Whey Protein Denaturation Research Articles

Whey Protein Solution Coating for Fat‐Uptake Reduction in Deep‐Fried Chicken Breast Strips

This study investigated the use of whey protein, as an additional coating, in combination with basic, well-described predust, batter, and breading ingredients, for fat-uptake reduction in fried chicken. Chicken breasts were cut into strips (1 x 5 x 10 cm) and coated with wheat flour (WF) as a predust, dipped in batter, coated with WF as a breading, then dipped in 10% denatured whey protein isolate (DWPI) aqueous solution (wet basis). A WF-batter-WF treatment with no DWPI solution dip was included as a control. Coated chicken strips were deep-fried at 160 degrees C for 5 min. A Soxhlet-type extraction was performed to determine the fat content of the meat fraction of fried samples, the coating fraction of fried samples, raw chicken, and raw coating ingredients. The WF-batter-WF-10% DWPI solution had significantly lower fat uptake than the WF-batter-WF control, by 30.67% (dry basis). This article describes applied research involving fat reduction in coated deep-fried chicken. The methods used in this article were intended to achieve maximized fat reduction while maintaining a simple procedure applicable to actual food processing lines.

Preparation of nanoparticles from denatured whey protein by pH-cycling treatment

Low temperature cross-linking of denatured whey protein through pH-cycling is proposed to develop nanoparticles with controlled size and properties. Soluble polymers were produced by heating whey protein dispersions at low ionic strength and neutral pH. Nanoparticulation was induced by acidification of diluted polymer dispersions followed by pH neutralization. The effect of aggregation conditions on the physicochemical characteristics and stability of nanoparticles was studied. Nanoparticles with a diameter ranging from 100 to 300 nm were produced depending on the pH of aggregation (5.0, 5.5, 6.0), the added calcium concentration (0, 2.5, 5 mM) and the ageing time at the aggregation pH (0–75 h). The size and the turbidity of nanoparticle dispersions increased with increasing ageing time and calcium concentration. Nanoparticle voluminosity decreased with increasing calcium concentration during pH-cycling, suggesting a more compact and less porous internal structure. The stability of nanoparticles in the presence of different dissociating buffers (EDTA, urea, SDS and DTT) was evaluated and the results showed that whey protein nanoparticles were covalently cross-linked by disulphide bonds.

MICROSTRUCTURE AND PHYSICAL PROPERTIES OF QUARG CHEESE AS AFFECTED BY DIFFERENT HEAT TREATMENTS

ABSTRACT The effects of different heat treatments on the rheological properties, microstructure and yield of production of quarg cheese were investigated. Three levels of time–temperature combination were used: 72C–16 s, 82C–5 min, 90C–5 min. Rheological properties were studied by means of frequency sweep experiment with the measurement of elastic modulus (G′). Microstructures of samples were observed by scanning electron microscopy (SEM). Maximum and minimum G′ and cheese yield were obtained at 90 and 72C, respectively (P < 0.05). Yield at 82 and 90C was higher than 72C but difference between heat treatment at 82 and 90C was not significant (P < 0.05). G′ values at 82 and 90C were higher than that at 72C. The difference between 82 and 90C was initially low; subsequently increase in frequency made G′ at 90C higher than 82C. SEM micrographs of samples at 82 and 90C were closely similar and no differences were observed between them. Micrographs showed the regular microstructure with branched clusters and numerous small pores at 82 and 90C, whereas micrographs of heat treatment at 72C had larger protein aggregates and fewer but larger pores. This study showed that heat treatments at 82 and 90C were more suitable for quarg cheese making than that at 72C. PRACTICAL APPLICATIONS Quarg cheese is one of the most popular acid-coagulated cheeses. This study shows that heat treatment at 82C–5 min is preferred for quarg production compared with other heat treatments. Contribution of denatured whey proteins in gel network led to higher cheese-making yield as well as high nutrition value. Heat treatment at 82C is also suggested in economic and energy consumption aspect.

Controlling milk protein interactions to enhance the reconstitution properties of whole milk powders – A minireview

Spray-dried milk powders are widely used in recombined milk products and processed foods. The interactions of the specific components in milk, i.e. casein micelles, whey proteins and fat globules, dictate how milk will behave during processing and the functional properties of the powder in different applications. The manufacture of milk powders involves heat treatments, evaporation, homogenisation and spray drying. The major effect of heat treatment is the denaturation of whey proteins and their association with casein micelles. During evaporation, the casein micelle size increases due mainly to the aggregation of some of the micelles and increased association of the whey proteins with the micelles. During whole milk powder manufacture, there are also considerable changes in the size of fat globules and the protein composition of the milk fat globule membrane (MFGM). This modified composition and the consequent reactivity of the MFGM play a major role in determining the functionality of whole milk powders, in particular its reconstitution properties.

