Functional properties of whey proteins affected by heat treatment and hydrodynamic high-pressure shearing

Two batches of native whey proteins (WP) were subjected to microfluidization or heat denaturation accompanied by microfluidization, followed by spray drying. Powders were assessed for their solubility, heat stability, coagulation time, and emulsifying and foaming properties. Effects of denaturation and shearing were examined by particle size analysis, differential scanning calorimetry, reducing and nonreducing sodium dodecyl sulfate-PAGE, and size exclusion-HPLC. Heat treatment significantly decreased solubility, whereas the number of microfluidization passes markedly improved solubility. The combined effect of heat and pressure significantly increased heat coagulation time. Emulsifying activity index substantially increased upon heat denaturation and was further enhanced by microfluidization. Emulsion stability appeared unaffected by the combined treatment, but the concentration of adsorbed protein on fat droplets was significantly increased. Foaming properties were diminished by heating. Particle size distribution patterns, sodium dodecyl sulfate-PAGE, and size exclusion-HPLC revealed disappearance of major WP and creation of relatively higher, as well as smaller, molecular weight aggregates as a result of the 2 treatments. The use of heat and microfluidization in combination could be used to stabilize WP against heat by producing microparticulated species that have different surface and colloidal properties compared with native WP. These results have implications for the use of WP as an additive in heat-processed foods.     

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.     

Functional properties of whey proteins microparticulated at low pH

The main aim of the study was to assess the effect of microparticulation at low pH on the functionality of heat-denatured whey proteins (WP). Spray-dried, microparticulated WP (MWP) powders were produced from 7% (wt/wt) WP dispersions at pH 3, acidified with citric or lactic acid, and microfluidized with or without heat denaturation. Nonmicroparticulated, spray-dried powders produced at neutral pH or pH 3 served as controls. The powders were examined for their functional and physicochemical properties. Denatured MWP had an approximately 2 orders of magnitude reduction in particle size compared with those produced at neutral pH, with high colloidal stability indicated by substantially improved solubility. The detection of monomeric forms of WP in PAGE also confirmed the particle size reduction. Microparticulated WP exhibited enhanced heat stability, as indicated by thermograms, along with better emulsifying properties compared with those produced at neutral pH. However, MWP powders created weaker heat-induced gels at neutral pH compared with controls. However, they created comparatively strong cold acid-set gels. At low pH, a combination of heat and high hydrodynamic pressure produced WP micro-aggregates with improved colloidal stability that affects other functionalities.     

Influence of heat and pH on structure and conformation of whey proteins

The aim of this study was to understand the fundamental interactions responsible for aggregation of whey proteins (WPs) at pH 6 and 3 during heating at 140 °C for 30 s in the presence of different acidulants. The conformational changes in the various heat-treated WP dispersions were studied using chemical bond blockers and analysed using differential scanning calorimeter thermograms, polyacrylamide gel electrophoresis and turbidity measurements. Overall, the results indicated that WPs were denatured mainly by disruption of hydrophobic interactions, and that the extent of WP denaturation at pH 3 was affected by the type of acidulant used. The type of acidulant affected the extent of formation of additional high or medium molecular weight aggregates during heating at pH 3, while the types of interactions involved in the formation of such aggregates were affected by the pH at heating.     

酶反应pH值对比萨干酪理化和功能特性的影响

研究了酶反应条件pH值对比萨干酪理化性质及功能特性的影响。选择在pH值为6.6与6.4时添加凝乳酶。通过对比萨干酪水分、脂肪及蛋白质质量分数的统计分析表明,酶反应条件pH值对比萨干酪的脂肪和蛋白质质量分数没有显著影响,对水分质量分数有显著影响。酶反应条件pH值为6.6比萨干酪水分质量分数为47.70%,pH值为6.4的水分质量分数为51.80%。通过测定干酪中pH值为4.6缓冲溶液及12%的TCA中可溶性氮质量分数,监测其水解情况。在贮藏过程中,可溶性氮质量分数不断增加。酶反应条件pH值影响比萨干酪的功能特性;酶反应条件pH值为6.6比萨干酪的硬度由最初为100.8N,50d后降低为88.9N,融化性增加了1.28cm,油析性增加了2.7%;pH值为6.4干酪功能特性的变化情况分别为:硬度降低为75.5N,融化性增加了2.16cm,油析性增加了3.1%。     

Invited review: Sensory and mechanical properties of cheese texture

Instrumental mechanical properties (instrumental tests that measure force and deformation over time) of cheese and cheese texture (sensory perception of cheese structure) are critical attributes. Accurate measurement of these properties requires both instrumental and sensory testing. Fundamental rheological and fracture tests provide accurate measurement of mechanical properties that can be described based on chemical and structural models. Sensory testing likewise covers a range of possible tests with selection of the specific test dependent of the specific goal desired. Establishing relationships between instrumental and sensory tests requires careful selection of tests and consideration and analysis of the results. A review of these tests and a critical analysis of establishing relationships between instrumental and sensory tests is presented.     

