36D-27 |
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J. ZHANG, C. R. Daubert, and E. A. Foegeding. Dept. of Food Science, North Carolina State Univ., Raleigh, NC 27695 Most applied functional properties of food gels are more closely related to large deformation and fracture properties than the small-deformation characteristics. In addition, certain sensory texture notes have been significantly correlated with fracture properties, suggesting that a fundamental understanding of food texture can be obtained by investigating the mechanisms responsible for fracture behaviors. Therefore, the investigation of large deformation and fracture properties of food gels has significant importance. The objectives of this research were to 1) determine how calcium and alginate concentration affect the fracture properties; 2) use a model to describe the fracture stress-strain relationship for alginate gels; and 3) investigate the gel fracture properties associated with deformation rate. The method used for this investigation was torsional tests. Gel samples were ground into a capstan shape and then were mounted onto a Haake VT550 viscometer for twisting to failure at a specified rotational speed. The gel fracture stress correlated with Ca2+ and alginate concentration, while 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 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 viscoelastic non-linearity. This investigation promoted an understanding of fracture mechanisms for biopolymer gels, especially polysaccharide gels, and helped interpret the relationship between gel formulation and fracture properties.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |