Optimization of inulin and polydextrose mixtures as sucrose replacers during sugar-free chocolate manufacture – Rheological, microstructure and physical quality characteristics

•Optimum level of inulin and polydextrose mixtures as sucrose replacers was investigated.•Casson viscosity, yield stress, colour, hardness and PSD were evaluated.•Increasing inulin concentration results in increase Casson viscosity.•Microscopy and PSD explain rheological trends.•Simplex lattice mixture design, a useful optimization tool. Inulin and polydextrose have in recent times form basic ingredients in the manufacture of many sugar-free products. However, the applicability and suitability of inulin and polydextrose mixtures as sucrose replacers during manufacture of sugar-free chocolate is yet to be fully understood. This work investigated optimum conditions as well as influences of inulin and polydextrose mixtures as sucrose replacers on rheological properties, microstructure and physical qualities during manufacture of sugar-free chocolate. Increasing inulin concentrations with simultaneous reduction in polydextrose resulted in consistent increases in the Casson plastic viscosity while that led to decreases in Casson yield stress. Chocolate formulated with 100% polydextrose revealed large crystals with dense smaller particles and minimal inter-particle spaces compared to large crystals with more void spaces in chocolates formulated with 100% inulin. Chocolate formulation consisting of 75.3594% polydextrose and 24.6406% inulin was found as the optimum concentrations producing the most acceptable rheological and physical quality characteristics.