Evaluation of Yield and Quality of Cheddar Cheese Manufactured from Milk with Added Whey Protein Concentrate

Cheddar cheese was produced from whole milk with blends of whey protein concentrates added. Two whey protein concentrate powders containing 35 or 55% protein were each reconstituted to a 15% (wt/wt) suspension and heat treated at 70°C for 15 min. Addition of the denatured whey protein concentrate suspension to the milk was at 5 or 10% by weight of the milk. Addition of reconstituted partially denatured whey protein concentrate increased cheese yields from 1.4 to 6.2% above those of the control on a 63% solids basis. The only significant (P<.05) increase in yield was from the 55% whey protein concentrate suspension at 10% replacement by weight of the milk. The correlation coefficient between percent denaturation in the whey protein concentrate and yield in this cheese was .62. Experimental cheese had decreased fat and total solids contents and increased total nitrogen, ash, and salt. Fat reduction varied from 4.3 to 18.2% below the control cheese, and total solids were from 1.7 to 8.9% below the control cheeses. Total nitrogen values of experimental cheese were from .73 to 5.64% above the control. Cheeses were evaluated organoleptically; more flavor defects were associated with increased whey protein concentrate in the experimental cheese. The most common criticism of the experimental cheese was an atypical (unclean) cheese flavor.     

Gel-Forming Characteristics of Milk Proteins. 1. Effect of Heat Treatment

Skim milk with or without preheating (60 to 80°C for 30 min) were acid coagulated at 60 to 80°C for 1 h with glucono-delta-lactone. Preheating below 70°C has no effect on gel firmness and water-holding capacity. When coagulated below 70°C, the gels were weak and had low water-holding capacity. When coagulated at 80°C, the gels were solid and had high water-holding capacity. Gels prepared from skim milks preheated to above 80°C had a different quality: when coagulated at less than 70°C, gel firmness increased slightly, and when coagulated at 80°C, gel firmness decreased sharply. Change in the accessibility of sulfhydryl groups in milk protein caused by heating, was also measured using Ellman's reagent. Changes in the gel-forming property of milk protein, caused by the heat treatment, were closely related to increase in available sulfhydryl groups in milk proteins, and also were related to heat denaturation of whey protein or the formation of β-lactoglobulin/κ-casein complex.     

Whey protein concentrate gels with honey and wheat flour

Structural and functional properties of whey protein concentrate (WPC) gels with different honey and wheat flour contents, prepared at pHs 3.75, 4.2 and 7.0, were analysed. Gel structure was observed by scanning electron microscopy. The apparent transition temperatures for protein denaturation and starch gelatinization were determined by differential scanning calorimetry. Gels were characterised through solubility assays in different extraction solutions and polyacrylamide gel electrophoresis of the soluble protein components. The firmness, elasticity, relaxation time, adhesivity and cohesiveness of gels were determined, and the water-holding capacity and superficial colour of gels were also studied. Results suggest that wheat flour could interact with whey proteins, and produces a decrease in the protein solubility of WPC gels, and in the temperature of whey protein denaturation. The effect of wheat flour on the functional properties of WPC gels was different at acidic than at neutral pH: the presence of wheat flour produced an increase in the relaxation time and in the cohesiveness of gels prepared at pH 3.75, whereas at neutral pH a decrease in both properties was observed. Honey and flour content increased the water-holding capacity and browning of WPC gels.     

Compositional and functional properties of buttermilk: a comparison between sweet, sour, and whey buttermilk

