Effect of processing and formulation on the microstructural properties of water-in-cocoa butter emulsions

Water-in-oil emulsions are colloidal systems, often used to replace part of the fat with water in high-fat foods, without dramatically changing sensorial or physical properties. The aims of our research were to investigate, firstly, the effect of processing conditions and, secondly, the effect of emulsion formulation on the droplets size, droplets stability, and melting characteristics of ‘tempered’ water-in-cocoa butter emulsions. The emulsions (10% or 20% w/w aqueous phase) were produced using a bench scale margarine line, a scraped surface heating exchanger (SSHE) in series with a pin stirrer (PS), or by using a SSHE only. The average droplet size (d3,2) was measured using pNMR. Thermal analysis of fast cooled (to -15°C) emulsions provided insight into the effect of continuous shear on cocoa butter polymorphic form. The results show that the shear applied by each mixer of the margarine line contributes to the reduction of the droplets size. However, smaller d3,2 values could be obtained using the SSHE only at top rotor rate. Cocoa butter polymorphic form depended upon the applied shear and, even if emulsified, it could be tempered to obtain polymorphic form V (melting 32-34°C) when experiencing high shear (˃900 rpm). This work shows that a continuous process can be used to produce stable and ‘tempered’ water-incocoa butter emulsions with desired microstructural properties.