Gelation Properties of Lipid-Reduced, and Calcium-Reduced Whey Protein Concentrates

Gels made from six experimental whey protein concentrate (WPC) processes using chemical pretreatment, ultrafiltration and microfiltration (MF) of Swiss cheese whey, and three commercial WPC, were compared for rheological, microstructural and sensory properties. Based on relations between shear stress (ST) and total sulfhydryl levels, we contirmed that disulfide bonding is important in gelation. Other components, i.e., lipids, lactose, calcium and sodium, interacting simultaneously, affected gel formation. Gel water holding capacity (WHC) was related to microstructure but not to ST. WHC was useful to characterize the 3-dimensional gel structure formations. Light microscopy showed the strongest gel had a fine-stranded, solvent-retaining structure.     

Gelation of Commercial Whey Protein Concentrates: Effect of Removal of Low-Molecular-Weight Components

Low-molecular-weight solutes were removed from reconstituted, commercial whey protein concentrate (WPC) and isolate (WPI) by centrifugal gel filtration. Effects on gelation properties were investigated as a function of pH, protein concentration, and mineral ion addition by least concentration endpoint (LCE) and uniaxial compression testing. Partial removal of low-molecular-weight solutes had little effect on WPC and WPI gelation. Lowest LCE values were obtained at pH 6, 0.2M ion addition, and with KC1 and CaCl₂ addition. Highest gel firmness (shear stress and strain) values were at pH 6 and 7.5, and at 0.1M ion addition. WPI functioned better than WPC by both test procedures.     

Gelation of Calcium-Reduced and Lipid-Reduced Whey Protein Concentrates as Affected by Total and Ionic Mineral Concentrations

Rheological and microstructural properties of five dialyzed whey protein concentrate (WPC) gels were investigated. Maximum WPC gel hardness as determined by shear stress (ST) was observed at 2.7–4.5 mM Ca and 0.6–1.1 mM Ca²⁺ concentrations with a Ca ionization of 20–25%. Gel cohesiveness by shear strain (SN) correlated with total lipid and phospholipid (PLP) concentrations and percent of lipid unsaturation. Microstructural characteristics of the gels, as determined by light microscopy (LM), confirmed their water holding capacity (WHC) and rheological properties.     

Interactive Effects of Factors Affecting Gelation of Whey Proteins

The individual effects of heating time (15–120 min), pH (3–9) and NaCl (0–2M), sucrose (0–30% w/v) and protein (10–30% w/v) concentrations on the strength, turbidity and water holding capacity were investigated on a commercial whey protein concentrate (WPC, 75% protein) when heated at temperatures ranging from 65 to 90°C. Interactive effects were investigated using a four-variable, five-level central composite rotatable design (CCRD) analyzed by response surface methodology (RSM). Gel strength (GS) and water holding capacity (WHC) increased with protein concentration, heating temperature and time. Increasing sucrose concentration decreased GS but increased WHC. Increasing NaCl concentration increased GS and WHC below pH 5 but resulted in weaker gels at high pH (>7).     

离子强度和温度对乳清蛋白凝胶的影响

本实验主要研究凝胶温度和CaCl2 浓度对乳清蛋白冷凝胶的影响。结果表明：较低的凝胶温度和增加CaCl2浓度能够致使乳清蛋白形成清亮的凝胶;在0、10、20℃凝胶温度条件下,增加CaCl2 浓度使得凝胶硬度有所增加;乳清蛋白凝胶的持水性在凝胶温度为0、10℃,CaCl2 浓度为20、40mmol/L 时受到影响;除了0℃ 和20mmol/LCaCl2 条件下,低温能够使乳清蛋白形成较高的凝胶硬度和持水性。凝胶温度和CaCl2 浓度是影响乳清蛋白冷凝胶的关键因素。     

Foaming and Emulsifying Properties of Whey Protein Concentrates As Affected by Lipid Composition

