Influence of photocrosslinking on the retrogradation of wheat starch based films

The ageing of wheat starch based materials was followed as a function of time for different systems suitably hydrated to be in the rubbery state. In particular, one aspect of retrogradation, that is to say the development of crystallinity is analysed in order to study the influence of a specific crosslinking treatment of starch films made by UV irradiation (photocrosslinking). Mechanical and thermal properties showed that an important limitation on this particular ageing occurs after photocrosslinking at room temperature. A process of accelerated ageing, monitored by modulated DSC, was also performed at 60 °C in order to increase retrogradation kinetics. The results showed a recrystallisation decrease and it appeared that the presence of the plasticiser enhances retrogradation. For a plasticised sample (17% glycerol), a decrease of 30% of the melting enthalpy was observed compared to 91% for an unplasticised one. A modification in the nature of the melting peaks, as recorded by modulated DSC, allowed us to propose a model for amylopectin retrogradation after crosslinking.