Cold-set whey protein–flaxseed gum gels induced by mono or divalent salt addition

Mixed cold-set whey protein isolate (WPI)–flaxseed gum (FG) gels, induced by the addition of CaCl₂ or NaCl at fixed ionic strength (150 mM), were evaluated with respect to their mechanical properties, water-holding capacity (WHC) and SEM microscopy. They were prepared by mixing FG and thermally denatured (90 °C/30 min) WPI solutions at room temperature, but the gels were formed at 10 °C using two methods of salt incorporation: diffusion through dialysis membranes and direct addition. The mixed systems formed using dialysis membranes showed phase separation with the development of two (axial) layers, and the CaCl₂-induced gels presented radial phase separation. In general the CaCl₂-induced gels were less discontinuous, stronger, and showing lower WHC and deformability than the NaCl-induced gels. An increase in the FG concentration reduced the gel strength and WHC for both systems, which was associated with a prevailing phase separation between the biopolymers over the gelation process. Using direct salt addition, apparently none of the mixed gels showed macroscopic phase separation, but the NaCl-induced gels showed much higher hardness and elasticity than the CaCl₂-induced gels. Since the gelation process occurred more quickly by direct salt addition, and more effectively for the divalent salts, the more fragile structure of the CaCl₂-induced gels was a consequence of disruption of the cross-link interactions of the aggregates during the agitation used to homogenize the salt added.     

Calcium-alginate microparticles for sustained release of catechin prepared via an emulsion gelation technique

Catechin-loaded Ca-alginate beads and microparticles were prepared by an emulsion gelation method using sunflower oil for efficient sustained release of catechin. The emulsion was prepared by sequential mixing of alginate, oil, and oleic acid ester as an emulsifier. Encapsulation efficiency (EE) and inhibition of catechin release of the beads were significantly increased approximately to 453.83 and 148.71% by the emulsion gelation technique, respectively (p<0.05). For the microparticles, the highest inhibition of catechin release after 1 h of incubation (78.82%) was observed at the microparticles prepared by 5% (w/w) oil, 3% (w/w) alginate, 4% (w/v) CaCl₂, and 200 mg catechin with the most hydrophilic emulsifier, decaglycerol mono-ester. Moreover, the catechin release was sustained at acidic conditions and increased with increase in pH of release medium. These results suggest that catechin encapsulation within Ca-alginate particles by emulsion gelation method can be an effective delivery system for catechin.     

Gelation behaviour of gelatin and alginate mixtures

Mixtures of alginate and gelatin were studied by rheology as a function of different parameters, such as temperature, biopolymer concentrations, calcium concentration and ionic strength. In particular conditions, the formation of a mixed gel of alginate and gelatin is obtained. A slow release of calcium ions leads first to an irreversible alginate gel and cooling results in a reversible gelatin gel. Depending on experimental conditions, non-linear behaviours upon gelation of alginate occur and a collapse of alginate gel is directly observable by rheology. These trends are favoured between 35 and 45 °C, by a high total biopolymer concentration or a high calcium concentration and ionic strength. Different mechanisms could be responsible for this collapse, such as a competition between alginate gelation and phase separation in the biopolymer mixture or an over-association of alginate chains at high Ca²⁺ concentration, favoured by the presence of gelatin.     

Similarities and differences between alginic acid gels and ionically crosslinked alginate gels

A Na-alginate solution can, under given conditions, undergo a sol–gel transition at pH below pKa for the uronides. These gels are presumably stabilised by intermolecular hydrogen bonds. This paper summarises the effect of alginate variables such as chemical composition and sequence and molecular weight on mechanical properties and network fine structure. Alginic acid gels resemble ionically crosslinked alginate gels in the sense that guluronic acid blocks are the building elements of most importance with respect to gel formation. The main difference is that mannuronic acid blocks, although with less efficiency compared polyguluronate, also support alginic acid gel formation. With the exception strictly alternating alginates made by treating mannuronan with the AlgE4 epimerase, the so-called alternating (random) sequence of the alginate molecule seems to destabilise alginic acid gel formation due to its lack of repeating structure. Small Angle X-ray Scattering (SAXS) reveal a scattering intensity for alginic acid gels being typically and order of magnitude higher than Ca-alginate gels, suggesting junction zones composed of random aggregates with a high degree of multiplicity. A molecular understanding of alginic acid gels is of importance in the general understanding of polyuronides at low pH as well as for the utilisation of alginates in drug delivery systems.     