Sensory properties of Cheddar cheese: changes during maturation

The aroma, flavour and texture of 16 samples of commercial Cheddar cheese have been profiled after ripening at 10 °C for 3, 4, 6, 8, 10 and 12 months. Systematic changes in sensory character have been studied and the main changes during maturation identified. Although sensory character changed slowly during ripening, assessment early in the maturation period was an unreliable estimate of ultimate sensory character. Progressive changes in Cheddar aroma and flavour, creamy flavour, acid flavour and mouth-coating character were noted during ripening. Changes in minor components of aroma and flavour were also observed but, on average, were small. Two samples eventually developed marked rancid character and another became excessively bitter. The relation between gross composition of the cheese and sensory properties was investigated. In the early stages of ripening, the ratings for Cheddar flavour and mouth-coating character were associated with the salt content of the cheese and with the concentration of fat in dry matter. However, as the cheese matured these associations weakened.     

Electrophoresis of cottage cheese whey proteins and their polymers.

Cottage cheese whey solutions containing sodium dodecyl sulfate were resolved electrophoretically on 5% sodium dodecyl sulfate polyacrylamide gels. Major bands were identified by comparing their electrophoretic mobilities to those of known whey components. Other components were identified principally from molecular weights determined from a calibration correlating mobility and molecular weight. Conditions which affect polymerization of proteins were studied in whey and solutions of purified beta-lactoglobulin. Formation of a number of polymers was induced by concentrating the whey samples, lowering the temperature, adjusting pH, or adding salts. The dimer, trimer, tetramer, and octamer of beta-lactoglobulin, the dimer and trimer of bovine serum albumin, and several unidentified components in the 100,000 to 300,000 molecular weight range were observed. The octamer state of beta-lactoglobulin was observed in whey at pH values between 5.1 and 8.0, at temperatures below 10 C, and with .2M addition of potassium thiocyanate, potassium iodide, calcium chloride, or sodium acetate. Similar polymer formation, and temperature and pH effects, were observed with solutions of purified beta-lactoglobulin, which contained dimers, trimers, and tetramers. The beta-lactoglobulin octamer in whey samples could be dissociated by the addition of acid. The bovine serum albumin dimer appeared in whey at pH above 6.2 and at -minus 1 C.     

Systematical characterization of functional and antioxidative properties of heat-induced polymerized whey proteins

Effects of pH (6–8), protein concentration (6–11%, w/v), heating temperature (70–95 °C) and time (5–30 min) on functional and antioxidative properties of heat-induced polymerized whey protein were systematically investigated. All samples were determined for solubility at pH 4.6, emulsion capacity and stability, and antioxidative properties involving 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis(2-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging abilities. Heating resulted in significant loss in solubility, emulsion capacity and stability for whey protein, p?<?0.05. Heating decreased DPPH but enhanced ABTS scavenging ability for whey protein significantly, p?<?0.05. Changes caused by pH variation were much stronger than those observed for other factors. Both protein concentration and heating time had negative effects while heating temperature had positive effect on emulsion capacity of whey protein. Data indicates that functional and antioxidative properties of whey protein could be altered by factors including pH, protein concentration, heating temperature and time.     

Ultrasound‐induced changes in physical and functional properties of whey proteins

Use of high‐intensity ultrasound to modify certain functional properties of whey proteins is an alternative to traditional method in food industry. Whey protein isolate (WPI) solutions were treated with an ultrasound probe (20 kHz) at different intensities (20% or 30% amplitude) and durations (10 or 20 min). Results showed that ultrasound treatment changed physical and several functional properties of whey proteins including decreased particle size (from 190.4 nm to 138.0 nm), increased surface hydrophobicity (from 5.13 × 10⁵ to 5.77 × 10⁵), free sulphydryl groups (from 52.64 μmol SH g^?1 to 53.64–58.77 μmol SH g^?1), solubility (from 74.95% to 89.70%), emulsion activity index (from 3.18 m² g^?1 to 3.59–5.32 m² g^?1) and emulsion stability index (from 62.26 min to 71.44–104.83 min), and changed viscosity (from 5.51 mPa.s to 4.81–5.64 mPa.s). Therefore, we conclude that high‐intensity ultrasound can be potentially applied to whey proteins to improve its specific functions during food processing.     

