Combined Effects of Proteins and Polysaccharides on Physical Properties of Whey Protein Concentrate-based Edible Films

ABSTRACT: The water-vapor permeability (WVP) and mechanical properties of edible films formed from dry blends or co-dried preparations of protein-polysaccharide powders prepared from whey protein concentrate (WPC)-45 and alginate, pectin, carrageenan, or konjac flour (WPC-45-to-polysaccharide ratio of 95:5 w/w) were investigated. Films were prepared from 8% WPC using WPC-45 (45% protein powder), consisting of 17.76 g of WPC-45 in 82.84 g of water per 100 g solution to give 8% protein w/w. Films formed from co-dried powders had lower WVP and higher tensile strength (TS), elastic modulus (EM) ( P < 0.05), and elongation (EL) than equivalent films formed from the dry blended powders. Films containing alginate had lower WVP and higher TS, EM, and EL than films containing pectin, carrageenan, or konjac flour. There is potential to alter the physical properties of hydrophilic films by combining whey protein and polysaccharide components.     

Whey protein hydrolysate: Functional properties,nutritional quality and utilization in beverage formulation

The objective of the study was to analyze the functional and nutritional properties of enzymatically hydrolyzed whey protein concentrate (WPC) and to formulate a beverage mix. WPC hydrolysates were produced using fungal protease and papain, at time intervals of 20, 40 and 60 min and were analyzed for proximate composition and functional properties. A beverage was formulated with hydrolyzed WPC, skim milk powder, cocoa, liquid glucose, sugar and vegetable fat and analyzed for physicochemical properties, sensory attributes and keeping quality. Results revealed that the protein content of WPC was 75.6% and decreased slightly on enzyme treatment (69.6%). The water absorption capacity of WPC was 10 ml/100 g and increased in enzyme treated samples from 16 to 34 ml/100 g with increase in the time of hydrolysis. Emulsion capacity (45 ml of oil/g of control WPC) showed a decreasing trend with increasing time of hydrolysis. Enzyme treatment slightly increased the foam capacity in three samples but lowered foam stability in all. The gel filtration pattern of enzyme treated samples showed an increase in low molecular weight fractions. The amino acid profile showed higher content of methionine in samples treated with enzymes, compared to the control. The in vitro protein digestibility of untreated WPC was 25% and increased in all treated samples to varying degrees (69–70%). Formulated beverage had 52% protein, 10% fat and 6.6% ash. There were no significant differences in the sensory attributes of formulated and commercial beverage. The formulated beverage could be stored well in a PET container for 30 days.     

Factors Influencing Whey Protein Gel Rheology: Dialysis and Calcium Chelation

Influence of dialyzable compounds on the Theological properties (shear stress and shear strain at failure) of heat-induced whey protein concentrate (WPC) and whey protein isolate (WPI) gels was examined. Dialyzing WPC and WPI suspensions prior to gelation increased the stress of two of three WPC gels and a WPI gel. Dialysis also significantly increased the strain of the same two WPC gels, normalizing all strain values. Replacement of calcium lost through dialysis did not significantly change gel rheology. However, chelating calcium caused a significant decrease in the stress of all gels: a minimum amount of calcium and/or a calcium complex appears to have a major role in whey protein gelation.     

Characterisation of heat-set milk protein gels

Milk protein solutions [10% protein, 40/60 whey protein/casein ratio containing whey protein concentrate (WPC) and low-heat or high-heat milk protein concentrate (MPC)] containing fat (4% or 14%) and 70–80% water, form gels with interesting textural and functional properties if heated at high temperatures (90 °C, 15 min; 110 °C, 20 min) without stirring. Adjustment of pH before heating (HCl or glucono-δ-lactone) produces soft, spoonable gels at pH 6.25–6.6, but very firm, cuttable gels at pH 5.25–6.0. Gels made with low-heat MPC, WPC and low fat gave some syneresis; high-fat gels were slightly firmer than low-fat gels. Citrate markedly reduced gel firmness; adding calcium had little effect on firmness, but increased syneresis of low-heat MPC/WPC gels. The gels showed resistance to melting, and could be boiled or fried without flowing. Microstructural analysis indicated a network structure of casein micelles and fat globules interlinked by denatured whey proteins.     

