INDUCTION OF MILKFAT CRYSTALLIZATION IN THE EMULSIFIED STATE BY HIGH HYDROSTATIC-PRESSURE

The effect of high hydrostatic pressure to milk fat in the emulsified state has been studied by transmission electron microscopy (TEM) and low resolution pulsed nuclear magnetic resonance (NMR) for the purpose of following pressure-induced crystallization processes. Pasteurized dairy creams (35 and 43 % fat) were subjected to pressures between 100 and 500 MPa for 1 to 15 minutes at a temperature of 23-degrees-C. By applying the freeze fracture technique for TEM studies it was demonstrated that pressurization induces fat crystallization within the emulsion droplets, predominantly at the globule periphery. The ultrastructural findings were confirmed by NMR which showed that the amount of crystallized fat formed depended both on intensity and time of pressurization. In the pressurized cream samples the crystallization proceeded during further storage at 23-degrees-C whereas the fat droplets in the original cream sample remained liquid under these conditions, provided that the cream sample was held at this temperature.