Factors Affecting the Gelation Properties of Hydrolyzed Sunflower Proteins

The effects of temperature and several chemicals on gelation time and strength of gels formed by heating (pH 8) 5% solutions of trypsin hydrolyzed sunflower proteins were studied by dynamic rheological methods. The storage modulus reached a maximum at 80°C. Ca₂Cl (and NaCl at > 0.2M) accelerated gelation and weakened the gel. NaCOCH₃Na₂SO₄ and NaSCN decreased the storage modulus. Urea decreased gelstrength and at high concentrations slowed gelation. Time for gelation diminished and gel strength increased with increasing mercaptoethanol concentration up to 0.1M. Propylene glycol at 5–20% concentrations accelerated gelation and at 5% also increased gel strength. Trypsin hydrolyzed sunflower proteins could be useful in products requiring strong gels at high temperatures.     

The effects of sodium alginate and calcium levels on pea proteins cold-set gelation

A multi-scale investigation of pea proteins – alginate cold-set gels was proposed in this study. The gel preparation followed a two-steps procedure. Globular pea proteins were first denatured and aggregated by a pre-heating step. Sodium alginate was then added at different concentrations. Thereafter the in situ gelation process was induced at 20 °C using glucono-δ-lactone (GDL) and two calcium carbonate (CC) levels; calcium cations were released as the pH decreased. Small-amplitude rheology measurements (storage modulus G′) showed that stronger mixed gels were obtained than single-biopolymer solutions. Confocal laser scanning microscopy (CLSM) revealed phase-separating microstructures of mixed gels, foremost owing to biopolymers incompatibility. Phase separation was kinetically entrapped by gelation at different evolution stages. According to the co-occurrence method and microstructure classification, image texture analysis disclosed that a continuous protein network dispersing small gelled alginate microdomains corresponded to the strongest mixed gels. Transmission electron microscopy (TEM) evidenced that during gelation, the pre-aggregated proteins were mainly associated into large agglomerates with no peculiar pattern. Higher cohesiveness between both networks was hypothesized, since protein agglomerates could expose “anchoring points” for alginate chains. Depending on both protein – alginate initial composition and calcium availability, non-specific inter-biopolymer cross-links via calcium were assumed to be the key factor of synergism within mixed gels.     

Acid-induced gelation of whey protein polymers: effects of pH and calcium concentration during polymerization

Heating whey protein dispersions (90°C for 15 min) at low ionic strength and pH values far from isoelectric point (pH>6.5) induced the formation of soluble polymers. The effect of mineral environment during heating on the hydrodynamic characteristics and acid-induced gelation properties of polymers was studied. Whey protein dispersions (80 g/l) were denatured at different pH (6.5–8.5) and calcium concentrations (0–4 mm) according to a factorial design. At pH 6.5, the hydrodynamic radius of protein polymers increased with increasing calcium concentration, while the opposite trend was observed at pH 8.5. Intrinsic viscosity results suggested that heating conditions altered the shape of protein polymers. Whey protein polymers were acidified to pH 4.6 with glucono-δ-lactone and formed opaque particulate gels. The storage modulus and firmness of gels were both affected by conditions used to prepare protein polymers. As a general trend, polymers with high intrinsic viscosity produced stronger gels, suggesting a relationship between polymer shape and gel strength.Acid gelation properties of whey protein polymers makes them suitable ingredients for yoghurt applications. Using whey protein polymers to standardize protein content increased yoghurt viscosity to 813 Pa.s while using skim milk powder at same protein concentration increased yoghurt viscosity to 393 Pa.s. Water holding capacity of protein polymers in yoghurt was 19.8 ml/g compared to 7.2 ml/g for skim milk powder protein. Acid gelation properties of whey protein polymers are modulated by calcium concentration and heating pH and offers new alternatives to control the texture of fermented dairy products.     

