Whey Protein Gels Research Articles

Numerical optimization of probiotic Ayran production based on whey containing transglutaminase and Aloe vera gel.

The purpose of this study was to optimize the functional properties of probiotic Ayran. Two-level fractional factorial design with four center points was used to investigate the effect of five independent variables including, reconstructed whey protein (70-90% of milk), salt (0.5-1g/100g), Aloe vera gel (0-30g/100g), transglutaminase enzyme (0-14 unit/100g) and storage time (1-21days). The viability of Lactobacillus acidophilus La-5 and other physicochemical properties such as pH, acidity, viscosity, sedimentation, and color were modeled and then optimized using desirability function method. Results showed that reconstructed whey protein and Aloe vera gel significantly affected the viability of L. acidophilus La-5 and other physicochemical properties (p < 0.05). The viability of L. acidophilus La-5 and viscosity decreased by increasing of whey protein percentage from 70 to 90. Maximum L. acidophilus La-5 count was observed in samples with a minimum level of whey protein and maximum level of Aloe vera gel. Milk replacement with whey protein up to 90% caused to decrease acidity and viscosity significantly but sedimentation increased (p < 0.05). Optimum condition for production of functional Ayran determined as follow: Aloe vera gel concentration: 25.7%, reconstructed whey protein: 70%, salt: 0.58% and transglutaminase enzyme: 5 unit/100mL.

Influence of γ-aminobutyric acid on gelling properties of heat-induced whey protein gels

γ-Aminobutyric acid (GABA) is a non-protein amino acid that has attracted considerable attention due to its various health promoting benefits. Great efforts have been made to enrich GABA in food while few studies have considered that GABA may influence the protein functional properties, which are imperative to food quality. The present study investigated the effects of GABA on gelling properties of heat-induced whey protein gels at different pHs. GABA greatly strengthened the whey protein gels at pH 2.0 while weakened the gels at pH 6.5 and 8.0 (P < 0.05). At pH 2.0, GABA decreased protein leachability and enhanced water holding capacity (P < 0.05) by encouraging the disulfide cross-linking of α-lactalbumin and β-lactoglobulin, which resulted in a well-structured gel network that can resist deformation and trap water. At pH 6.5, GABA increased the leach-out of β-lactoglobulin which explained the reduced gel hardness and improved gel swelling ratio (P < 0.05). At pH 8.0, GABA treatment resulted in a less cohesive gel despite a decreased protein leachability (P < 0.05) and an increased incorporation of α-lactalbumin, β-lactoglobulin, and BSA into the gel network. In summary, the presence of GABA exhibited a pH-dependent impact on the gelling properties of heat-induced whey protein gels.

Starch gelatinization inside a whey protein gel formed by cold gelation

Native potato starch (PS) granules were trapped within a whey protein network formed by cold gelation. Heat treatment of these composite gels induced PS gelatinization inside the protein network, which was studied with a DSC/hot-stage system and confocal laser scanning microscopy. Gelatinization inside the protein network was also indirectly followed by rheological measurements and mechanical properties of the composite gels measured before and after heat treatment. The presence of the protein network shortened the gelatinization by 3°C, reduced the gelatinization enthalpy by 42% and significantly restricted granules swelling. The rheological and mechanical properties of the gels were influenced by PS swelling, depending on starch concentration. After reheating to 90°C, the addition of 1% PS resulted in a weakening of the gel. However, the addition of 9% PS led to a reinforcement of the gel, probably due to the formation of an interpenetrating network between whey proteins and the gelatinized PS.

Surface Properties of Whey Protein Gels

Surface properties of whey protein gels are reviewed based on traditional microscopic techniques and new methods, as optical profilometer and contact angle measurements. Optical profilometer is an instrument allowing measurement of surface roughness and contact angle measurements to determine the surface wettability behavior (hydrophobicity/hydrophilicity) of the gels. Investigation of surface properties of whey protein gels is very important, as it can transform this product to a new level of application. It could be used as a matrix for an active ingredient release, material for tissue engineering, e.g. scaffolds, i.e. temporally structures biodegraded in the human organism.