Effect of thermal treatment on whey protein polymerization by transglutaminase: Implications for functionality in processed dairy foods

The effect of thermal treatment of whey proteins (50 g/100 g) at 75, 80, 85, 90 and 95 °C before enzymatic treatment with microbial transglutaminase was evaluated by rheological measurements. Thermal denaturation of whey proteins was determined by differential scanning calorimetry (DSC); and the gel point and turbidity were also evaluated after addition of transglutaminase at different pH values in protein solutions. A significant ( p < 0.05) interaction was observed between transglutaminase and thermal treatments. At temperatures higher than 85 °C the apparent viscosity measurements of whey protein solutions with transglutaminase were significantly higher than those of the control samples. DSC analysis showed that thermal denaturation occurred at temperatures close to 82 °C, and the enzymatic reaction was enhanced at higher temperatures. The gel point of whey proteins decreased with transglutaminase addition. This decrease became greater as a function of reaction time due to the formation of high weight protein polymers catalyzed by transglutaminase, which was also observed in the turbidity analysis.

Use of reconstituted concentrated nonfat milk for the production of UHT milk: physical and chemical effects and stability

The objective of this work was to evaluate the use of reconstituted concentrated nonfat milk for the production of UHT milk and to evaluate its physical and chemical effects and stability. The study considered three treatments related to the raw material and processing parameters. Increasing the intensity of thermal treatments resulted in increased hydroxymethylfurfural (HMF) content as well as the denaturation of whey protein. During storage, the milk that was produced from reconstituted concentrate displayed a lesser degree of proteolysis and higher pH value, sedimentation index and HMF, compared to natural milk. Under higher storage temperatures, the degree of proteolysis, HMF and pH decreased and the sedimentation index increased.

ELECTROPHORETIC PATTERNS AND FREE AMINO ACIDS OF CAMEL’S MILK CASEINS AND WHEY AS AFFECTED BY DIFFERENT HEAT TREATMENTS

Camel (Camelus dromedarius) milk caseins and whey proteins compared to bovine milk proteins and its relation to different heat treatments were detected using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Camel milk whey proteins such as serum albumin (SA) and alpha-lactalbumin (a-La) appear to possess molecular weights similar to the respective bovine whey proteins. In camel milk, no protein bands homologous to bovine neither beta-lactoglobulin (b-Lg) nor k-casein could clearly be detected in the electrophoretic pattern and consists of large amount of serum albumin, compared to bovine whey. Camel milk whey protein showed higher heat stability than those of cow’s milk. After an initial higher denaturation of whey proteins in camel milk at 65°C/30 min, which represents the conditions of conventional pasteurization caused no visible change (denaturation) in whey proteins, whilst higher heat treatment at 80 and 100°C for 30 min which is more excessive than pasteurization, resulted visible changes of the whey proteins. The present study demonstrates the most predominated values of free amino acids (FAA) glutamic, aspartic, isoleucine and alanine respectively in both of heated caseins and whey separated from camel's milk. The FAA concentrations of camel's milk caseins appear to be more heat stable than those of camel's milk whey, which has high loss percentages in FAA than of caseins

Heat damage evaluation in ultra-high pressure homogenized milk

The evaluation of heat damage in ultra-high pressure homogenized (UHPH)-treated samples has been studied by analyzing different thermal indicators such as compounds that absorb at 340 nm, hydroxymethylfurfural, free sulphydryl content, furosine, lactulose and whey protein denaturation. Milk was treated at 200 and 300 MPa with inlet temperature of 30 and 40 °C and was compared to high-pasteurized milk (PA; 90 °C, 15 s) and to commercial UHT, in bottle-sterilized and pasteurized milks. UHPH samples were differentiated from PA milk, basically by the determination of absorbance at 340 nm and β-Lactoglobulin denaturation. Both parameters indicated a reduced thermal effect in UHPH samples over PA milk. Comparison of UHPH samples with UHT and sterilized milks showed an increase of all heating indicators when severe heat process was applied. Overall, in spite of the increase of temperature during UHPH treatments, heat damage was lower compared to PA milk, suggesting the potential of this technology as an alternative to pasteurization.

