Material properties of cocoa butter emulsions: effect of dispersed phase droplet size and compression speed on mechanical response

Water-in-cocoa butter (CB) emulsions material properties were investigated using uniaxial compression test. Emulsions containing 20% (wt%) water and with a range of droplet size were manufactured to assess the role of defect size on emulsions mechanical properties. Although differences were not significant within the tested droplet size range, results showed a decreasing trend in the values of mechanical parameters at fracture with increasing structural defect size. The mechanical response of bulk CB and emulsions was also investigated at different compressive rates. Materials visco-elastic behaviour was confirmed by their strain-hardening behaviour at increasing test speed with bulk CB always displaying the highest mechanical strength. In the light of these results and microscopy evidences, it was hypothesised that droplets are only partially bonded to the CB network therefore playing a stress-concentration role by promoting fracture initiation. The addition of water droplets also resulted in a reduction of the overall network internal degree of connectivity: when large deformations are applied, droplet-matrix de-bonding occurs at the particle-fat network interface promoting fracture propagation and thus explaining the weakening structural effect of droplets