@article{ikeda_nishinari_foegeding_2001, title={Mechanical characterization of network formation during heat-induced gelation of whey protein dispersions}, volume={56}, ISSN={["0006-3525"]}, DOI={10.1002/1097-0282(2000)56:2<109::aid-bip1056>3.0.co;2-u}, abstractNote={The formation of gel network structures during isothermal heating of whey protein aqueous dispersions was probed by mechanical spectroscopy. It was anticipated that the pathway of the sol-to-gel transition of whey protein dispersions is quite different from that of ordinary cross-linking polymers (e.g., percolation-type transition), since aqueous solutions of native whey proteins have been shown to be highly structured even before gelation, in our previous study. At 20 degrees C, aqueous dispersions of beta-lactoglobulin, the major whey protein, and those of whey protein isolate (WPI), a mixture of whey proteins, exhibited solid-like mechanical spectra, i.e., the predominant storage modulus G' over the loss modulus G", in a certain range of the frequency omega (1-100 rad/s), regardless of the presence or absence of added NaCl. The existence of the added salt was, however, a critical factor for determining transitions in mechanical spectra during gelation at 70 degrees C. beta-Lactoglobulin dispersions in 0.1 mol/dm(3) NaCl maintained the solid-like nature during the entire gelation process and, after passing through the gelation point, satisfied parallel power laws (G' approximately G" approximately omega(n)) that have been proposed for a critical gel (i.e., the gel at the gelation point) that possesses a self-similar or fractal network structure. In contrast, beta-lactoglobulin dispersions without added salt exhibited a transition from solid-like [G'(omega) > G"(omega)] to liquid-like [G'(omega) < G"(omega)] mechanical spectra before gelation, but no parallel power law behavior was recognized at the gelation point. During extended heating time (aging), beta-lactoglobulin gels with 0.1 mol/dm(3) NaCl showed deviations from the parallel power laws, while spectra of gels without added NaCl approached the parallel power laws, suggesting that post-gelation reactions also significantly affect gel network structures. A percolation-type sol-to-gel transition was found only for WPI dispersions without added salt.}, number={2}, journal={BIOPOLYMERS}, author={Ikeda, S and Nishinari, K and Foegeding, EA}, year={2001}, pages={109–118} }
 @article{ikeda_foegeding_hardin_2000, title={Phospholipid/fatty acid-induced secondary structural change in beta-lactoglobulin during heat-induced gelation}, volume={48}, ISSN={["0021-8561"]}, DOI={10.1021/jf990434h}, abstractNote={Effects of phosphatidylcholine (PC) and the predominant fatty acids (FAs) in milk, butyrate, oleate, and palmitate, on secondary structural changes in beta-lactoglobulin (beta-LG) during heat-induced gelation were analyzed on the basis of circular dichroism (CD) spectra. Small-strain oscillatory measurements were carried out to characterize viscoelastic properties of the heat-induced gels. In the absence of added salt, PC and FAs induced helix formation of beta-LG on heating to 80 degrees C and increased the storage moduli (G') of heat-induced gels. In the presence of 500 mM NaCl, PC did not change the CD spectrum of beta-LG but decreased G'. In contrast, butyrate substantially unfolded beta-LG in 500 mM NaCl on heating, forming very elastic gels with increased G' values. Palmitate and oleate induced beta-LG gel formation at 25 degrees C without heating; heating to 80 degrees C almost completely unfolded beta-LG in 500 mM NaCl.}, number={3}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Ikeda, S and Foegeding, EA and Hardin, CC}, year={2000}, month={Mar}, pages={605–610} }
 @article{ikeda_foegeding_1999, title={Dynamic viscoelastic properties of thermally induced whey protein isolate gels with added lecithin}, volume={13}, ISSN={["1873-7137"]}, DOI={10.1016/S0268-005X(99)00006-5}, abstractNote={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.}, number={3}, journal={FOOD HYDROCOLLOIDS}, author={Ikeda, S and Foegeding, EA}, year={1999}, month={May}, pages={245–254} }
 @article{ikeda_foegeding_1999, title={Effects of lecithin on thermally induced whey protein isolate gels}, volume={13}, ISSN={["1873-7137"]}, DOI={10.1016/S0268-005X(99)00005-3}, abstractNote={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/dm3 NaCl but slightly decreased the fracture modulus at concentrations >100 mmol/dm3. The fracture strain and water holding capacity were decreased by lecithin addition across the NaCl concentration range examined (30–500 mmol/dm3). 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.}, number={3}, journal={FOOD HYDROCOLLOIDS}, author={Ikeda, S and Foegeding, EA}, year={1999}, month={May}, pages={239–244} }
 @article{ikeda_foegeding_hagiwara_1999, title={Rheological study on the fractal nature of the protein gel structure}, volume={15}, ISSN={["0743-7463"]}, DOI={10.1021/la9817415}, abstractNote={The effects of ionic strength on fractal structures in heat-induced gels prepared from globular proteins were investigated in the framework of a fractal aggregation of colloidal particles. All gels formed at 90 °C exhibited power law relationships between the storage shear modulus (G‘) and protein concentration. At 25 mM NaCl, the fractal dimension, d (∼2.2), calculated based on the value of the power law exponent agreed with those for reaction-limited cluster−cluster aggregation. Further addition of NaCl (50, 80, 500, 1000 mM) decreased the values of d (∼1.8), which agreed with d for diffusion-limited cluster−cluster aggregation. These results suggest that the predominant effect of an increase in ionic strength on globular protein gelation is ascribed to shielding charges on the surface of the proteins, thereby increasing the reaction probability of protein aggregation. The effective structure-determining rheological properties of heat-induced protein gels are characterized by fractal dimensions deduced ...}, number={25}, journal={LANGMUIR}, author={Ikeda, S and Foegeding, EA and Hagiwara, T}, year={1999}, month={Dec}, pages={8584–8589} }