Rheological properties and structure of inulin–whey protein gels

The rheological properties, structure and synergistic interactions of whey proteins (1–7%) and inulin (20% and 35%) were studied. Gelation of whey proteins was induced with Na⁺. Inulin was dissolved in preheated whey protein solutions (80 °C, 30 min). Inulin gel formation was strongly affected by whey proteins. The presence of whey proteins at a level allowing for protein gel network formation (7%) significantly increased the G′ and G″ values of the gels. Scanning electron micrographs showed a thick structure for the mixed gel. Whey proteins at low concentrations (1–4%) were not able to form a gel; further, these low concentrations partly or wholly impaired formation of a firm inulin gel. Although interactions between inulin and whey proteins may be concluded from hydrophobicity measurements, the use of an electrophoretic technique did not show any inulin–whey protein complexes.     

Effect of added water, sodium erythorbate and storage time on the functional properties of prerigor beef preblends in a model system

Singular and combined effects of added water, sodium erythorbate and storage time on salt soluble protein extractability, bacteriological and chemical characteristics of preblended hot-boned beef were evaluated. Waterholding and gel forming capacities of preblended hot-boned beef containing either 0, 10 or 20% added water were determined. Significant interactions between added water level and storage time on microbial counts and between sodium erythorbate level and storage time on thiobarbituric acid values and residual nitrite levels were noted. The presence of sodium erythorbate resulted in a more (P < 0·05) rapid rate of nitrite disappearance, but it did not affect (P > 0·05) microbial counts. Salt-soluble protein extractability was not affected (P > 0·05) by added water, but more protein could be extracted with increasing storage time. A trend existed to suggest that the presence of added water in the meat preblends slightly improved the gel formation and waterholding capacities.     

CONJUGATED LINOLEIC ACID CONCENTRATIONS IN COOKED BEEF CONTAINING ANTIOXIDANTS AND HYDROGEN DONORS

Conjugated linoleic acid (CLA) is a potential anticarcinogenic compound found in beef. The ability of antioxidants and hydrogen donors to influence CLA concentrations in ground beef during cooking (broiled, 80C) and storage was determined. Addition of food additives such as carnosine, cysteine, ascorbate, whey protein concentrate or beef plasma to ground beef did not result in any significant increases or decreases in CLA concentrations in freshly cooked beef. Additives which inhibited formation of thiobarbituric acid reactive substances in stored meat including 2.0% WPC, 0.5 and 2% beef plasma, ascorbate (0.5%) and carnosine (0.5%) were not any more effective at increasing or decreasing total CLA concentrations than additives which did not inhibit lipid oxidation during storage (0.5% WPC and 0.5% cysteine). Lack of changes in CLA in the presence of antioxidants suggests that these additives could be used to inhibit flavor deterioration of cooked beef products without decreasing CLA concentrations.     

四种常用香辛料对牛肉盐溶蛋白热诱导凝胶特性的影响

肌肉盐溶蛋白热诱导凝胶成型是低温肉制品加工的技术核心,凝胶成型的好坏决定最终产品的品质。本实验以牛肉为原材料提取盐溶蛋白,添加蒜、胡椒、辣椒和生姜粉被常用在低温西式肉制品中的四种香辛料于牛肉盐溶蛋白中,制备牛肉盐溶蛋白热诱导凝胶。通过测定蛋白凝胶硬度、弹性、剪切力和保水性,以及SDS—PAGE电泳分析,首次研究了蒜、胡椒、辣椒和生姜粉对牛肉盐溶蛋白热诱导凝胶特性的影响并初步探讨其作用机理,旨在为牛肉低温制品加工提供一定理论依据。结果表明,蒜粉明显改善牛肉盐溶蛋白热诱导凝胶特性,通过SDS—PAGE电泳分析,蒜粉增加了盐溶蛋白溶解性,增加了蛋白含量,并发现一种分子量介于14.3和6.5KDa的未知蛋白质;添加生姜粉后蛋白含量降低,同时肌球蛋白轻链LC1和LC2消失,从而导致蛋白凝胶特性劣化,;辣椒粉对蛋白热诱导凝胶特性有一定影响;胡椒粉对牛肉盐溶蛋白热诱导凝胶特性无显著影响。     

