Small and large deformation rheology and microstructure of κ-carrageenan gels containing commercial milk protein products

The rheological behaviour of commercial milk protein/κ-carrageenan mixtures in aqueous solutions was studied at neutral pH. Four milk protein ingredients; skim milk powder, milk protein concentrate, sodium caseinate, and whey protein isolate were considered. As seen by confocal laser microscopy, mixtures of κ-carrageenan with skim milk powder, milk protein concentrate, and sodium caseinate showed phase separation, but no phase separation was observed in mixtures containing whey protein isolate. For κ-carrageenan concentrations up to 0.5 wt%, the viscosity of the mixtures at low shear rates increased markedly in the case of skim milk powder and milk protein concentrate addition, but did not change by the addition of sodium caseinate or whey protein isolate. For κ-carrageenan concentrations from 1 to 2.5 wt%, small and large deformation rheological measurements, performed on the milk protein/κ-carrageenan gels, showed that skim milk powder, milk protein concentrate or sodium caseinate markedly improved the strength of the resulting gels, but whey protein isolate had no effect on the gel stength.     

Viscosity,microstructure and phase behavior of aqueous mixtures of commercial milk protein products and xanthan gum

The behavior of commercial milk protein/xanthan mixtures was studied at neutral pH. Four milk protein ingredients; skim milk powder, milk protein concentrate, sodium caseinate and whey protein isolate were considered. For the xanthan concentrations used, up to 1wt%, the viscosity of the mixtures was dominated by the viscosity of xanthan. Mixtures of xanthan with skim milk powder or milk protein concentrate showed phase separation, as seen by confocal micrographs, and phase diagrams have been established for these two systems. No visible phase separation was observed in the case of mixtures of sodium caseinate or whey protein isolate systems. However, mixtures of sodium caseinate and xanthan, under certain conditions, showed formation of ‘thread-like’ xanthan-rich regions by confocal microscopy. We believe that the phase separation occurring in milk protein concentrate/xanthan or skim milk powder/xanthan mixtures was a result of depletion flocculation of casein micelles by the xanthan macromolecules, but thermodynamic incompatibility was likely to occur in sodium caseinate/xanthan mixtures.     

A non-invasive method for the characterisation of milk protein foams by image analysis

An apparatus for the investigation of milk protein foams was introduced based on three jacket columns and exclusively image analysis. The method had a repetition coefficient <10%, and offered a high sample throughput and an expandable design. Sodium caseinate, micellar casein concentrate, whey protein isolate and whey protein concentrate foams were analysed as an application. Foaming properties depended on the protein, the composition of the preparations and the foaming conditions, e.g., stable foams at 20 °C were observed for micellar casein, while sodium caseinate showed a half-life of 22 min. At 50 °C, the stability of sodium caseinate decreased by about 70%. Additionally, a direct link between the foaming properties of sodium caseinate and its degree of enzymatic hydrolysis was found. No changes in foaming properties using Alcalase^® 2.5L occurred up to a degree of hydrolysis of about 3%, while higher degrees of hydrolysis led to decreased foaming properties.     

Interfacial composition and stability of emulsions made with mixtures of commercial sodium caseinate and whey protein concentrate

The interfacial composition and the stability of oil-in-water emulsion droplets (30% soya oil, pH 7.0) made with mixtures of sodium caseinate and whey protein concentrate (WPC) (1:1 by protein weight) at various total protein concentrations were examined. The average volume-surface diameter (d₃₂) and the total surface protein concentration of emulsion droplets were similar to those of emulsions made with both sodium caseinate alone and WPC alone. Whey proteins were adsorbed in preference to caseins at low protein concentrations (<3%), whereas caseins were adsorbed in preference to whey proteins at high protein concentrations. The creaming stability of the emulsions decreased markedly as the total protein concentration of the system was increased above 2% (sodium caseinate >1%). This was attributed to depletion flocculation caused by the sodium caseinate in these emulsions. Whey proteins did not retard this instability in the emulsions made with mixtures of sodium caseinate and WPC.     

Effect of hydrodynamic and physicochemical changes on critical flux of milk protein suspensions

The critical flux during ultrafiltration of whey protein concentrate and sodium caseinate suspensions was investigated. The weak form of critical flux was found for both suspensions. Critical flux of sodium caseinate was higher than that of whey protein concentrate. This could be due to the differences in particle size of the suspensions, resulting in a slower particle back transportation for small particles (whey proteins) compared to the larger casein micelles. Critical flux increased as crossflow velocity increased and decreased as concentration increased, suggesting that critical flux was determined by competition between rate of particle removal from the membrane surface and rate of particle movement towards the membrane surface. Influence of changing pH, addition of NaCl and CaCl2 on the critical fluxes of both protein suspensions was also studied. Increasing pH led to an increase in critical flux for both protein suspensions, suggesting that electrostatic repulsive forces are involved in determining critical flux in both cases. Addition of NaCl gave rise to a decrease in electrostatic interactions due to an increase in ionic strength and zeta potential, and resulted in a decrease in critical flux for sodium caseinate, but had no significant effect for whey protein concentrate. Addition of CaCl2 resulted in a decrease in the critical flux and had a more pronounced influence than NaCl. These results suggest that, in addition to electrostatic repulsive forces, other factors such as structure of protein may be involved in determining the critical flux.     

