Shear and longitudinal ultrasonic measurements of solid fat dispersions

Dispersions of coating fat in corn oil (2.5-12.5 wt%) were prepared following two different protocols: Type A dispersions had an average crystal size of 30-36 mum, whereas type B dispersions were less than 1 mum. In both dispersions the fat crystals were aggregated into larger structures (up to 80 mum). The longitudinal ultrasonic properties (i.e., velocity, attenuation, and reflectance) were linearly related to the solid fat content, but only attenuation was sensitive to the different microstructures. The velocity and reflectance measurements were modeled using the Urick equation. Shear ultrasonic reflectance and oscillatory viscometry were used to measure the dynamic viscosity of all dispersions. According to both methods, type B samples were always more viscous than type A at a similar solids content. The correlation between the two techniques was good (r(2) > 0.99), but the numeric agreement was different for both systems.