Foam fractionation of α‐lactalbumin and β‐lactoglobulin from a whey solution

AbstractWhey, a byproduct of cheese production, is often considered a waste stream. Separation and purification of whey proteins is a difficult and expensive task. Occasionally, it is transported out of the dairy plant for a per volume charge. One possible method to reduce the waste volume and disposal cost is to concentrate whey by foam fractionation and potentially produce a valuable coproduct, a concentrated whey protein solution. Foam fractionation is an adsorptive bubble separation method based on the hydrophobic/hydrophilic properties of proteins. In this study, foam fractionation was evaluated for the concentration of whey proteins, specifically α‐lactalbumin and β‐lactoglobulin, from a dilute whey protein solution. The effects of initial whey protein concentration (0.075 and 0.15 mg/ml), pH (3.8–5.5), superficial gas velocity (0.85 and 0.95 cm/s) and temperature (4 and 65 °C) on protein enrichment and recovery were examined. Higher enrichment was achieved with the lower initial protein concentration (0.075 mg/ml), and at pH values that were near the isoelectric points (pI) of α‐lactalbumin and β‐lactoglobulin (pH 3.8, 4.2, 4.5, and 5.2). Higher superficial gas velocity enhanced the amount of proteins recovered with a decrease in the enrichment. Cold temperature treatment and partial heat denaturation of whey proteins reduced enrichment and increased protein recovery simultaneously. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

The effect of the pH at cooking on the properties of processed cheese spreads containing whey proteins

Processed cheese spreads were made with and without whey proteins under varying cooking pH conditions. The processed cheeses were cooked at one pH value and at the end of the cooking process the pH was adjusted to the final product pH of 5.7. The rheological properties and whey protein denaturation levels of the processed cheese spreads were measured. The rheological properties and texture of the processed cheeses containing whey proteins could be markedly modified by varying the cooking pH during processing, whereas those without whey proteins were unaffected. These textural modifications could not be explained solely by the changes in whey protein denaturation during cooking. It is proposed that the interactions of the whey proteins during cooking affect the processed cheese texture, and that these interactions are affected by the pH of the processed cheese during processing.

Studies on the impact of glycation on the denaturation of whey proteins

It could be shown for technologically relevant whey protein powders that denaturation of β-lactoglobulin (β-Lg) is affected significantly by the extent of covalent modification of lysine residues by lactose. The amount of acid soluble β-Lg as measured via RP-HPLC with UV detection after heating for 10 min at 80 °C increased from 40% (4.6% lysine modification) to 82% (22.4% lysine modification). An increase in glycation leads to a slower denaturation-induced oligomerisation, as shown by SDS-PAGE. Concomitant with an increase in lysine modification, the denaturation temperature increased from 79.5 to 84 °C, as measured by differential scanning calorimetry (DSC). Covalent attachment of lactose to whey proteins during preparation or storage significantly improves the heat stability of whey proteins, which may be of particular importance for the technological use of whey proteins varying in the degree of lysine modification.

Rheological properties of dairy desserts prepared in an indirect UHT pilot plant

Abstract The Viscolab (Tetra Pak), an indirect ultra-high treatment (UHT) pilot plant, was used to prepare dairy desserts containing kappa-carrageenan, skimmed milk powder (SMP), adipate cross-linked acetyl-substituted waxy maize starch, sucrose and water. Effects of varying concentrations of carrageenan, milk powder and starch on the dessert rheology were studied, while the sucrose and water content were kept constant. The rheological measurements included both small amplitude oscillation tests and large deformation penetration tests. To investigate the influence of shear during the process, the scraped-surface heat exchangers of the UHT pilot plant were run at two rotation speeds. At a low rotation speed of 70 rpm, both the complex modulus and gelation temperature were found to increase with increasing carrageenan content and upon substitution of SMP by starch. These findings are in line with the previously reported exclusion effect of starch, demonstrated by the authors for lab-scale and sterilized dairy desserts. However, more intense shearing at 350 rpm mainly affects the starch granules, which results in a lower complex modulus and gelation temperature of dairy desserts containing high amounts of starch. Where starch granules seem to considerably contribute to small oscillatory deformation measurements, they appear to contribute little to the gel strength. Compared to earlier reported lab-scale experiments, the dessert preparation in an UHT pilot plant involves a more intense heat treatment. As a result, a more extensive whey protein denaturation and subsequent complexation with casein micelles is believed to contribute to the rheological properties of the UHT desserts.

Combined effect of dynamic heat treatment and ionic strength on the properties of whey protein foams – Part II

Abstract The aim was to investigate the effect of dynamic thermal treatment in a tubular heat exchanger on the denaturation and foaming properties of whey proteins, such as overrun, foam stability and texture. A 2% w/v WPI solution (pH 7.0), with and without NaCl addition (100 mM), was submitted to heat treatment at 100 °C. The results demonstrated that heat treatment slightly reduced overrun, whereas NaCl and heat treatment improved foam stability, enhanced texture and provided smaller bubble diameters with more homogeneous bubble size distributions in foams. The foaming properties of proteins, especially stability, were shown to depend not only on the amount of protein aggregates, but also on their size. While insoluble aggregates (larger than 1 μm diameter) accelerated drainage, soluble aggregates (about 200 nm diameter) played a key role on the stabilization of gas–liquid interfaces.