Influence of the Maillard reaction on the properties of cold-set whey protein and maltodextrin binary gels

The Maillard conjugation of proteins and reducing saccharides is used to modify the technological functionality of whey proteins. In this study, whey protein isolate (WPI) was conjugated with maltodextrin (at 1:1 ratio and two total solid contents of 100 and 200 mg mL−1) through the Maillard reaction and used to form cold-set gels. The glycation reaction increased the strength of hydrogen bonding of whey proteins and preferentially modified α-lactalbumin, in comparison with β-lactoglobulin. It also increased the reducing power of binary protein-saccharide solution and allowed formation of self-standing cold-set WPI gel at a low protein content (i.e., ≈50 mg mL−1). Microscopic imaging showed micro-phase separated maltodextrin domains, interrupting the protein network, in gels made of protein-maltodextrin physical mixtures, whereas Maillard conjugation resulted in more homogenous microstructures at both total solid contents. The Maillard reaction increased gel firmness and water-holding capacity and caused a reduction in the extent of gel swelling.

Effect of a whey protein and rapeseed oil gel feed supplement on milk fatty acid composition of Holstein cows

Isoenergetic replacement of dietary saturated fatty acids (SFA) with cis-monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) can reduce cardiovascular disease risk. Supplementing dairy cow diets with plant oils lowers milk fat SFA concentrations. However, this feeding strategy can also increase milk fat trans fatty acids (FA) and negatively affect rumen fermentation. Protection of oil supplements from the rumen environment is therefore needed. In the present study a whey protein gel (WPG) of rapeseed oil (RO) was produced for feeding to dairy cows, in 2 experiments. In experiment 1, four multiparous Holstein-Friesian cows in mid-lactation were used in a change-over experiment, with 8-d treatment periods separated by a 5-d washout period. Total mixed ration diets containing 420 g of RO or WPG providing 420 g of RO were fed and the effects on milk production, composition, and FA concentration were measured. Experiment 2 involved 4 multiparous mid-lactation Holstein-Friesian cows in a 4 × 4 Latin square design experiment, with 28-d periods, to investigate the effect of incremental dietary inclusion (0, 271, 617, and 814 g/d supplemental oil) of WPG on milk production, composition, and FA concentration in the last week of each period. Whey protein gel had minimal effects on milk FA profile in experiment 1, but trans-18:1 and total trans-MUFA were higher after 8 d of supplementation with RO than with WPG. Incremental diet inclusion of WPG in experiment 2 resulted in linear increases in milk yield, cis- and trans-MUFA and PUFA, and linear decreases in SFA (from 73 to 58 g/100 g of FA) and milk fat concentration. The WPG supplement was effective at decreasing milk SFA concentration by replacement with MUFA and PUFA in experiment 2, but the increase in trans FA suggested that protection was incomplete.

Analysis and modeling of enhanced green fluorescent protein diffusivity in whey protein gels

During gastric digestion, hydrolysis of proteins by pepsin contributes largely to the breakdown of protein-rich food. We hypothesized that the effect of pepsin is limited by its diffusivity, which is co-determined by the food structure and the local pH in the food during digestion. To investigate the principle mechanism of enzyme diffusion in food matrices, we used enhanced green fluorescent protein (EGFP) as probe to study the diffusivity of proteins in whey protein isolate gels, using fluorescence correlation spectroscopy (FCS). Gels made with different ionic strength showed distinctive elastic moduli but did not show differences in diffusivity of EGFP. Some models for diffusion in hydrogels yield good description of the obtained data, and can approximate the enzyme diffusion in diverse food matrices. However, the enzyme pepsin is more complicated than the probe EGFP, to yield more accurate predictions, electrostatic and enzyme-substrate interaction also need to be considered.

Characterizing wear behaviors of κ-carrageenan and whey protein gels by numerical modeling

Soft solid foods commonly undergo processing steps such as extrusion, slicing, and shredding. Food tribological behaviors, especially wear behaviors, may be a good indication of their ability to be successfully sliced, shredded, or extruded. However, food wear behaviors are currently unknown. Thus, the objective of this study was to characterize the wear behavior of gels with different structures using a numerical model. Wear behaviors of whey protein isolate and κ-carrageenan gels were evaluated under several normal forces. An empirical model for penetration depth was developed that accounted for deformation due to applied force and removal of material. All models had mean absolute error <16 μm indicating good fit. κ-carrageenan gels had the greatest penetration depth among the gels tested; whey protein isolate gels had the lowest. These results were attributed to gel microstructural differences.

