Gérard Cuvelier

Effects of carrageenan type on the behaviour of carrageenan/milk mixtures

Abstract The apparent hydrodynamic diameter of casein micelles was determined as a function of hydrocolloid concentration at 60°C and during cooling to 20°C. The systems studied contained skim milk 100-fold diluted in permeate in the presence of either lambda-, iota-, kappa-carrageenan or guar gum. These measurements show that all three forms of carrageenan adsorb onto casein micelles, whereas guar gum does not. Lambda-carrageenan (which is always in the coil conformation) adsorbs at all the temperatures studied, whereas the iota and kappa forms adsorb only at temperatures below the onset of the helix–coil transition. The results agree with the idea that adsorption of carrageenan occurs only above a certain minimum charge density. Phase diagrams were established at 60°C for the three carrageenans and the rheological behaviour was followed on cooling and at 25°C. The results suggest that the lambda-carrageenan bridges the casein micelles at low carrageenan concentrations, leading to the sedimentation of carrageenan/milk mixtures at 60°C and structure formation on cooling. At 60°C, iota- and kappa-carrageenan induce depletion flocculation of casein micelles above a critical carrageenan concentration. On cooling, systems containing iota-carrageenan clearly form a network at the helix–coil transition temperature. The network is formed by mixed carrageenan/casein micelle crosslinks. In the presence of excess carrageenan, this network is reinforced by carrageenan/carrageenan crosslinks. For the kappa-carrageenan/casein micelle mixtures the existence of mixed carrageenan/casein micelle crosslinks is less obvious but seems likely.

Viscosity of locust bean, guar and xanthan gum solutions in the Newtonian domain: a critical examination of the log (ηsp)o-log c[η]o master curves

The viscosity in the low shear rate Newtonian domain of three biopolymers, locust bean gum, guar gum and xanthan gum was studied as a function of temperature and of polymer concentration in various aqueous solvents. The intrinsic viscosities [η]o of both galactomannans are not modified in the presence of 10 or 40% sucrose. In this case, a master curve relating the Newtonian specific viscosity (ηsp)o, to the reduced concentration c[η]o is obtained and allows (in good agreement with theoretical conjectures), two critical concentrations C∗ and C∗∗ to be defined, from which the value of the expansion coefficient α may be estimated. For xanthan, as expected for a polyelectrolyte, [η]o depends strongly on salt concentration and on added sucrose and the results did not obey the above-mentioned master curve. However, it is shown that (ηsp)o depends only on xanthan concentration when C > C∗∗, and then it is assumed that chain dimensions have attained their unperturbed values whatever the solvent. Considering that both types of chains, random coils (galactomannans) and semi-rigid (xanthan) should give the same (ηsp)o-C[η]o master curve for C > C∗∗ when [η]o is replaced by its unperturbed counterpart [η]θ, a method for estimating [η]θ for the xanthan sample is proposed. In conclusion, the numerous exceptions to the widely accepted (ηsp)o vs C[η]o “universal” behaviour are mainly ascribed to significant differences in expansion coefficient values which depend on both the polymer and the solvent.

Xanthan/locust bean gum interactions at room temperature

Abstract Rheological and ultracentrifugation studies have been conducted on heated and unheated mixtures of xanthan with whole locust bean gum, and temperature fractions of the latter possessing different mannose: galactose ratios. The results suggest that xanthan and galactomannans may interact by two distinct mechanisms. One takes place at room temperature, gives weak elastic gels, and has little dependence upon the galactose content of the galactomannan, whilst the second requires significant heating of the polysaccharide mixture, gives stronger gels, and is highly dependent upon galactomannan composition. The results are discussed with reference to existing models proposed for the xanthan/galactomannan interaction.

Casein micelle/iota carrageenan interactions in milk: influence of temperature

Abstract The behaviour of iota carrageenan/skim milk mixtures was studied at 60°C and on cooling. At 60°C, iota carrageenan flocculates casein micelles by depletion. Comparison of the gelling properties of iota carrageenan in skim milk and permeate during cooling and heating shows that the presence of micelles increases the gelation temperature, the gel rigidity, and the gel melting temperature. These observations lead to the hypothesis that a double network is formed. It is suggested that the first is because of casein micelles bridged by adsorbed carrageenan. This network is responsible for the differences in properties between gels in permeate and skim milk. The second network requires a minimum carrageenan concentration and has properties very similar to those of an iota carrageenan gel in permeate. The apparent micelle size was determined as a function of temperature in milk 100-fold diluted in permeate in the presence of iota carrageenan or guar gum. These measurements confirm the existence of a specific attractive interaction between carrageenan and casein micelles. The interaction seems to require a certain charge density on the polymer. An attractive interaction between casein micelles and iota carrageenan only occurs when the latter is at least partially in the more densely charged helical form.

Gelation and flocculation of casein micelle/carrageenan mixtures

The specific attractive interaction between carrageenan and casein micelles is widely exploited in the dairy industry to tailor the texture of dairy desserts. However, in industrial practice it has been observed that the addition of carrageenan can cause casein micelles to sediment rapidly when the mixture is above the gelation temperature. To better understand this undesirable phenomenon, carrageenan/skim milk mixtures have been observed over a wide range of compositions at 65 and 25°C. Interactions occurred for iota, kappa and lambda carrageenan at both temperatures. At 65°C sedimentation was observed when the carrageenan concentration was above 0.2%. At 25°C either phase separation or gelation could occur. Depletion flocculation is suggested as a partial explanation for these observations. The effects of casein micelles on the viscoelastic properties of iota carrageenan have been measured in the absence of flocculation. Their presence decreases carrageenan s gelation concentration and increases both the gelation temperature and the elastic modulus.

