Influence Of Protein Concentration Research Articles

Development of high internal phase emulsions using coconut protein isolates modified by pulsed light: Relationship of interfacial behavior and emulsifying stability

Protein-stabilized high internal phase emulsions (HIPEs) are attracting considerable attention in the food industry. Herein, we reported a simple method to fabricate HIPEs by modifying coconut protein isolates. Coconut protein isolates were extracted using isoelectric precipitation, and modified by low-intensity pulsed light (0.76 W/cm2/nm). The influence of protein concentration (1–4%, w/v) on interfacial adsorption behavior was analyzed by dissipative quartz crystal microbalance and interfacial dilatational rheology. The results indicated that the increase of concentration was beneficial to form a thick and more elastic interfacial layer at oil-water interface for modified coconut protein isolates by pulsed light (PCPI). At high concentration, the interfacial layer exhibited the better ability to resist the perturbation of amplitude and frequency sweep. In addition, HIPEs could be stabilized by PCPI solely, all emulsions were dispersed well. Apart from the emulsion stabilized by 1% PCPI, other HIPEs exhibited a gel-like behavior when the containers were inverted. Increasing protein concentration caused a decrease in emulsion particle size, and rheological analysis showed that the viscosity of HIPEs was positively correlated with the content of PCPI. Moreover, the HIPEs stabilized by PCPI exhibited better centrifugal stability. This study demonstrated that coconut protein isolates could be an efficient stabilizer to prepare HIPEs after simple modification, which was useful for developing applications of coconut protein.

Emulsifying Capacity of Cowpea Protein Isolates. Effect of Thermal and Hydrolytic Treatment.

In this work, modifications due to the effect of thermal treatments (TT 70 and 90°C) and partial hydrolysis by digestion with alcalase (LH) on the emulsifying properties of cowpea protein isolates (CPIs) extracted at pH 8 and 10 were analyzed. In addition, the influence of protein concentration [0.1 and 1% (w/v)] was evaluated. Emulsions (O:W) were prepared and particle size, stability, interfacial composition, and microstructure were studied. Fresh emulsions formulated with TT CPIs presented lower values of volume-weighted mean droplet size (D4.3), with the increase in temperature and treatment time, compared to the untreated CPIs. After seven days of storage, D4.3 and the indexes of flocculation (FI) and coalescence (CI) increased, mainly at 90°C. On the other hand, the emulsions with LH CPIs presented lower D4.3 values compared to all the conditions tested, remaining unchanged during the storage time. The destabilization process in the TT CPIs emulsions revealed coalescence at 0.1% (w/v) and cremated-flocculation at 1% (w/v). The presence of polypeptides of low molecular mass (MM) at the interface would be responsible for the better stability found in emulsions with LH CPIs, compared to those formulated with untreated and TT CPIs. Increasing the protein concentration resulted in a significant improvement of all emulsifying properties.

The influence of protein concentrations in basal diet on metabolizable energy of full-fat soybeans and soy protein isolate determined by the difference procedure in pigs

