Changes In Whey Proteins Research Articles

Changes in whey protein produced by different sterilization processes and lactose content: Effects on glycosylation degree and whey protein structure

In this study, the interaction patterns between whey protein and lactose were investigated after different ratios of whey protein and lactose (1:2.5; 1:3.0; 1:3.5; 1:4.0; 1:4.5) were treated with two typical sterilization process parameters in powdered products (68 °C, 20 min; 72 °C, 15 min) and two typical sterilization process parameters in liquid products (121 °C, 10 min and 121 °C, 15 min). It was found that the degree of the Maillard reaction of whey protein-lactose solution increased with increasing lactose content, increasing sterilization temperature, or extending sterilization time, which was accompanied by changes in the protein structure of whey protein. In addition, glycosylation accelerates the decrease in free sulfhydryl content, decreasing surface hydrophobicity and decreasing fluorescence intensity. These findings highlight the advantages of designing protein-carbohydrate formulations with a high ratio of whey protein-lactose (1:2.5) to meet the requirements of the product standards for preterm/low-birth-weight infant formulas. When comparing only the sterilization processes of powder and liquid products, the pasteurization process of powder products significantly reduced the degree of the Maillard reaction caused by heat treatment and reduced protein denaturation.

Label-free quantitative proteomic analysis of functional changes of goat milk whey proteins subject to heat treatments of ultra-high-temperature and the common low-temperature

This work investigated the functional changes in whey proteins obtained from goat milk subject to various temperature treatments. Ultra-high temperature instantaneous sterilization (UHTIS) caused less damage than the common low-temperature, whereas spray-drying treatment had the opposite effect. A total of 426 proteins were identified in UHTIS and control treatment groups, including 386 common proteins and 16 and 14 unique proteins. The UHTIS treatment upregulated 55 whey proteins while down-regulated 98. The UHTIS-treated whey proteins may upregulate three metabolic pathways but downregulate one. Overall, UHTIS only slightly impacted the composition and functions of whey proteins from goat milk compared to the common low-temperature treatments.

Comparative analysis of changes in whey proteins of goat milk throughout the lactation cycle using quantitative proteomics.

The composition and content of goat milk proteins are affected by many factors and have been extensively studied. However, variation in whey protein composition in goat milk throughout the lactation cycle has not been clarified. In the current study, 15 dairy goats were selected, and milk samples were collected at 1, 3, 30, 90, 150, and 240 d after delivery. Whey proteins were separated and digested and then identified using data-independent acquisition (DIA) and data-dependent acquisition proteomics approaches. Protein profiles identified using DIA were consistent with those of the data-dependent acquisition proteomics approach according to clustering and principal component analyses. Significant differences in the abundance of 238 proteins around the lactation cycle were identified using the DIA approach. Developmental changes of the whey proteome corresponding to lactation stage were revealed: plasminogen, α-2-macroglobulin, and fibronectin levels decreased from d 1 to 240, whereas polymeric immunoglobulin receptor, nucleobindin 2, fatty acid-binding protein 3, and lactoperoxidase increased from d 1 to 240. Protein-protein interaction analysis showed that fibronectin with a higher degree of connectivity is a central node. The findings are of great significance to better understanding the potential role of specific proteins and the mechanism of protein biosynthesis or intercellular transport in the mammary glands related to the physiological changes of dairy goats.

Relationship between whey protein nitrogen index of skim milk powder and the heat stability of recombined filled evaporated milk

In this study, it was evaluated whether the whey protein nitrogen index (WPNI) of a range of skim milk powder (SMP) samples was correlated with the heat stability of the corresponding recombined filled evaporated milk (RFEM), as well as with the extent of lactosylation and changes in whey proteins (WPs). Pulsed field gradient NMR results showed that the diffusion coefficients of lactose in all samples varied only to a small extent, while the diffusion coefficients of the WP fraction ranged more widely. A lower heat stability of RFEM produced from SMP with a lower WPNI was found as compared with those with a higher WPNI: principal component analysis (PCA) and correlation analysis revealed that the decreased heat stability could be at least partly explained by the increased calcium solubilization induced by the lower pH of dispersions of SMP with a lower WPNI. Although it was claimed over the years that high-heat SMP (with a low WPNI) is beneficial to ensure a better heat stability of RFEM, it is clear from our results that a low WPNI of SMP alone was not sufficient to guarantee a better RFEM-heat stabilizing functionality.