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.     

Viscoelastic properties of caseinmacropeptide isolated from cow,ewe and goat cheese whey

Caseinmacropeptide (CMP) is a C‐terminal glycopeptide released from κ‐casein by the action of chymosin during cheese‐making. It is recognised as a bioactive peptide and is thought to be an ingredient with a potential use in functional foods. CMP occurs in sweet cheese whey and whey protein concentrate (WPC). Its composition is variable and depends on the particular whey source and the fractionation technology employed in the isolation. There were no significant (P < 0.05) differences in the relative apparent viscosities between species of CMPs (cow, ewe and goat). Analyses at different pH (2, 4, 7, 10), ionic strength (0, 0.2, 0.4 and 0.7 as NaCl molarity) and protein concentration (50, 100 and 200 g kg^?1) at temperatures from 10 to 90 °C carried out found pH 7 and high protein concentration (200 g kg^?1) conditions to be the best for CMP solutions to keep low and constant relative viscosity values with increasing temperature up to 75 °C. The viscoelastic properties–storage modulus, loss modulus and phase angle–of the different CMPs and WPC solutions were determined. Heat‐induced rheological changes in CMP solutions occurred at moderate temperatures (40–50 °C) with no appreciable differences in viscosity. Gelation took place significantly (P < 0.05) earlier in goat CMP (41 °C), followed by cow CMP (44 °C), ewe CMP (47 °C) and WPC (56 °C). Heating at 90 °C showed that WPC required significantly (P < 0.05) longer times to form gels (>5 min) than the CMPs (<5 min). WPC gels had higher (>20°) phase angle than CMP (<20°), which could be associated with untidy structures, limiting elastic properties of the gel. Copyright © 2006 Society of Chemical Industry     

Production of a high gel strength whey protein concentrate from cheese whey

In order to develop a process for the production of a whey protein concentrate (WPC) with high gel strength and water-holding capacity from cheese whey, we analyzed 10 commercially available WPC with different functional properties. Protein composition and modification were analyzed using electrophoresis, HPLC, and mass spectrometry. The analyses of the WPC revealed that the factors closely associated with gel strength and water-holding capacity were solubility and composition of the protein and the ionic environment. To maintain whey protein solubility, it is necessary to minimize heat exposure of the whey during pretreatment and processing. The presence of the caseinomacropeptide (CMP) in the WPC was found to be detrimental to gel strength and water-holding capacity. All of the commercial WPC that produced high-strength gels exhibited ionic compositions that were consistent with acidic processing to remove divalent cations with subsequent neutralization with sodium hydroxide. We have shown that ultrafiltration/diafiltration of cheese whey, adjusted to pH 2.5, through a membrane with a nominal molecular weight cut-off of 30,000 at 15 degrees C substantially reduced the level of CMP, lactose, and minerals in the whey with retention of the whey proteins. The resulting WPC formed from this process was suitable for the inclusion of sodium polyphosphate to produce superior functional properties in terms of gelation and water-holding capacity.     

Gelation of mixed systems whey protein concentrate–gluten in acidic conditions

Gels of whey protein concentrate (WPC)–gluten were prepared by heating WPC–gluten dispersions (10% whey protein/0–5–10% gluten protein, w/w; pH 3.75 or 4.2). Gels were characterized through solubility assays in different extraction solutions, measures of water-holding capacity (WHC), firmness, elasticity and relaxation time, and light microscopy. Differential scanning calorimetry (DSC) of WPC–gluten dispersions was also performed. Gluten increases the firmness and elasticity of gels, mainly at pH 4.2. The WHC also increases with gluten content, being higher at pH 3.75 than at pH 4.2. Solubility assays indicate that electrostatic forces, hydrophobic and H bindings would be involved in maintaining the gel structure of WPC gels at pH 3.75 and 4.2, whereas in mixed gels of WPC–gluten, the principal forces responsible for the maintenance of the gel structure at these pHs would be hydrophobic and H bindings, and in gels prepared at pH 4.2 also disulfide bonds, but in a minor extent. The presence of gluten shifts the apparent transition temperature for whey protein denaturation towards lower temperatures. Gels with gluten present a smooth network with gaps and a more elastic appearance, as observed by light microscopy.     

