w). As a coherent protein layer (multilayer) saturates the interface, at higher protein concentrations, the emulsion instability is due to flocculation and/or creaming. The coalescence and creaming rates correlate well with the protein concentration in solution (thus with the surface pressure and/or surface dilatational modulus). [Copyright &y& Elsevier]

Abstract: The aim of this work is to perform a comparative study of the long-term relaxation phenomena and surface dilatational characteristics in protein and monoglyceride (monopalmitin, monoolein and monolaurin) mixed monolayers spread at the air–water interface as a function of processing variables (surface composition, surface pressure and temperature) and aqueous phase pH. The study has been centred on a real protein (caseinate), to see if the relaxation phenomena observed in protein–monoglyceride mixed films with a model protein (β-casein) are generic. Different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial dilatational rheology) have been used to analyse the static (structure, reflectivity, miscibility, and interactions) and dynamic characteristics (long-term relaxation phenomena and surface dilatational properties) of protein–monoglyceride mixed films spread on the air–water interface. The static and dynamic characteristics of the mixed films depend on the protein–monoglyceride ratio and the surface pressure. At higher surface pressures, collapsed protein residues may be displaced from the interface by monoglyceride molecules with important repercussions on the interfacial characteristics of the mixed films. From the frequency dependence of the surface dilatational modulus we have deduced the relationships between interfacial dilatational rheology and changes in molecular structure, interactions, miscibility, and relaxation phenomena. [Copyright &y& Elsevier]

Abstract: Monolayer technique has been used successfully to study the properties of mixed emulsifiers spread at the air–water interface. In this contribution we are concerned with the analysis of structural characteristics of mixed monolayers formed by milk proteins (β-casein and β-lactoglobulin) and monoglycerides (monopalmitin and monoolein), and how these differ depending on the method used for the formation of the mixed film at the air–water interface (spreading, penetration or by spreading of a lipid into a previously adsorbed protein film). Measurements of the π-A isotherm were obtained in Langmuir- and Wilhelmy-type film balances coupled with Brewster angle microscopy (BAM). The π-A isotherm deduced for adsorbed β-lactoglobulin monolayer in this work is practically the same as that obtained directly by spreading. However, for β-casein the adsorbed monolayer is more condensed than the spread one. For protein–monoglyceride mixed films, the π-A isotherms for adsorbed and spread monolayers at surface pressure (π) higher than the equilibrium spreading pressure of protein (π e protein) are practically coincident, a phenomenon which may be attributed to protein displacement by the monoglyceride from the interface. At π<π e protein and monoglyceride coexist at the interface and the adsorbed and spread π-A isotherms (monolayer structure) are different. Monopalmitin has a higher capacity than monoolein for the displacement of protein from the air–water interface. However, some degree of interaction exists between proteins and monoglycerides and these interactions are higher for adsorbed than for spread films. The topography of the monolayer corroborates these conclusions. [Copyright &y& Elsevier]

Abstract: In this contribution we present a systematic comparison of the two major fractions of globulin from a soy protein isolate (β-conglycinin and glycinin, including the chemical reduction of glycinin with dithiothreitol (DTT)) and typical milk proteins (β-casein, caseinate, and WPI). The comparison is centred on the most important functional properties of spread and adsorbed protein films at the air–water interface (such as adsorption, structural, topographical, and dynamic characteristics), as a function of the aqueous phase pH and the protein concentration in the bulk phase and at interface. A combination of surface techniques (tensiometry, surface film balance, Brewster angle microscopy and surface dilatational rheology) was used in this study. A notable feature of soy proteins is the strong pH dependence of the molecular conformation and the associated functional properties, such as surface activity, film structure, surface dilatational viscoelasticity, and especially, the rate of adsorption at a fluid interface. Optimum functionality occurs at pH<5, which limits the application of soy globulins as food ingredients. In this respect the behaviour of milk and soy proteins is quite different. [Copyright &y& Elsevier]

