The addition of calcium chloride in combination with a lower draining pH to change the microstructure and improve fat retention in Cheddar cheese

Calcium chloride addition and the whey draining pH are known to impact on cheese making. The effect of 100 or 300 mg kg⁻¹ calcium chloride (CaCl₂) and the whey draining pH (6.2 or 6.0) on the microstructure of Cheddar cheese was assessed using confocal and cryo scanning electron microscopy. The gel made with 300 mg kg⁻¹ CaCl₂ was found to have a denser protein network and smaller pores than the gel with lower or no CaCl₂ addition. CaCl₂ addition reduced fat lost to the sweet whey. The texture of the cheeses with a lower draining pH was harder and moisture content lower. Our results show that the combination of calcium addition and lower draining pH could be used to increase network formation at the early stages of cheese making to improve fat retention while maintaining a similar level of total calcium in the final cheese.     

Gelation of gellan – A review

Gellan is an anionic extracellular bacterial polysaccharide discovered in 1978. Acyl groups present in the native polymer are removed by alkaline hydrolysis in normal commercial production, giving the charged tetrasaccharide repeating sequence: → 3)-β-d-Glcp-(1 → 4)-β-d-GlcpA-(1 → 4)-β-d-Glcp-(1 → 4)-α-l-Rhap-(1 →. Deacylated gellan converts on cooling from disordered coils to 3-fold double helices. The coil–helix transition temperature (T_m) is raised by salt in the way expected from polyelectrolyte theory: equivalent molar concentrations of different monovalent cations (Group I and Me₄N⁺) cause the same increase in T_m; there is also no selectivity between different divalent (Group II) cations, but divalent cations cause greater elevation of T_m than monovalent. Cations present as counterions to the charged groups of the polymer have the same effect as those introduced by addition of salt. Increasing polymer concentration raises T_m because of the consequent increase in concentration of the counterions, but the concentration of polymer chains themselves does not affect T_m. Gelation occurs by aggregation of double helices. Aggregation stabilises the helices to temperatures higher than those at which they form on cooling, giving thermal hysteresis between gelation and melting. Melting of aggregated and non-aggregated helices can be seen as separate thermal and rheological processes. Reduction in pH promotes aggregation and gelation by decreasing the negative charge on the polymer and thus decreasing electrostatic repulsion between the helices. Group I cations decrease repulsion by binding to the helices in specific coordination sites around the carboxylate groups of the polymer. Strength of binding increases with increasing ionic size (Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺); the extent of aggregation and effectiveness in promoting gel formation increase in the same order. Me₄N⁺ cations, which cannot form coordination complexes, act solely by non-specific screening of electrostatic repulsion, and give gels only at very high concentration (above ∼0.6 M). At low concentrations of monovalent cations, ordered gellan behaves like a normal polymer solution; as salt concentration is increased there is then a region where fluid “weak gels” are formed, before the cation concentration becomes sufficient to give true, self-supporting gels. Aggregation and consequent gelation with Group II cations occurs by direct site-binding of the divalent ions between gellan double helices. High concentrations of salt or acid cause excessive aggregation, with consequent reduction in gel strength. Maximum strength with divalent cations comes at about stoichiometric equivalence to the gellan carboxylate groups. Much higher concentrations of monovalent cations are required to attain maximum gel strength. The content of divalent cations in commercial gellan is normally sufficient to give cohesive gels at polymer concentrations down to ∼0.15 wt %. Gellan gels are very brittle, and have excellent flavour release. The networks are dynamic: gellan gels release polymer chains when immersed in water and show substantial recovery from mechanical disruption or expulsion of water by slow compression. High concentrations of sugar (∼70 wt % and above) inhibit aggregation and give sparingly-crosslinked networks which vitrify on cooling. Gellan forms coupled networks with konjac glucomannan and tamarind xyloglucan, phase-separated networks with kappa carrageenan and calcium alginate, interpenetrating networks with agarose and gelling maltodextrin, and complex coacervates with gelatin under acidic conditions. Native gellan carries acetyl and l-glyceryl groups at, respectively, O(6) and O(2) of the 3-linked glucose residue in the tetrasaccharide repeat unit. The presence of these substituents does not change the overall double helix structure, but has profound effects on gelation. l-Glyceryl groups stabilise the double helix by forming additional hydrogen bonds within and between the two strands, giving higher gelation temperatures, but abolish the binding site for metal ions by changing the orientation of the adjacent glucuronate residue and its carboxyl group. The consequent loss of cation-mediated aggregation reduces gel strength and brittleness, and eliminates thermal hysteresis. Aggregation is further inhibited by acetyl groups located on the periphery of the double helix. Gellan with a high content of residual acyl groups is available commercially as “high acyl gellan”. Mixtures of high acyl and deacylated gellan form interpenetrating networks, with no double helices incorporating strands of both types. Gellan has numerous existing and potential practical applications in food, cosmetics, toiletries, pharmaceuticals and microbiology.     