Freeze-dried WPC, containing 35 and 75% protein were manufactured by pretreating whey with calcium chloride and heat. These and commercial WPC were subjected to proximate analysis and lipid classes, phospholipid classes, free fatty acids (FFA), and monoacylglycerols (MAG) composition were determined. Solubility, thermal, foaming, and emulsifying properties of the WPC were studied. Pretreatment increased calcium and phosphorus contents and decreased the contents of all other minerals. The pretreatment had no effect on solubility, denaturation enthalpy, and onset temperature of denaturation of WPC. These values were comparable to those of commercial WPC. Foaming capacity and emulsion stability were unaffected, but foam stability increased and emulsifying capacity decreased due to pretreatment. Overall, total lipids and lipid class contents of experimental WPC were too low to affect surface properties of WPC.     

Insolubilized Whey Protein Concentrate and/or Chicken Salt-Soluble Protein Gel Properties

Properties of gels prepared from five whey protein concentrates (WPC) with protein solubilities ranging from 27.5% to 98.1% in 0.1M NaCl, pH 7.0, chicken breast salt-soluble protein (SSP), or a combination of SSP and WPC at pH 6.0, 7.0 or 8.0 were compared. WPC did not form gels when heated to 65°C. SSP gels heated to 65°C were harder than those heated to 90°C at all pHs and hardness decreased as pH was increased. Hardness of combination gels heated to 65°C increased as WPC solubility decreased at all pHs; however, the opposite trend was observed at 90°C. Combination gels of the same WPC solubility at 65°C were more deformable than those heated to 90°C.     

Foaming Properties of Lipid-Reduced and Calcium-Reduced Whey Protein Concentrates

The ability of whey protein concentrates (WPC) to form highly expanded and stable foams is critical for food applications such as whipped toppings and meringue-type products. The foaming properties were studied on six experimental and three commercial WPC, manufactured by membrane fractionation processes to contain reduced lipids and calcium. Lipid-reduced WPC had excellent foaming properties. Experimental delipidized WPC MF 0.45 and commercial delipidized WPC E had higher (P < 0.05) foam expansion than egg white protein (EWP). However. WPC B made bv low-pH UF and isoelectric orecinitation did not form a foam. Lipids and ash were the main factors affecting foaming properties.     

Emulsifying Properties of Lipid-Reduced, and Calcium-Reduced Whey Protein Concentrates

Emulsifying properties of six experimental and three commercial control, lipid-reduced, and calcium-reduced whey protein concentrates (WPC) were evaluated on the basis of mean droplet size and creaming intensity in model emulsions. Mean droplet sizes ranged from 225 to 395 nm. Model emulsions made with a commercial control (WPC F), experimental lipid-reduced (WPC MF. 1, MF. 45), commercial lipid-reduced (WPC E), and experimental calcium and lipid-reduced (WPC B) samples had low stabilities. Emulsion stabilities of the WPC most strongly correlated with protein solubility and fatty acid compositions, but did not correlate with mean droplet size.     

Protease-Induced Aggregation and Gelation of Whey Proteins

Aggregation and gelation of whey proteins induced by a specific protease from Bacillus licheniformis was revealed by turbidimetry, size exclusion chromatography, dynamic light scattering and rheology. The microstructure of the gel was examined by transmission electron microscopy. During incubation of 12% whey protein isolate solutions at 40°C and pH 7, the major whey proteins were partly hydrolyzed and the solution gradually became turbid due to formation of aggregates of increasing size. The viscosity of the hydrolysate simultaneously increased and eventually a gel formed. The gel had a particulate type of microstructure. We hypothesized that the aggregates forming the gel were held together by noncovalent interactions.     

Ca2+-Induced Gelation of Pre-heated Whey Protein Isolate

Addition of CaCl₂ to pre-heated whey protein isolate (WPI) suspensions caused an increase in turbidity when pre-heating temperatures were ≥ 64°C. Pre-heating to ≥ 70°C was required for gelation. WPI suspensions which contained CaCl₂ became turbid at 45°C and formed thermally induced gels at 66°C. Thermally and Ca²⁺-induced gels showed significant time/temperature effects but the penetration force values in the Ca²⁺-induced gels were always lower. However, Ca²⁺-induced gels were higher in shear stress at fracture. The Ca²⁺-induced gels had a fine-stranded protein matrix that was more transparent than the thermally induced gels, which showed a particulate microstructure.     