In the difference procedure, a potential influence of crude protein (CP) concentrations of basal diets on accurate metabolizable energy (ME) determination of a test ingredient is of an issue. The objective of the present study was to determine the influence of CP concentrations in the basal diet and test ingredients on the ME:digestible energy (DE) of full-fat soybeans (FFSB; 377 g/kg CP) and soy protein isolate (SPI; 876 g/kg CP) using the difference procedure. Twelve barrows (73.7 ± 5.5 kg body weight) individually housed in metabolism crates were used. A low-protein basal diet (LPBD; 74 g/kg CP) was composed of 975 g/kg corn as the sole energy source and a high-protein basal diet (HPBD; 143 g/kg CP) was mainly composed of 780 g/kg corn and 196 g/kg soybean meal as the sole energy sources. Four additional diets were prepared by including FFSB or SPI at 200 g/kg at the expense of the energy sources in the basal diets. The 6 experimental diets were fed to the 12 pigs employing a replicated 6 × 4 incomplete Latin square design with 4 periods. While the urinary energy output from the pigs fed the SPI diet in the HPBD group was greater (P < 0.05) than that in the LPBD group, the urinary energy output was not affected by CP concentration in the basal diet in pigs fed the basal diets or the FFSB diets. The ME:DE of the SPI diet in the LPBD group was greater (P < 0.05) than that in the HPBD group, whereas ME:DE was not affected by the basal CP concentrations in pigs fed the basal diets or the FFSB diets. The one-slope broken-line analysis indicated that the CP concentration in the diet needs to be less than 170 g/kg (P < 0.05) to avoid potential interaction between a basal diet and a test ingredient on ME:DE. While ME:DE of the SPI in the LPBD group was greater (P < 0.05) than that in the HPBD group, ME:DE of the FFSB was not different between the 2 basal diet groups. Overall, ME in a high-protein ingredient can be underestimated if a relatively high-protein basal diet is used in the difference procedure mainly due to increased urinary energy output from pigs. Experimental diets in the difference procedure need to contain less than 170 g/kg of protein for finishing pigs to accurately determine biologically available energy concentrations of soybean protein sources.

Protein isolates from Cajanus cajan L. as surfactant for o:w emulsions: pH and ionic strength influence on protein structure and emulsion stability

This work has focused on the study of the influence of pH (2.1, 3.9, 6.3, 8.3) and ionic strength (μ) (0.10 and 0.54) on the formation and stability of oil in water (o:w) emulsions using a protein isolate of Cajanus cajan (PPI8) as emulsifier. Also, the influence of protein concentration was evaluated. Interfacial tension was better at pH2.1 and pH8.3, and it was improved at pH6.3 with the increase in ionic strength. Most emulsions showed a monomodal droplet size distribution, except at pH8.3 (μ: 0.54) where a bimodal distribution was observed. The critical concentration range of proteins was between 1.5 and 2.0% (μ: 0.10) and 1.0–1.5% (μ: 0.54). At pH6.3, the surface average diameter was independent of ionic strength (0.5%, 1.0%, and 2.0%). At low ionic strength, stable emulsions (protein concentration ≥1.0%) were obtained (up to 7 days) at pH2.1, pH6.3, and pH8.3, despite the differences in flocculation index (FI) observed. FI of emulsions remained constant up to 7 days of storage, except at pH2.1 (1.0%) and pH8.3 (2.0%). The emulsion stability at high ionic strength was pH dependent, at pH3.9 was improved even at low protein concentration due to the increase in protein solubility and apparent viscosity of emulsion. Because of their techno-functional properties, PPI8 could lead to the development of innovative products suitable for those consumers that demands for alternative plant-based protein sources.

The Role of Concentration on Drop Formation and Breakup of Collagen, Fibrinogen, and Thrombin Solutions during Inkjet Bioprinting.

The influence of protein concentration on drop formation and breakup of aqueous solutions of fibrous proteins collagen and fibrinogen and globular protein thrombin in different concentration regimes has been investigated during drop-on-demand (DOD) inkjet printing. The capillary-driven thinning and breakup of dilute collagen, fibrinogen, and thrombin solutions, the solutions in which protein molecules are far away from each other, are predominantly resisted by inertial force. Although the capillary-driven thinning and breakup of semidilute unentangled collagen and fibrinogen solutions, the solutions in which protein molecules begin to interpenetrate each other, are predominantly resisted by inertial force on the initial onset of necking, the breakup of droplets is delayed because of the resistance of elastic force. The resistance of viscous force to the necking and breakup of both the dilute and semidilute unentangled protein solutions is negligible. Aggregates or subvisible particles (between 1 and 100 μm) constantly disrupt the formation of droplets for the semidilute unentangled protein solutions, even when their inverse Ohnesorge number (Z) is within the printability range of 4 ≤ Z ≤ 14. Although aggregates are present in the dilute protein solutions, they do not disrupt the formation of droplets.