Thermal gelation of commercial whey protein concentrate: influence of pH 4.6 insoluble protein on thermal gelation

Thermal gels were prepared from solutions of seven commercial whey protein concentrates (WPCs) and were found to vary considerably in strength, as determined by a compressive rheological measurement method. Further studies were carried out on one WPC (WPC5) which had far superior gelling properties to the other six WPCs and revealed that this WPC had a substantial level of protein that was insoluble (sedimentable) at pH 4.6 on centrifugation at 10000 g for 30 min but not insoluble under similar conditions at pH 7.0. When this pH 4.6 insoluble material was removed the gelling properties of WPC5 decreased considerably. Alkaline treatment (pH 9.0 for 3 hours) of a WPC5 supernatant devoid of pH 4.6 insoluble material resulted in a substantial improvement in gelling properties and generation of further pH 4.6 insoluble material. Gel electrophoresis studies and differential scanning calorimetry confirmed that the pH 4.6 insoluble material recovered from WPC5 and the alkaline treated WPC5 supernatant contained denatured protein which was associated via covalent and non-covalent interactions. Transmission electron microscopy of thermal gels prepared from WPC5 solutions containing and devoid of pH 4.6 insoluble material indicated that gel micro structure was dependent on the presence or absence of this denatured aggregated protein material in dispersion prior to heat treatment. Overall, the results suggested that the pH 4.6 insoluble, but pH 7.0 soluble, protein present in a WPC5 dispersion influenced gel microstructure on heating in a manner that had a positive influence on gel rheology.     

Purification and characterization of lysozyme from filipino venus, Ruditapes philippinarum

Lysozyme from Filipino venus (Ruditapes philippinarum) was purified by ion-exchange and gel filtration chromatography. The purification fold and yield were 3,402 and 32.4%, respectively. The molecular weight was determined to be 13.4 kDa by SDS-PAGE. The specific activity of lysozyme was 3.76×10⁵ units/mg protein with Micrococcus lysodeikticus as a substrate. The optimum temperature and pH of lysozyme were 75°C and 5.5, respectively. Lysozyme activity was decreased with about 45% after heat treatment for 30 min at 80°C, and completely inactivated at 100°C. It was activated by NaCl (10–70 mM), MgCl₂, and CaCl₂ (2–5 mM) whereas it was inhibited by ZnCl₂ (2–30 mM).     

Development and quality evaluation of a cereal-based breakfast product from yellow maize (Zea mays), sesame (Sesamum indicum) and mushroom (Pleurotus ostreatus) flour blends

Composite flours were prepared from blends of yellow maize (Zea mays), sesame seed (Sesamum indicum) and oyster mushroom (Pleurotus ostreatus) powder in the ratio of 80:20:0; 75:20:5; 70:20:10; 65:20:15 and 60:20:20, respectively to produce the cereal-based breakfast product coded as YSB, SMB, TMB, PMB and OMB with YSB as the control. The breakfast cereals were produced by hydration and toasting of yellow maize and sesame to 160°C for 25 min and blended together with oven-dried and packaged oyster mushroom. The developed products were analysed for proximate, vitamins, minerals and sensory properties. The proximate composition (%) of different blends ranged as moisture (4.07–7.08), ash (3.09–2.28), crude fat (16.04–12.83), crude fibre (4.30–8.22), protein (16.14–22.54), carbohydrate (56.34–47.04) and energy (434.34–393.83 Kcal). Vitamin A (7.99–5.98 mg/100 g), vitamin B₁ (0.08–0.42 mg/100 g), vitamin B₂ (0.06–0.15 mg/100 g), vitamin B₃ (1.91–4.52 mg/100 g) and vitamin C (3.55–3.32 mg/100 g) were u while minerals (mg/100 g) were calcium (75.31–58.02), potassium (0.65–4.01), magnesium (12.25–12.62), iron (1.21–4.15) and zinc (0.40–1.32). Sensory scores revealed that the cereal-based breakfast product were acceptable to the panellist with oyster mushroom supplementation up to 10%.     