Characteristics of enzymatically-deesterified pectin gels produced in the presence of monovalent ionic salts

Pectin methylesterases (PMEs) from Valencia orange (p-PME) and Aspergillus aculeatus (f-PME) were used to produce pectin gels in the presence of 0.2 M monovalent ionic salts. At pH 5.0, pectin gels were induced following enzymatic deesterification of high methoxy pectin, with greater deesterification observed using p-PME compared to f-PME. Under these conditions, the deesterification limit of f-PME ended up with a pectin of DE 30.5–31.9 which did not gel at the PME reaction completion, while p-PME reduced the pectin's DE to 16.0–17.2, resulting in gel formation. The pectin gel induced by KCl was significantly stronger than the NaCl-induced gel, but LiCl did not induce pectin gelation. The gel strength was influenced by both DE and species of monovalent cation. The KCl-induced gels released less water than NaCl-induced gels. A synergistic effect on gel strength was observed from the pectin treated with a combination of (p + f)-PMEs, producing even more stable gels. These results indicated that the pectin gelation of our system would be enhanced both by using larger monovalent cation and by lowering the DE value, which would presumably be attributed to the different action patterns recognized for p- and f-PMEs. This pectin gelation system could provide a useful alternative to acid-sugar or calcium cross-linked gels in food and other industrial applications.     

Characterization of cold-set gels produced from heated emulsions stabilized by whey protein

This paper reports the cold gelation of preheated emulsions stabilized by whey protein, in contrast to, in previous reports, the cold gelation of emulsions formed with preheated whey protein polymers. Emulsions formed with different concentrations of whey protein isolate (WPI) and milk fat were heated at 90 °C for 30 min at low ionic strength and neutral pH. The stable preheated emulsions formed gels through acidification or the addition of CaCl₂ at room temperature. The storage modulus (G′) of the acid-induced gels increased with increasing preheat temperature, decreasing size of the emulsion droplets and increasing fat content. The adsorbed protein denatures and aggregates at the surface of the emulsion droplets during heat treatment, providing the initial step for subsequent formation of the cold-set emulsion gels, suggesting that these preheated emulsion droplets coated by whey protein constitute the structural units responsible for the three-dimensional gel network.     

Effects of molecular weight and elastic segment flexibility on syneresis in Ca-alginate gels

Syneresis in Ca-alginate gels was studied as a function of the alginate molecular weight and the degree of flexibility of the elastic segments. Small angle X-ray scattering of alginate gels reveals an increased lateral association of junction zones when entering a Ca²⁺ regime giving syneresis. This suggests growth of junction zones to be the primary driving force for syneresis. Ca-alginate gels prepared from alginates with different molecular weights show a reduced syneresis with decreasing M_w. A reduced syneresis is also observed when fractions of a high M_w alginate is replaced by short alginate molecules enriched in guluronate residues. The effect of altering the monomer sequence of the elastic segments spanning the junction zones was studied by converting poly-mannuronate regions to alternating guluronate/mannuronate sequences by the mannuronan C5-epimerase AlgE4. This epimerisation reaction gives a more flexible elastic segment. The epimerased alginates yielded gels with larger syneresis compared to the non-epimerased, native alginate samples. Thus, both molecular weight and elastic segment flexibility are needed in a molecular model for describing syneretic behaviour in alginate gels. These parameters will to a large extent determine to which degree the non-equilibrium nature of the alginate gel is macroscopically expressed (syneresis).     

Encapsulationof lycopene from watermelon in calcium‐alginate microparticles using an optimised inverse‐gelation method by response surface methodology

Lycopene exhibits strong antioxidant activity due to its unsaturated molecular bonds, which also contributes to its susceptibility for degradation. Encapsulation techniques can reduce lycopene degradation, increasing its potential applications in functional foods and nutraceuticals. The objective of this study was to optimise the encapsulation of lycopene from watermelon in alginate microparticles using the inverse gelation method. Box–Behnken design was used for the optimisation of three variables: concentrations of alginate (w/v %) and CaCl₂ (g L^?1), and gelation time (min). Two types of alginate were investigated (low viscosity and high viscosity) and optimised separately using encapsulation efficiency and loading capacity as responses. Results indicated that the models had a good fit to the experimental data and the optimal conditions varied depending on the type of alginate. In general, particles prepared with low‐viscosity alginate exhibited higher encapsulation efficiency and loading capacity and could be used for further research.     

