@article{zhang_daubert_mulligan_foegeding_2008, title={Additive effects on the rheological behavior of alginate gels}, volume={39}, DOI={10.1111/j.1745-4603.2008.00159.x}, abstractNote={ABSTRACT The effects of dextran and glycerol on the rheological properties of 1.25% alginate gels were studied. Although the dextran and glycerol dramatically changed the viscosity of the alginate solution, the gelation kinetics was not affected. This observation may be attributed to the fact that the gelling process was controlled by the combination of carboxylic groups in alginate chains with Ca2 + , and not by the diffusion process of alginate molecules and Ca2 + through the viscous medium. The small‐strain shear modulus of alginate gels with either low molecular‐weight dextran (MW: 140,000 Da) or glycerol remained nearly constant, as did the large deformation and fracture properties. The addition of high molecular‐weight dextran (MW: 4–5 million Da) altered the small‐strain shear modulus and lowered the gel fracture stress of the alginate gels, while the fracture strain remained the same. The change in small‐strain shear modulus and large deformation and fracture properties for alginate gels with high MW dextran cannot simply be explained by the change in viscosity of the gel liquid phase. A plausible explanation for this behavior is that, in some manner, large dextran molecules influenced the alginate gel network. PRACTICAL APPLICATIONSA common characteristic of food gels is a three‐dimensional network formed by primary gel‐forming materials, such as proteins and polysaccharides. Alongside the gelling material(s), additives are frequently included to attain desirable functionality. The gel network stabilizes the system, and the physiochemical properties of gels are dominated by structural organization at the molecular level. The inclusion of additives may affect physical and chemical properties of the gels, and subsequently, the rheological properties. Rational optimization of product formulations and processing conditions of food gels depends on a better understanding of the impact of additives on processing and rheological properties.}, number={5}, journal={Journal of Texture Studies}, author={Zhang, J. and Daubert, C. R. and Mulligan, J. H. and Foegeding, E. A.}, year={2008}, pages={582–603} } @article{zhang_daubert_foegeding_2007, title={A proposed strain-hardening mechanism for alginate gels}, volume={80}, ISSN={["0260-8774"]}, DOI={10.1016/j.jfoodeng.2006.04.057}, abstractNote={The non-linear viscoelastic properties of alginate gels were investigated using torsion and compression rheological tests. Like many biopolymers, alginate gels showed strain-hardening behavior during large deformation, and the degree of strain-hardening depended on gel composition. The strain-hardening behavior of alginate gels was attributed to the deformation of rod-like junction zones serving as physical crosslinks in the gel. A constitutive equation based on the deformation of junction zones and a Gaussian distribution network of chains was developed to predict deformation behavior. The resulting equation effectively described the experimental data during torsion and compression, supporting the proposed mechanism that strain-hardening originates from the deformation of alginate junction zones.}, number={1}, journal={JOURNAL OF FOOD ENGINEERING}, author={Zhang, Junhua and Daubert, Christopher R. and Foegeding, E. Allen}, year={2007}, month={May}, pages={157–165} } @article{hamann_zhang_daubert_foegeding_diehl_2006, title={Analysis of compression, tension and torsion for testing food gel fracture properties}, volume={37}, ISSN={["1745-4603"]}, DOI={10.1111/j.1745-4603.2006.00074.x}, abstractNote={ABSTRACT Three fracture test methods: uniaxial compression, uniaxial tension and torsion were examined by interpreting results using theories upon which the methods were based. In each of these tests, the fracture of gels can occur as a result of shear, compression or tension. The fracture properties determined from uniaxial compression and tension were compared with torsion testing, a suitable reference technique. Shear stress and strain in uniaxial compression were comparable with shear stress and strain in torsion. However, the tensile stress in compression is not in agreement with that in torsion. Tensile stress or shear stress values in uniaxial tension were generally comparable with tensile or shear stress values in torsion, while the