Buttermilk is a dairy ingredient widely used in the food industry because of its emulsifying capacity and its positive impact on flavor. Commercial buttermilk is sweet buttermilk, a by-product from churning sweet cream into butter. However, other sources of buttermilk exist, including cultured and whey buttermilk obtained from churning of cultured cream and whey cream, respectively. The compositional and functional properties (protein solubility, viscosity, emulsifying and foaming properties) of sweet, sour, and whey buttermilk were determined at different pH levels and compared with those of skim milk and whey. Composition of sweet and cultured buttermilk was similar to skim milk, and composition of whey buttermilk was similar to whey, with the exception of fat content, which was higher in buttermilk than in skim milk or whey (6 to 20% vs. 0.3 to 0.4%). Functional properties of whey buttermilk were independent of pH, whereas sweet and cultured buttermilk exhibited lower protein solubility and emulsifying properties as well as a higher viscosity at low pH (pH ≤ 5). Sweet, sour, and whey buttermilks showed higher emulsifying properties and lower foaming capacity than milk and whey because of the presence of milk fat globule membrane components. Furthermore, among the various buttermilks, whey buttermilk was the one showing the highest emulsifying properties and the lowest foaming capacity. This could be due to a higher ratio of phospholipids to protein in whey buttermilk compared with cultured or sweet buttermilk. Whey buttermilk appears to be a promising and unique ingredient in the formulation of low pH foods.     

Structure and Functionality of Whey Protein Concentrate-Based Products with Different Water Contents

Properties of different heated mixtures of whey protein concentrate, starch, gelatin, and sucrose with different water contents were studied. The water activity of samples was determined. The structural properties were analyzed by confocal laser scanning microscopy, solubility assays in different extraction solutions, polyacrylamide gel electrophoresis, and differential scanning calorimetry. Color, texture, and water-holding capacity of samples were also determined. Results show that a certain water content it is needed to form a structure with solid characteristics in these mixtures. The temperature for starch gelatinization is lower than the temperature for whey proteins denaturation, but when sucrose is present, whey proteins are denatured, before the gelatinization of starch. Sucrose is major contributor to the adhesiveness of the samples and to the decrease of their water activity. Also, sucrose decreases the firmness and cohesiveness of the samples. The main component that contributes to the browning of the samples during the heat treatment is whey protein concentrate, whereas starch is the main component responsible for the water-holding capacity in these samples. Gelatin does not modify appreciably the properties of the mixtures in the proportion used in these assays.     

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.     

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.     

Use of chitosan for selective removal of beta-lactoglobulin from whey

A method is described for selective removal of undenatured β-lactoglobulin from cheese whey based on interactions between whey proteins and chitosan. Whey was previously clarified at pH 4.5 with addition of chitosan (25 mg/100 mL), and selective removal of β-lactoglobulin was studied in the pH interval 4.6 to 6.5. Addition of chitosan caused selective precipitation of β-lactoglobulin that increased with pH. The content of β-lactoglobulin in whey decreased as the amount of chitosan added was increased. At pH 6.2, addition of 1.9 to 3.0 mg/mL of chitosan led to complete removal of β-lactoglobulin, whereas at least 80% of the rest of whey proteins remained in solution. The production of cheese whey without β-lactoglobulin could help to expand the applications of dairy by-products in food processing, and to isolate hypoallergenic whey protein concentrates.     

Preliminary observations on the effects of milk fortification and heating on microstructure and physical properties of stirred yogurt

The aim of this work was to study how milk fortification and heating affect yogurt microstructure (micellar characteristics, protein network) and physical properties (viscosity, water-holding capacity (WHC), and graininess). Milk was fortified with skim milk powder (control), whey protein concentrate (WPC), caseinate, or a mixture of caseinate and whey protein. Two heat treatments were applied, giving average whey protein denaturation levels of 58% and 77%. For caseinate-enriched yogurts, the heating effect was negligible. When milk was enriched with WPC, heating led to a high level of cross-linking within the gel network. Heating increased yogurt viscosity and WHC, but also graininess. When milk was fortified with a blend of WPC and caseinate giving a whey protein-to-casein ratio of 0.20, the yogurt viscosity was greatly improved, while graininess was kept low. The results show a relationship between micelle solvation and yogurt microstructure, as well as micelle size in milk base and yogurt graininess.     