The thermostability of spray dried imitation coffee whiteners

Imitation creamer formulations were spray dried and agglomerated on a pilot scale tall-form drier in order to evaluate the stability of the resulting powders when added to hot aqueous coffee solutions. The study explored the effects of different protein ingredients (sodium caseinate; milk protein concentrate; whey protein concentrate; milk proteinate; soluble wheat protein) in combination with non-protein emulsifiers and disodium hydrogen orthophosphate. Adaptation of coffee stability test methodology was necessary to take account of the presence of significantly more 'floaters' in the case of imitation coffee whiteners which did not sediment during centrifugation. A new non-dairy protein, soluble wheat protein, proved to have exceptional stabilizing ability compared to all other protein ingredients evaluated. Sodium caseinate performed the best out of the dairy proteins, while formulations incorporating milk protein concentrate tended to be the least stable. When working with whey protein concentrate as the principal ingredient source, an emulsifier system based on mono/diglycerides was inadequate, and it was necessary to use a combination of polysorbate and sodium stearoyl lactylate in its place.     

THERMO-RHEOLOGY,QUALITY CHARACTERISTICS,AND MICROSTRUCTURE OF FRANKFURTERS PREPARED WITH SELECTED PLANT AND MILK ADDITIVES1

The purpose of this study was to evaluate substitution of nonmeat proteins for meat protein on the thermo-rheology, quality characteristics, and microstructure of frankfurters. Batters were formulated to contain either 2% sodium caseinate or soy protein isolate, or 3.5% whey protein concentrate or wheat germ flour. The storage modulus (G') of all treatments initially decreased during temperature ramping from 20–50C, then increased rapidly from 60–80C, with all-meat batter exhibiting the highest G' at 80C. Substitution with nonmeat proteins decreased G', shear force, compression force, and red color of meat compared with all-meat frankfurters. Increased protein content, cooking yield, and decreased fat content were obtained with nonmeat protein formulations. Electron micrographs showed that nonmeat proteins were able to bind to the meat protein and fat, forming a protein-fat matrix with less coalescence of fat droplets. Sodium caseinate, soy protein isolate, whey protein concentrate, and wheat germ flour can be used as protein additives in comminuted meat products without adversely affecting their physical characteristics.     

酶法改性对各种蛋白膜的溶解特性和体外消化率的影响

以大豆分离蛋白SPI-1、大豆分离蛋白SPI-2、酪蛋白酸钠NaCas-1、酪蛋白酸钠NaCas-2、明胶G-1、明胶G-2、乳清蛋白浓缩物WPC、小麦面筋蛋白WG、花生分离蛋白PPI这9种蛋白质为原料制备蛋白膜,主要研究了谷氨酰胺转移酶(TGase)改性对这9种蛋白膜的溶解特性和体外消化率这2种性能的影响。TGase的作用使SPI-1膜、NaCas膜和WPC膜的水分含量呈显著性降低(P≤0.05)。TGase的处理使各种蛋白质膜的总可溶性物质量均比对照膜明显降低,SDS-PAGE分析表明,TGase作用明显降低了这几种蛋白膜在水溶液中的溶解性。与对照膜相比,TGase改性显著降低了蛋白膜的消化率,其中NaCas、SPI和G蛋白膜的下降幅度较大。这可能是因为TGase催化改性的蛋白膜中产生了新的交联。     

Functional characterization of protein stabilized emulsions: Emulsifying behaviour of proteins in a valve homogenizer

Protein stabilised emulsions have been prepared in a valve homogeniser incorporated into a recirculating emulsification system, where the power input and number of passes have been varied. The food proteins studied were a soy-bean protein isolate, a whey protein concentrate (WPC) and a sodium caseinate. The emulsions obtained were characterized in terms of particle size distribution and amount of protein adsorbed on to the fat surface (protein load). Generally, the final fat surface area of the emulsions obtained increases more as a function of power input than as a function of number of passes. Distribution width, c_s, decreases mostly with increasing power supply and number of passes, but at the highest power input c_s increases. The protein load on the fat globules is largely determined by the fat surface area and by the type of protein adsorbed. The soy proteins give a high protein load and the caseinates give a low protein adsorption at small fat surface areas created. This relation is reversed at large surface areas of the fat globules. The relation between percentage protein adsorbed from bulk as a function of surface area suggests that the caseinates mainly cover the newly created interface by adsorption from the bulk, whereas the soy proteins fulfil this task mostly by spreading at the interface. Salt addition to 0.2M-NaCl enhances protein adsorption at the fat globule interface in the case of soy protein and caseinate, but for the whey proteins protein load is higher in distilled water.     