On heating milk, the dissociation of κ-casein from the casein micelles can precede interactions with the denatured whey proteins

When kappa-casein (kappa-CN) was added to milk, and the milk was subsequently pH adjusted (pH 6.5-6.9) and heated (90 degrees C/15 min), the serum contained considerably higher levels of denatured whey proteins than the milks without added kappa-CN. When milk at pH 6.5-6.9 was heated at 90 degrees C for different times, kappa-CN was found in the serum in the early stages of heating and before significant levels of whey proteins were denatured. kappa-CN reached its maximum level in the serum before the whey proteins were fully denatured. When milk at pH 6.5-6.9 was heated at 20-90 degrees C for 15 min, kappa-CN dissociated from the casein micelles at all temperatures, with the level in the serum increasing with the temperature and the pH at heating. kappa-CN dissociated from the micelles at temperatures below those at which significant levels of the whey proteins were denatured. When taken together, the results from these experiments strongly indicate that the dissociation of kappa-CN from the micelles can precede the interaction of the denatured whey proteins with kappa-CN, and that there is a preferential interaction of the denatured whey proteins with serum-phase kappa-CN.

Effect of high-pressure treatment at various temperatures on activity of indigenous proteolytic enzymes and denaturation of whey proteins in ovine milk

The effect of high-pressure (HP) processing (200, 450 or 650 MPa) at various temperatures (20, 40 or 55 °C) on the total plasmin plus plasminogen-derived activity (PL), on plasminogen activators (PA), on protease activity (which seemed to be equivalent to cathepsin D), and on denaturation of major whey proteins in ovine milk was investigated. There were synergistic effects between pressure and temperature at 450 and 650 MPa for partial inactivation of PL, PA and cathepsin D. In contrast, processing at 200 MPa did not affect the activity of these enzymes. Treatment at 650 MPa was necessary for the denaturation of α-lactalbumin, and denaturation was enhanced with increasing temperature. In contrast, denaturation of β-lactoglobulin occurred at all combinations of HP and temperature studied. In conclusion, HP affected the activity of various indigenous proteolytic enzymes and the denaturation of major whey proteins of ovine milk, which may influence its behaviour during the manufacturing of dairy products.

Heat and/or high‐pressure treatment of skim milk: changes to the casein micelle size, whey proteins and the acid gelation properties of the milk

Skim milk was subjected to heat, pressure or combined processes. In general, higher levels of whey protein denaturation were observed for milk subjected to combined processes than those heat‐ or pressure‐treated only. Heat treatment caused small changes to the casein micelle size. Pressure treatment decreased the casein micelle size; however, the effect was less marked when heat and pressure treatments were combined. Acidification of the skim milks produced gels with a range of firmness, yield stresses and yield strains depending on the treatments applied. These changes in acid gel properties were not related only to whey protein denaturation levels in the milks.

Effect of high-pressure treatment at various temperatures on indigenous proteolytic enzymes and whey protein denaturation in bovine milk

The objective of the present study was to determine the effect of high pressure (HP) processing (200, 450 and 650 MPa) at various temperatures (20, 40 and 55 degrees C) on the total plasmin plus plasminogen-derived activity (PL), plasminogen activator(s) (PA) and cathepsin D activities and on denaturation of major whey proteins in bovine milk. Data indicated that transfer of both PL and PA from the casein micelles to milk serum occurred at all pressures utilized at room temperature (20 degrees C). In addition to the transfer of PL and PA from micelles, there were reductions in activities of PL (16-18%) and PA (38-62%) for the pressures 450 and 650 MPa, at room temperature. There were synergistic negative effects between pressure and temperature on residual PL activity at 450 and 650 MPa and on residual PA activity only at 450 MPa. Cathepsin D activity in the acid whey from HP-treated milk was in general baroresistant at room temperature. The residual activity of cathepsin D decreased significantly at 650 MPa and 40 degrees C and at the pressures 450 and 650 MPa at 55 degrees C. Synergistic negative effects on the amount of native beta-lactoglobulin were observed at 450 and 650 MPa and on the amount of native alpha-lactalbumin at 650 MPa. There were significant correlations between enzymatic activities (PL, PA and cathepsin D) and the residual native beta-lactoglobulin and alpha-lactalbumin in bovine milk. In conclusion, HP significantly affected the activity of indigenous proteolytic enzymes and whey protein denaturation in bovine milk. Reduction in activity of indigenous enzymes (PL, PA and cathepsin D) and transfer of PL and PA from the casein to milk serum induced by HP is expected to have a profound effect on cheese yield, proteolysis during cheese ripening and quality of UHT milk during storage.

