The objective of this study was to assess the effect of process variables on the droplet size distribution in the o/w emulsions manufactured by membrane emulsification. The model emulsions were composed of milk (MPC 75) and whey protein (WPC 80) concentrates, maltodextrin (DE»10) dissolved in water phase and the rapeseed oil as the dispersed phase. In the emulsification process tubular ceramic membranes with nominal pore sizes of 1.4 and 0.8 mm were used. During the experiments the continuous phase was circulated with the velocity 3.3-8.3 m s-1 enabling the shear rate at the membrane wall over the range of 4400 - 11000 s-1. The oil was forced to the flowing liquid through membrane pores at the pressure 0.3 or 0.5 MPa. The mass fraction of dry solids (DS) in the resulting emulsions was equal to 0.3, with 0.3 w/w oil and 0.7 w/w protein-maltodextrin mixture in DS.
The droplet size distributions in the emulsions prepared with MPC were mono- or bimodal and the droplet sizes ranged from 3.0 mm (d0.1) to 26 mm (d0.9) regardless the pore sizes in the membranes. The pore sizes in the membranes had little effect on the average droplet diameters, since the d0.5 values in the emulsions obtained were comparable i.e. 10.1 and 11.1 mm for 1.4 and 0.8 mm membranes respectively. However, when greater oil feed pressure was applied, the increase in the droplet diameters and in the width of particle distribution was observed.
The emulsions composed with WPC were characterized by narrow, monomodal droplet size distribution and the negative influence of oil feed pressure was less pronounced. The crucial process magnitude was the flow velocity of the continuous phase, which determined the shear rate and therefore shear stress at the membrane wall. The greater was the velocityu, the smaller oil droplets were formed and this relationship could be expressed by the power-type regression equation d32=41.1×u-0.725 [m] at R2=0.96.
Research performed in the frames of COST Action FA1001.
Research supervisor: Prof. Lidia Zander lidia.zander@uwm.edu.pl