Microemulsions as nanoreactors to produce whey protein nanoparticles with enhanced heat stability by thermal pretreatment

Native whey proteins (NWPs) may form gels or aggregates after thermal processing. The goal of this work was to improve heat stability of NWPs by incorporating protein solutions in nanoscalar micelles of water/oil microemulsions to form whey protein nanoparticles (WPNs) by thermal pretreatment at 90 °C for 20 min. The produced WPNs smaller than 100 nm corresponded to a transparent dispersion. The WPNs produced at NWP solution pH of 6.8 had a better heat stability than those produced at pH 3.5. The salt concentration (0–400 mM NaCl) in NWP solutions did not significantly change the size of corresponding WPNs. Compared to NWPs, the 5% (w/v) dispersion of WPNs at pH 6.8, 100 mM NaCl did not form a gel after heating at 80 °C for 20 min. The improved heat stability and reduced turbidity of WPNs may enable novel applications of whey proteins in beverages.     

MECHANICAL PROPERTIES OF FISH AND BEEF GELS PREPARED WITH AND WITHOUT WASHING AND SODIUM CHLORIDE

Excellent gels, as measured by fold test, were prepared from three species of fish without first washing the minced tissue. Dependent on species (red hake, cod, or winter flounder), excellent to adequate gels, as determined by the fold test, could be prepared from fish muscle without NaCl provided that the minced tissue was washed prior to gel formation. Postrigor beef formed inadequate gels while excellent to good gels could be produced from prerigor beef although salt was a requirement. The concentration of contractile proteins in fish gels was estimated and they did not appear to be a major factor determining gel quality. Soluble muscle protein did not appear to interfere with gel formation either. Percent expressible moisture, percent recovery, and modulus of deformability did not relate well to fold test scores.     

食盐和大豆蛋白对牛肉凝胶特性的影响

主要研究了食盐和大豆蛋白对牛肉凝胶特性及颜色的影响,结果表明:随食盐添加量的增加,牛肉糜的凝胶硬度、弹性和粘聚性均增加,亮度L值显著降低,对红色度a值影响不显著;随大豆分离蛋白添加量的增加,凝胶硬度逐渐增加,弹性逐渐降低,对粘聚性的影响不显著,并使牛肉糜的亮度L值显著降低,但对红色度a值影响不显著。     

Protein Extraction from Beef Heart using Acid Solubilization

ABSTRACT: The recovery of myofibrillar protein from beef heart using nonthermal acidic solubilization was evaluated. Postmortem time, 3 or 24 h, did not affect protein solubility ( p > 0.05). Protein solubility and yield were detrimentally affected by salt addition. Recovery of extracted protein (yield) was maximized with 0 mM NaCl (60.8 ± 3.9%). SDS-PAGE confirmed myosin solubilization below pH 5 and suggested reduced protein solubility below pH 2.5. Extracted protein from beef heart was significantly lower in fat, cholesterol, ash, and total collagen. In addition, the protein profile using a 7% SDS-Page gel consisted mainly of heavy chain myosin (36%), 150 kDa proteins (15%), and actin (21%).     

Effect of protein concentration, pH, lactose content and pasteurization on thermal gelation of acid caprine whey protein concentrates

The influence of pH (4.5-6.5), sodium chloride content (125-375 mM), calcium chloride content (10-30 mM), protein concentration (70-90 g/l) and lactose content on the gel hardness of goat whey protein concentrate (GWPC) in relation to the origin of the acid whey (raw or pasteurized milk) was studied using a factorial design. Gels were obtained after heat treatment (90 degrees C, 30 min). Gel hardness was measured using texture analyser. Only protein concentration and pH were found to have a statistically significant effect on the gel hardness. An increase in the protein concentration resulted in an increase in the gel hardness. GWPC containing 800g/kg protein formed gels with a hardness maximum at the pHi, whereas GWPC containing 300 g/kg protein did not form true gels. Whey from pasteurized milk formed softer gels than whey from raw milk. A high lactose content (approximately 360 g/kg) also reduced the gelation performance of GWPC.     

