Heat-induced Whey Protein Isolate Research Articles

Smart antimicrobial system based on enzyme-responsive high methoxyl pectin-whey protein isolate nanocomplex for fresh-cut apple preservation

The increase in pectin methylesterase (PME) activity on fresh-cut apple surface can smartly trigger the controlled release of bactericidal agents encapsulated within intelligent responsive Pickering emulsions. In this study, we developed a PME-responsive nanocomplex (W-H-II) to stabilize Pickering emulsion containing thyme essential oil (TEO), preserving fresh-cut apples. W-H-II, formed by heat-induced whey protein isolate (WPI) and high methoxyl pectin (HMP) (pH 4.5, 85 °C, 15 min, WPI:HMP ratio 1:2), exhibited good pH stability due to the stabilizing effects of hydrophobic, hydrogen bonding, and electrostatic interactions. The presence of PME triggered the demethylation of HMP within W-H-II, conferring PME response characteristics. Subsequently, a bacteriostasis experiment with pectinase-producing Bacillus subtilis provided evidence of PME-triggered TEO release from W-H-II-stabilized Pickering emulsion. Furthermore, microscopy techniques were employed to verify the demulsification behavior of the emulsion when PME activity ranged from 0.25 to 2.50 U mL−1. Finally, the PME-responsive TEO Pickering emulsion effectively preserved fresh-cut apples. Stored for 6 days at 5 °C and 10 °C, as the PME activity on the apple surface increased, the decay rate of the coated group was 0 %, with a total colony count below 3.0 log CFU g−1. This study introduces a novel intelligent preservation strategy for storing fresh-cut apples.

The effect of sweet tea polysaccharide on the physicochemical and structural properties of whey protein isolate gels

In this study, we investigated the effect of sweet tea polysaccharide (STP) on the physicochemical and structural properties of heat-induced whey protein isolate (WPI) gels, and explored the potential mechanism. The results indicated that STP promoted the unfolding and cross-linking of WPI to form a stable three-dimensional network structure, and significantly improved the strength, water-holding capacity and viscoelasticity of WPI gels. However, the addition of STP was limited to 2 %, too much STP would loosen the gel network and affect the gel properties. The results of FTIR and fluorescence spectroscopy suggested that STP affected the secondary and tertiary structures of WPI, promoted the movement of aromatic amino acids to the protein surface and the conversion of α-helix to β-sheet. In addition, STP reduced the surface hydrophobicity of the gel, increased the free sulfhydryl content, and enhanced the hydrogen bonding, disulfide bonding, and hydrophobic interactions between protein molecules. These findings can provide a reference for the application of STP as a gel modifier in the food industry.

Rheological and microstructural characterisation of heat-induced whey protein isolate gels affected by the addition of caseinomacropeptide.

Caseinomacropeptide (CMP) is derived from the chymosin cleavage of κ-casein during cheese production. This study developed gels from CMPs, which were isolated by different ultrafiltration systems, and whey protein isolate (WPI), and studied their rheological and ultrastructural characteristics. The 30% WPI gel showed high elastic modulus (G') values and stronger structure than the other samples with CMP. Another gel, with 50% protein, 30% WPI and 20% CMP sample isolated from the 30 kDa retentate, had a weaker structure and lower G' value. The third gel, with 30% WPI and 20% CMP sample from the 5 kDa retentate derived from the 30 kDa retentate, presented intermediate structural strength. Despite the increase in protein concentration from the addition of CMP, there was a decrease in the strength of the gel network. Different CMP isolation processes also contributed to differences in the microscopic analysis of gel structures with the same protein content.

