Incorporation of Lepidium perfoliatum seed gum into wheat starch affects its physicochemical, viscoelastic, pasting and freeze-thaw syneresis properties.

This study aimed to investigate the influence of incorporating Lepidium perfoliatum seed gum (LPSG) into wheat starch (WS) at various mixing ratios on its FTIR, DSC, steady and dynamic rheological properties, pasting attributes, syneresis, and particle size distributions characteristics. The interaction between WS and LPSG was purely based on hydrogen-bonding. It was found that the onset (To) and peak (Tp) temperatures of the LPSG-rich mixtures increased by 10 % and 8 %, respectively, while the enthalpy (ΔH) decreased by 70 % compared to WS. A higher LPSG ratio led to a decrease in the frequency dependence of storage modulus (G'), as well as an increase in the pseudoplasticity of the mixtures. The in-shear structural recovery test showed that the rate of recovery (R, %) increased with an increasing LPSG ratio. The pasting results demonstrated that the 9/1 ratio had the highest final viscosity and the lowest relative breakdown. Applying 1 to 5 freeze-thaw cycles resulted in a 50 % to 70 % decrease in syneresis for the 9/1 mixing ratio in comparison to WS, respectively. The incorporation of LPSG into WS resulted in higher static and dynamic magnitudes of yield stress, as well as an increase in particle size when compared to WS.

Sulfate groups position determines the ionic selectivity and syneresis properties of carrageenan systems.

The salt sensitivity and selectivity feature of α-carrageenan (α-Car) were investigated and compared with κ-carrageenan (κ-Car) and iota-carrageenan (ι-Car). These carrageenans are identified by one sulfate group on the 3,6-anhydro-D-galactose (DA) for α-Car, D-galactose (G) for κ-Car and on both carrabiose moieties (G and DA) for ι-Car. The viscosity and temperature, where order-disorder transition have been observed, were greater in presence of CaCl2 for α-Car and ι-Car compared with KCl and NaCl. Conversely, the reactivity of κ-Car systems were greater in presence of KCl than CaCl2. Unlike κ-Car systems, the gelation of α-Car in presence of KCl was observed without syneresis. Thus, the position of sulfate group on the carrabiose determines the importance of counterion valency too. The α-Car could be a good alternative to κ-Car to reduce the syneresis effects.

Helicity degree of carrageenan conformation determines the polysaccharide and water interactions.

The polysaccharide in solution at critical concentration, Cc (g/L), is assimilated to a nano hydrogel (nHG) made of a single polysaccharide chain. Taking as reference the characteristic temperature of 20 ± 2 °C at which kappa-carrageenan (κ-Car) nHG swelling is greater with a Cc = 0.55 ± 0.05 g/L, the temperature of the minimum deswelling in the presence of KCl was found at 30 ± 2 °C for 5 mM with a Cc = 1.15 ± 0.05 g/L but not measurable above 100 °C for 10 mM of which Cc = 1.3 ± 0.05 g/L. Lowering the temperature to 5 °C, contraction of the nHG and further coil-helix transition with self-assembly increases the sample's viscosity, which steadily evolves with time in a logarithmic scale. Accordingly, the relative increment of the viscosity per unit of concentration, Rv (L/g), should increase in agreement with increasing polysaccharide concentration. But the Rv decreases for κ-Car samples above 3.5 ± 0.5 g/L in the presence of 10 mM KCl under steady shear 15 s-1. This reflects a decrease of κ-Car helicity degree knowing that the polysaccharide is rather hydrophilic when its helicity degree is the lowest.

Rheological study of α- and κ-carrageenan expansion in solution as effects of the position of the sulfate group.

