Rheological behaviour of fibre-rich plant materials in fat-based food systems

The potential use of fibre-rich materials as bulking agents to replace sucrose in chocolate confectionary products is investigated. Since the rheological behaviour of the molten chocolate mass is key in chocolate production, the rheology of fibre-rich materials in medium chain triglycerides (MCT) is studied and compared to the rheology of sucrose in MCT. The materials studied are side streams of the fruit and vegetable processing industry: lemon peels, spent grain, grape pomace and pecan fibre. All suspensions showed shear thinning behaviour at volume fractions >0.2, where side stream materials showed lower shear thinning behaviour than sucrose. The values for the maximum packing fraction, obtained via the Maron–Pierce equation and using the Casson Plastic Viscosities, were lower for the side stream materials than for sucrose. Addition of lecithin resulted in a decrease in the Casson Yield Value of sucrose suspensions, which was not observed with the fibre-rich materials. The rheological behaviour of the fibre-rich materials suspended in MCT is explained by the effective volume of the irregularly shaped particles. The behaviour of sucrose suspensions is explained by the formation of aggregates, which seem to be promoted by water bridges between the particles. Overall, the behaviour of the sucrose dispersions was very different compared to the other materials with respect to the shear thinning behaviour, the impact of lecithin as well as the impact of water. Therefore it is suggested that only partial replacement of sucrose by fibre-rich materials will be successful in industrial product development.