Modification of heat-induced whey protein isolate hydrogel with highly bioactive glass particles results in promising biomaterial for bone tissue engineering

This study deals with the design and comprehensive evaluation of novel hydrogels based on whey protein isolate (WPI) for tissue regeneration. So far, WPI has been considered mainly as a food industry by-product and there are very few reports on the application of WPI in tissue engineering (TE). In this work, WPI-based hydrogels were modified with bioactive glass (BG), which is commonly used as a bone substitute material. Ready-to-use, sterile hydrogels were produced by a simple technique, namely heat-induced gelation. Two different concentrations (10 and 20% w/w) of sol–gel-derived BG particles of two different sizes (2.5 and <45 µm) were compared. µCT analysis showed that hydrogels were highly porous with almost 100% pore interconnectivity. BG particles were generally homogenously distributed in the hydrogel matrix, affecting pore size, and reducing material porosity. Thermal analysis showed that the presence of BG particles in WPI matrix reduced water content in hydrogels and improved their thermal stability. BG particles decreased enzymatic degradation of the materials. The materials underwent mineralization in simulated biological fluids (PBS and SBF) and possessed high radical scavenging capacity. In vitro tests indicated that hydrogels were cytocompatible and supported MG-63 osteoblastic cell functions.

Effect of low-methoxy pectin on interfacial and emulsion stabilizing properties of heated whey protein isolate (WPI) aggregates

• QCM-D study of heated WPI and heated biopolymer complexes on hydrophobic surface. • A higher ratio of pectin to WPI increased the adsorbed mass on the surface. • A higher ratio of pectin to WPI decreased the protein load from 15.11 to 9.19 mg/m 2 . • Interfacial properties of the heated WPI-LMP affected the emulsion stability. In this study, we have investigated the interfacial and emulsion stabilizing properties of heat-induced whey protein isolate (WPI) aggregates prepared in the presence or absence of low-methoxy pectin (LMP). Sub-micron complex particles were formed by heating of oppositely charged WPI and LMP at different WPI:LMP mass ratios. The Quartz Crystal Microbalance with Dissipation (QCM-D) technique was used to better understand the adsorption properties of these biopolymeric particles at a model hydrophobic surface. Clear correlations were observed between the interfacial properties of WPI and WPI:LMP aggregates and the resulting emulsion characteristics. Compared to WPI aggregates (which led to emulsions containing larger flocculated droplets), the heated complexes (formed at a higher ratio of LMP to WPI) were highly efficient as Pickering stabilizers leading to emulsions with smaller droplets (5.5–6.8 μm). Cryo-SEM analysis clearly revealed the manipulation of the emulsions’ interfacial microstructure due to the adsorption of a WPI:LMP inter-polymeric film onto the surface of the droplets. The effectiveness of the colloidal particles in stabilizing emulsions depended largely on the formation of a sufficiently ‘dense layer’ of particles at the oil-water interface where these properties were controlled by the composition of WPI and LMP at the oil droplet surface. Moreover, the emulsion physical stability was greatly influenced by the formation of an inter-connected film at the oil droplet interface, whereby these viscoelastic films increased the steric hindrance against coalescence of emulsion droplets. This work provides the mechanism of emulsion stabilization by WPI particles formed by heating in the absence or presence of pectin.

Heat-induced whey protein isolate gels improved by cellulose nanocrystals: Gelling properties and microstructure

Cellulose nanocrystals (CNC) were successfully prepared from wheat bran, and their effects on the gelling properties and microstructure of heat-induced whey protein isolate (WPI) gels were investigated. The results showed that the water holding capacity, gel strength, viscoelasticity, and thermal stability of the composite gels were improved by increasing the CNC concentration from 0 to 1.0 % (w/v). The incorporation of CNC restricted water mobility and facilitated conformation conversion of the secondary structure from α-helix to β-sheet. CNC has good compatibility with the protein matrixes at relatively low concentrations. At higher CNC concentrations, the agglomerated CNC can serve as an active dehydrating agent to absorb moisture in the protein matrixes, which promotes unfolding and cross-linking of the protein molecules. Moreover, the active filling effects of CNC contributed to the formation of a compact and homogeneous gel structure. Therefore, naturally sourced CNC is suggested as a potential gel modifier in food industry.