The viscosity of carrageenan solutions in the coil state was greater for α-carrageenan (α-Car) compared with that for κ-carrageenan (κ-Car); thus, the impact of one sulfate group on 3,6-anhydro-D-galactose was compared with the impact of one sulfate group on D-galactose units of the carrabiose residues. The thermal expansion coefficient of the solutions, B2 × Tc, characterizes the way the viscosity decreases because of extension of the physical bonds of the systems to their rupture point (Tc) under increasing temperature. The Tc and B2 × Tc of water were equal to (100 ± 5) °C and (1.57 ± 0.05) × 10-2/°C, respectively. The Tc of the α-Car and κ-Car systems increased after the addition of CaCl2 and KCl, respectively, and with increasing polysaccharide concentration. However, the B2 × Tc of the α-Car and κ-Car systems were rather sensitive to CaCl2 and KCl, respectively. In the overall solutions examined, the expansion of α-Car systems was found to be between 1.5 × 10-2/°C and 1.61 × 10-2/°C, greater than the expansion of κ-Car systems, which was between 1.5 × 10-2/°C and 1.2 × 10-2/°C. Thus, α-Car is a good alternative to κ-Car for reducing syneresis phenomena, and its sensitivity as ι-Car to divalent cations would be due to the anhydro cycle.

Study on the impact of temperature, salts, sugars and pH on dilute solution properties of Lepidium perfoliatum seed gum.

The functional properties of food gums are remarkably affected by the quality of solvent/cosolutes and temperature in a food system. In this work, for the first time, the chemical characterizations and dilute solution properties of Lepidium perfoliatum seed gum (LPSG), as an emerging carbohydrate polymer, were investigated. It was found that xylose (14.27%), galacturonic acid (10.70%), arabinose (9.07%) and galactose (8.80%) were the main monosaccharaide components in the LPSG samples. The uronic acid content of LPSG samples was obtained to be 14.83%. The average molecular weight and polydispersity index of LPSG were to be 2.34 × 105 g/mol and 3.3, respectively. As the temperature was increased and the pH was decreased and the concentration of cosolutes (Na+, Ca2+, sucrose and lactose) presented in the LPSG solutions was enhanced, the intrinsic viscosity [η] and coil dimension (R coil , V coil , υ s ) of LPSG molecular chains decreased. Activation energy and chain flexibility of LPSG were estimated to be 0.46 × 107 J/kg.mol and 553.08 K, respectively. The relative stiffness parameter (B) of LPSG in the presence of Ca2+ (0.079) was more than that of Na+ (0.032). Incorporation of LPSG into deionized water (0.2%, w/v) diminished the surface activity from 76.75 mN/m to 75.70 mN/m. Zeta potential (ζ) values (-46.85 mV--19.63 mV) demonstrated that dilute solutions of LPSG had strong anionic nature in the pH range of 3-11. The molecular conformation of LPSG was random coil in all the selected solution conditions. It can be concluded that temperature and presence of cosolutes can significantly influence on the LPSG properties in the dilute systems.

Lower critical concentration temperature as thermodynamic origin of syneresis: Case of kappa-carrageenan solution.

Polysaccharide ubiquity is trimmed for applications of low syneresis impact. This syneresis may be crucial for specific applications that are very sensitive to gel dimension stability, namely, 3D scaffolds for cell culture for disease diagnosis and tissue engineering. We hypothesized that the syneresis origin results from the kappa-carrageenan (kC) polysaccharide thermodynamic instability, and we demonstrated this by measuring the critical (coil-to-coil contact) concentration as a function of temperature. The impact of 5 mM, 10 mM and 15 mM KCl salt on the critical concentration of the solution and the lower critical concentration temperature (LCCT) were particularly investigated. For the kC polysaccharide, the gelation temperature (Tg) falls at temperatures below the LCCT, which explains the shrinking or syneresis reaction of the polysaccharide gels. The gap between Tg and LCCT would be the thermomotive force of the syneresis of many colloidal gels.

Salt-induced gelation of globular protein aggregates: structure and kinetics.