Heat-induced denaturation and bioactivity changes of whey proteins

As the second most abundant protein in milk, whey contains many bioactive proteins, which play important role in the health benefits and defence system of consumers. Whey proteins usually undergo different heating treatments during dairy processing. Although heat treatment kills pathogens and bacteria to guarantee the safety of dairy products, it also causes changes in the structure and bioactivity of whey proteins. This review first introduces a few abundant whey proteins as well as their biological functions, then describes the changes in the physicochemical properties, Maillard reaction, oxidation, cross-linking and aggregation of whey proteins. Last but not least, we also discuss heat induced the changes in digestibility, allergenicity, and other bioactivity of whey proteins. In summary, the heat induced denaturation of whey proteins may not only influence the nutritional value, but may also change the properties of dairy products, the immunological reaction and bioactivity.

Effects of ohmic heating on structural and physicochemical changes of whey proteins

Effects of ohmic heating on structural and physicochemical changes of whey proteins

The influence of the addition of transglutaminase at different phase on the film and film forming characteristics of whey protein concentrate-carboxymethyl chitosan composite films

Abstract To reveal how transglutaminase (TG) affects the forming characteristics of whey protein concentrate (WPC)-carboxymethyl chitosan (CMCS) composite films and to develop the optimum approach for TG-modifying WPC-CMCS composite films, TG was added at different phases to WPC-CMCS composite films, and the properties and structural characteristics of the composite films and their film-forming solutions were investigated. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) results confirmed that TG could promote protein intermolecular polymerization to form macromolecular substances. TG could improve the mechanical and rheological properties of WPC-CMCS composite films, which depended on the TG addition phase during film preparation. The results from the film characterization showed that the mechanical properties and rheological property of WPC-TG-CMCS films are better than those of WPC-CMCS-TG films, which indicated that TG had stronger cross-linking ability with whey protein in WPC-TG-CMCS films. FTIR analysis showed that TG caused conformational changes in whey protein in composite films. X-ray diffraction analysis suggested that TG could promote the polymerization of protein molecules and reduce the porosity of the protein network structure, thus improving crystallinity. All the results suggested that the suitable addition phase of TG had a positive effect on the film-forming characteristics of WPC-CMCS composite films, and the films can be applied as an alternative for some petroleum-based packaging materials.

Heat induced conformational changes of whey proteins in model infant formulae: Effect of casein and inulin

The effect of casein (CAS) and inulin (INUL), at ratios commonly found during infant formula processing, on the conformational changes of whey proteins (WP) was investigated. Model systems were prepared as aqueous dispersions of WP isolate alone or with calcium caseinate and/or INUL, and heated for 30 min at 66, 70 or 75 °C. Heat treatment of WP induced denaturation and aggregation. Solubility of WP system decreased by 25% when heated at 75 °C. Upon heating, the presence of CAS did not prevent WP denaturation, but increased protein solubility up to 100% in WP–CAS system and prevented aggregation. INUL affected the secondary structure of WP and increased the denaturation temperature, although it did not prevent aggregation nor solubility loss at 75 °C. In conclusion, presence of CAS prevented aggregation and solubility loss of WP during heating while INUL induced WP conformational changes impacting the denaturation stage.

Sensory, physico-chemical, microbial and textural changes in whey protein concentrate based extruded snack food during storage

Extruded snacks are gaining recognition as well as appreciation these days due to their ready-to-eat nature, delicious taste and appealing look. Combination of lysine rich whey protein concentrate with lysine deficient cereal protein has synergistic effect that imparts a high nutritional value to the mixed protein in the product. The milk solids based extruded snack food and control sample were stored at room temperature (37±2 °C) after packaging in MET PET material. The whey protein concentrate based extruded snack food samples and control sample were analyzed for changes in sensory characteristics, physico-chemical properties and textural properties as well as for microbiological quality at 15 days interval. Sensory scores, fracturability for experimental sample and control decreased while moisture, water activity and hardness increased during entire storage period. The Standard plate count decreased while coliform count and yeast and mold count were found absent till 180 days of storage.

Comparison of dry- and wet-heat induced changes in physicochemical properties of whey protein in absence or presence of inulin.

