Microfluidization of model dairy emulsions. II. Influence of composition and process factors on the protein surface concentration

Abstract

Summary -The influence of some composition variables (butter oil, sodium caseinate and monoglyceride contents) and process variables (pressure and tempe rature) on the relative adsorbed protein fraction (Fads,%) and on the protein load (I", mg m-2 ) of fat globules was studied in a model dairy emulsion (oil-in-water produced by microfluidization). The amount of adsorbed proteins (Fads and F) was evaluated immediately after emulsification by coupling the separation of oil and aqueous phases of the emulsion produced by centrifugation to the determination of protein content. The specifie surface area (Asp) of oil-water interface was obtained by photon correlation spectroscopy after the protein aggregates were dissociated by an appropriate butter. A central composite experimental design was used to obtain Iwo nonlinear multiple regression equations relating Fads and f to sodium caseinate (0.5 to 3.9 wt%), butter oil (5.2 to 14.7 wt%) and monoglyceride (0.08 to 0.88 wt%) contents, and to the emulsification pressure (7.8 to 76.3 MPa) and temperature (35 to 100 OC). These two functions explained 92.7 and 90.6% of the variation in Fads and in F, respectively, and made it possible to evaluate the independent influence of each experimental variable. The results indicate that the sodium caseinates (NaCas), as a group, seem much less easily adsorbed th an monoglyceride (glycerol monostearate, GMS) molecules when the GMS:NaCas molecular ratio (R) is higher th an 5: more numerous and possibly more surface active th an proteins, monoglycerides probably settle at the interface quicker th an proteins. A qualitative model is also presented to illustrate this possible competition and estimate its influence on the parameters that characterize protein adsorption (Fads and F) and fat globule size (dvs aFads: variance of the adsorbed protein fraction (dimensionless); a r : variance of the protein load (g2 rrr").Microfluidizalion of model dairyemulsions.Il

Composition of fat protein layer in complex food emulsions at various weight ratios of casein-to-whey proteins

“…The process variables such as homogenization pressure and temperature were also studied [42,43], but little attention was paid to the effects of the protein structural state (micellar, globular, random coil) on the physico-chemical characteristics and stability of complex emulsions.…”