Aggregates of the globular protein beta-lactoglobulin were formed by heating solutions of native proteins at pH 7, after which gels were formed by the addition of salt. The second step does not necessitate elevated temperatures and is therefore often called cold gelation. The structure of the gels was studied during their formation using light scattering and turbidity. Complementary confocal laser scanning microscopy measurements were done. We compared the structure with that of gels formed by heating native beta-lactoglobulin under the same conditions. Whereas in the latter case, microphase separation occurs above 0.2 M NaCl, no microphase separation was observed during cold gelation up to at least 1 M NaCl. The dependence of the kinetics and the final gel structure on the protein concentration, the temperature, the salt concentration, and the aggregate size was quantified. A few measurements on gels formed by adding CaCl(2) confirmed the higher efficiency of this bivalent cation but revealed no qualitative differences with gels formed by adding NaCl.

Influence of osmotic and weight pressure on water release from polysaccharide ionic gels.

Kappa-carrageenan (kC) is a polyelectrolyte biopolymer that forms gels if the kC concentration, the salt and the temperature are adequately chosen. Actually, under certain conditions, kC gels release water in a process called syneresis. In this contribution, the syneresis of gels containing 2g/L of kC has been studied as a function of potassium chloride concentration [KCl]. The syneresis decreases if the [KCl] is increased in the biopolymer solution (sol) before the gelation but increases if the [KCl] is increased after gelation by immersing the gels in KCl solution. The surrounding phase induces an osmotic pressure (Π), which increases if the [KCl] difference between the inside and outside of the gel increases. Swelling has been observed for negative Π. A method that enables the exudate to be removed continuously demonstrated the effect of the strain caused by the gel's own weight on syneresis. Increasing the KCl concentration in the sol promotes syneresis due to strain. The analysis of the syneresis kinetics of different systems has enabled the creation of a pressure-induced syneresis diagram. This diagram will contribute to controlling the mouthfeel of chewing products.

Yield study with the release property of polysaccharide-based physical hydrogels.

Water-release from kappa-Carrageenan (kC) hydrogels (syneresis) has been studied by two experimental methods (1) one in which the exudate is enabled to surround the gel and (2) one in which the exudate is continuously removed from the gel surfaces. The pressures Pg caused by the gel weight decrease from 1Pa for method (1) and 500Pa for method (2). The syneresis of the gels at 2g/L kC with 40mM KCl has been observed to decrease with Pg for the highest pressures. However, for the lowest pressures, the pressure-dependence of the syneresis has not been found, although this gel shrank remarkably. This gel exhibits yielding at approximately 0.15Pa during rheological testing and exhibits creep at stress well below its yield stress. The result is consistent in demonstrating that similar gels in the conditions of method (1) or (2) yield while releasing fluid. The release kinetics have been fitted with a sum of two exponential decay functions, one for shrinkage and the other for yielding. The kinetic rate, k1 for shrinkage, is almost 0.035±0.005h-1 for all of the gels studied, except for very soft and stiff gels; for that of yielding, k2 increases in the range of 0.07-0.33±0.01h-1 when the gel is modulated from soft to stiff.

Influence of elasticity on the syneresis properties of κ-carrageenan gels.

Kappa-carrageenan hydrogels spontaneously release fluid (syneresis) under certain elasticity conditions, which depend on the temperature, the salt concentration in the gel (KCl) and the polysaccharide concentration. Strong and weak gels exhibit notably weak syneresis properties. The maximum syneresis was found at intermediate elasticity where the gel was neither strong nor weak. The variation in the gel composition indicated that the fluid is released according to the thermal retraction coefficient, which depends on the elasticity. Experiments revealed a dynamic equilibrium of the syneresis process where syneresis fluid was not withdrawn. However, once the fluid was removed from the gel surface, the release of solvent starts again if the elasticity is below the compressive pressure in the gel. Therefore, swelling of the gel is suggested as an explanation for the dynamic equilibrium of the syneresis process.