Gel Properties of Whey Protein Concentrates as Influenced by Ionized Calcium

Ionic calcium in four whey protein concentrates (WPC) was decreased using sodium tripolyphosphate (NaTPP) or ethylenediamine tetraacetic acid (EDTA) and effects on gel properties were determined. Total calcium ranged from 0.22–0.41 g/100g WPC and ionic calcium 2.98–47.25 mg/100g protein. Hardness was maximized and expressible moisture (EM) minimized in three WPC gels with 10 mM NaTPP. EDTA had a similar effect on one WPC gel. Addition of 10 mM NaTPP decreased ionic calcium to 5.23–10.31 mg/100g protein. NaTPP or CaCl₂ did not improve hardness or EM of one WPC gel which contained the lowest total and ionized calcium. Chelating agents were effective in improving gel properties of WPC containing higher than optimal calcium.     

The influence of gelation rate on the physical properties/structure of salt-induced gels of soy protein isolate–gellan gum

The cold-set gelation of soy protein isolate (SPI)-gellan gum was induced by the addition of salts (KCl or CaCl₂) using two different procedures: the direct addition of salts (fast gelation) or the diffusion of salts through a membrane (slow gelation). The mechanical properties, syneresis and microstructure of the mixed gels were evaluated, as well as for gellan and SPI gels. The mixed gels induced by calcium diffusion were stronger and more deformable than gels induced by the direct addition of calcium, while the opposite occurred for potassium-induced gels. All the mixed gels were macroscopically homogeneous, but at the microscopic level two independent networks could be observed. These two separate networks were more evident for the calcium-induced gels, and the structural characteristics depended strongly on the concentration of the protein and the polysaccharide. However an organized microstructure with the formation of microtubes surrounded by other network was only observed for the mixed gels induced by calcium diffusion at the higher protein/polysaccharide (10:1) ratio. Thus besides the composition and concentration of the biopolymers, the results showed that the type of salt and its velocity of incorporation led to gels with different structures and consequently different mechanical properties.     

Rheological investigation of alginate chain interactions induced by concentrating calcium cations

Chain interactions of sodium alginate during its gelation were investigated by a new gelation method which was based on a Ca²⁺-concentrating gelling process (CCGP) produced by water evaporation of an alginate solution containing CaCl₂. For two commercially available sodium alginate samples (low viscosity (LA) and medium viscosity (MA)) having different molecular weight distributions but the same G/M blocks, the critical Ca²⁺ concentrations for their gelation were found to be 4.6 (for LA) and 4.5 (for MA) μmol/mL after evaporating water from 1% of alginate solutions containing 4 μmol/mL of CaCl₂. The CCGP gelation method for alginate under the above conditions were confirmed by rheological measurements and the observed highly ordered and uniform mesh structure of the CCGP-formed alginate gels shown in cryo-SEM images. Combinations of LA and MA at different ratios (0:4, 1:3, 2:2, 3:1, 4:0 on weight basis) were studied using the CCGP gelation method to further the understanding of the alginate chain interactions during gelation. Different LA/MA mixtures exhibited different rheological properties in either non-gelled or gelled systems, indicating that the molecular weight distributions of the sodium alginates influence the alginate chain interactions mediated by Ca²⁺. Thus, an appropriate combination of LA and MA is required for a strong alginate interchain interaction during CCGP, and alginate products with desirable characteristics can be produced by manipulating the mixing ratios of sodium alginates having different molecular weight distributions even at the same total composition and distribution of G/M blocks.     

鹰嘴豆分离蛋白的胶凝性

研究了蛋白质浓度、pH、NaCl及CaCl2对鹰嘴豆分离蛋白胶凝性的影响。pH3.0、无盐加入时,蛋白质分散液以溶液状存在;pH3.0、0.1mol/LNaCl与pH7.0、高离子强度(NaCl:0.5～1.0mol/L)条件下,蛋白质分散液表现出半溶液状性质。pH3.0、高离子强度(NaCl:0.5～1.0mol/L)与pH7.0、低离子强度(NaCl:0～0.1mol/L)条件下,蛋白质分散液以凝胶状存在。pH3.0、NaCl浓度0.5～1.0mol/L与pH7.0、NaCl浓度0～0.1mol/L时具有相似的胶凝动力学。CaCl2对蛋白质的胶凝性影响与NaCl基本相同。pH3.0时,CaCl2的浓度为0.1和0.3mol/L时的凝胶强度分别为24和26.4g;NaCl浓度为0.1、0.5、1.0mol/L时的凝胶强度分别为7.6、8.4和9.3g。     

Gel properties,physicochemical properties,and sensory attributes of white leg shrimp (Litopenaeus vannamei) surimi gel treated with sodium chloride (NaCl) substitutes

