Effects of High Pressure on the Physico-chemical Characteristics of Dairy Creams and Model Oil/Water Emulsions

Abstract

A pasteurized liquid dairy cream (pH 6.7–6.8; 350 g/kg fat) was not significantly modified by high pressure processing (HPP) at 450 MPa and 25 °C for 15–30 min, or at 10 °C for 30 min, from the physical standpoint of fat globule size distribution and flow behaviour. Physical stability was also unchanged, in spite of some fat globule aggregation, upon HPP at 450 MPa and 40 °C for 30 min. With a UHT sterilized dairy cream (pH 6.7; 350 g/kg fat), HPP induced formation of fat globule aggregates and markedly increased viscosity, whether carried out at 450 MPa and 25 °C for 15 or 30 min, or at 10 or 40 °C for 30 min. This aggregation was partly reversed during chilled storage. Both types of creams remained physically stable for 8 d at 4 °C, without any phase separation. When the pasteurized cream was first held at 60 °C to melt fat crystals, then processed at 25 °C and 450 MPa for 30 min, an extensive formation of fat crystals was observed in the fat globules by cryofracture and SEM, as previously reported by other authors. Model liquid oil/water emulsions of pH 7.0, containing 50 g/kg sodium caseinate and 300 g/kg peanut oil or glycerol trioleate were processed at 450 MPa and 10, 25 or 40 °C for 30 min, without changes in droplet size distribution or emulsion viscosity. No droplet coalescence or aggregation was observed. Emulsions with the same composition, except with ß-lactoglobulin as an emulsifying agent and stabilizer in place of sodium caseinate, were also processed at 450 MPa and 10 or 25 °C for 30 min, without any changes in oil droplet size. However, HPP at 450 MPa and 25 °C for 30 min increased emulsion viscosity, while gelled emulsions were formed upon HPP at 450 MPa and 40 °C for 30 min. The viscosity of emulsions pressurized at 25 °C further increased during chilled storage, and was higher for emulsions with peanut oil than with triolein. Hence, HPP at 450 MPa for 30 min did not break down or coalesce oil droplets in any of the model emulsions, but did change the rheology of emulsions stabilized by a pressure-sensitive protein (ß-lactoglobulin). It may thus become possible to induce desirable texture modifications in specific food, pharmaceutical or cosmetic emulsions, simultaneously to microbial inactivation.