The influence of protein concentration, temperature and cathodic polarization on the surface status of CoCrMo biomedical grade alloys

CoCrMo alloys have been widely used in hip replacements. On the one hand they have exhibited excellent long-term survival rates, but recently high failure rates have been observed, associated with adverse local tissue reactions. It is still a puzzle why CoCrMo alloys sometimes work very well, while at the other times the failure rate is unacceptably high. The current work aims to investigate the influence of protein adsorption on the oxide layer properties and consequently on corrosion behaviour of CoCrMo biomedical grade alloys in different surface and media conditions. Electrochemical Impedance Spectroscopy (EIS), SEM and AFM were employed to characterise the surfaces. TEM was also used to reveal the subsurface chemical composition. The results showed a significant drop in the resistance of the oxide layer on the surfaces after some cathodic potential polarization. It was also shown that higher protein content and temperature reduced the oxide layer/metal surface interface resistivity. EDX quantitative chemical composition spot analysis of the subsurface after cathodic polarization showed a depletion of chromium in the outermost layer. AFM imaging and peak-force quantitative nanomechanical mapping QNM revealed lower adhesion forces for a relatively thick proteinaceous adsorbed layer on the surface after high cathodic polarization in particular at 50 °C.

Influence of protein concentration and coagulation temperature on rennet-induced gelation characteristics and curd microstructure

This study characterized the coagulation properties and defined the cutting window (CW; time between storage modulus values of 35 and 70 Pa) using rheometry for milk standardized to 4, 5, or 6% protein and set at 28, 32, or 36°C. Milks were standardized to a protein-to-fat ratio of approximately 1 by blending ultrafiltration retentate, skim milk, and whole milk. The internal curd microstructure for selected curd samples was analyzed with transmission electron microscopy and scanning electron microscopy. Lowering the coagulation temperature caused longer rennet coagulation time and time to reach storage modulus of 35 Pa, translating into a wider CW. It also led to a lower maximum curd-firming rate (MCFR) with lower firmness at 40 min at a given protein level. Increasing protein levels resulted in the opposite effect, although without an effect on rennet coagulation time at a given temperature. On coagulation at 28°C, milk with 5% protein resulted in a similar MCFR (∼4 Pa/min) and CW (∼8.25 min) compared with milk with 4% protein at 32°C, which reflects more standard conditions, whereas increasing milk to 6% protein resulted in more than doubling of the curd-firming rate (MCFR = 9.20 Pa/min) and a shorter CW (4.60 min). Gels set at 28°C had lower levels of rearrangement of protein network after 40 min compared with those set at 36°C. Protein levels, on the other hand, had no influence on the levels of protein network rearrangement, as indicated by loss tangent values. The internal structure of curd particles, as investigated by both scanning electron microscopy and transmission electron microscopy, appeared to have less cross-linking and smaller casein aggregates when coagulated at 28°C compared with 36°C, whereas varying protein levels did not show a marked effect on aggregate formation. Overall, this study showed a marked interactive effect between coagulation temperature and protein standardization of milk on coagulation properties, which subsequently requires adjustment of the CW during cheesemaking. Lowering of the coagulation temperature greatly altered the curd microstructure, with a tendency for less syneresis during cutting. Further research is required to quantify the changes in syneresis and in fat and protein losses to whey due to changes in the microstructure of curd particles arising from the different coagulation conditions applied to the protein-fortified milk.