Modification of heat-induced whey protein gels by basic amino acids

Various amino acids have been studied as gelation enhancers. This study investigated the effect of histidine, lysine, and arginine on gelling properties of heat-induced whey protein isolate (WPI) gels at different pHs. Basic amino acids modified WPI gels in a pH- and amino acid-dependent manner. Hardness and gumminess of the WPI gel was improved by arginine at pH 7.59 while springiness was enhanced by histidine at pHs 7.59 and 9.74 and by lysine at pH 7.59 (P < 0.05). At pH 2.0, WPI formed a weak gel. Lysine and arginine facilitated β-lactoglobulin cross-linking at pH 2.0 and reduced protein leach out from the gel (P < 0.05). At pH 5.2, WPI formed a particulate gel with poor water holding capacity (WHC). Lysine improved WHC of the WPI gel at pH 5.2 by changing the structure of the gel network. At pHs away from 5.2, basic amino acid treatments resulted in a more uniform and porous gel matrix and a greater WHC (P < 0.05). In conclusion, different basic amino acids may be applied as WPI gel enhancers depending on the pH and desired attributes of the product.

High intensity ultrasound effects on heat-induced whey protein isolate gels depend on α-lactalbumin: β-lactoglobulin ratio

The effects of high intensity ultrasound (HIU) treatment on physical properties of whey protein isolate (WPI) gels, i.e., water holding capacity, gel strength and elasticity, were studied. WPIs with different α-lactalbumin:β-lactoglobulin (α-la:β-lg) ratios were subjected to ultrasonication (24 kHz, 300 W cm−2, 2078 J mL−1) with and without temperature control, i.e., T < 20 °C and T < 65 °C, respectively. Effects of ultrasonication were greatly affected by the relative amount of α-la, most likely due to the type of interactions formed during gelation after ultrasonication. For WPI with relative high α-la content ultrasonication improved the water holding capacity and gel strength of the heat-induced gels. To the contrary, for WPIs with intermediate or low α-la content, no changes in physical properties were observed. These results contribute to clarifying the mechanisms underlying the effects of HIU on WPI, linking effects on protein level to physical properties.

Influence of Xanthan-Curdlan Hydrogel Complex on Freeze-Thaw Stability and Rheological Properties of Whey Protein Isolate Gel over Multiple Freeze-Thaw Cycle.

The effect of adding xanthan-curdlan hydrogel complex (XCHC) at 2 concentrations (0.25 and 0.5% w/w) on the freeze-thaw stability of heat-induced whey protein isolate (WPI) gel was investigated. Samples were stored at 4 °C for 24 h before subjected to 5 freeze-thaw cycles alternating between -16 °C (18 h) and 25 °C (6 h). Adding XCHC to the WPI solution resulted in the reduction of a significant amount of syneresis up to 5 repeated freeze-thaw cycles. Addition of XCHC decreased the amount of syneresis from 45% in the control sample (pure WPI gel) to 31.82% and 5.44% in the samples containing 0.25% and 0.5% gum, respectively, after the 5th freeze-thaw cycle. XCHC increased the storage modulus (G') of the gels and minimized the changes of the G' values over the 5 freeze-thaw cycles, indicating improvement of the stability of the system. Furthermore, the minimum protein concentration for gel formation decreased in the presence of the XCHC. Scanning electron microscopy (SEM) images showed that addition of XCHC resulted in the formation of a well-structured gel with numerous small pores in the network, which consequently improved the water retention ability during the temperature abuses up to 5 freeze-thaw cycles. These results have important implications for using XCHC in the formulation of the frozen WPI-based products with improved freeze-thaw stability and rheological properties. Application of XCHC in the formulation of frozen dairy-based food products has the potential to enhance freeze-thaw stability and minimize moisture migration caused by temperature abuses of the products during distribution and consumer application.

Effect of calcium chloride on the structure and in vitro hydrolysis of heat induced whey protein and wheat starch composite gels

The formation of heat induced whey protein isolate (WPI) and wheat starch (WS) gels in the presence of added calcium chloride (5–192 mM) has been examined. Thermal properties, including the onset temperature of starch gelatinization and protein denaturation, are defined by low amplitude oscillation on shear and modulated temperature differential scanning calorimetry. Upon heating and subsequent cooling, comparison of the storage modulus values bear information on the enhancement of protein aggregation by the electrolyte and the occurrence of phase separation phenomena between the two polymeric constituents in the mixture. Further confirmation of observed trends has been provided by measurements on textural hardness of gels in single cycle compression tests. Porous and aggregated microstructures are identified upon visual examination by environmental scanning electron microscopy. The gels were subjected to in vitro enzymatic hydrolysis and the role of calcium in reducing the extent of starch degradation by α-amylase has been established. It is evident from the results that ionic strength in the form of added calcium ions largely influences gelation kinetics of whey protein leading to significant variability in the hydrolytic potential of α-amylase on wheat starch.