Combined effect of dynamic heat treatment and ionic strength on denaturation and aggregation of whey proteins – Part I

The aim was to investigate the effect of dynamic thermal treatment in a heat exchanger on the denaturation and aggregation of whey proteins. A 2% w/v WPI solution (pH 7.0), with or without NaCl addition (100 mM), was submitted to heat treatment at 100 °C. At low ionic strength, a nearly complete denaturation was observed, while the heat-treated samples at 100 mM ionic strength registered only 10% denaturation. It was shown that not only denaturation was reduced by the presence of NaCl, but also that the size of the aggregates formed during heat treatment was far smaller and remained essentially below 1 μm. Surface tension measurements showed a faster adsorption and lower σ values for the non-polymerized proteins, whereas insoluble aggregates played only a poor role on the σ curves. Finally, experimental results demonstrated the strong interaction between ionic strength and dynamic thermal treatment on protein aggregation and properties.

Conformational ordering and gelation of gelatin in mixtures with soluble polysaccharides

Previous studies have shown that conformationally disordered, soluble biopolymers cause large enhancements in self-association of calcium pectinate, thermally denatured whey protein and gelling maltodextrin under conditions where the pre-gel solutions remained as a single phase. The purpose of the present work was to screen for similar enhancements in gel strength and rate of conformational ordering of gelatin on incorporation of soluble, disordered polysaccharides. Type B gelatin was used at a fixed concentration of 5.0 wt%, at a pH well above its isoelectric point of ∼4.5. Mixtures were prepared at 45 °C, where the gelatin is in the disordered coil form. Gel strength was characterised as Young's modulus ( E), derived from the initial slope of compression curves for gels formed by holding for 16 h at 5 °C. Rate of conformational ordering of gelatin (triple-helix formation) was monitored by changes in optical rotation during and after rapid quenching from 45 to 5 °C. The polysaccharides studied were carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), guar gum, gum arabic, dextran and inulin, all of which were used in compression testing. Combinations of gelatin with HPMC and guar gum became immediately turbid on mixing and could not, therefore, be included in the samples characterised by optical rotation. The other mixtures remained homogeneous (i.e. single-phase) on holding at 45 °C. The results obtained were entirely negative. Incorporation of the soluble polysaccharides caused no significant changes in Young's modulus, and optical rotation values remained within ∼10% of those for gelatin alone. It is suggested that the enthalpic advantage of segregation is sufficient to overcome the small reduction in entropy from association of conformationally immobile subunits in gelation of calcium pectinate, whey protein and maltodextrin, but not sufficient to overcome the much greater loss of entropy from conversion of flexible gelatin coils to rigid triple helices.

Rheological Properties of Rennet Gels Containing Milk Protein Concentrates

Different milk protein concentrates (MPC), with protein concentrations of 56, 70, and 90%, were dispersed in water under different treatments (hydration, shear, heat, and overnight storage at 4°C), as well as in a combination of all the treatments in a factorial design. The particle size distribution of the dispersions was then measured to determine the optimal conditions for the dispersion. Heating at 60°C for 30min with 5min of shear was chosen as the best condition to dissolve MPC powders. The samples were also characterized for composition, presence of protein aggregates, and ratio of calcium to protein. The total calcium present in MPC increased with increasing concentration of protein; however, the total calcium-to-protein ratio was lower in MPC90 than in MPC56 and MPC70. The level of whey protein denaturation, the presence of κ-casein-whey protein aggregates in the supernatant after centrifugation, and the amount of caseins dissociated from the micelle increased as the protein concentration in the powder increased. The total amount of casein macropeptide released was lower in samples from powders with a higher protein concentration than for MPC56 or the skim milk control. The gelation behavior of reconstituted MPC was tested in systems dispersed in water (5% protein) as well as in systems dispersed in skim milk (6% protein). The gelation time of MPC dispersions was considerably lower and the gel modulus was higher than those of reconstituted skim milk with the same protein concentration. When MPC dispersions were dialyzed against skim milk, a significant decrease in the gelation time and modulus were shown, with a complete loss of gelling functionality in MPC90 dispersed in water. This demonstrated that the ionic equilibrium was key to the functionality of MPC.