In the present work we have studied the characteristics of propylene glycol alginates (PGA) adsorption at the air–water interface and the viscoelastic properties of the films in relation to its foaming properties. To evaluate the effect of the degree of PGA esterification and viscosity, different commercial samples were studied—Kelcoloid O (KO), Kelcoloid LVF (KLVF) and Manucol ester (MAN). The temperature (20 °C) and pH (7.0) were maintained constant. For time-dependent surface pressure measurements and surface dilatational properties of adsorbed PGA at the air–water interface an automatic drop tensiometer was used. The foam was generated by whipping and then the foam capacity and stability was determined. The results reveal a significant interfacial activity for PGA due to the hydrophobic character of the propylene glycol groups. The kinetics of adsorption at the air–water interface can be monitored by the diffusion and penetration of PGA at the interface. The adsorbed PGA film showed a high viscoelasticity. The surface dilatational modulus depends on the PGA and its concentration in the aqueous phase. Foam capacity of PGA solutions increased in the order KO > MAN > KLVF, which followed the increase in surface pressure and the decrease in the viscosities of PGA solutions. The stability of PGA foams monitored by the drainage rate and collapse time follows the order MAN > KLVF > KO. The foam stability depends on the combined effect of molecular weight/degree of esterification of PGA, solution viscosity and viscoelasticity of the adsorbed PGA film. [Copyright &y& Elsevier]

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)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

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)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

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.

In this work we have analyzed the penetration of betalactoglobulin into a monoglyceride monolayer (monopalmitin or monoolein) spread at the air-water interface and its effects on the structural, dilatational, and topographical characteristics of mixed films. Dynamic tensiometry, surface film balance, Brewster angle microscopy (BAM), and surface dilatational rheology have been used, maintaining the temperature constant at 20 degrees C and the pH and ionic strength at 7 and 0.05 M, respectively. The initial surface pressure (mN/m) of the spread monoglyceride monolayer (pii(MONOGLYCERIDE)) at 10, 20, and the collapse point is the variable studied. Beta-lactoglobulin can penetrate into a spread monoglyceride monolayer at every surface pressure. The penetration of beta-lactoglobulin into the monoglyceride monolayer with a more condensed structure, at the collapse point of the monoglyceride, requires monoglyceride molecular loss by collapse and/or desorption. However, the structural, topographical, and dilatational characteristics of monoglyceride penetrated by beta-lactoglobulin mixed monolayers are essentially dominated by the presence of monoglyceride (either monopalmitin or monoolein) in the mixed film. In fact, monoglyceride molecules have the capacity to re-enter the monolayer after expansion and recompression of the mixed monolayer. Thus, monoglyceride molecular loss by collapse and/or desorption is reversible. The topography of the monolayer under dynamic conditions corroborates these conclusions.

In this contribution we are concerned with the study of structure, topography, and surface rheological characteristics under shear conditions of monoglyceride (monopalmitin and monoolein) and milk protein (beta-casein, kappa-casein, caseinate, and WPI) spread monolayers at the air-water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy: BAM) techniques have been applied in this study to pure emulsifiers (proteins and monoglycerides) spread at the air-water interface. To study the shear characteristics of spread films, a homemade canal viscometer was used. The experiments have demonstrated the sensitivity of the surface shear viscosity (eta(s)) of protein and monoglyceride films at the air-water interface, as a function of surface pressure (or surface density). The surface shear viscosity was higher for proteins than for monoglycerides. In addition, eta(s) was higher for the globular WPI than for disordered beta-casein and caseinate due to the strong forces acting on spread globular proteins. This technique makes it possible to distinguish between beta-casein and caseinate spread films, with the higher eta(s) values for the later due to the presence of kappa-casein. The eta(s) value varies greatly with the surface pressure (or surface density). In general, the greater the surface pressure, the greater the values of eta(s). Finally, the eta(s) value is also sensitive to the monolayer structure, as was observed for monoglycerides with a rich structural polymorphism (i.e., monopalmitin).

In this work we have analyzed the structural and topographical characteristics of mixed monolayers formed by an adsorbed whey protein isolate (WPI) and a spread monoglyceride monolayer (monopalmitin or monoolein) on the previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm were obtained at 20 degrees C and at pH 7 for protein-adsorbed films from water in a Wilhelmy-type film balance. Since the surface concentration (1/A) is actually unknown for the adsorbed monolayer, the values were derived by assuming that the A values for adsorbed and spread monolayers were equal at the collapse point of the mixed film. The pi-A isotherm deduced for adsorbed WPI monolayer in this work is practically the same as that obtained directly by spreading. For WPI-monoglyceride mixed films, the pi-A isotherms for adsorbed and spread monolayers at pi higher than the equilibrium surface pressure of WPI are practically coincident, a phenomenon which may be attributed to the protein displacement by the monoglyceride from the interface. At lower surface pressures, WPI and monoglyceride coexist at the interface and the adsorbed and spread pi-A isotherms (i.e., the monolayer structure of the mixed films) are different. Monopalmitin has a higher capacity than monoolein for the displacement of protein from the air-water interface. However, some degree of interactions exists between proteins and monoglycerides and these interactions are higher for adsorbed than for spread films. The topography of the monolayer corroborates these conclusions.