Changes in whey protein (10%, w/v) induced by dry-heating (60°C for 5days at a relative humidity of 63%), wet-heating (85°C for 30min) or the two-combined heating in absence or presence of inulin (8%, w/v) were studied. Mixture of whey protein and inulin showed significantly higher absorbance at 290nm than whey protein alone in all heating conditions while only dry-heated samples showed significantly increased absorbance value at 420nm (p < 0.05). Whey protein after heating showed significantly lower zeta potential and inulin decreased the value of all heated samples further (p < 0.05) except for samples after dry-heating. Heating decreased the free sulfhydryl group content of whey protein samples while presence of inulin decreased further (p < 0.05). Dry-heating decreased while wet-heating increased the surface hydrophobicity of whey protein. Inulin had no effect on the surface hydrophobicity of heated whey protein under dry-heating but decreased under wet-heating.

Liposome-whey protein interactions and its relation to emulsifying properties

The interactions between liposomes and whey proteins (WP) were investigated using sodium dodecyl sulfate polyacrylamide gel electropheresis, intrinsic fluorescence, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, turbidity, particle size, and zeta potential. These results indicated that WP interacted with liposomes via electrostatic force, hydrophobic force, and hydrogen bonds. The interactions between WP and liposomes also led to the alteration of WP secondary structure, and it could be observed that the interactions induced an increase in random coil content at the cost of a decrease in α-helix. Furthermore, the emulsifying properties of WP significantly increased in the presence of liposomes. Emulsifying activity index and emulsifying stability index of WP increased from 12.12 to 20.36 m2/g, from 64.24% to 89.25%, respectively. However, the emulsifying properties of WP were also influenced by liposomal composition, pH, and temperature. The changes of WP structures were important reason for the changes of WP emulsifying properties. Our work provides new insights into the application of liposomes in food.

Effects of gamma radiation on microbial, physicochemical, and structural properties of whey protein model system

Gamma radiation has been used in food processing for many years, though it has certain effects on food components. Whey protein solutions (10%/30%, wt/vol) were treated with gamma radiation at various dosages (10-25 kGy) and evaluated for microbial changes in the solutions and physicochemical and structural changes of whey proteins. Whey protein solutions after gamma radiation showed substantially lower populations of all viable microorganisms than those of controls. The 10% whey protein solution treated at radiation of 20 or 25 kGy remained sterile for up to 4 wk at room temperature. Gamma radiation increased viscosity and turbidity and decreased soluble nitrogen of whey protein solutions compared to nonradiated control samples regardless of radiation dosage. Nonreducing sodium dodecyl sulfate-PAGE suggested that whey proteins under gamma radiation treatment formed aggregates with high molecular weights. Reducing sodium dodecyl sulfate-PAGE showed that disulfide bonds played a role in gamma radiation-induced whey protein cross-linking. Scanning and transmission electron microscopy micrographs exhibited large aggregates of whey proteins after gamma radiation treatment. Results suggested that gamma radiation could be applied to whey protein solution for purposes of reducing microbial counts and cross-linking protein molecules.

Physical and chemical changes in whey protein concentrate stored at elevated temperature and humidity

In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9g of protein/100g (WPC34) and 76.8g of protein/100g (WPC80) were stored for up to 18mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35°C were removed from the study by 12mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80had a shelf life of 9mo at 35°C but at least 18mo at lower temperatures, which should extend the market for these products.

Changes in whey protein of colostrum milk

Changes in whey protein of colostrum milk

Decoupling macronutrient interactions during heating of model infant milk formulas.

Understanding macronutrient interactions during heating is important for controlling viscosity during infant milk formula (IMF) manufacture. Thermal behavior of macronutrients (casein, whey, lactose, fat) was studied, in isolation and combination, over a range of concentrations. Addition of phosphocasein to whey protein solutions elevated denaturation temperature (Td) of β-lactoglobulin and the temperature at which viscosity started to increase upon heating (Tv). Secondary structural changes in whey proteins occurred at higher temperatures in dispersions containing phosphocasein; the final extent of viscosity increase was similar to that of whey protein alone. Addition of lactose to whey protein solutions delayed secondary structural changes, increased Td and Tv, and reduced post heat treatment viscosity. This study demonstrated that heat-induced changes in IMF associated with whey protein (denaturation, viscosity) are not only a function of concentration but are also dependent on interactions between macronutrients.