Influence of sucrose on cold gelation of heat‐denatured whey protein isolate

A solution of heat‐denatured whey proteins was prepared by heating 100 g kg⁻¹ whey protein isolate (WPI) at pH 7.0 to 75 °C for 15 min in the absence of salt. Heat treatment caused the globular protein molecules to unfold, but electrostatic repulsion opposed strong protein–protein aggregation and so prevented gel formation. When the heat‐denatured whey protein solution was cooled to room temperature and mixed with 15 mM CaCl₂, it formed a gel. We investigated the influence of the presence of sucrose in the protein solutions prior to CaCl₂ addition on the gelation rate. At relatively low concentrations (0–100 g kg⁻¹), sucrose decreased the gelation rate, presumably because sucrose increased the aqueous phase viscosity. At higher concentrations (100–300 g kg⁻¹), sucrose decreased the gelation rate, probably because sugar competes for the water of hydration and therefore increases the attraction between proteins. These data have important implications for the application of cold‐setting WPI ingredients in sweetened food products such as desserts. © 2000 Society of Chemical Industry     

Amaranthus and buckwheat protein concentrate effects on an emulsion-type meat product

The utilization of Amaranthus (five genotypes) and buckwheat protein concentrates in an emulsion-type meat product comprising beef lean, pork fat, salt and water was studied. 15% of the beef protein was replaced with the protein concentrates and the resulting meat emulsions were evaluated by thermorheology and thermal analysis. The cooking loss and physical properties of the meat gel were determined. The use of Amaranthus and buckwheat protein concentrates considerably affected both the emulsion and the cooked meat gel properties. The most favorable outcome was obtained with the buckwheat protein, which had similar effects to soy proteins. The Amaranthus protein concentrates generally did not give favorable results, although that derived from genotype K112 showed some positive effects. Correlation analysis showed that most of the observed variation in meat product properties could be explained by the emulsifying activity of the protein additive used.     

Aerated whey protein gels as a controlled release system of creatine investigated in an artificial stomach

A controlled creatine-release system has been developed from whey protein-based gels. Their functionalization was carried out by aeration and sodium ions induced “cold gelation” processes. The effect of protein concentration in the aerated whey protein gels at pH 7.0 and 8.0 was analyzed. Physicochemical properties of the aerated gels were evaluated. It was possible to obtain the ions induced whey protein aerated gel with well distributed creatine and different microstructure as well as rheological properties. Different protein concentrations and pH enabled obtaining gels with different rheological properties, texture, air fraction, diameter of air bubbles, microstructure and surface roughness. An increase in the protein concentration enhanced the hardness of the samples, regardless of their pH. The mechanical strength of gels prepared at pH 8 were higher than those obtained at pH 7, as was manifested by the smaller storage modulus of the latter. The former gel exhibited a microstructure between particulate and fine-stranded. A stronger gel matrix produced smaller air bubbles. Aerated gels produced at pH 7.0 had higher roughness than those obtained at pH 8.0. Optimal conditions for inclusion of air bubbles into the gel matrix were: 9% protein concentration at pH 8.0 and this aerated gel was selected for digestion in the artificial stomach. There is a small conversion of creatine to creatinine in the artificial stomach digestion process (9.6% after 6 h). The diffusion of creatine crystals from the aerated gel matrix was the mechanism responsible for the release process. Aerated whey protein gels can be used as matrices for time extended releasing of creatine in the stomach.     

CHARACTERIZATION OF TEXTURED WHEY PROTEIN PRODUCED AT VARYING PROTEIN CONCENTRATIONS

This research investigated the range of whey protein in a whey protein/starch mixture needed to produce an extrusion-textured whey product that contained a fibrous texture. It was determined that protein levels ranging from 48 to 64% were necessary for fiber formation. The functionality of textured whey protein (TWP) extrudates produced at three protein levels (48, 53 and 64%) from three different whey sources was characterized at three pH values (3, 5 and 7) and four temperatures (25, 50, 70 and 90C) with respect to solids lost (SL) and water-holding capacity (WHC). Significant differences were found in SL and WHC for each of the four variables. The consumer acceptability of beef patties extended by 50% TWP containing 48% protein was more acceptable to consumers than patties containing 50% textured vegetable protein, but scored lower than the 100% beef patties.