Study on the rheological properties of heat-induced whey protein isolate–dextran conjugate gel

Effect of glycosylation on the rheological properties of whey protein isolate (WPI) during the heat-induced gelation process was evaluated. Significant changes in browning intensity, free amino groups content and SDS-PAGE profile showed that the conjugate of WPI and dextran (150 kDa) was successfully prepared using the traditional dry-heating treatment. For the conjugate, during the heating and cooling cycle, the curves of G′ and G″ were considerably shifted to lower values and their shapes varied comparing to the corresponding spectra of initial WPI and WPI + dextran mixture. After holding at 25 °C, G' reached a value of about 2200 Pa, only a tenth of the value that obtained in the initial WPI gel. Moreover, frequency sweep measurements revealed that the stiffness of gel was greatly reduced in the conjugate, although a typical elastic gel was still formed. All data showed that the rheological properties of thermal gelation could be modified upon the covalent attachment of dextran.

Heat-induced whey protein isolate fibrils: Conversion, hydrolysis, and disulphide bond formation

Fibril formation of individual pure whey proteins and whey protein isolate (WPI) was studied. The heat-induced conversion of WPI monomers into fibrils at pH 2 and low ionic strength increased with heating time and protein concentration. Previous studies, using a precipitation method, size-exclusion method, or proton NMR spectroscopy, reported a wide range of values for the conversion. An alternative method was developed, namely centrifugal filtration, giving a consistent picture of the conversion. The present results help to explain the disparities reported in literature. No fibrils formed upon heating pure α-lactalbumin or pure BSA at pH 2, whereas fibrils formed in pure β-lactoglobulin ( β-lg) and WPI solutions. Experiments indicate that β-lg was the only whey protein involved in fibril formation. In all whey protein samples, hydrolysis occurred during heating at pH 2, as determined by HPLC and SDS-PAGE. When WPI fibrils formed at pH 2 were stored at pH 7 or 10, disulphide bonds were formed in the samples.

Influence of glycerol on optical properties and large-strain rheology of heat-induced whey protein isolate gels

The influence of glycerol (0–50 wt%) on the properties of gels formed by heating 10 wt% whey protein isolate (WPI) solutions (pH 7.0, 100 mM NaCl) at 90 °C has been studied. The elastic modulus, breaking stress and breaking strain of the gels were measured using uniaxial compression. The optical properties of protein solutions were characterized by turbidity or colorimetry measurements. The onset of gelation at 90 °C was delayed in the presence of glycerol, presumably because the cosolvent increased the thermal stability of the globular proteins and reduced the protein–protein collision frequency. On the other hand, the elastic modulus, breaking stress and breaking strain of gels heated at 90 °C for 60 min increased with glycerol concentration, presumably because the glycerol increased the strength of the intermolecular attraction between fully denatured proteins. Glycerol decreased the lightness of the gels because it reduced the scattering efficiency of the protein aggregates. This study shows that glycerol can be used to modulate the physicochemical properties of whey protein gels.