Effects of Ca++, Mg++ and Na+ on Heat Aggregation of Whey Protein Concentrates

Effect of Ca⁺⁺ on the heat aggregation of whey protein concentrates (WPC) was compared with that of Na⁺ and Mg⁺⁺. On the alkaline side of the isoelectric zone, aggregation of WPC was increased by the addition of CaCl₂, MgCl₂ or NaCl, among which CaCl₂ showed the greatest effect. The denaturation temperature of WPC determined by differential scanning calorimetry significantly decreased in the presence of CaCl₂ or MgCl₂, but increased slightly in the presence of NaCl. In the electrophoretic patterns of heated WPC, the most sensitive protein to Ca⁺⁺ was β-lactoglobulin.     

Compression resistance,sweetener's diffusion and sweetness of hydrocolloids gels

The effects of the type and concentration of two hydrocolloids—κ-carrageenan and gellan gum—and of the type and concentration of two sweeteners—sucrose and aspartame—on the gel resistance to compression, on the sweetener diffusion and on the intensity of the gel sweetness and the relationships between the gel physical properties and their perceived sweetness were studied. The gels true rupture stress increased with hydrocolloid concentration, this increase being higher for gellan gels. Gellan gels showed lower true rupture strain values, which in contrast with carrageenan gels, decreased on increasing hydrocolloid concentration. The addition of sucrose produced a bigger increase in gel strength at the higher hydrocolloid concentration. The main effect detected on the sweeteners’ diffusion constant was the higher value observed in low concentration (3 g L⁻¹) κ-carrageenan gels. Gellan gels were perceived as sweeter than κ-carrageenan gels. The decrease in sweetness due to an increase in hydrocolloid concentration was greater in gellan than in carrageenan gels. Variations in sweetener concentration, true rupture strain, and deformability modulus values explained 93% of the variability in sweetness for gels with sucrose and 94% for gels with aspartame.     

Influence of sucrose on cold gelation of heat‐denatured whey protein isolate

A solution of heat‐denatured whey proteins was prepared by heating 100 g kg⁻¹ whey protein isolate (WPI) at pH 7.0 to 75 °C for 15 min in the absence of salt. Heat treatment caused the globular protein molecules to unfold, but electrostatic repulsion opposed strong protein–protein aggregation and so prevented gel formation. When the heat‐denatured whey protein solution was cooled to room temperature and mixed with 15 mM CaCl₂, it formed a gel. We investigated the influence of the presence of sucrose in the protein solutions prior to CaCl₂ addition on the gelation rate. At relatively low concentrations (0–100 g kg⁻¹), sucrose decreased the gelation rate, presumably because sucrose increased the aqueous phase viscosity. At higher concentrations (100–300 g kg⁻¹), sucrose decreased the gelation rate, probably because sugar competes for the water of hydration and therefore increases the attraction between proteins. These data have important implications for the application of cold‐setting WPI ingredients in sweetened food products such as desserts. © 2000 Society of Chemical Industry     

Effect of temperature on the dielectric properties of low acyl gellan gel

Gellan gum is an increasingly popular and a naturally occurring hydrocolloid. It is widely used in the food, chemical, and pharmaceutical industries as a stabilizer, emulsifier, thickener, and gelling agent. The gel is also used as a model material to study microwave heating dynamics of biological materials in the food processing industry. In this study, baseline data on dielectric properties of 1% gellan gel containing 0.17% and 0.3% CaCl₂ were collected at frequencies between 0.2 and 20 GHz and temperatures between 10 and 100 °C. These data are compared with those of distilled water containing similar ionic concentrations. Models describing the behavior of the dielectric constant, loss factor, loss tangent and the penetration depth for 0.2–3.2 GHz were developed. These models can be effectively used in microwave food processing applications of gellan gel, which will save considerable time and effort often used in empirically determining the dielectric spectra.     

