Heat-induced Whey Protein Isolate Gels Research Articles

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.

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.

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 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.