Effect of Enzymatic Deamidation on the Heat-induced Conformational Changes in Whey Protein Isolate and Its Relation to Gel Properties

The effect of protein-glutaminase (PG) on the heat-induced conformational changes in whey protein isolate (WPI) and its relation to gel properties was investigated. The structural properties of WPI treated with PG were examined by several analytical methods. The analysis of the fluorescence spectrum and the binding capacity of a fluorescent probe demonstrated that deamidation prevented the increase in the fluorescence intensity caused by subsequent heat treatment. Measurements of the molecular weight distribution of WPI showed that PG-treated WPI was not likely to polymerize even after heating. This is thought to be due to an increase in electrostatic repulsion between carboxylic acid groups and a decrease in the formation of disulfide bonds, which results in the decrease in heat-induced aggregation. The properties of heat-induced WPI gels were modified by deamidation. PG-treated WPI gels had a soft texture and a high water-holding capacity in the presence of salts.

Structural Changes Imposed on Whey Proteins by UV Irradiation in a Continuous UV Light Reactor

The objective of this study was to investigate the structural changes of whey proteins during exposure in a continuous-flow UV reactor. Varying UV irradiation dosages were obtained by controlling the flow rate and the mixing speed. Whey protein isolate (WPI) solutions at concentrations of 1% and 5% (w/v) were circulated at flow rates ranging from 30 to 800 mL·min(-1), and changes in physicochemical properties of the proteins were investigated. Intrinsic fluorescence spectra and surface hydrophobicity measurements suggested changes in the tertiary structure of the proteins with UV exposure. The UV treatment also increased the concentration of total and accessible thiol groups in 1% WPI solutions, while no change was measured in 5% WPI solutions. Size-exclusion chromatography demonstrated the formation of UV-induced aggregates and oxidation products (N-formylkynurenine and dityrosine) of aromatic amino acids. Furthermore, the UV-induced changes in protein conformation increased the susceptibility of whey proteins to pepsin hydrolysis.

Behavior of Protein in the Presence of Calcium during Heating of Whey Protein Concentrate Solutions

The effect of added CaCl(2) on heat-induced changes in whey protein (WP) solutions prepared from whey protein isolate (WP1), acid whey protein concentrate (WP2), and cheese whey protein concentrate (WP3) was investigated. The loss of native-like, proteins, aggregation, and gel firmness of WP were maximum at certain levels of added CaCl(2). These levels were different for different WP products. The effect of added CaCl(2) on these changes appeared to be related to the initial calcium concentrations of these solutions. The higher the calcium content of the product, the less available sites for added CaCl(2) to bind. It was considered that addition of CaCl(2) changed the types of protein interactions that formed the protein aggregates during heating. Added calcium caused dramatic decreases in fracture stress of WP gels due to the formation of large protein aggregates.

Composition and renneting properties of raw bulk milk in Estonia

Seasonal variations in milk composition and renneting properties were determined in more than 1000 raw bulk milk samples from individual farms in Estonia. Pooled milk from tank trucks and dairy silos originating from the same milkings was also analysed. Changes in whey protein to casein ratio, due to partial degradation of κ- and β-casein fractions, were observed in pooled milk from tank trucks and dairy silos. Likewise, rennet flocculation time (RFT) was 1 min longer compared with that of milk from individual farms. Milk pH correlated significantly with curd firmness and RFT, whereas curd firmness correlated also with protein content and with κ-casein fraction in particular ( r = 0.45). The important correlations between milk composition and renneting characteristics observed earlier in the case of milk from individual cows were essentially the same in the case of bulk milk delivered for processing.

A Kinetic Study on the Heat-Induced Changes of Whey Proteins Concentrate at Two pH Values

Whey protein concentrate (WPC) is used as food ingredients due to their commercially important functional properties. The effects of heat treatment on the components of milk are very important for the final product character, since they undergo modifications that affect sensorial and nutritional quality of milk. The heat-induced changes on dispersions of whey proteins concentrate were monitored by measurement of thiol availability, protein solubility, and turbidity at pH 6.6 and 7.5. The fractional conversion model was used to quantitatively describe the effect of different temperature–time combination on denaturation mechanism. The results demonstrate that heat-induced changes of WPC greatly influence their solubility, expressed as degree of denaturation at pH 4.6 and were related to the heating conditions. The denaturation mechanism involved a number of consecutive conformational changes in the molecules. A curvature in Arrhenius plots was observed around 75 °C, indicating changes in the reaction mechanism. The deflection of Arrhenius plot reflects the generally accepted two-step denaturation/aggregation process of whey proteins.