Composition and Properties of Spherosil-QMA Whey Protein Concentrate

The Spherosil-QMA ion exchange process was used to prepare whey protein concentrate (WPC) from cheese whey. The process recovered about 64% of the proteins from whey as a 63% protein WPC. The WPC contained about 20.8% lactose, glucose, and galactose. The WPC proteins ranged in solubility from about 32–42% as a function of pH 3–7 and appeared to have undergone substantial denaturation by HPLC but not by palyacrylamide gel electrophoresis. The gelation properties of WPC were compared with those of commercial and ultrafiltration WPCs as a function of pH 3–7.5 and 0.0–0.15M NaCl and CaCl₂. The WPC did not function well as egg replacer in model cake and custard formulations.     

The roles of disulphide and non-covalent bonding in the functional properties of heat-induced whey protein gels

Heat-induced gelation (80 degrees C, 30 min or 85 degrees C, 60 min) of whey protein concentrate (WPC) solutions was studied using transmission electron microscopy (TEM), dynamic rheology and polyacrylamide gel electrophoresis (PAGE). The WPC solutions (150 g/kg, pH 6.9) were prepared by dispersing WPC powder in water (control), 10 g/kg sodium dodecyl sulphate (SDS) solution or 10 mM-dithiothreitol (DTT) solution. The WPC gels containing SDS were more translucent than the control gels, which were slightly more translucent than the gels containing DTT. TEM analyses showed that the SDS-gels had finer aggregate structure (approximately equal to 10 nm) than the control gels (approximately equal to 100 nm), whereas the DTT-gels had a more particulate structure (approximately equal to 200 to 300 nm). Dynamic rheology measurements showed that the control WPC gels had storage modulus (G) values (approximately equal to 13,500 Pa) that were approximately equal to 25 times higher than those of the SDS-gels (approximately equal to 550 Pa) and less than half those of the DTT-gels after cooling. Compression tests showed that the DTT-gels were more rigid and more brittle than the control gels, whereas the SDS-gels were softer and more rubbery than either the control gels or the DTT-gels. PAGE analyses of WPC gel samples revealed that the control WPC solutions heated at 85 degrees C for 10 min contained both disulphide bonds and non-covalent linkages. In both the SDS-solutions and the DTT-solutions, the denatured whey protein molecules were in the form of monomers or small aggregates. It is likely that, on more extended heating, more disulphide linkages were formed in the SDS-gels whereas more hydrophobic aggregates were formed in the DTT-gels. These results demonstrate that the properties of heat-induced WPC gels are strongly influenced by non-covalent bonding. Intermolecular disulphide bonds appeared to give the rubbery nature of heat-induced WPC gels whereas non-covalent bonds their rigidity and brittle texture.     

Formation of Soy Protein Isolate Cold-set Gels: Protein and Salt Effects

ABSTRACT: The influence of protein and calcium concentration on soy protein cold-set gel formation and rheology has been investigated. Cold-set gels can be formed at soy protein concentrations from 6% to 9% and calcium concentrations from 10 to 20 mM. Gel properties can be modulated by changing the protein and/or CaCl₂ concentrations. An increase in CaCl₂ concentration from 10 to 20 mM increased gel opacity while an increase in protein concentration from 6% to 9% decreased opacity. Water-holding capacity improved with increasing protein concentration and decreasing CaCl₂ concentration. The elastic modulus (G') increased with protein and calcium chloride concentrations. Microscopy revealed an increase in the diameters of aggregates and pores as CaCl₂ concentration increased and as protein concentration decreased. Cold-set gels with a broad range of characteristics can be obtained from soy protein.     