Transglutaminase Cross-linking of Whey/Myofibrillar Proteins and the Effect on Protein Gelation

ABSTRACT: Transglutaminse (TGase)-catalyzed interactions of whey (WPI)/myofibrillar (MPI) protein isolates were investigated under 5 conditions: (1) ionic strengths; (2) calcium/ethylenediaminetetra-acetic acid (EDTA); (3) enzyme:substrate ratio; (4) WPI:MPI ratio; and (5) preheating of WPI (80 °C). TGase treatments of MPI in distilled water converted myosin heavy chain and actin into lower-molecular-weight polypeptides. The reaction, accelerated by the presence of WPI but diminished by NaCl, was completely reversed upon extended incubation. There was no visible WPI/MPI cross-linking; and the enzyme:substrate or WPI:MPI ratio, preheating, calcium, and EDTA did not influence the enzyme reaction. TGase treatment did not alter the melting pattern of WPI/MPI mixtures, but markedly enhanced their thermal gelling ability.     

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.     

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.     

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.     

Dynamic Rheological Properties and Microstructure of Partially lnsolubilized Whey Protein Concentrate Gels

Viscoelasticity and microstructure of gels prepared with four whey protein concentrates (WPC) with solubilities from 27.5 to 98.1% in 0.1M NaCl, pH 7.0 were evaluated. Dynamic moduli were determined while 16% (w/w protein) WPC in 0.6M NaCl, pH 7.0, was heated isothermally at 90°C for 15 min. Storage moduli (G′) increased and tangent δ decreased when 80.0 and 98.1% soluble WPC were heated, whereas G' and tangent δ of 27.5 and 41.0% soluble WPC did not change. The 27.5% soluble WPC had the highest G' throughout the heating period. Rheological measurements suggested that globular aggregates observed in 80.0% and 98.1% soluble WPC were formed during heating, whereas aggregates in 27.5 and 41.0% WPC were present prior to heating.     

Gelling Properties of Whey Proteins After Enzymic Fat Hydrolysis

ABSTRACT: The effect of residual fat hydrolysis upon the gelation of whey protein concentrate (WPC) was studied. Gelling properties of a commercial WPC and lipase-treated WPC were evaluated on the basis of least concentration endpoint gelation, penetration test, texture profile analysis and water-holding capacity. Heat treatment of lipase-treated WPC led to gels with the highest hardness, springiness, cohesiveness and water retention. Such transformed WPC could be advantageously used to help improve texture in formulated meat, bakery, and confectionery products.     

内源乳化凝胶化法制备海藻酸钙微胶珠的工艺优化

通过单因素和正交试验对内源乳化凝胶化法制备海藻酸钙微胶珠的工艺参数进行优化,研究包括海藻酸钠（sodium alginate,NaAlg）质量浓度、Span 80质量浓度、水/油（液体石蜡）两相体积比和CaCO3与NaAlg质量比对海藻酸钙微胶珠粒径分布、外观形态和产率等指标的影响。结果表明：海藻酸钙微胶珠的平均粒径随着NaAlg质量浓度的增大而增大,随着Span 80质量浓度和水油两相体积比值增加而变小,而CaCO3与NaAlg质量比对微胶珠的平均粒径无显著影响。制备粒径在300～600 μm,且分布均匀、形态良好、产率较高的海藻酸钙微胶珠的最佳工艺参数为表面活性剂Span 80用量2 g/L、NaAlg质量浓度12 g/L、CaCO3和NaAlg质量比1∶4、水油两相体积比值1∶3。此外,进一步实验表明液体石蜡在重复利用10 次后,制得的微胶珠仍保持了良好的形态和得率。     

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.