Protein and Salt Effects on Ca2+-Induced Cold Gelation of Whey Protein Isolate

Increasing whey protein concentration (from 6 to 10% w/v) decreased gel opacity but increased gel strength and water-holding capacity (WHC). Increasing CaCl₂, concentration (from 5 to 150 mM) increased gel opacity and gel strength at the high protein concentration (i.e., 10%). However, it lowered gel strength at protein concentration > 10%. Young's modulus and distance to fracture values indicated that gels were most rigid at 30 mM CaCl₂, at which point the extent of aggregation (measured by turbidity) was the highest. Increasing CaCl₂ concentration from 5 to 150 mM slightly affected the WHC of Ca²⁺-induced gels. Protein concentration was the major factor in determining fracture properties and WHC.     

Mechanical and physical properties of calcium-treated gellan films

The physicochemical properties of Ca²⁺-treated gellan films plasticized with glycerol were investigated as a function of CaCl₂ concentration (0–20%, w/w) in an aqueous soaking solution. Films were examined based on their mechanical properties, water vapor permeability (WVP), swelling index (SI), thickness and opacity. The SI was lower for Ca²⁺-treated films relative to a control, however, above 13% (w/w) CaCl₂ no differences in SI were found. At 13% (w/w) CaCl₂, tensile and puncture strengths reached a maximum. Tensile elongation, puncture deformation, film thickness and WVP were lower for CaCl₂-treated films than untreated, however, all increased with CaCl₂ concentration. Opacity of gellan films increased with the Ca²⁺-treatment relative to the untreated film, however declined as CaCl₂ concentration increased. In general, Ca²⁺-treated gellan films were stronger, acted as better water vapor barriers, swelled less when in contact with water, and became less pliable and transparent.     

Water holding capacity of sodium-reduced chicken breast myofibrillar protein gel as affected by combined CaCl2 and high-pressure processing

The water holding capacity (WHC) of sodium-reduced (0.3 m sodium chloride, corresponding to the salt percentage (w/v) of 1.755%) myofibrillar protein (MP) gel in response to combined calcium chloride (CaCl₂, 20, 60, 100 mm ) and high-pressure processing (HPP, 200 MPa, 10 min) was investigated. The results showed that 200 MPa + 20 mm CaCl₂ synergistically increased the WHC of MP gel via reducing particle size of MP solutions, strengthening hydrogen-bonding and disulphide-bonding, promoting formation of β-sheet and uncoiling of α-helix, exposing tryptophan residues, enhancing hydrophobic interactions of aliphatic residues and forming a compact and continuous networked gel structure. However, high concentrations (≥60 mm ) of CaCl₂ could attenuate the enhancing effects of HPP on the WHC by inducing decreased hydrogen bonds, fewer tryptophan residues exposed and coarser and aggregated gel structures with large cavities. Therefore, a combined moderate HPP and low concentration of CaCl₂ is a potential alternative for developing sodium-reduced meat products.     

Calcium and chitosan-mediated clustering of whey protein particles for tuning their colloidal stability and flow behaviour

Whey protein microgel (WPM) particles were prepared by heating whey protein dispersions (40 mg mL⁻¹) at pH 5.8 and 80 °C for 15 min. Supplementation with 5 mm CaCl₂ at pH 6.0 increased the hydrodynamic diameter of WPMs, but did not influence the ζ-potential of the particles. The latter was attributed to clustering of WPMs by Ca²⁺ bridges. Supplementing WPM suspension with chitosan (0.5 mg mL⁻¹) at pH 5.0 caused formation of micron-sized clusters and a progressive increase in suspension viscosity over the subsequent 48 h. The latter was ascribed to development of a complexed lattice that inhibited sedimentation of WPMs. Immediately after chitosan supplementation, the WPM suspension changed from Newtonian to shear-thinning fluid. Fourier transform infra-red spectroscopy results suggested that microgelation proceeded by formation of inter-molecular β-sheets and loss of α-helix structure. It also indicated that chitosan may interact with WPMs at pH 6.0 through its acetyl groups.     