The effect of acidification of liquid whey protein concentrate on the flavor of spray-dried powder

Off-flavors in whey protein negatively influence consumer acceptance of whey protein ingredient applications. Clear acidic beverages are a common application of whey protein, and recent studies have demonstrated that beverage processing steps, including acidification, enhance off-flavor production from whey protein. The objective of this study was to determine the effect of preacidification of liquid ultrafiltered whey protein concentrate (WPC) before spray drying on flavor of dried WPC. Two experiments were performed to achieve the objective. In both experiments, Cheddar cheese whey was manufactured, fat-separated, pasteurized, bleached (250 mg/kg of hydrogen peroxide), and ultrafiltered (UF) to obtain liquid WPC that was 13% solids (wt/wt) and 80% protein on a solids basis. In experiment 1, the liquid retentate was then acidified using a blend of phosphoric and citric acids to the following pH values: no acidification (control; pH 6.5), pH 5.5, or pH 3.5. The UF permeate was used to normalize the protein concentration of each treatment. The retentates were then spray dried. In experiment 2, 150 μg/kg of deuterated hexanal (D₁₂-hexanal) was added to each treatment, followed by acidification and spray drying. Both experiments were replicated 3 times. Flavor properties of the spray-dried WPC were evaluated by sensory and instrumental analyses in experiment 1 and by instrumental analysis in experiment 2. Preacidification to pH 3.5 resulted in decreased cardboard flavor and aroma intensities and an increase in soapy flavor, with decreased concentrations of hexanal, heptanal, nonanal, decanal, dimethyl disulfide, and dimethyl trisulfide compared with spray drying at pH 6.5 or 5.5. Adjustment to pH 5.5 before spray drying increased cabbage flavor and increased concentrations of nonanal at evaluation pH values of 3.5 and 5.5 and dimethyl trisulfide at all evaluation pH values. In general, the flavor effects of preacidification were consistent regardless of the pH to which the solutions were adjusted after spray drying. Preacidification to pH 3.5 increased recovery of D₁₂-hexanal in liquid WPC and decreased recovery of D₁₂-hexanal in the resulting powder when evaluated at pH 6.5 or 5.5. These results demonstrate that acidification of liquid WPC80 to pH 3.5 before spray drying decreases off-flavors in spray-dried WPC and suggest that the mechanism for off-flavor reduction is the decreased protein interactions with volatile compounds at low pH in liquid WPC or the increased interactions between protein and volatile compounds in the resulting powder.     

芦丁诱导猪肉肌原纤维蛋白结构变化对蛋白凝胶特性的改善作用

向猪肉肌原纤维蛋白氧化体系（40?mg/mL蛋白、10?μmol/L?FeCl3、100?μmol/L?VC和1?mmol/L?H2O2）中添加不同量的芦丁（0、10、50、100、150?μmol/g,以蛋白计）,测定蛋白质的巯基含量、表面疏水性、电泳、溶解度、凝胶强度和保水性、流变特性,研究芦丁对肌原纤维蛋白结构和凝胶特性的影响。结果表明,添加芦丁使肌原纤维蛋白的巯基含量显著下降（P＜0.05）,表面疏水性先下降后上升;芦丁使肌球蛋白重链（myosin heavy chain,MHC）强度减弱,肌动蛋白条带强度在其较高含量下（100?μmol/g和150?μmol/g）降低,添加β-巯基乙醇后,MHC和肌动蛋白条带大部分被还原;溶解度随着芦丁添加量的增加而降低;芦丁用量增加,蛋白的凝胶强度与保水性显著增强（P＜0.05）,凝胶最终形成阶段的储能模量（G’）提高。因此,芦丁可通过与肌原纤维蛋白的共价交联或适度增加蛋白的表面疏水性而改善蛋白的凝胶特性。     

