Thermal transitions and fat droplet stability in ice-cream mix model systems - Effect of milk fat fractions

We studied thermal transitions and physical stability of oil-in-water emulsions containing different milk fat compositions, arising from anhydrous milk fat alone (AMF) or in mixture (2:1 mass ratio) with a high melting temperature (AMF-HMT) or a low melting temperature (AMF-LMT) fraction. Changes in thermal transitions in bulk fat and emulsion samples were monitored by differential scanning calorimetry (DSC) under controlled cooling and reheating cycles performed between 50 and -45 degrees C (5 degrees C min(-1)). Comparison between bulk fat samples and emulsions indicated similar values of melting completion temperature, whereas initial temperature of fat crystallization (T-onset) seemed to be differently affected by storage temperature depending on triacylglycerols (TAG) composition, After storage at 4 degrees C, T-onset values were very similar for emulsified and non-emulsified AMF-HMT blend, whereas they were lower (by approx. 6 degrees C) for emulsions containing AMF or mixture of AMF-LMT fraction. After storage at -30 degrees C, T-onset values of re-crystallization were higher in emulsion samples than in bulk fat blends, whatever the TAG fat composition. Light scattering measurements and fluorescence microscopic observations indicated differences in fat droplet aggregation-coalescence under freeze-thaw, procedure, depending on emulsion fat composition. It appeared that under quiescent freezing, emulsion containing 14 AMF-LMT fraction was much less resistant to fat droplet aggregation-coalescence than emulsions containing AMF or AMF-HMT fraction. Our results indicated the role of fat droplet liquid-solid content on emulsion stability.