Investigation of the thermal shift assay and its power to predict protein and virus stabilizing conditions

Protein thermal shift assay (TSA) has been extensively used in investigation of protein stabilization (for protein biopharmaceutics stabilization, protein crystallization studies or screening of recombinant proteins) and drug discovery (screening of ligands or inhibitors). This work aimed to analyze thermal shift assay results in comparison to protein polymerization (multimerization and aggregation) propensity and test the most stabilizing formulations for their stabilization effect on enveloped viruses. Influence of protein concentration, buffer pH and molarity was tested on three proteins (immunoglobulin G, ovalbumin, and albumin) and results showed that each of these factors has an impact on determined shift in protein melting point Tm, and the impact was similar for all three proteins. In case of ovalbumin, molecular dynamics simulations were performed with the goal to understanding molecular basis of protein’s thermal stability dependence on pH. Effect of three denaturing agents in a wide concentration range on Tm showed nicely that chemical denaturation occurs only at the highest concentrations. Results showed similar effect on Tm for most formulations on different proteins. Most successful formulations were tested for enveloped virus stabilizing potential using cell culture infectivity assay (CCID50) and results showed lack of correlation with TSA results. Only weak correlation of Tm shift and protein polymerization measured by SEC-HPLC was obtained, meaning that polymerization cannot be predicted from Tm shifts.

Influence of protein concentration and quality in a canned diet on urine composition, apparent nutrient digestibility and energy supply in adult cats

BackgroundProtein concentration and quality in cat food can vary considerably, and the impact on feline urine composition and nutrient supply is of high practical relevance. In the present study, 6 canned diets with varying protein concentrations and qualities were fed to 10 healthy adult cats. Protein quality in the diet differed depending on the amount of collagen-rich ingredients. Hydroxyproline concentrations were 2.56–4.45 g/kg dry matter in the high quality and 3.76–9.44 g/kg dry matter in the low quality diets. Protein levels were 36.2, 43.3 and 54.9% in the high quality and 36.7, 45.0 and 56.1% in the low quality groups. Each diet was fed for 6 weeks, using a randomized cross-over design. In the last 2 weeks of each feeding period, urine and faeces of the cats were collected.ResultsRenal calcium (Ca), oxalate (Ox) and citrate excretion were unaffected by the dietary protein concentration, possibly mediated by a high urine volume (24.2–34.2 ml/kg bodyweight (BW)/day) in all groups. However, renal Ox excretion was lower when the high quality diets were fed (P = 0.013). Urinary relative supersaturation (RSS) with calcium oxalate (CaOx) was low in general, but reduced in the high quality groups (P = 0.031). Urinary RSS values for magnesium ammonium phosphate (MAP) were high (2.64–5.00) among all groups. Apparent digestibility of crude protein and most minerals was unaffected by the different diets. Feed intake was higher in the low quality groups (P = 0.026), but BW of the cats did not differ depending on dietary protein quality. BW of the cats increased with increasing dietary protein concentrations (P = 0.003).ConclusionIn conclusion, a high protein canned diet might not be a specific risk factor for CaOx urolith formation in cats. In contrast, all diets resulted in high RSS MAP values, which might be critical concerning MAP crystallization. Protein quality had a minor, but significant impact on urine composition, necessitating further research on this subject. A lower energy supply when feeding a low protein quality can be assumed. Changes in BW were only small and require a careful interpretation.

Rheological and physical properties of O/W protein emulsions stabilized by isoelectric solubilization/precipitation isolated protein: The underlying effects of varying protein concentrations

To better understand the potential of using isoelectric solubilization/precipitation (ISP)-isolated protein on emulsion-type meat products, the influences of protein concentration on the physical and rheological properties of protein emulsions were investigated. An oil-in-water (O/W) emulsion containing 20% soybean oil was stabilized by pale, soft and exudative (PSE)-like muscle protein (CON) and ISP-isolated PSE-like muscle protein (ISP) at the concentrations of 50, 100 and 150 mg/ml. Morphologically, the ISP-isolated protein demonstrated better emulsion capacity compared to the CON group, which formed uniform, long-lasting emulsions and dispersed smaller emulsified oil droplets. The apparent viscosity of all emulsion samples was fitted well by the Ostwald-de-Waele model (R2 > 0.9). All emulsions exhibited non-Newtonian, pseudoplastic behaviors with the fitting parameters being highly dependent on both protein type and concentration. In the frequency sweep, all emulsion systems were classified as a “strong gel” because G’’ >> G’, especially when concentrations were 100 or 150 mg/ml. Based on a temperature sweep oscillatory curve, the heat-induced gelation behaviors of PSE-like protein emulsions were modified by ISP processing. In addition, the elasticity of the final emulsion gel was higher in the ISP group when compared to the CON group. The thermal gelling properties of ISP-isolated protein emulsions appeared to be impaired when the concentrations reached 150 mg/ml. It was concluded that ISP processing could effectively improve the emulsion properties of PSE-like meat protein.

