Rheology and Flocculation of High-Pressure-Treated β-Lactoglobulin-Stabilized Emulsions: Comparison with Thermal Treatment

Abstract

High-pressure treatment (HPT) has been shown to induce significant levels of flocculation in model oil-in-water emulsions stabilized by β-lactoglobulin at neutral pH, as indicated by changes in droplet size distribution and rheological behavior. Light microscopy has also provided additional evidence of extensive droplet flocculation following severe treatment. The proportion of unadsorbed protein greatly influences the extent of flocculation, and this may explain in part the nature of these pressure-induced effects. It has been observed that severe HPT (800 MPa for 60 min) is equivalent to relatively mild thermal treatment (TT) (65 °C for 5 min) in terms of the associated changes in emulsion gel rheology. Since HPT destabilizes these emulsion systems to a much lesser degree than TT, it can be considered to be a gentler processing operation in comparison. Emulsion flocculation is more sensitive to pressure and temperature at pH values closer to the isoelectric point and at higher ionic strength. That is, conditions favoring a loss of electrostatic stability tend to cause an increase in sensitivity toward pressure and temperature, although HPT consistently appears to be a gentler process than TT under all conditions studied. Keywords: High-pressure treatment; thermal treatment; protein functionality; flocculation; rheology; emulsion stability; emulsion gel