Dietary fat is an important component of formulated foods as it contributes to both the flavour and mouthfeel that we associate with fattiness. However, the current trend in low-fat reformulation is challenging, because simply removing fat has a significant negative impact on the eating experience. The loss in functionality (provided by the fat) can be balanced through microstructural design. In traditionally high fat foods such as cream based confectionery, replicating the luxurious creamy mouthfeel is especially important if low-fat alternatives are to be successful.

Fluid gels are proposed by many authors as a promising option for fat replacement. Fluid gels are concentrated dispersions of gelled particles formed when gelation occurs within a shear field. Their characteristic hair-like protrusions and soft particles give rise to rheological properties that are typically associated with creaminess: high viscosity, yield stress, and shear thinning behaviour. They are also found to provide ball-bearing lubrication in soft tribological contacts. However, these inherently “creamy” rheological and tribological properties are strongly influenced by sugars, often present at high concentrations in confectionery fillings. Applying fluid gels as fat replacers in confectionery requires understanding of the effect of sugar on the rheological and tribological properties, from which the influence on mouthfeel can be inferred.

In this research, rheology and tribology were used in conjunction to predict the effect of sucrose on the mouthfeel of agar fluid gels. Sucrose is found to positively contribute to fat-related rheological properties but detrimentally affect the lubricity of the formulation, indicating a trade-off between thickness and slipperiness, both of which are required for “creaminess” perception. High sugar environments appear to promote gel particle nucleus formation, slow particle growth, and yield fluid gels with significantly smaller, stiffer particles. The conformation of unbound agar in the serum phase changes as solvent quality reduces (with sucrose addition), reducing the functionality of the serum phase to maintain interparticle connectivity at dilution.

The interdependency of these variables and range of effects that sucrose has on the system makes it difficult to pin-point individual contributions to the final material properties. By systematically varying fluid gel size, shape and stiffness, the mechanisms underlying fluid gel rheology and tribology are elucidated. Hence, this work provides mechanistic insight essential for tailoring hydrocolloid systems to achieve desirable texture and mouthfeel in low-fat, high-sugar products, directly supporting enhanced product development.