Impact of technology and whipping conditions on dairy topping fabricationThe continuous manufacturing of dairy toppings has been studied using first the conventional industrial technology, the axial rotor-stator mixer. The influence of process parameters including operating pressure, residence time and rotational speed has been investigated in terms of overrun, bubble size distribution, as well as foam texture and stability using a model dairy emulsion. The performance of the rotor-stator mixer has then been confronted to that of alternative technologies, such as narrow gap annular columns and scraped surface heat exchangers. Experimental results have highlighted the significant role of operating pressure, the ambiguous role of high residence times that make easier the achievement of desired overrun values, but provide larger bubble sizes, and also the negative interaction between high rotational speed and high residence times. Scale effects have been quantified using a generalized Reynolds number that takes into account the shearthinning behaviour of the emulsion, the increase in viscosity due to the gas phase and all the geometrical characteristics of a rotor-stator unit. The results have also shown that scraped surface heat exchangers constitute an attractive alternative to other foaming devices: they behave globally as a rotor-stator unit with long residence time, but provide foams with smaller bubble sizes than other types of units.

Whipped emulsions were prepared at pilot scale from fresh milk, whole egg, and other ingredients, for example, sugars and stabilizers (starch, polysaccharides). Egg content was varied: 4 recipes were studied differing in their egg to milk protein ratio (0, 0.25, 0.38, and 0.68). Protein and fat contents were kept constant by adjusting the recipes with skim-milk powder and fresh cream. Emulsions were prepared by high-pressure homogenization and whipped on a pilot plant. Particle-size distribution determined by laser-light scattering showed an extensive aggregation of fat globules in both mix and whipped emulsions, regardless of recipe. Amount of protein adsorbed at the oil-water interface and protein composition of adsorbed layer were determined after isolation of fat globules. Protein load is strongly increased by the presence of egg in formula. Values obtained for the whipped emulsions were dramatically lower than those obtained for the mix by a factor of 2 to 3. Sodium dodecyl sulfate-PAGE indicated a preferential adsorption of egg proteins over milk proteins at the oil-water interface, regardless of recipe. This phenomenon was more marked in aerated than in unaerated emulsions, showing evidence for desorption of some milk proteins during whipping. Egg proteins stabilize mainly the fat globule surface and ensure emulsion stability before whipping. Air bubble size distribution in whipped emulsions was measured after 15 d storage. When the egg to milk protein ratio is decreased to 0.25, large air cells appear in whipped emulsions during storage, indicating mousse destabilization. The present work allows linking the protein composition of adsorbed layers at the fat globule surface to mousse formula and mousse stability.