Influence of NaCl on optical properties, large-strain rheology and water holding capacity of heat-induced whey protein isolate gels

The influence of NaCl (0–1000 mM) on the physical properties of gels formed by heating 10 wt% whey protein isolate (WPI) solutions (pH 6.9) at 80 °C for 15 min has been studied. Elastic modulus, elastic recoverability and water loss of gels were measured during uniaxial compression/decompression. Optical properties of gels were characterized by spectral reflectance and colorimetry measurements. Below 60 mM NaCl, no gels were formed and the WPI solutions remained optically transparent. From 60 to 150 mM NaCl, gel elastic modulus increased, elastic recoverability remained high, water loss remained low and lightness remained low. From 150 to 200 mM NaCl, gel elastic modulus decreased, elastic recoverability decreased, water loss increased, and gel lightness increased. Above 200 mM NaCl, the elastic modulus, elastic recoverability, water loss and lightness of the gels were relatively insensitive to salt concentration. Theoretical predictions indicated that the lightness ( L) of dyed gels had a maximum value at protein particle radius of 100 nm and that L increased with protein particle concentration (especially from 0 to 1 wt%). Differences in gel physicochemical properties are interpreted in terms of differences in the microstructure and interactions of the protein molecules within the gel network.

Gelation properties of dispersions containing polymerized and native whey protein isolate

Whey protein polymers (WP-polymers) were prepared by heating whey protein isolate below the critical concentration for gelation at neutral pH and low salt conditions. The effects of WP-polymers and salt types (CaCl 2 or NaCl) on rheological properties (large-strain and small-strain analysis), water holding properties, turbidity and microstructure of heat-induced whey protein isolate gels were investigated. Replacement of native whey protein isolate with WP-polymers increased fracture stress, fracture modulus, held water, and the translucency of gels. With both salt types, the addition of WP-polymers changed the gel structure from particulate to fine-stranded. However, the effect of WP-polymers on rheological properties was salt specific. Addition of 20–100% WP-polymers in the presence of 10 mM CaCl 2 caused a continued increase in fracture stress. In contrast, protein dispersions containing 30 mM NaCl did not form self-supporting gels when ≥60% WP-polymers were added. Dispersions containing 200 mM NaCl formed self supporting gels at all levels of WP-polymer addition but fracture stresses for gels containing 20–100% WP were similar. Dispersions containing 80% WP-polymers and 200 mM NaCl had lower gel points (time and temperature) than dispersions with 80% WP-polymers and 10 mM CaCl 2. It appeared that CaCl 2 was more effective in increasing gel fracture stress while NaCl was more effective in decreasing gelation time. Different gel properties may be prepared by altering the amount of WP-polymers and salt types.

Dynamic viscoelastic properties of thermally induced whey protein isolate gels with added lecithin

The effect of crude egg yolk lecithin on the formation of heat-induced whey protein isolate (WPI) gels was investigated using dynamic small-strain rheometry. Three different types of gel networks, fine-stranded, mixed, and particulate network, were formed by varying NaCl concentration. In all conditions, storage modulus ( G′) increased during holding at 80°C, development of which was well-described by first-order reaction kinetics. There was an additional increase in G′ during cooling to 25°C. The final values of G′ and the fracture modulus showed similar trends in the effect of lecithin addition: a substantial reinforcing effect on fine-stranded and mixed gels and slightly negative effect on particulate gels. For fine-stranded and mixed networks, lecithin addition decreased the gelation time and increased the gelation rate constant at 80°C. In contrast, lecithin addition to particulate gels did not affect these rate parameters. The positive effect of lecithin on rheological properties of WPI gels with fine-stranded or mixed networks was not only due to the acceleration of gelation rates during the heating process but also due to the enhancement of the elastic nature of the networks during cooling.

Effects of lecithin on thermally induced whey protein isolate gels

The effect of lecithin on fundamental fracture properties (true shear stress and true shear strain at fracture) and water holding capacity of heat-induced whey protein isolate (WPI) gels were investigated. Adding egg yolk lecithin to WPI gels substantially increased the fracture stress of gels containing ≤50 mmol/dm 3 NaCl but slightly decreased the fracture modulus at concentrations >100 mmol/dm 3. The fracture strain and water holding capacity were decreased by lecithin addition across the NaCl concentration range examined (30–500 mmol/dm 3). These results suggest that the gel network type and/or the dispersed state of lecithin changing with NaCl concentration in the system is responsible for the mechanism of lecithin–whey protein interactions. Lecithin can play a beneficial role in promoting gel strength but there is an optimal level which is strongly related to the amount of NaCl in the system.