Impact of the dairy product structure and protein nature on the proteolysis and amino acid bioaccessiblity during in vitro digestion

Elderly people exhibit specific nutritional needs, in particular they require higher protein intake. The objective of this study was to compare, using an in vitro digestion protocol, the nutritional performance of novel dairy products, based on whey proteins and which mimicked different commercial cheese textures. Whey proteins have replaced caseins in these different gels for their known ability to promote muscle synthesis in the elderly thanks to their high amount of leucine.The hydrolysis of proteins and the bioaccessibility of amino acids have been evaluated from the simulated gastro-intestinal digestion of four whey-based products of identical composition but different structural properties. Heat-induced gelation of a whey-based dairy emulsion was performed by applying different combination of pH, stirring and heat treatment, in order to obtain a range of different gel structures, from liquid to more or less firm and or whipped gels. A commercial Mozzarella cheese has been tested as the casein-based control.Results showed that both the kinetics of protein hydrolysis and the amino acid release were significantly higher in the casein-based gel than in whey protein matrices. The extent of protein hydrolysis was higher in the whey protein gels compared to the liquid control sample, due to a facilitated hydrolysis of the heat-denatured proteins compared to native proteins. Peptide release and amino acid bioaccessibility were however not significantly influenced by the matrix structure. Further studies, using an in vivo digestion model will allow assessing the amino acids bioavailability of these matrices.

Interaction between lactoferrin and whey proteins and its influence on the heat-induced gelation of whey proteins

In this paper, the influence of lactoferrin (LF) on the structural development of whey protein isolate (WPI) gels during heating was investigated. The results demonstrated that the presence of sufficient LF could improve the strength and elasticity of WPI gels. When 30% LF was added, the elastic modulus of WPI gels increased from 254 ± 31 and 413 ± 58 Pa to 3222 ± 105 and 2730 ± 131 Pa at pH 6.7 and 5.8, respectively. The addition of LF improved the water holding capacity (WHC) of WPI gels at pH 6.7, while no improvement was observed at pH 5.8. LF interacted with whey proteins differently at pH 6.7 and 5.8 during heating. The LF/whey proteins complexes formed at pH 6.7 had smaller sizes and narrower size distributions than those formed at pH 5.8.

A detailed investigation of whey protein isolate solutions and gels reveals a number of novel characteristics

• Anomalous structures and behaviour in WPI solutions and gels found at pH 6.2. • Maximum onset temperature of β-lactoglobulin denaturation occurred at pH 3.4. • Order of aggregate formation determined transition region gel microstructure. • Spherical aggregates gelled more rapidly; fine-stranded gels firmed more on cooling. • G′ correlated positively with fracture stress and negatively with fracture strain.

Effects of high intensity ultrasound on acid-induced gelation properties of whey protein gel

Pre-heated whey protein isolate (WPI) solution (10% w/v, 85°C for 30min) was prepared and subjected to high-intensity ultrasound (HUS, 20kHz) at different durations (5–40min) before acidification to determine the effects of HUS on glucono-δ-lactone (GDL)-induced gelation properties of whey protein gel. Results showed that HUS reduced the particle size and increased surface free sulfhydryl groups of pre-heated whey protein solution. Free sulfhydryl (-SH) content of the acid-induced WPI gels (GIWG) and protein solubility in presence of 8M urea were significantly reduced (P<0.05) by HUS (20 or 40min), indicating that HUS facilitated formation of more disulfide bonds during/after the gelation process. HUS significantly increased (P<0.05) the water holding capacity (WHC), gel strength, gel firmness (G′) as well as the frequency dependence of GIWG. The WHC, gel strength and gel firmness were positively correlated with surface free -SH content of pre-heated WPI and negatively correlated with particle size of pre-heated WPI and free -SH content of GIWG. The results indicated that high intensity ultrasound could be used for modifying whey protein to improve its gelling properties.