Biochemical studies on proteins from cheese whey and blood plasma by-products

Efforts have been done to recover proteins from waste liquors rich in protein in a soluble form. Cheese whey and animal bloods are byproducts from the manufacture of cheese and meat. It contains a variety of proteins which can be reclaimed. The efficiency of protein precipitation from the sweet-cheese whey by the use of hydroxyethyl cellulose (HEC) was similar to that precipitated by the use of carboxymethyl cellulose (CMC). Both are greater than that precipitated by trichloro acetic acid. The same results of the efficiency of precipitation were attained when the plasma protein was precipitated. It was found that cheesewhey protein-HEC-complex and plasms protein-HEC-complex contain a large amount of essential amino acids. Electrophoretic separation of whey protein complex showed that β-Lactoglobulin forms the major fraction while in case of plasma protein complex albumin forms the major fraction. The fractionation patterns of different complexes with HEC, CMC or TCA gave the same components and about the same ratio. It appears from these results that HEC-protein complexes are preferable than CMC-protein complexes or proteins precipitated by TCA. Chemical analysis of whey protein complexes revealed that lactose content of whey protein-HEC-complex was higher than that of CMC-complex or protein precipitated by TCA. Elemental analysis of protein complexes showed that the level of sodium, phosphorus, and potassium was increased while that of copper or zinc decreased. Cellulose derivative protein complexes showed no significant effects on the liver or kindney function of albino rat and these results indicated that no toxic effect was observed from the uses of these protein complexes in feeding.     

Effect of pH and calcium concentration on some textural and functional properties of mozzarella cheese

The effects of Ca concentration and pH on the composition, microstructural, and functional properties of Mozzarella cheese were studied. Cheeses were made using a starter culture (control) or by direct acidification of the milk with lactic acid or lactic acid and glucono-delta-lactone. In each of three trials, four cheeses were produced: a control, CL, and three directly-acidified cheeses, DA1, DA2, and DA3. The cheeses were stored at 4 degrees C for 70 d. The Ca content and pH were varied by altering the pH at setting, pitching, and plasticization. The mean pH at 1 d and the Ca content (mg/g of protein) of the various cheeses were: CL, 5.42 and 27.7; DA1, 5.96 and 21.8; DA2, 5.93 and 29.6; DA3, 5.58 and 28.7. For cheeses with a high pH (i.e., approximately 5.9), reducing the Ca content from 29.6 to 21.8 mg/g of protein resulted in a significant decrease in the protein level and increases in the moisture content and mean level of nonexpressible serum (g/g of protein). Reducing the Ca concentration also resulted in a more swollen, hydrated para-casein matrix at 1 d. The decrease in Ca content in the high-pH cheeses coincided with increases in the mean stretchability and flowability of the melted cheese over the 70-d storage period. The fluidity of the melted cheese also increased when the Ca content was reduced, as reflected by a lower elastic shear modulus and a higher value for the phase angle, delta, of the melted cheese, especially after storage for <12 d. The melt time, flowability, and stretchability of the low-Ca, high-pH DA1 cheese at 1 d were similar to those for the CL cheese after storage for > or = 12 d. In contrast, the mean values for flowability and stretchability of the high-pH, high-Ca DA2 cheese over the 70-d period were significantly lower than those of the CL cheese. Reducing the pH of high-Ca cheese (27.7 to 29.6 mg/g of protein) from -5.95 to 5.58 resulted in higher flowability, stretchability, and fluidity of the melted cheese. For cheeses with similar pH and Ca concentration, the method of acidification had little effect on composition, microstructure, flowability, stretchability, and fluidity of the melted cheese.     