Influence of protein concentration on surface composition and physico-chemical properties of spray-dried milk protein concentrate powders

Surface composition, moisture sorption behaviour and glass–rubber transition temperature (Tgr) were determined for spray-dried milk protein concentrate (MPC) powders over a range of protein contents (35–86 g 100 g−1). Surface characterisation of MPC powders indicated that fat and protein were preferentially located on the surface of the powder particles, whereas lactose was located predominantly in the bulk. Moisture sorption analysis at 25 °C showed that MPC35 exhibited lactose crystallisation, whereas powders with higher protein contents did not and continually absorbed moisture upon humidification up to 90% RH. The GAB equation, fitted to sorption isotherms of MPCs, gave increases in monolayer moisture value (mm) with protein content. Tgr, measured with a rheometer, decreased significantly (P < 0.05) with increasing water content and increased with increasing protein content (P < 0.05). In conclusion, increasing protein concentration of MPCs resulted in altered surface composition and increased mm value and Tgr values.

Destabilization and removal of immobilized enzymes adsorbed onto polyethersulfone ultrafiltration membranes by salt solutions

In this work the effectiveness of two saline solutions (NaCl and Na2SO4) to clean a permanently hydrophilic polyethersulfone (PESH) ultrafiltration (UF) membrane with a molecular weight cut-off (MWCO) of 30kDa previously fouled with enzymatic solutions was investigated. The influence of protein concentration in the enzymatic solution during the fouling step and the effect of salt type during the cleaning procedure were studied.The protein aggregation was analyzed in solution and onto the membrane surface by using several techniques including Dynamic Light Scattering (DLS), Atomic Force Microscopy (AFM) and Infrared Spectroscopy with Attenuated Total Reflectance (ATR-FTIR). In addition, mechanisms that dominate membrane fouling were studied by fitting some mathematical models (Hermia׳s models adapted to crossflow filtration, a combined model based on the complete blocking and cake formation equations and a resistance-in-series model) to the experimental data.Fouling results showed that the complete blocking/adsorption on membrane surface was the predominant fouling mechanism. Regarding the cleaning results, higher cleaning efficiency and low residual protein concentration was obtained with NaCl solutions for all the feed solutions tested due to the favorable interaction between Cl− and proteins.

Influence of protein concentration on the stability of oil-in-water emulsions formed with aggregated milk proteins during spray drying

The ability of aggregated milk proteins to stabilize oil-in-water emulsions during the spray drying process is not well understood and has been highlighted in this study. We investigated the behavior of oil droplets in emulsions (12.0%, w/w, maltodextrin; 20.0%, w/w, soya oil) stabilized with either milk protein concentrate (MPC) or calcium caseinate (CaCas) (0.5–5.0%, w/w) before and after spray drying. In comparison with the respective parent emulsions, spray drying and redispersion caused a shift in the droplet size distribution toward larger values for emulsions made using low concentrations (0.5–2.0%) of MPC or CaCas. However, the droplet size distribution was affected very slightly by spray drying when the protein concentration was between 3.0 and 5.0%. The average droplet diameters of redispersed CaCas emulsions were noticeably larger than those of redispersed MPC emulsions. The unadsorbed protein concentrations in the parent emulsions were comparable for emulsions containing CaCas and MPC, except at 5.0% (w/w) when emulsions containing MPC had a higher concentration of unadsorbed protein in the bulk phase. The amount of extractable oil in MPC-containing powders decreased with an increase in the protein concentration in the emulsions prior to spray drying. However, the amount of extractable oil in CaCas emulsion powders was nearly twice that in MPC emulsion powders even at 5.0% protein in the emulsion. The results obtained from this study clearly show that aggregated milk proteins are able to provide stability to oil droplets during the spray drying process, albeit a higher concentration of protein is required as compared to non-aggregated protein products.

