Influence of thermal treatments on the structure and stability of gelatin gels

The influence of thermal history on the structure of gelatin gels has been investigated by measuring the specific optical rotation [α]_λ at λ = 436 nm. The helix content χ in the gels was derived by reference to the native collagen. Two types of thermal treatments have been applied: (a) cooling and heating at constant rates, and (b) quenching and annealing for long periods. Our results support the idea that the gels are non-equilibrium systems and exhibit thermal hysteresis. The kinetics of helix formation were analysed by the Avrami theory and compared to other techniques. The stability of the structures formed suggests the existence of several mechanisms of hydrogen bonding of the helices: disordered aggregation or partial collagen renaturation.