Development of iron-rich whey protein hydrogels following application of ohmic heating – Effects of moderate electric fields

The influence that ohmic heating technology and its associated moderate electric fields (MEF) have upon production of whey protein isolate cold-set gels mediated by iron addition was investigated. Results have shown that combining heating treatments (90°C, 5min) with different MEF intensities let hydrogels with distinctive micro and macro properties – i.e. particle size distribution, physical stability, rheological behavior and microstructure. Resulting hydrogels were characterized (at nano-scale) by an intensity-weighted mean particle diameter of 145nm, a volume mean of 240nm. Optimal conditions for production of stable whey protein gels were attained when ohmic heating treatment at a MEF of 3V∙cm−1 was combined with a cold gelation step using 33mmol∙L−1 of Fe2+. The consistency index of hydrogels correlated negatively to MEF intensity, but a shear thickening behavior was observed when MEF intensity was increased up to 10V∙cm−1. According to transmission electron microscopy, ohmic heating gave rise to a more homogenous and compact fine-stranded whey protein-iron microstructure. Ohmic heating appears to be a promising technique, suitable to tailor properties of whey protein gels and with potential for development of innovative functional foods.

Surface properties of ion-inducted whey protein gels deposited on cold plasma treated support

So far no studies have been undertaken on the influence of plasma processing of different solid surfaces on the properties of subsequently formed protein coat. Calcium chloride, magnesium chloride or iron (II) chloride inducing whey protein isolate gels were obtained on glass support previously treated with the plasma at the electric voltage 160 V per 1 min. Dynamic oscillatory and ultrasound viscosity measurements, scanning electron microscopy imaging, surface roughness and contact angles measurements have been performed. Apparent surface free energy was determined using the two approaches: van Oss, Good and Chaudchury (LWAB) and contact angle hysteresis (CAH). Gels surface roughness increased with the increasing of ions concentration. Both approaches used for determination of apparent surface free energy give comparable results. When the air plasma was applied for the support activation, polar groups deposited on the surface had a greater effect on the surface wettability than roughness. Plasma treatment of glass support caused the increase of hydrophobic properties of deposited layers. Wettability properties were affected by the electron donor parameter of energy whose value increased for the samples obtained on the plasma activated supports especially the air treated ones. Plasma treatment of glass plates might have an effect on food processing, production efficiency, microbiological aspects and cleaning process of the gels deposited on their surfaces.

Nonthermal gelation of whey proteins induced by organic acids

ABSTRACTGelation of native whey proteins induced by organic acids at ambient temperature was investigated by fundamental small‐deformation oscillatory rheology. Gelling capability, gelation time, and final viscoelastic properties of the gel were dependent on type of acid, protein and acid concentrations, and pH value. Increasing organic acid concentration or increasing the pH (below pI) resulted in lower gelation times and higher gel modulus values. Differential scanning calorimetry demonstrated that the presence of acetic acid significantly reduced denaturation temperature and enthalpy implying a destabilization effect of the protein structure against thermal unfolding, contrarily to what was observed in the presence of HCl at similar pH values. The gelling ability and the denaturing effectiveness of the acids increase with increasing chain length of the alkyl chain, thus suggesting an important contribution of hydrophobic effects promoting denaturation and fostering the establishment of new interactions between the proteins leading to a nonthermal gelation process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45134.

Rheology and microstructure of kefiran and whey protein mixed gels.

The effect of kefiran on cold-set gelation of whey protein isolate (WPI) at 25°C was studied using rheological measurements and environmental scanning electron microscopy (ESEM). The gelation of samples was induced by the addition of glucono-δ-lactone to the dispersions. WPI concentration was maintained at 8% (w/v) and the concentration of kefiran varied from 0 to 0.08% (w/v). According to rheological measurements, the addition of kefiran into WPI dispersions resulted in a significant increase in the gel strength, the yield stress, and the shear stress values at the flowing point. The gelling point and gelation pH of samples decreased significantly with an increase in kefiran concentration. ESEM micrographs showed that the presence of kefiran played an important role in the microstructure formation of gels. The microstructure of kefiran-WPI mixed gels was more compact and dense, compared to the WPI gel. Depletion interactions between kefiran and whey protein aggregates can be regarded as the chief factor which was responsible for these effects. The present work demonstrated that rheological and microstructural properties of acid-induced whey protein gels were improved by the addition of kefiran.