PRACTICAL APPLICATIONS

This study determined the maximum and minimum amount of whey protein in a whey protein/starch mixture required to produce an extrusion-textured whey product that contained a fibrous texture for use as a meat extender. There were no functional benefits of increasing the concentration of whey protein from 48%, which would not likely be practiced because whey protein is more costly than starch. Beef patties extended with 50% textured whey protein showed less cook loss, fat loss and diameter reduction than 100% beef patties while having sensory scores that were higher than patties extended with 50% textured vegetable protein.     

Heat stability of whey protein ingredients based on state diagrams

A state diagram approach was used to compare heat stability among whey protein ingredients. Solutions were thermal processed and solubility, turbidity, and colloidal structure (sol, precipitate, or gel) were plotted against the variables of pH (3–7) and protein concentration (1–10%, w/w) to form state diagrams. Each of the whey protein ingredients produced state diagrams with unique patterns in the protein concentrations associated with colloidal structures and in heat stability regions. Relative heat stability among ingredients depended on the pH-thermal processing combination, in that patterns observed at pH ≤ 4.5 were not equivalent to patterns produced at pH > 4.5. Heating at temperatures of <100 °C for extended time did not produce the same results as heating at > 100 °C for short times. State diagrams were able to differentiate among the whey protein ingredients, but absolute values were determined by the heating treatment.     

Effects of fat level, tapioca starch and whey protein on frankfurters formulated with 5% and 12% fat

The effects of fat level (5% and 12%), tapioca starch and whey protein on the hydration/ binding properties, colour, textural and sensory characteristics of frankfurters were investigated. Decreasing the fat content increased cook loss and decreased emulsion stability and product lightness. Fat reduction increased smoke, spice and salt intensities and increased overall flavour intensity and juiciness. Texture profile analysis (TPA) indicated that fat reduction decreased gumminess and cohesiveness but the other parameters measured were unaffected. Addition of tapioca starch or whey protein reduced cook loss and increased emulsion stability. Whey protein did not effect the sensory characteristics but tapioca starch increased overall flavour intensity. Both ingredients increased hardness, adhesiveness, gumminess and chewiness as measured by TPA. Two-factor interactions between fat level and ingredient were observed for several parameters. The results indicate that both ingredients can partially offset some of the changes which occur in low-fat frankfurters when fat is replaced with added water and protein level is constant.     

添加不同水平NaCl对蛋黄浆质凝胶性的影响研究

为了探究腌制过程中NaCl对蛋黄浆质凝胶品质的影响,本实验主要研究了不同NaCl腌制浓度(处理浓度0%、0.5%、1%、1.5%、2%)下蛋黄浆质凝胶的保水性、浆质凝胶质构特性、浆质色度、粒径分布、流变特性、蛋白成分、显微结构。研究结果表明,在2%浓度NaCl的作用下,蛋黄浆质凝胶保水性最好,保水性显著增加(p0.05);而在2%NaCl添加量时,浆质凝胶质构特性中硬度、咀嚼性显著下降(p0.05),弹性基本不变;流变学研究发现,NaCl作用下浆质凝胶交联程度下降,形成凝胶性能下降;蛋黄浆质在NaCl的作用下,完整的乳状液体系破坏,部分蛋白产生聚集,浆质粒径变大;浆质中脂质、蛋白呈现不规则分布,NaCl的作用对浆质蛋白肽链结构并不造成影响;结果说明,NaCl作用降低了蛋黄浆质形成凝胶品质。该研究结果可为腌制过程中蛋黄浆质变化提供理论依据。     

Effect of milk protein composition and amount of β-casein on growth performance,gut hormones,and inflammatory cytokines in an in vivo piglet model