High pressure microfluidization treatment of heat denatured whey proteins for improved functionality

Solutions (5% protein) of a whey protein concentrate (WPC) in fresh acid whey or in water, as well as the fresh whey alone, were adjusted to pH 5.8, 4.8 or 3.8, heat treated at 90 °C for 10 min and further exposed to high pressure (150 MPa) microfluidization treatment. The volumes of sediment after centrifugation were recorded as a measure of the degree of insolubility of the proteins. Microfluidization disrupted the heat-induced aggregates into non-sedimenting whey protein polymers so that in some cases, especially at pH 3.8, the products studied were almost completely resistant to sedimentation after the microfluidization treatments. Heat denatured/microfluidized whey proteins reaggregated upon subsequent heating, with the pH having a major impact on the amount of sediment produced. Microfluidization of aqueous WPC solutions heat-treated before spray- or freeze-drying substantially increased the solubility of the powders upon reconstitution. Heat-induced viscoelastic gels were produced from freeze-dried microfluidized samples processed at pH 3.8 and reconstituted to solutions containing 12% (w/w) protein.     

Effect of incorporation of denatured whey protein on the yield and quality of Cheddar cheese

Concentrated suspensions of a denatured protein-fat complex were prepared by centrifugation of whey which had been heated in acid conditions. Significant improvements in cheese yield were obtained on adding the concentrate to milk for cheesemaking before renneting. A maximum increase in yield of 7% was attained in manufacturing Cheddar cheese which satisfied the legal requirements for moisture content. No consistent texture or flavour defects were evident in the cheese during the first jive months of maturation.     

大豆乳清蛋白功能特性的研究

对经过膜分离技术提取的大豆乳清蛋白的功能特性进行研究。主要研究了pH对大豆乳清蛋白的溶解特性、起泡性能及乳化性能的影响,并对大豆乳清蛋白的组成成分进行了电泳分析。结果表明,大豆乳清蛋白具有较好的溶解性及起泡性,但泡沫稳定性及乳化性不如大豆分离蛋白。大豆乳清蛋白主要包含6种成分。     

Compositional and physical properties of yogurts manufactured from milk and whey cheese concentrated by ultrafiltration

Yogurts made with 80% milk retentate (MR) [Volume Reduction Factor (VRF) = 1.5] and 20% cheese whey retentate (WR; VRF = 8.0) (yogurt 1) and yogurts made with 100% MR through ultrafiltration have been evaluated as to flow, texture profile analysis (TPA) and syneresis index. As with MR and WR, their physico‐chemical composition was also determined. The yogurt to which WR had been added showed; less apparent viscosity and greater tixotrophya; less firmness and adhesiveness and greater cohesiveness; higher syneresis index, less protein and mineral content, and greater lipid content in comparison with the yogurt made only with MR.     

Water sorption by proteins: milk and whey proteins

The content and physical state of water in foods influence their physical, chemical, quality, safety, and functional behavior. Information concerning the sorption behavior of dairy proteins, in the water activity (Aw) range 0 to 0.9, is collated in this paper. The sorption behavior of proteins in general, the kinetics of absorption, factors affecting water binding, the phenomenon of desorption hysteresis, and the chemical and physical nature of water/protein interactions are reviewed in general terms. This is followed by a discussion of thermodynamic aspects of sorption phenomena and the adequacy of the various equations for describing sorption isotherms of proteins. After a discussion of the methods available for measuring sorption by milk proteins, the sorption behavior of various milk protein preparations, i.e., nonfat dry milk, whey proteins, caseins, and milk powders is summarized. Finally, the water activity of cheese and its relationship to solute mobility and solvent water are discussed. Some of the unique features of protein behavior, i.e., conformational changes, swelling, and solubilization are cited as possible sources of disparities between various reports.     

Interactions between whey proteins and salivary proteins as related to astringency of whey protein beverages at low pH

Whey protein beverages have been shown to be astringent at low pH. In the present study, the interactions between model whey proteins (β-lactoglobulin and lactoferrin) and human saliva in the pH range from 7 to 2 were investigated using particle size, turbidity, and ζ-potential measurements and sodium dodecyl sulfate-PAGE. The correlation between the sensory results of astringency and the physicochemical data was discussed. Strong interactions between β-lactoglobulin and salivary proteins led to an increase in the particle size and turbidity of mixtures of both unheated and heated β-lactoglobulin and human saliva at pH ∼3.4. However, the large particle size and high turbidity that occurred at pH 2.0 were the result of aggregation of human salivary proteins. The intense astringency in whey protein beverages may result from these increases in particle size and turbidity at these pH values and from the aggregation and precipitation of human salivary proteins alone at pH <3.0. The involvement of salivary proteins in the interaction is a key factor in the perception of astringency in whey protein beverages. At any pH, the increases in particle size and turbidity were much smaller in mixtures of lactoferrin and saliva, which suggests that aggregation and precipitation may not be the only mechanism linked to the perception of astringency in whey protein.