高酰基结冷胶对乳清分离蛋白热诱导凝胶特性的影响

蛋白质-多糖凝胶具有良好的稳定性和机械强度,在稳定和传递生物活性物质、营养强化剂方面的应用前景广阔。该研究以乳清分离蛋白、高酰基结冷胶为原料制备热诱导混合凝胶,分析高酰基结冷胶对乳清分离蛋白-高酰基结冷胶混合凝胶的凝胶强度、保水性及显微结构等,揭示乳清蛋白-高酰基结冷胶凝胶形成机理。结果表明,高酰基结冷胶促使蛋白质巯基暴露从而使凝胶形成稳定结构,提高混合凝胶的凝胶强度和保水性,且随着高酰基结冷胶含量增加而显著增大,其质量浓度为4 g/L时,复合凝胶的凝胶强度最大,为26.97 g;保水性最好,为97.41%;透光率最低,为1.87%。温度扫描结果表明,增加高酰基结冷胶可以提高乳清分离蛋白的相转变温度,傅里叶红外光谱显示,乳清分离蛋白与高酰基结冷胶存在分子间作用力,扫描电子显微镜表明高酰基结冷胶诱导混合凝胶形成结构紧密的三维网络结构。该研究为拓展乳清分离蛋白和结冷胶的新型凝胶食品,提高传统食品的质量,改善食品的加工工艺提供基础理论数据。     

Impact of divalent salts and bovine gelatin on gel properties of phosphorylated gelatin from the skin of unicorn leatherjacket

The impact of zinc chloride (ZnCl₂) and calcium chloride (CaCl₂) as well as bovine gelatin (BG) on the gel strength of phosphorylated fish gelatin (PFG) from the skin of unicorn leatherjacket was investigated. The gel strength of PFG increased with increasing concentrations of ZnCl₂ and CaCl₂ (2.5–40 μmol L⁻¹). A higher gel strength was observed with CaCl₂, compared with ZnCl₂. The gel strength of PFG with 20 μmol L⁻¹ CaCl₂ increased by 15.7%, compared to the control gel. Nevertheless, at higher concentration (40 μmol L⁻¹) of both salts, gel strength of PFG decreased. Hardness of gels decreased with increasing PFG content (P < 0.05). Nevertheless, no differences in hardness were found amongst gels with BG/PFG ratios of 4:0 and 3:1 (P ≥ 0.05). Thus, PFG could be used in combination with CaCl₂ to substitute for BG at a level of 25%.     

The effect of calcium chloride addition on the microstructure and composition of Cheddar cheese

The addition of calcium is widely accepted as a tool in cheese-making but the effect on the microstructure of cheese during and following manufacture is not known. In this study, cheeses made with milk containing 200–600 mg L⁻¹ of additional CaCl₂ had significantly lower fat loss into the whey collected after cooking; however, the final fat composition or yield of cheese did not change. The microstructure of the gel with 300 or 600 mg L⁻¹ CaCl₂ addition was less porous and the cooked curd consisted of a denser protein network that may retain more fat during the early stages of manufacture. In contrast, the cheddared curd and cheese contained more micro-pores than cheeses with lower or no calcium addition. Such micro-pores could possibly be the channels by which fat escaped during pressing. This study shows that calcium addition altered the microstructure and pattern of fat loss during Cheddar manufacture.     

Influence of NaCl and CaCl2 on Cold-Set Gelation of Heat-denatured Whey Protein

Heat‐denatured whey‐protein isolate (HD‐WPI) solutions were prepared by heating a 10 wt% WPI solution (pH 7) to 80 °C for 10 min and then cooling it back to 30 °C. Cold‐set gelation was initiated by adding either NaCl (0 to 400 mM) or CaCl₂ (0 to 15 mM). Both salts increased the turbidity and rigidity of the HD‐WPI solutions. Gelation rate and final gel strength increased with salt concentration and were greater for CaCl₂ than NaCl at the same concentration because the former is more effective at screening electrostatic interactions and can form salt bridges.     

Rheological properties and structure of inulin–whey protein gels

The rheological properties, structure and synergistic interactions of whey proteins (1–7%) and inulin (20% and 35%) were studied. Gelation of whey proteins was induced with Na⁺. Inulin was dissolved in preheated whey protein solutions (80 °C, 30 min). Inulin gel formation was strongly affected by whey proteins. The presence of whey proteins at a level allowing for protein gel network formation (7%) significantly increased the G′ and G″ values of the gels. Scanning electron micrographs showed a thick structure for the mixed gel. Whey proteins at low concentrations (1–4%) were not able to form a gel; further, these low concentrations partly or wholly impaired formation of a firm inulin gel. Although interactions between inulin and whey proteins may be concluded from hydrophobicity measurements, the use of an electrophoretic technique did not show any inulin–whey protein complexes.     