Heat-induced gelation of porcine blood plasma proteins as affected by pH.

Porcine plasma is a by-product of the meat industry that can be used as a food ingredient. It is a protein mixture, hence its composition can be modified to meet specific functionality requirements. In the present paper, the gelation properties of plasma and its two major fractions (serum and albumin) have been studied at pH 4.5, 6.0 and 7.5. Polyacrylamide gel electrophoresis (SDS-PAGE) revealed that albumin was the constituent that remained soluble to a larger extent during heat-treatments, and that acidic coagulation occurred at pH 4.5, making weak interactions the predominating ones between protein aggregates. Differential scanning calorimetry (DSC) and rheological tests showed that both the thermal stability and the gelation point of protein solutions were lower as pH decreased. The textural properties and water-holding capacities of plasma and albumin gels were more pH-dependent than serum. Albumin gels were the weakest and those of plasma at pH 7.5, the strongest. It has been determined that interactions between protein fractions play a key role in the gelling properties due to synergistic effects. This knowledge should be useful in the engineering of a plasma derivative product designed for specific food requirements, by reformulating its natural composition and enhanced by controlling pH.

Study of the compatibility/incompatibility of gelatin/iota-carrageenan/water mixtures

The incompatibility of acid gelatin/iota-carrageenan mixtures has been studied. Both these biopolymers undergo a conformational coil-helix transition under suitable conditions of temperature and salt. The aim of this work was to study the concentration at which mixtures are incompatible and the influence of pH, salt and temperature on the phase diagram. Incompatibility occurred over a wide range of concentrations for mixtures prepared in deionized water. Compatibility was increased by increasing the pH or the salt concentration. Temperature did not greatly influence the size of the incompatible region. This is in agreement with the hypothesis that attractive electrostatic interactions lead to associative phase separation (traditionally called complex coacervation).

Iota-carrageenan/casein micelles interactions: evidence at different scales

Abstract The effect of temperature on the behaviour of iota-carrageenan (CI) 0.1 wt.%/casein micelles (CM) 0–5 wt.% mixtures has been studied using three techniques: confocal laser scanning microscopy (CLSM), differential scanning calorimetry (DSC) and spectrophotometry. The microscopy clearly shows that those mixed systems separate in two phases, one being enriched in CM. It has been shown that the CM concentration seems to have an effect on the extent of the phase separation phenomenon. The DSC experiments show that addition of CM modifies the helix to coil transition temperature of carrageenan. The enthalpy of melting of helices decreases as the CM concentration increases, and the peak is shifted towards higher temperature. Local electrostatic interactions between carrageenan chains and CM have been studied by a spectrophotometric method using methylene blue (MB) properties of absorption. The absorption spectra of MB in presence of CI and CM were compared with the one of MB in presence of carrageenan alone at temperatures above and below the carrageenan coil to helix transition. The modifications of the spectrum by addition of CM are discussed in terms of interactions and rigidification of the carrageenan chains.

Viscoelastic properties of ι-carrageenan/gelatin mixtures

Abstract The storage ( G ′) and loss ( G ′) moduli of transparent mixtures of ι-carrageenan and gelatin have been measured during gelation and melting and compared with those of gelatin and ι-carrageenan systems alone. The moduli of the mixtures were always higher than the sum of those of their components alone. Gelatin and ι-carrageenan seem to reinforce each other. Three specific temperature domains can be distinguished, delimited by the melting and helix-coil transition temperatures of gelatin and ι-carrageenan. An interpretation based on conformational changes and an attractive electrostatic interaction between the two biopolymers is suggested. The temperature dependence of G ′ and G ″ for mixtures has been studied as a function of thermal history (time and temperature of gel ageing), sodium chloride concentration and molecular weight of the ι-carrageenan.

Gelatin/iota-carrageenan interactions in non-gelling conditions

The negatively charged polysaccharide, iota-carrageenan has been mixed with two types of gelatin (PS and LH) which differ by their pI, about 9 and 4.5, respectively. At pH 7, gelatin PS chains have a net positive charge and gelatin LH chains have a net negative charge. Phase diagrams in non-gelling conditions (60°C) and pH 7 have been established in both 25 and 100 mM NaCl. The iota-carrageenan/gelatin PS phase diagrams are typical of systems involving attractive interactions leading to the formation of complexes: both polymers are mostly in the lower phase and increasing salt concentration leads to a reduction of the phase separated domain. The iota-carrageenan/gelatin LH mixture shows a very different behavior. No macroscopic bulk phase separation is observed. However, an increase in the turbidity measured by spectrophotometry is observed for certain compositions which would indicate microscopic phase separation. From the limit between the turbid and transparent concentration domains, the binodal may be drawn. Considering the negative net charge of gelatin LH chains at pH 7, repulsive interactions were expected to govern the phase separation. However, in this case too, by increasing salt concentration the phase-separated domain is reduced, where an increase would have been expected for thermodynamic incompatibility. By following the evolution of the absorption spectrum of a methylene blue/iota-carrageenan/gelatin LH mixture as a function of the salt concentration, it has been shown that gelatin LH chains associate with carrageenan ones in low salt conditions up to 200 mM NaCl.