Kinetics of cream formation by the mechanism of consolidation in flocculating emulsions

In this work we propose a theoretical description of the process of creamin g of batch emulsions when a sharp boundary exists between a clear serum pha se and the sedimenting drops. The creaming is represented as a continuous c onsolidation of partially aggregated network. The treatment reproduces corr ectly the trend for gradually decreasing rate of sedimentation as time goes on. The theoretical results are compared quantitatively with experimental measurements of the creaming rate. Oil-in-water systems, stabilized by prot eins (beta -lactoglobulin (BLG), bovine serum albumin, and mixtures BLG + b eta -casein) were investigated. Faster creaming is attributed to larger siz e of the sedimenting objects (flocs of emulsion droplets). In systems obeyi ng the creaming mechanism with sharp boundary (SB) the flocs are smaller wh en the protein concentration is higher. This supports the hypothesis for th e stabilizing role of the excess amount of protein (forming lumps and multi layers on the interface). Theoretical analysis demonstrates that the format ion of flocs by gravitational coagulation is a much faster process than the consolidation of the cream. Hence, the dispersions first flocculate and th en cream. With increasing beta -casein content in mixtures BLG beta -casein the emulsions depart from the SE-type behavior and are characterized by th e presence of small nonflocculated droplets, which do not sediment (the ser um is turbid and the boundary with the concentrated dispersion is diffuse, DB behavior). This is connected with hindered flocculation, perhaps due to beta -casein's augmented ability to prevent droplet aggregation, (C) 2000 A cademic Press.