strain levels in uniaxial tension were typically much lower than those in uniaxial compression or torsion. This result could be related to the fracture strain being a function of elongation necessary to reduce the specimen cross section to an area producing the critical fracture stress. The comparison among different methods revealed shear stress and strain can be the fracture criteria for uniaxial compression, and tensile stress can be the fracture criterion for uniaxial tension, whereas the fracture strain criterion in uniaxial tension cannot be specified. Possible mechanisms for differences among methods are discussed in the manuscript. }, number={6}, journal={JOURNAL OF TEXTURE STUDIES}, author={Hamann, Donald D. and Zhang, Junhua and Daubert, Christopher R. and Foegeding, E. Allen and Diehl, Kenneth C., Jr.}, year={2006}, month={Dec}, pages={620–639} } @article{zhang_daubert_foegeding_2006, title={Polyacrylamide gels as elastic models for food gels: Fracture properties affected by dextran and glycerol}, volume={37}, DOI={10.1111/j.1745-4603.2006.00046.x}, abstractNote={ABSTRACT Influence of dextran and glycerol on fracture properties of 10% polyacrylamide (PAAm) gels was studied as a representative model system for food gels. No direct relationship was found between the fracture properties and gel liquid‐phase viscosity. In general, addition of dextran and glycerol did not affect gel network crosslink density and chain length. With minimal dextran addition, fracture stress and strain experienced large increases. Increase of the fracture stress and strain was attributed to fracture mode transition from elastic to elasto‐plastic fracture, resulting from dextran addition. Plastic deformation at the crack tips, acting as fracture‐initiating points, prior to fracture propagation lowered stress concentration effect. Sensitivity of 10% PAAm gels, with/without dextran, to induced imperfections showed the fracture stress to be higher than expected based on Griffith's energy balance criteria, manifesting in a delayed fracture process. The plastic deformation was ascribed to the delayed crack nucleation resulting from dextran addition. The fracture stress and strain of 10% PAAm gels increased with glycerol addition. The increase in fracture properties was attributed to plastic deformation, caused by a delayed crack nucleation prior to fracture propagation. The mechanism of delayed crack nucleation remains unclear, but the results obtained from this investigation can be used to understand reasons for the change in fracture property of food gels created by additives. }, number={2}, journal={Journal of Texture Studies}, author={Zhang, J. H. and Daubert, C. R. and Foegeding, E. A.}, year={2006}, pages={200–220} } @article{zhang_daubert_foegeding_2005, title={Characterization of polyacrylamide gels as an elastic model for food gels}, volume={44}, ISSN={["1435-1528"]}, DOI={10.1007/s00397-005-0444-5}, number={6}, journal={RHEOLOGICA ACTA}, author={Zhang, JH and Daubert, CR and Foegeding, EA}, year={2005}, month={Jul}, pages={622–630} } @article{zhang_daubert_foegeding_2005, title={Fracture analysis of alginate gels}, volume={70}, ISSN={["1750-3841"]}, DOI={10.1111/j.1365-2621.2005.tb11471.x}, abstractNote={ABSTRACT:The fracture properties of alginate gels were investigated using torsion and compression. The gel fracture stress correlated with Ca2+ and alginate concentration, whereas the fracture strain was insensitive to composition. Considering the relationship of fracture stress with gel network crosslink density and the energy to break covalent and noncovalent bonds, the fracture of alginate gels is hypothesized to result from the disruption of junction zones. Consequently, the fracture stress was the stress required to overcome electrostatic forces that formed junction zones. The fracture stress‐strain relationship for alginate gels can be described by the Blatz, Sharda, adn Tschoegl (BST) equation, suggesting that for a given gel, the fracture strain can be predicted based on fracture stress, small‐strain shear modulus, and a fitted parameter describing nonlinearity of the gel. In addition, the fracture properties were affected by deformation rate. The influence of deformation rate on fracture was ascribed to structural changes among the alginate junction zones.}, number={7}, journal={JOURNAL OF FOOD SCIENCE}, author={Zhang, JH and Daubert, CR and Foegeding, EA}, year={2005}, month={Sep}, pages={E425–E431} }