The objective of this work was to better understand the effect of differences in milk protein composition, and specifically, a change in β-casein to total casein in a milk-based matrix, on growth performance and metabolic and inflammatory responses using a piglet model. Three formulas were optimized for piglets, with similar metabolizable energy, total protein content, and other essential nutrients. Only the protein type and ratio varied between the treatments: the protein fraction of the control diet contained only whey proteins, whereas 2 other matrices contained a whey protein to casein ratio of 60:40, and differed in the amount of β-casein (12.5 and 17.1% of total protein). Piglets fed formula containing whey proteins and caseins, regardless of the concentration of β-casein, showed a significantly higher average daily gain, average daily feed intake, and feed efficiency compared with piglets consuming the formula with only whey protein. Consumption of the formula containing only whey protein showed higher levels of plasma glucagon-like peptide-1 and ghrelin compared with the consumption of formula containing casein and whey protein. A positive correlation was observed between postprandial time and glucagon-like peptide-1 response. The intestinal pro-inflammatory cytokine tumor necrosis factor α increased significantly in piglets fed the whey protein/casein diet compared with those fed whey protein formula. All formula-fed piglets showed a lower level of IL-6 cytokine compared with the ad libitum sow-fed piglets, regardless of composition. No significant differences in the anti-inflammatory IL-10 concentration were observed between treatment groups. Milk protein composition contributed to the regulation of piglets‘ metabolic and physiological responses, with whey protein/casein formula promoting growth performance and a different immune regulatory balance compared with a formula containing only whey protein. Results indicated no differences between treatments containing different levels of β-casein.     

RHEOLOGICAL AND PHYSICOCHEMICAL PROPERTIES OF DERIVATIZED WHEY PROTEIN CONCENTRATE POWDERS

ABSTRACT

The gelling ability of whey proteins provides important textural and water holding properties in many foods. However, because many products cannot be heated to the temperature needed for thermal gelation of whey proteins, cold-set gelation of whey proteins could be very advantageous to the food industry. A derivatization procedure for the production of a cold gelling whey protein isolate (WPI) consisting of protein hydration, pH adjustment, thermal gelation, freeze drying, and milling was applied to three commercial whey protein concentrates (WPC). The resulting derivatized WPC powders were reconstituted in water and evaluated through a range of rheological and physical property studies. The effects of temperature, concentration, and shear on viscosity as well as water holding capacity and intrinsic viscosity were assessed. Although the composition of the starting materials influenced the functionality of the final derivatized powders, all samples exhibited a dramatic increase in thickening and water holding ability. All samples were able to form cold-set weak gel structures suitable for contributing viscosity and texture to a wide range of food systems.     

APPLICATION OF SURFACE FRICTION MEASUREMENTS FOR SURFACE CHARACTERIZATION OF HEAT-SET WHEY PROTEIN GELS

The surface properties of heat‐set whey protein gels (14 wt %) was studied by measuring the friction at the gel's surface. A simple device was constructed that can be conveniently attached to a Texture Analyzer. Surface friction forces of gels with and without addition of salt were measured as a function of sliding speed and surface load. Surface friction strongly depended on the sliding speed for all three gel systems over the speed range 0.01 mm/s to 10 mm/s. The gel without salt addition showed the highest speed dependency, while the gel containing 200 mM NaCl had the lowest speed dependency. Surface load tests showed nearly linear relationships for both protein gels (with and without salt addition). Unlike solid materials, both protein gels exhibited a surface friction even as the surface load approached zero. Possible contributions of surface attraction and viscous flow to the measured forces are discussed. Results from surface friction tests were further confirmed by optical observation of the surface using a confocal laser scanning microscope (CLSM), where a very smooth surface was observed for the whey protein gel without salt addition, but a much rougher surface was observed for the gel containing 200 mM NaCl.     

Viscous properties of microparticulated dairy proteins and sucrose

Slurries of whey protein concentrate (WPC) or sodium caseinate (Na-CN) mixed with sucrose (36% T.S.) were subjected to microparticulation by a high shear homogenizer operated at 27,000 rpm for 2, 4, and 6 min to facilitate gel formation. After microparticulation treatment, the milk protein and sucrose slurries were evaporated at 85 degrees C for 60 min under a partial vacuum (20 to 45 mm of Hg) to form composite gels. Particle sizes and viscoelastic properties were determined before microparticulation treatment. Microparticulation reduced the particle size of WPC-sucrose slurries from an average size of 330 to 188 nm after 4 min and NaCN-sucrose slurries from 270 to 35 nm after 2 min. The WPC-sucrose composites were gel-like, but NaCN-sucrose composites did not gel. Viscoelastic properties of heated WPC-sucrose composites were liquid-like, exhibiting significant reduction in storage modulus and complex viscosity. Microparticulation reduced particle sizes, which resulted in softer gels as time of shearing increased.