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

Flocculation of protein-stabilized oil-in-water emulsions

“…Liquidlike emulsions can be converted into solid-like emulsion gels on heating [111]. Static high-pressure treatment of ␤-lactoglobulin in emulsions can also have a significant influence on protein aggregation and emulsion stability [112][113][114].…”

Physicochemical and rheological properties of soybean protein emulsions processed with a combined temperature/high-pressure treatment

“…On the other hand, Dickinson and James (1998) have studied the HP effect on emulsions stabilized with b-lactoglobulin. They observed an increase in flocculation with HP treatment, especially at high non-adsorbed protein concentrations.…”

“…HP technology can both preserve foods and modify functional properties of food components (Dickinson & James, 1998;Montero, Ferna´ndez-Dı´az, & Go´mez-Guille´n, 2002). It is well known that pressure has a disruptive effect on the tertiary and quaternary structure of most globular proteins (Puppo et al, 2004;Tedford, Smith, & Schaschke, 1999).…”

Emulsifying properties of ovalbumin in mixtures with sulphated polysaccharides: effects of pH, ionic strength, heat and high-pressure treatment

“…Examination of the overall droplet size distributions for the high- pressure-treated emulsions suggests that treatment induces extensive droplet¯occulation. It is interesting to note that previous studies carried out on b-Lg emulsions have also shown¯occulation, 43 although the effect of high pressure on d 43 and creaming behaviour was somewhat less when the treatment was applied after emulsion formation. 14 On the basis of the experimental results presented in this paper and data from previous studies 10,20,22 we assume that high-pressure processing leads to the dissociation of the electrostatic protein±polysacchar-ide complex(es).…”