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.     

Influence of the Maillard reaction on the properties of cold-set whey protein and maltodextrin binary gels

The Maillard conjugation of proteins and reducing saccharides is used to modify the technological functionality of whey proteins. In this study, whey protein isolate (WPI) was conjugated with maltodextrin (at 1:1 ratio and two total solid contents of 100 and 200 mg mL⁻¹) through the Maillard reaction and used to form cold-set gels. The glycation reaction increased the strength of hydrogen bonding of whey proteins and preferentially modified α-lactalbumin, in comparison with β-lactoglobulin. It also increased the reducing power of binary protein-saccharide solution and allowed formation of self-standing cold-set WPI gel at a low protein content (i.e., ≈50 mg mL⁻¹). Microscopic imaging showed micro-phase separated maltodextrin domains, interrupting the protein network, in gels made of protein-maltodextrin physical mixtures, whereas Maillard conjugation resulted in more homogenous microstructures at both total solid contents. The Maillard reaction increased gel firmness and water-holding capacity and caused a reduction in the extent of gel swelling.     

Characterizations of fish gelatin films added with gellan and κ-carrageenan

Fish gelatin is known to be inferior to mammalian gelatins. Gellan and κ-carrageenan were added to improve properties of the fish gelatin films. Initially, polysaccharides were added to make fish gelatin gels, and tested for the melting point. Mechanical, barrier, color and microstructure properties, as well as Fourier transform infrared (FTIR) and thermal analysis (DSC) of the modified fish gelatin films were evaluated. The addition of gellan and κ-carrageenan increased the melting point of fish gelatin gels, gellan being more effective. Polysaccharides modified fish gelatin films by increasing tensile strength and barrier against water vapor, but made films slightly darker. Scanning electron microscopy (SEM) microstructure analysis revealed that gellan eliminated cracks present in the film matrix resulting in a more uniform structure. FTIR and DSC analyses showed that both polysaccharides effectively interacted with fish gelatin, and moreover, gellan being more effective. Overall, addition of gellan up to 2 g/100 g of gelatin performed better in enhancing fish gelatin films properties.     

Influence of pH and CaCl2 on the stability of dilute whey protein stabilized emulsions

The influence of pH and CaCl₂ on the physical stability of dilute oil-in-water emulsions stabilized by whey protein isolate has been studied. The particle size, zeta potential and creaming stability of 0.05 wt% soy bean oil-in-water emulsions (d ≈ 0.53 μm) were measured with varying pH (3 to 7) and CaCl₂ concentration (0 to 20 μM). In the absence of CaCl₂ extensive droplet aggregation occurred around the isoelectric point of the whey proteins (4 < pH < 6) because of their low electrical charge, which led to creaming instability. Droplet aggregation occurred at higher pH when CaCl₂ was added to the emulsions. The minimum concentration of CaCl₂ required to promote aggregation increased as the pH increased. Aggregation was induced in the presence of CaCl₂ probably because of the reduction in electrostatic repulsion between droplets, caused by binding of counter ions to droplet surfaces and electrostatic screening effects.     

Effect of CaCl2 on 2 heat-induced whey protein concentrate fibrillation pathways: Spontaneous and nuclear induction

Amyloid fibrils have many excellent functional properties that facilitate their applications in the food industry. There are 2 pathways for whey protein concentrate (WPC) to form amyloid fibril aggregates: spontaneous pathway and nuclear induction pathway. Low ionic strength is a necessary condition for the spontaneous pathway to proceed successfully. In this paper, the effect of salt ions on 2 WPC fibrillation pathways was investigated by adding CaCl₂. The results demonstrated WPC fibrils were unable to form normally through spontaneous pathway as adding CaCl₂; but still could form through nuclear induction pathway with 20 to 30 mM CaCl₂, the nuclei accelerated the fibrillation process led to the resistance to the disordered aggregation brought by CaCl₂. Moreover, divalent cations (Ca²⁺, Mg²⁺) had much stronger effects than monovalent cations (Na⁺) on fibril formation, and the results of X-ray photoelectron spectrum together with Fourier-transform infrared spectroscopy suggested that Ca²⁺ had a greater effect on the fibril formation than Cl^?.