A Comparative Study of Partial Replacement of Wheat Flour with Whey and Soy Protein on Rheological Properties of Dough and Cookie Quality

The development of wheat-based foods that are enriched with proteins is increasingly popular. The purpose of this study was to compare the effects of partial replacement of wheat flour with whey and soy proteins (0–30%) on the rheological properties of dough and cookie-making quality. The incorporation of whey protein (WP) diluted the concentration of gluten, leading to an increase in dough development time (MDT) and breakdown torque and a decrease in stability time (MST) and minimum torque (MMT). The gelation of WP during the heat treatment increased dough peak torque (MPT), G′, and G′′. As a contrast, the addition of soy protein (SP) increased dough MST, MDT, and MMT. The aggregation of SP helped increase G′ and decrease tan δ of the dough in oscillatory shear tests. The weak gelling effects and higher water absorption of SP decreased MPT, G′, and G′′ of the dough during heat treatment. With SP, the spread ratio of cookies first decreased from 6.39 to 5.66 and then increased to 6.86, and the overall acceptability scores ranged from 6.62 to 7.02, indicating that the formed soy protein network helped maintain the dough structure for obtaining an improvement in the quality of bakery products.

Pepsin diffusivity in whey protein gels and its effect on gastric digestion

Protein is essential to human health, but its digestion kinetics in varied structures are not yet well understood. We previously found different kinetics of protein hydrolysis in solution and in gels, and we hypothesized that the difference stemmed from the steric hindrance of gel structure to the diffusion of pepsin and its hydrolysates. To better understand the pepsin diffusivity in food matrices and its effect on digestion, we determined the diffusivity of pepsin in water and in whey protein isolate (WPI) gels by fluorescence correlation spectroscopy (FCS). We estimated the pepsin concentration gradient during digestion based on the determined diffusivity, which showed that the pepsin is constrained within a thin layer from the gel surface. Gel composition analysis confirmed this constraint: peptides as protein fragments were observed only in the first 2 mm of the WPI gels after 6 h of in vitro gastric digestion. Scanning electron microscopy indicated that pepsin loosened the microstructure of whey protein gel surfaces, which may accelerate pepsin diffusion and consequently gel surface disintegration. We conclude that the mode of whey protein gel digestion is determined by the summed effect of diffusion limitation, hydrolysis rate and microstructure transformation.

Inhibition and Promotion of Heat-Induced Gelation of Whey Proteins in the Presence of Calcium by Addition of Sodium Caseinate.

Heat-induced aggregation and gelation of aqueous solutions of whey protein isolate (WPI) in the presence of sodium caseinate (SC) and CaCl2 was studied at pH 6.6. The effect of adding SC (0-100 g/L) on the structure of the aggregates and the gels was investigated by light scattering and confocal laser scanning microscopy at different CaCl2 concentration ([CaCl2] = 0-30 mM). The gelation process was studied by oscillatory shear rheology. At the whey protein concentrations studied here (34 and 60 g/L), no gels were formed in the absence of CaCl2 and SC. However, WPI solutions gelled above a critical CaCl2 concentration that increased with increasing SC concentration. In the absence of CaCl2, WPI gels were formed only above a critical SC concentration. The critical SC concentration needed to induce WPI gelation decreased weakly when CaCl2 was added. In an intermediate range of CaCl2 concentrations, gels were formed both at low and high SC concentrations, but not at intermediate SC concentrations. Finally, at high CaCl2 concentrations gels were formed at all SC concentrations. The gelation rate and the gel structure of the gels formed at low and high casein concentrations were very different. The effect of SC on the thermal gelation of WPI was interpreted by competition for Ca2+, a chaperon effect, and microphase separation.

Spatial quantification of hydrogels swelling using wide-field fluorescence microscopy

Wide-field fluorescence microscopy (WFM) is used to spatially quantify the protein content of large hydrogels during swelling. Whey protein gels made at different protein concentrations, labelled with rhodamine B isothiocyanate (RITC), were used as a model system. Labelling and swelling measurement conditions were optimized. Dynamic swelling experiments at different pH agree very well with the expected fluorescence decrease for isotropic gels using overall volumetric data, despite the existence of internal gradients. Deviations are observed at large swelling degrees, provably due to protein-dye leakage, and at high protein concentrations. This simple and ubiquitous technique is used to spatially quantify the swelling of protein hydrogels in 2D at different swelling times, highlighting the existence of a variety of swelling profiles inside the gels with time.