The stability of recombined milk fat globules

The stability of the fat globules in recombined milk products against creaming, flocculation, clustering, partial coalescence and real coalescence, with the emphasis on partial coalescence, was studied. (partial) Coalescence was characterized by determining changes in globule size distribution and fat content. Without crystals the emulsions were mostly stable at rest and during flow. If crystals were present, natural cream and emulsions of milk fat-in-whey were unstable in a flow, while emulsions of milk fat and skimmilk or milk fat and buttermilk remained fairly stable and only gave partial coalescence if high shear rates were applied to emulsions with a high fat content and a large average diameter.

In some cases partial coalescence resulted in the formation of a few large clumps that coalesced into floating fat upon heating the emulsion to above the melting point of milk fat thus causing a reduction of the fat content of the underlying emulsion, in other cases partial coalescence resulted in the formation of many small clumps that coalesced into larger fat globules upon heating, thus causing an increase in average globule size. Coalescence course and rate appeared to depend on emulsion type and applied treatment. Partial coalescence of milk fat-in-whey emulsions nearly always resulted in a decrease of the fat content. With a model starting from a small fraction of reactive globules gradually growing into clumps during the treatment, the coalescence process of these emulsions was fairly good quantitatively described. The ideas whereupon this model is based were used to qualitatively explain the different partial coalescence processes observed with the other emulsions.