QUALITY OF COFFEE CREAMERS AS A FUNCTION OF PROTEIN SOURCE

Many U.S. consumers add a sweetener or creaming agent to their brewed coffee. An ideal creamer, when added to coffee, should remain stable, dissolve readily, and provide whitening ability. In general, these properties are imparted by the protein component. Four different proteins – sodium caseinate, isolated wheat protein, soy protein isolate and whey protein concentrate – were used to formulate coffee creamers, individually and in combination, and the resultant creamers were evaluated for functionality. Coffee creamers containing plant proteins had significantly greater apparent viscosity but lower L* values than did creamers made with dairy proteins. Creamers made with higher concentrations of isolated wheat protein exhibited syneresis, whereas no syneresis occurred if sodium caseinate was the predominant protein. Only the creamer formulated with soy protein isolate alone exhibited feathering when added to hot, brewed coffee. These results indicate that coffee creamers can be formulated with plant proteins and sodium caseinate.     

Emulsification of Commercial Dairy Proteins with Exhaustively Washed Muscle

The addition of dairy proteins to exhaustively washed chicken breast muscle improved the emulsion stability in heated cream layers (emulsions) containing whey protein concentrate (WPC) or whey protein isolate (WPI). The initial weight of the heated cream layers made with WPC or WPI was heavier than those for sodium caseinate (CNate) or milk protein isolate (MPI). The addition of CNate or MPI resulted in decreased emulsion stability and increased inhibition of myosin heavy chain and actin participation in the emulsion formation compared to WPC or WPI.     

Milk Protein Coatings Prevent Oxidative Browning of Apples and Potatoes

ABSTRACT Color analysis on apple and potato slices coated with calcium caseinate or whey protein solutions showed that the 2 coatings efficiently delayed browning by acting as oxygen barriers. The antioxidant properties of the films were realized using a model allowing the release of oxidative species by electrolysis of saline buffer. Whey proteins were a better antioxidant capacity than calcium caseinate. Furthermore, addition of carboxymethyl cellulose (CMC) to the formulations significantly improved their antioxidative power. Best scavenging of oxygen free radicals and reactive oxygen species was found for films based on whey proteins and CMC which inhibited by 75% the formation of colored compounds produced by the reaction of the oxidative species with N,N‐diethyl‐p‐phenylenediamine.     

Heat-induced aggregation of whey proteins in the presence of κ-casein or sodium caseinate

Aggregates were formed by heating mixtures of whey protein isolate (WPI) and pure κ-casein or sodium caseinate at pH 7 and 0.1 M NaCl. The aggregates were characterized by static and dynamic light scattering and size exclusion chromatography. After extensive heat-treatment at 80 °C for 24 h, almost all whey proteins and κ-casein formed mixed aggregates, but a large proportion of the sodium caseinate did not aggregate. At a given WPI concentration the size of the aggregates decreased with increasing κ-casein or sodium caseinate concentration, but the overall self-similar structure of the aggregates was the same. The presence of κ-casein or caseinate therefore inhibited growth of the heat-induced whey protein aggregates. The results were discussed relative to the reported chaperone-like activity of casein molecules towards heat aggregation of globular proteins.     

不同pH及时间对大豆乳清蛋白溶液色值的影响

以大豆异黄酮和酪蛋白酸钠为参照,采用Lab模型考察不同pH及时间下大豆乳清蛋白溶液色值的变化,分析影响大豆乳清蛋白溶液颜色的因素。结果发现:随p H的升高,大豆乳清蛋白溶液的亮度下降,红色和黄色值增加;中性和碱性条件下,随着时间的延长,大豆乳清蛋白溶液的亮度下降,红色值增加,而黄色值在中性条件下不变,在碱性条件下增加。通过对大豆异黄酮溶液和酪蛋白酸钠溶液的色值比较发现,大豆异黄酮及其在碱性环境下的显色反应是造成大豆乳清蛋白溶液呈现黄色的关键因素,而羰氨反应是大豆乳清蛋白溶液变红的重要影响因素。因此,在生产过程中pH控制在7.5以内,生产周期尽量缩短,有利于大豆乳清蛋白溶液黄色和红色的控制。     

A Collaborative Study to Develop a Standardized Food Protein Solubility Procedure

A colaborative study was conducted to develop a rapid, simple and reliable procedure for determining the solubility of food protein products, e.g., spray-dried whey protein concentrate, sodium caseinate, egg white protein and soy protein isolate. The procedure was developed by modifying the nitrogen solubility index (NSI) procedure. Protein content and soluble protein were determined by micro-Kjeldahl or biuret procedures with standard deviations of 0.83-4.12 for all proteins except caseinate which had a value of 13.95. Although the biuret and micro-Kjeldahl procedures generally provided comparable accuracy and precision for protein content and solubility of certain proteins, the biuret procedure exhibited considerable error and variability for other proteins.     

