Deformation and fracture behavior of physical gelatin gel systems

• Gelatin gel systems with different stiffness are prepared by varying formulation.
• Large strain deformation and fracture toughness parameters are determined.
• Experimental trends between mechanical parameters are explored.
• Strain hardening decreases exponentially with increasing shear modulus.
• Fracture toughness increases linearly with increasing shear modulus.

Food scientists usually used biopolymer physical gels as model systems because they are structurally and mechanically similar to many gel-like food products. In this paper, eight gelatin gel systems with different stiffness were prepared by varying gelatin concentration (10–30%w/w), collagen source (bovine/porcine) and solvent composition (0/40%w/w glycerol/buffer mixture). The swelling behavior was evaluated and the mechanical response was characterized through puncture tests, uniaxial compression experiments and wire cutting fracture tests. From these tests, apparent gel strength, first order Ogden constitutive parameters (shear modulus, μ, and strain hardening capability, α) and fracture toughness (Gc) were determined. Samples that display apparent gel strength and swelling behavior consistent with a more physically cross-linked structure exhibit larger μ and Gc and lower α values. It is shown that α and Gc are related with μ independently of gelatin concentration, collagen source and glycerol presence. α decreases exponentially with increasing μ whereas Gc increases linearly with μ. The found experimental trends suggest that in the quasi-static range the overall mechanical behavior of gelatin gel systems is mainly controlled by the initial shear modulus, which is a direct measure of gel stiffness.

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