Roselle (Hibiscus sabdariffa L.) and soybean oil effects on quality characteristics of pork patties studied by response surface methodology

Response surface methodology was used to investigate the effect and interactions of processing variables such as roselle extract (0.1–1.3%), soybean oil (5–20%) on physicochemical, textural and sensory properties of cooked pork patties. It was found that reduction in thickness, pH, L* and b* values decreased; however, water-holding capacity, reduction in diameter and a* values increased, respectively, as the amount of roselle increased. Soybean oil addition increased water-holding capacity, reduction in thickness, b* values of the patties. The hardness depended on the roselle and soybean oil added, as its linear effect was negative at p < 0.01. The preference of color, tenderness, juiciness, and overall quality depend on the addition of roselle and soybean oil. The maximum overall quality score (5.42) was observed when 12.5 g of soybean oil and 0.7 g of roselle extract was added. The results of this optimization study would be useful for meat industry that tends to increase the product yield for patties using the optimum levels of ingredients by RSM.     

Functional properties of native and cheese whey protein concentrate powders

The objective of this study was to compare microfiltered native whey protein concentrate and traditional cheese whey protein concentrate powders and their functional properties. Solubility, viscosity, gelation, foaming properties, emulsification and water-holding capacity were studied. The effect of spray and freeze drying methods on functional properties was evaluated. Gel strength varied from 0.11 to 0.65 N. Foaming stability and overrun varied from 0 to 29.3 min and from 230 to 2200%, respectively. Foaming and gelation properties were clearly better with native whey protein powders. Differences between drying methods were not observed but higher heat load decreased solubility.     

Enhancement of lactase activity in milk by reactive sulfhydryl groups induced by heat treatment

The effects of heat treatments of milk and whey prior to lactose hydrolysis with Kluyveromyces lactis beta-galactosidase were studied. It was observed that heat treatment of milk significantly increases lactase activity, with a maximum activity increase found when milk was heated at 55 degrees C. In whey from 55 up to 75 degrees C, beta-galactosidase activity decreased slightly. Nevertheless, heating whey at 85 degrees C for 30 min raised the rate of hydrolysis significantly. Electrophoretic patterns and UV spectra proved that the activity change correlated with milk protein denaturation, particularly that of beta-lactoglobulin. Heating whey permeate did not increase the enzyme activity as heating whole whey; but heating whey prior to ultrafiltration also resulted in enzyme activation. Measurement of free sulfhydryl (SH) groups in both whey and heated whey permeate showed that the liberation of free SH is highly correlated to the change of the activity. Furthermore, this activation can be reversed by oxidizing the reactive sulfhydryl groups, proving that the observed effect may be related to the release of free SH to the medium, rather than to the denaturation of a thermolabile protein inhibitor.     

Physicochemical changes of myofibrillar proteins during processing of Cantonese sausage in relation to their aggregation behaviour and in vitro digestibility

The physicochemical changes of myofibrillar proteins, especially oxidation behaviour, were measured to determine their mechanism of action on in vitro protein digestibility during Cantonese sausage processing. The results indicated that the carbonyl level significantly increased (p < 0.05) during the process. The SH group level decreased, while S–S group level increased gradually. Protein aggregation was induced by oxidation and heat treatment. Result from Fourier transform infrared (FTIR) spectroscopy confirmed protein aggregation occurred. The analysis of in vitro digestibility showed a highly significant (p < 0.05) correlation between pepsin activity and carbonyl group formation, S–S group level, protein surface hydrophobicity, D_4,3. A negative and highly significant correlation between trypsin, α-chymotrypsin activity and carbonyl group formation was measured, while no significant correlation with S–S groups, protein surface hydrophobicity, D_4,3 was observed. It indicated that not only protein oxidation and aggregation but also degradation by pepsin would influence proteolysis with trypsin and α-chymotrypsin.     

Effect of protein supplementation on the rheological characteristics of milk permeates fermented with exopolysaccharide-producing Lactococcus lactis subsp. cremoris

This research studied the effect of addition of whey proteins on the rheological properties of ultrafiltration permeate fermented with the exopolysaccharide (EPS)-producing strain Lactococcus lactis subsp. cremoris JFR1. Milk permeates containing 8% solids and various levels of added whey proteins (0, 2, 4, 6 and 8%) were fermented for 12 h at 30 °C. The rheological properties of the fermented samples were then evaluated and compared to controls fermented with a non-EPS producing strain. Scanning electron microscopy was also employed to confirm the existence of interactions between whey protein aggregates and EPS. The presence of EPS considerably increased the viscosity and viscoelastic properties of the media, especially in samples containing >2% whey protein added. The results obtained demonstrate the importance of EPS–protein interactions in structure formation and may help explain the viscosifying mechanism of EPS in fermented dairy products. Production of highly viscous material could potentially be employed in the future as a novel fiber-rich functional ingredient in dairy products.     

Granulomorphometry: a suitable tool for identifying hydrophobic and disulfide bonds in β-lactoglobulin aggregates. Application to the study of β-lactoglobulin aggregation mechanism between 70 and 95°C

This work deals with the investigation of β-lactoglobulin (β-LG) aggregation by granulomorphometry. In the first part of this study, we showed that the binding interactions involved in aggregate structure could be identified by their appearance in granulomorphometric pictures. The reliability of this analytical approach was demonstrated by comparing the appearance of β-LG aggregates in the presence and absence of a thiol-blocking agent (N-ethylmaleimide). The translucency of the aggregates was associated with hydrophobic interactions and their opacity was associated with disulfide bonds. We state, based on the morphology of the aggregates, along with the color of protein aggregates and insoluble materials, that hydrophobic interactions had a better water-holding capacity than disulfide bonds. Additionally, our results suggest that disulfide and hydrophobic bonds compete for β-LG aggregate shaping. In the second part of this work, interesting features of granulomorphometry useful for identifying aggregate binding interactions were highlighted to clarify the effect of temperature on the aggregation mechanisms occurring in a β-LG concentrate with a moderate calcium content (6.6mmol·L(-1)). Heat treatment experiments were performed between 70 and 95°C, and granulomorphometric measurements (aggregate size, aggregate number, and gray level of the picture) were conducted at different sampling times up to 4h. Results, which were interpreted in light of calculated β-LG denaturation levels, revealed that the aggregation mechanism could be split into 2 steps. Initially, β-LG denatured quickly, leading to fast β-LG aggregation by disulfide bonds. The denaturation rate then declined, which drastically slowed the disulfide aggregation mechanism. From that point on, a second aggregation path became preponderant. It consisted of the agglomeration of small aggregates by hydrophobic interactions and resulted in the formation of large aggregates containing both interaction types. This second aggregation mechanism was clearly favored at high temperatures because it was not detected in our experiments at temperatures below 85°C.     

L-组氨酸修饰乳清蛋白结构及其热诱导凝胶特性

采用L-组氨酸（L-His）作为蛋白凝胶功能性的增强剂,将其加入乳清分离蛋白溶液中制备热诱导凝胶,研究L-His对乳清蛋白结构及其凝胶特性的影响。结果表明：在乳清蛋白等电点（pI 5.2）时蛋白形成尺度约1 700 nm、具有极小比表面积且几乎不带电的蛋白聚集体,远离蛋白等电点时则所形成的聚集体大小约为400 nm;L-His抑制蛋白聚集体的形成而减小粒径、显著提高聚集体比表面积,促进蛋白分子结构展开并提高其带电量。在经历热诱导后,乳清蛋白在其等电点时形成持水性差的白色凝胶,而在其他pH值时则形成持水性高的黄色凝胶且越远离等电点,胶体黄度值越大;L-His的加入对凝胶颜色变化无显著影响,但能够显著提高凝胶的持水性（P＜0.05）;有效提高凝胶的质地特性,特别是在pH 7.59和pH 9.74时显著提高乳清蛋白凝胶的弹性及咀嚼性（P＜0.05）。这些质构变化可能主要归结于L-His改变了凝胶内的氢键、二硫键和疏水作用力的重排。总之,L-His修饰乳清蛋白结构而改变其凝胶性能且同时受到pH值的影响。     

Heat-induced Gelation Properties of Salt-Soluble Muscle Proteins as Affected by Non-Meat Proteins

Addition of whey protein concentrate (WPC), whey protein isolate (WPI) or soy protein isolate (SPI) to salt-soluble muscle proteins (SSP) decreased the gel strength. WPI:SSP gels had higher water-holding capacity than SSP, SSP:WPC or SSP:SPI gels. Myosin heavy chain was a principal contributor to gel network formation in SSP, SSP:WPC, SSP:WPI and SSP:SPI systems. The characteristic fibrous network formed by SSP was the dominant feature of the microstructure of SSP:WPC and SSP:WPI gels. SSP:SPI gels had a more aggregated appearance due to the occurrence of clusters of SPI throughout the gel matrix.     

