Rheological, Thermal, and Moisture Sorption Characterisation of cocoa-flavoured Confectionery Coatings Elaborated with Isomalt as Sucrose Substitute

The objective of this work was to analyse the effect of partial sucrose replacement by isomalt on the thermal, rheological, and moisture sorption behaviour of cocoa-flavoured confectionery coatings. Formulations were elaborated using sucrose, isomalt, cocoa powder, vegetable oil, lecithin, glycerol, and water. Full-sugar sample (0%) was used as control and reduced-sugar formulations were obtained by replacing 25% and 50% of the sucrose by isomalt. Flow behaviour and thixotropy of liquid formulations were evaluated. Thermal properties (by differential scanning calorimetry) and moisture adsorption and desorption isotherms at 25 °C of films (dried by casting at 40 °C and 26% relative humidity for 24 h) were obtained in the water activity range of 0.225–0.927. Rheological behaviour was described by the Cross model and a first-order structural kinetic model. Sorption isotherms were analysed applying the Generalised D’Arcy and Watt (GDW) and Chi models. The presence of isomalt affected the rheology of liquid formulations, especially in the 50% sample. Similar thixotropic behaviour was found between 0% and 25% samples, with a ~ 100% recovery, indicating a better coating performance. The range of the mean onset (36–41 °C) and melting (95–155 °C) temperatures obtained was high, suggesting that the solid structure of films will be preserved at room storage conditions. The sorption isotherms showed a type-III shape, evidencing two characteristic surfaces with different sorption energies, and hysteresis between adsorption and desorption. The GDW and Chi models accurately described the isotherms. These results are useful to control the elaboration and conservation of reduced-sugar confectionery coatings.