The dual effects of Maillard reaction and enzymatic hydrolysis on the antioxidant activity of milk proteins

The objective of this study was to determine the enhanced effects on the biological characteristics and antioxidant activity of milk proteins by the combination of the Maillard reaction and enzymatic hydrolysis. Maillard reaction products were obtained from milk protein preparations, such as whey protein concentrates and sodium caseinate with lactose, by heating at 55°C for 7 d in sodium phosphate buffer (pH 7.4). The Maillard reaction products, along with untreated milk proteins as controls, were hydrolyzed for 0 to 3 h with commercial proteases Alcalase, Neutrase, Protamex, and Flavorzyme (Novozymes, Bagsværd, Denmark). The antioxidant activity of hydrolyzed Maillard reaction products was determined by reaction with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, their 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, and the ability to reduce ferric ions. Further characteristics were evaluated by the o-phthaldialdehyde method and sodium dodecyl sulfate-PAGE. The degree of hydrolysis gradually increased in a time-dependent manner, with the Alcalase-treated Maillard reaction products being the most highly hydrolyzed. Radical scavenging activities and reducing ability of hydrolyzed Maillard reaction products increased with increasing hydrolysis time. The combined products of enzymatic hydrolysis and Maillard reaction showed significantly greater antioxidant activity than did hydrolysates or Maillard reaction products alone. The hydrolyzed Maillard reaction products generated by Alcalase showed significantly higher antioxidant activity when compared with the other protease products and the antioxidant activity was higher for the whey protein concentrate groups than for the sodium caseinate groups. These findings indicate that Maillard reaction products, coupled with enzymatic hydrolysis, could act as potential antioxidants in the pharmaceutical, food, and dairy industries.     

Incorporation of dairy ingredients into wheat bread: effects on dough rheology and bread quality

 Dairy ingredients are used in breadmaking for their nutritional benefits and functional properties. The effects of the traditionally-used whole and skimmed milk powder, sodium caseinate, casein hydrolysate and three whey protein concentrates on dough rheology and bread quality were studied. Whole and skimmed milk powders improved sensory characteristics. Sodium caseinate and hydrolysed casein displayed beneficial functional properties in breadmaking including low proof time, high volume and low firmness. Both ingredients increased dough height measured with the rheofermentometer. Bread with 2% or 4% sodium caseinate added was rated highly in sensory evaluation. Incorporation of whey protein concentrates generally increased proof time, decreased loaf volume and decreased dough height measured with the rheofermentometer. Received: 6 April 1999 / Revised version: 13 July 1999     

Nutritional quality evaluation of commercial protein supplements

Protein supplements have received increasing attention by consumers over the last few decades. However, hundreds of them have recently exhibited irregularities including lower quantities of proteins than disclosed values. This study aimed to evaluate the nutritional quality of six commercial protein supplement powders (calcium caseinate, milk protein concentrate, egg white, pea protein isolate, whey protein concentrate and soy protein isolate). The chemical composition, amino acid content and in vitro digestibility were examined. Thus, calculate the amino acid scores corrected for amino acid and protein digestibility. In vitro digestion was also conducted and protein hydrolysis was monitored by SDS-page. Calcium caseinate powder and whey protein concentrate were only composed of proteinogenic amino acids and exhibited the highest essential amino acid content. As regards in vitro digestibility, these two supplements perfectly meet the quality expectations of the Food and Agricultural Organization (FAO). Conversely, the other four supplements exhibited a lower quality than the FAO reference protein. This was due to low digestibility (for egg white and milk concentrate) and/or lack of a specific essential amino acid (for milk concentrate and pea isolate).     

Vanillin Interaction with Milk Protein Isolates in Sweetened Drinks

The impact of heat processing and emulsifier addition on the interaction of vanillin and sodium caseinate and whey protein isolate was examined in a model system. Free vanillin in the protein drink was evaluated by a sensory panel and HPLC. Sensory analysis indicated that emulsifier, heat × protein, and heat × emulsifier affected perception of vanillin flavor. Analysis of free vanillin by HPLC indicated only a significant protein effect, with sodium caseinate interacting more with vanillin than did whey protein isolate. No correlation was found between sensory and HPLC results.