Production and partial purification of proteases from Aspergillus oryzae grown in a medium based on whey protein as an exclusive nitrogen source

Several attempts have been made to incorporate whey proteins into curd to increase cheese yield. For some types of cheese, degradation of whey proteins that have been incorporated into the curd would be required to obtain acceptable flavor and texture. On the basis of the high potential for protease synthesis in Aspergillus oryzae, sodium nitrate as a nitrogen source in a minimal medium for fungi, known as Czapek-Dox medium, was replaced with whey protein isolate to induce the protease to hydrolyze whey protein using A. oryzae AHU7146. A solid-phase medium adjusted to pH 6 was suitable for this purpose when incubation was carried out at 25°C for 2 wk. The application of column chromatography enabled the resolution of 3 proteolytic components (1, 2, and 3). With respect to optimal temperature and zymographic analysis, component 1 was similar to component 3. In contrast, component 2 was less abundant than the other components and exhibited activity in the alkaline pH region. The degradation of β-lactoglobulin and α-lactalbumin in whey protein isolate solution by the crude enzyme was primarily attributed to the action of components 1 and 3, based on HPLC analysis and the N-terminal amino acid sequences; however, zymography demonstrated evident proteolysis due to component 2. Because heat-denatured whey protein aggregates were digestible by the crude enzyme, the proteolytic system from A. oryzae has the potential as an additive to stimulate the ripening of cheese enriched with whey protein.     

Effect of heating whey proteins in the presence of milk fat globule membrane extract or phospholipids from buttermilk

The objective of this study was to determine the contribution of phospholipids from buttermilk as a nucleus in the heat-induced aggregation of whey proteins. Solutions of whey proteins (5%, w/v) were adjusted to pH 4.6 or 6.8 and then heated at 65 or 80 °C for 25 min with or without 1% (w/v) of milk fat globule membrane (MFGM) extract or phospholipid powder. The aggregation mechanisms were characterised using analysis with Ellman's reagent, one-dimensional gel electrophoresis, thin-layer chromatography, and three-dimensional confocal laser-scanning microscopy. Three-dimensional images showed protein/phospholipid interactions in the presence of MFGM extract or phospholipids, and thin-layer chromatography plates showed no trace of free phospholipids after 20 min at pH 4.6. Overall, the results demonstrate that phospholipids from buttermilk were involved in the formation of protein aggregates through the MFGM fragments at a low temperature, whereas phospholipids could interact directly with the proteins at a higher temperature (80 °C).     

Effects of varying time/temperature-conditions of pre-heating and enzymatic cross-linking on techno-functional properties of reconstituted dairy ingredients

The effects of varying time/temperature-conditions of pre-heating and cross-linking with transglutaminase (TG) on the functional properties of reconstituted products from skim milk, WPC and sodium caseinate was analyzed. The degree of cross-linking (DC) of skim milk proteins could be increased from 54.4% to 70.5% by varying process conditions. Thereby the water-holding capacity (WHC) increased from 10% to 20%, while the heat stability decreased. The burning-on was lower than that of the non-treated products at optimum pre-heating conditions (90 °C/30 s). Using sodium caseinate as substrate for TG the DC increased from 39.2% to 100% due to the improvement of the process. As a result the WHC increased by 30% and the heat stability up to 380%. However, the burning-on of casein increased as well. TG-treated sodium caseinate started to gel at 10% protein, whereas untreated sodium caseinate gelled not before 15% protein. The WHC of enzyme-treated whey proteins was lowered. The heat stability of WPC could be doubled by TG-treatment, and the burning-on of the products was, especially at optimum pre-heating conditions, less pronounced. The degree of denaturation of TG-treated whey proteins was 2–5% higher than that of untreated samples.