Dynamic adsorption and dilatational properties of BSA at oil/water interface: Role of conformational flexibility

The influence of protein concentration (c) and/or disulfide bond (S–S) cleavage with β-mercaptoethanol (2-ME) on interfacial adsorption dynamics, including diffusion, penetration and structural rearrangement at the interface, as well as dynamic dilatational properties of bovine serum albumin (BSA) was systematically investigated using drop shape analysis. The results indicated that for native BSA increasing the c from 0.01 to 0.5% (w/v) progressively improved the rate of diffusion and the ‘equilibrium’ surface pressure (π), while a further increase in c (to 1.0%, w/v) contrarily impaired these characteristics; increasing the c progressively improved the penetration and structural rearrangement at the interface. In contrast, the surface dilatational modulus (E) development was less dependent on the c than that for the π. On the other hand, the S–S cleavage with 2-ME at any test c value progressively improved the diffusion and penetration, as well as ‘equilibrium’ π, while the structural rearrangement was highly dependent on the c. At c < 0.5% (w/v), increasing the 2-ME concentration progressively improved the rearrangement, while at c values of 0.5% or above, a contrary trend was observed. The S–S cleavage generally improved the E or its elasticity development over the whole adsorption, regardless of the c. The E-π plots indicated that besides the adsorption, the lateral macromolecular interactions at the interface could be affected by variation in c and/or 2-ME concentration. The relationships between the conformational flexibility and interfacial characteristics of BSA, as well as between its interfacial and emulsifying properties have been well established.

Influence of protein concentration on the physical characteristics and flow properties of milk protein concentrate powders

This study investigated the physical characteristics and flow properties of seven milk protein concentrate (MPC) powders, ranging from 36.6 (MPC35) to 89.6 (MPC90) % (w/w) protein in dry-matter. MPC80, MPC85 and MPC90 had the smallest particle sizes (P<0.05) and significantly higher (P<0.05) specific surface areas, as measured using nitrogen adsorption. The bulk density of MPC powders decreased with increasing protein content, due to increased (P<0.05) levels of interstitial and occluded air. Flow testing indicated that high protein MPC powders were more compressible (P<0.05), had lower flow index values (P<0.05) and required larger (P<0.05) outlet diameters for optimal flow in mass-flow hoppers compared to lower protein MPC powders.

The influence of protein concentration on the biotribological properties of the stem-cement interface

The stem-cement interface in total hip replacement experiences fretting wear following debonding under cyclical physiological loading. However, the influence of protein concentration on the biotribological properties of this interface has not been well taken into consideration. In the present study, a series of fretting frictional tests were performed using polished Ti6Al4V and bone cement, lubricated by bovine serum albumin solutions of different concentrations (5%, 30%, and 75%). Surface characterizations of Ti6Al4V pins were conducted by optical interferometer, scanning electron microscope, and Raman spectroscopy. The results show that the friction coefficient decreases with the increase of protein concentration, although the difference is not significant. In addition, bovine serum albumin is adsorbed onto Ti6Al4V surface, forming a protective film to prevent the metal substrate from wear. The elemental and spectroscopic analyses of the film confirm the presence of protein molecules adsorbed on Ti6Al4V surface, with a thickness of 2.5 μm. It is indicated from this study that fretting wear at the stem-cement interface can be postponed by promotion of protein adsorption on the metal surface.

