Evolution of fat crystallinity in anhydrous milk fat-in-water emulsion, as studied by different physical combined techniques.

摘要

The structural characteristics of a same milk fat-in-water emulsion was determined using different physical techniques. The emulsion stability was monitored through determination of the fat droplet size distribution and proportion of adsorbed proteins at the fat droplet-water intersurface. Thermograms observed by differential scanning colorimetry (DSC) showed that Delta T (difference between temperature of initial crystallization and melting completion) was higher by approximately 10 degrees C in the emulsified milk fat than in the bulk fat sample. Moreover, isothermal treatment at 4 degrees C led to a peak time value (tmax=4 degrees C) which was ~12 min longer than in bulk fat. The evolution of viscoelastic properties under cooling and reheating reflected not only the contribution of crystalline fat in the emulsion during the ageing step at 4 degrees C but also the contribution of gelatin which was added for structuration of the aqueous continuous phase. The coupling with DSC of time-resolved synchotron X ray diffraction at both small and wide angles showed that fat crystallization behaved differently under cooling and reheating. Under cooling and reheating, (sub alpha ) -> alpha polymorphic transition and alpha -> beta ' were observed, respectively. Separation of proton relaxation between aqueous and fat phases observed by low field nuclear magnetic resonance showed that the crystalline fat formed at 4 degrees C was more affected by the presence of emulsifiers than by emulsification. The results obtained using different approaches were presented in regard to their potential of giving complementary information on emulsion structural properties..