Effect of heating temperature, pH, concentration and starch/whey protein ratio on the viscoelastic properties of corn starch/whey protein mixed gels

Abstract

The viscoelastic properties of corn starch (CS) gels were more dependent on heating temperature, while the properties of whey protein isolate (WPI) gels were more dependent on pH. Thus heating temperature (75, 85, 95°C) and pH (5, 7, 9) were varied to obtain a series of mixed gels with interesting viscoelastic properties. WPI gels showed extensive stress relaxation (SR) indicative of a highly transient network structure, while CS gels relaxed very little in 2000 s. Based on SR results, it appeared that CS/WPI mixed gels with 25 and 50% CS formed compatible network structures at 15% total solids only at pH 9. This supposition was supported by SEM microstructures obtained for dehydrated gels and a synergistic increase in the large-strain fracture stress for these gels. Some synergy was also found for mixed gels at 30% total solids at pH 9, while at pH 7 the mixed gels seemed to contain separate additive WPI and CS networks unlike the case for pH 7 at 15% total solids. In both cases (15 and 30% total solids) the degree of elasticity of the mixed gels decreased as the WPI content increased. Mixed gels (CS:WPI = 0.5) at pH 9 showed increased fracture stress and fracture strain relative to the same gels at pH 7. This suggests that a unique chemical compatibility exists at pH 9 and results in gels that combine the elasticity of CS and the internal stress dissipation of WPI.

Rheological characterizations of texturized whey protein concentrate-based powders produced by reactive supercritical fluid extrusion

“…The main factor in this study that could influence and dominate the structural changes in WP was extrusion pH. Hudson and Daubert (2002), and Shim and Mulvaney (2001) indicated that changes in WP structure were significantly dependent on pH while starch was relatively insensitive to pH changes. The extrusion process was more severe in alkaline than in acidic conditions.…”

“…It was reported that the absolute difference between G 0 and G 00 over a range of frequencies and the degree of frequency independency of moduli demonstrated the typical characteristics of gels (Clark, 1998;Rodd, Davis, Dunstan, Forrest, & Boger, 2000;Shim & Mulvaney, 2001). Table 3 shows the frequency dependence of the moduli (G 0 and G 00 ) analyzed quantitatively by fitting simple power law relationships…”

“…It was indicated that gels with tan d > 0.1 had a paste-like quality (weak gel), while gels with tan d < 0.1 were firm, self-standing (true) gels (Clark, 1998;Shim & Mulvaney, 2001). In this study, TWPC samples showed a broader range of tan d compared at the same frequency of 1 rad/s (0.183 to 0.550) which is greater than 0.1, indicating a weak gel or paste-like structure.…”

Weighing up whey fortification of foods: Implications for kinetics of starch digestion and estimated glycemic index of model high-protein-low-carbohydrate food systems

“…pressure and specific mechanical energy) have also been reported. During heat-moisture-shear-(pressure) treatments as obtained in extrusion, starch and protein can respectively be gelatinised and denatured, with the possibility of starch-protein complexes (Allen, Carpenter, & Walsh, 2007;Matthey & Hanna, 1997;Schmitt, Sanchez, DesobryBanon, & Hardy, 1998;Shim & Mulvaney, 2001;Zhang, Maladen, & Hamaker, 2003). These transformations influence digestibility of starch, protein and their mixtures, and although in vitro protein digestibility of whey fortified foods has been reported (e.g.…”

Macromolecular Interactions During Gelatinisation and Retrogradation in Starch-Whey Systems as Studied by Rapid Visco-Analyser

“…Although complex modulus decreased in the presence of WPI (weakened gel structure), it increased as WPI was increased, and this was related to increased enhancement of hydrophobic interactions. In studies of heated mixed WPI and regular or cross-linked waxy maize starch dispersions at pH 7, Shim and Mulvaney (2001) and Ravindra et al (2004) identified three phase-separated networks depending on the composition of the blend; a WPI continuous network weakened by dispersed phase of starch granules when WPI fraction > 60% (WPIdominated), two continuous phases (20% < WPI < 75%), and a starch continuous phase weakened by WPI aggregates when WPI < 20% (starch-dominated). While Champenois et al (1998) found the storage and loss moduli of gluten-starch dispersions (6 -30%) to increase with an increase in starch content, Shim and Mulvaney measured the complex modulus of 100% WPI to be greater than that of 100% starch (0% WPI), while at 5% or 15% total solids, the modulus exhibited a quadratic relationship with WPI content.…”