Preparation of chitosan nanoparticles for encapsulation and release of protein

Chitosan nanoparticles were prepared by ionic cross-linking with tripolyphosphate (TPP). The major effect on encapsulation and release of protein in chitosan-TPP nanoparticles was investigated in order to control the loading and release efficiency. A set of the same molecular weight (MW) proteins with different pI and a set of the same pI proteins with different MW were studied. The influence of protein concentration, pH of solution, and the activity of released protein were examined. It was found that the encapsulation efficiency (EE) of a set of the different MW protein decreased with increasing of MW of protein and protein concentration. The protein with having pI higher than pH of solution was attracted to the positively charged chitosan, resulting in increasing of EE. The release of protein from the nanoparticles showed that the protein release decreased with increasing of chitosan concentration, high MW protein, low pH, and less swelling of the particle. The released protein in chitosan-TPP matrix was still active in the buffer solution.

Investigating Antibody Interactions with a Polar Liquid Using Terahertz Pulsed Spectroscopy

In this article, we use terahertz spectroscopy to study the dielectric properties of the peroxidase-conjugated affinity purified goat anti-cat immunoglobulin G and the fluorescein-conjugated affinity purified goat anti-cat immunoglobulin G when they interact with polar liquids. The influence of protein concentration, as well as presence of glycerol as a cosolvent, is determined by estimation of the effective hydration shell radius of the protein in solution. The dielectric spectra in this study are measured over the frequency range 0.1–1.3 THz and it is found that the dielectric properties are dependent on the type of the charges in the hydrogen-bonded antibodies' networks. Our results indicate that the terahertz dielectric properties of polar liquids are strongly affected by the presence of the antibody and suggest that the dielectric spectrum is particularly powerful in the study of structural and conformational properties of proteins. Therefore, terahertz spectroscopy is a very sensitive approach to investigate structural features of biological systems.

Influence of the presence of monoglyceride on the interfacial properties of wheat gluten

The physical stability of several food systems depends strongly on their interfacial properties, which may be modified by adding proteins and low-molecular-weight surfactants to their formulation. This study deals with the possibility of using wheat gluten to alter the surface and interfacial properties of an aqueous system, considering the effects of protein concentration, pH and the presence of monostearin. It was generally found that the surface tension decreased as the protein concentration increased, reaching a minimum value at 0.5 g kg(-1). The influence of protein concentration on surface tension was much greater than the effect of pH owing to the low ionic character of wheat gluten protein. At acidic and alkaline pH values the interfacial viscosity of the protein system underwent a significant increase with time. The addition of monostearin either promoted the displacement of protein molecules at the interface or generated an interfacial mixed film with surface tension values lower than those of both single components, depending on the pH. The results obtained indicate that gluten can contribute to the stabilisation of air/water and oil/water interfaces in some food systems (emulsions, foams, etc.).

Effects of protein concentration and oil-phase volume fraction on the stability and rheology of menhaden oil-in-water emulsions stabilized by whey protein isolate with xanthan gum

The influences of protein concentration (0.2, 1, 2 wt%) and oil-phase volume fraction (5%, 20%, 40% v/v) on emulsion stability and rheological properties were investigated in whey protein isolate (WPI)-stabilized oil-in-water emulsions containing 0.2 wt% xanthan gum (XG). The data of droplet size, surface charge, creaming index, oxidative stability, and emulsion rheology were obtained. The results showed that increasing WPI concentration significantly affected droplet size, surface charge, and oxidative stability, but had little effect on creaming stability and emulsion rheology. At 0.2 wt% WPI, increasing oil-phase volume fraction greatly increased droplet size but no significant effect on surface charge. At 1 or 2 wt% WPI, increasing oil-phase volume fraction had less influence on droplet size but led to surface charge more negative. Increasing oil-phase volume fraction facilitated the inhibition of lipid oxidation. Meanwhile, oil-phase volume fraction played a dominant role in creaming stability and emulsion viscosity. The rheological data indicated the emulsions may undergo a behavior transition from an entropic polymer gel to an enthalpic particle gel when oil-phase volume fraction increased from 20% to 40% v/v.