This study investigated the effects of different NaCl substitutes on the gel properties, physicochemical properties, and sensory attributes of shrimp surimi gel to produce high-quality reduced-salt shrimp surimi gel. The results showed that CaCl₂, calcium ascorbate (Vc-Ca), and L-arginine (L-Arg) could significantly improve the gel strength and texture of shrimp surimi gel compared to NaCl. The addition of CaCl₂, Vc-Ca, and L-Arg significantly increased the number of disulphide bonds and the content of β-sheet structures compared to NaCl. The electrophoretic analysis revealed that CaCl₂, Vc-Ca, and L-Arg had protective effects on the myosin heavy chain during thermal gelation. Additionally, CaCl₂ and L-Arg promoted the cross-linking of myofibrillar proteins to form the denser and less porous microstructures, and thus improved the gel properties of shrimp surimi gel. In general, the introduction of L-Arg as a substitute for NaCl acquired the best gel properties and sensory attributes of shrimp surimi gels, followed by CaCl₂ and Vc-Ca.     

Effects of CaCl<Subscript>2</Subscript> on chemical interactions and gel properties of surimi gels from two species of carps

Effects of CaCl₂ on chemical interactions, textural properties and expressible moisture content of suwari and kamaboko gels from yellowcheek carp and grass carp were investigated. And the correlations between the contents of chemical interactions and physical properties of surimi gels were analyzed. The contents of chemical interactions, especially non-disulfide covalent bonds, disulfide bonds and hydrophobic interactions of suwari and kamaboko gels, varied with addition concentration of CaCl₂ and fish species. Suwari and kamaboko gels from yellowcheek carp exhibited higher breaking force, deformation and gel strength than these from grass carp. Surimi gels (suwari and kamaboko gels) from yellowcheek carp and grass carp exhibited their maximum gel strength when 40 mmol/kg and 100 mmol/kg CaCl₂ was added, respectively. Addition of CaCl₂ at high concentration resulted in low water holding capacity of surimi gels. Correlation analysis indicated that the contents of nonspecific associations, ionic bonds, hydrophobic interactions and sulfhydryl groups exhibited significant correlation with breaking force of surimi gels from yellowcheek carp and grass carp. Additionally, the content of non-disulfide covalent bonds had significant positive correlations with breaking force and expressible moisture of surimi gel from yellowcheek carp.     

Water-Holding Capacity in Hard-to-Cook Beans (Phaseolus vulgaris): Effect of pH and Ionic Strength

The effect of pH and ionic strength (IS) of soaking solution on the water holding capacity (WHC) of hard-to-cook (HTC) and control black beans (Phaseolus vulgaris) was evaluated. Beans were soaked 18 hr in solutions covering the pH range 1–7 at constant IS (1.0 M) or in solutions ranging in IS from 0.01 to 1.3M (prepared with either NaCl or CaCl₂) at pH 7. WHC was significantly reduced in the pH range 3.5 to 5.1 in control beans but the effect was not as pronounced with HTC samples which had a lower WHC at each pH. Solutions prepared with NaCl produced significantly lower WHC values than CaCl₂ solutions in the control but not in the HTC beans. WHC values in control beans tended to increase with higher IS, although this effect was not as apparent for HTC beans.     

Control of temperature dependence of microbial time–temperature integrator (TTI) by microencapsulation of lactic acid bacteria into microbeads with different proportions of alginate

This study has been conducted to investigate the temperature dependence and mass transfer kinetics of a microbial time–temperature integrator (TTI) developed by using emulsification/internal ionotropic gelation method. We report the effect of the Na-alginate concentrations (0.5%, 2.0%, 4.0% and 6.0% w/v) and temperature (8, 15, 20, 25 and 30 °C) on the TTI responses (changes in pH and titratable acidity [TA]). Results revealed that Ca-alginate microbeads (Ca-AMs) prepared from 2.0% Na-alginate were more uniform and smaller, with a narrow size distribution, in comparison with the other Ca-AMs. For microbeads with above 2.0% Na-alginate, the TTI response rates decreased because of the lower diffusion efficiency. Linearity in the TA was greatest for the 2.0% Ca-AMs. Therefore, the mass transfer and TTI response kinetics data demonstrated that 2.0% Na-alginate was optimal for producing Ca-AMs from which an ideal microbial TTI could be developed to monitor food spoilage processes with accuracy and precision.     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.