Study of the Molecular Forces Involved in the Gelation of Plasma Proteins at Alkaline pH

The effects of vaious reagents on the rheological properties of heat-induced (90°C) gels formed from plasma protein solutions (pH 9.0) were studied. Both propylene glycol (5–20%, w/v) and ethanol (5–20,%, w/v), which enhance hydrogen and electrostatic interactions, increased gel compressive strength, whereas mercaptoethanol (25–100 mM) which reduces disulfides, and the sulfhydryl-blocking agent, p-hydroxymcrcuribenzoate (25–100 mM), reduced gel strength. High levels of guanidine hydrochloride (> 1M) or urea (> 2M), which weaken both hydrogen and hydrophobic interactions, decreased gel strength. On the basis of the results, we conclude that hydrophobic interactions and hydrogen and disulfide bonding are involved in the gelation of plasma proteins.     

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.     

Enhanced functionalities of whey proteins treated with supercritical carbon dioxide

The functionality of whey proteins can be modified by many approaches; for example, via complexation with carbohydrates, enzymatic cross-linking, or hydrolysis, and the objective of this work was to research the effects of supercritical carbon dioxide (scCO₂) treatments on the functionalities of commercial whey protein products including whey protein isolates (WPI) and whey protein concentrates (WPC). The WPI and WPC powders and a 10% (wt/vol) WPI solution were treated with scCO₂. The WPI solution was treated at 40°C and 10 MPa for 1 h, whereas WPI and WPC powders were treated with scCO₂ at 65°C and 10 or 30 MPa for 1 h. Dynamic rheological tests were used to characterize gelation properties before and after processing. Compared with the unprocessed samples and samples processed with N₂ under similar conditions, scCO₂-treated WPI, whether dispersed in water or in the powder form during treatments, formed a gel with increased strength. The improvement in gelling properties was more significant for the scCO₂-treated WPC. In addition, the scCO₂-processed WPI and WPC powders appeared to be fine and free-flowing, in contrast to the clumps in the unprocessed samples. Proximate compositional and surface hydrophobicity analyses indicated that both compositional and structural changes may have contributed to enhanced whey protein functionalities. The results suggest that functionalities of whey proteins can be improved by scCO₂ treatment to produce novel ingredients.     

Emulsion properties of algae soluble protein isolate from Tetraselmis sp.

To study possible applications of microalgae proteins in foods, a colourless, protein-rich fraction was isolated from Tetraselmis sp. In the present study the emulsion properties of this algae soluble protein isolate (ASPI) were investigated. Droplet size and droplet aggregation of ASPI stabilized oil-in-water emulsions were studied as function of isolate concentration (1.25–10.00 mg/mL), pH (3–7), and ionic strength (NaCl 10–500 mM; CaCl₂ 0–50 mM). Whey protein isolate (WPI) and gum arabic (GA) were used as reference emulsifiers. The lowest isolate concentrations needed to reach d₃₂ ≤ 1 μm in 30% oil-in-water emulsions were comparable for ASPI (6 mg/mL) and WPI (4 mg/mL). In contrast to WPI stabilized emulsions ASPI stabilized emulsions were stable around pH 5 at low ionic strength (I = 10 mM). Flocculation only occurred around pH 3, the pH with the smallest net droplet ζ-potential. Due to the charge contribution of the anionic polysaccharide fraction present in ASPI its droplet ζ-potential remained negative over the whole pH range investigated. An increase in ionic strength (≥100 mM) led to a broadening of the pH range over which the ASPI stabilized emulsions were unstable. GA emulsions are not prone to droplet aggregation upon changes in pH or ionic strength, but much higher concentrations are needed to produce stable emulsions. Since ASPI allows the formation of stable emulsions in the pH range 5–7 at low protein concentrations, it can offer an efficient natural alternative to existing protein–polysaccharide complexes.