Binary blends of anhydrous milk fat and cocoa butter - solidification, thermal and polymorphic behaviour

This work investigated the phase behaviour of a binary system consisting of anhydrous milk fat (AMF) and cocoa butter (CB). AMF and CB were mixed at wt% ratios from 10-90 to to 90-10 AMF-CB in 10 wt% increments. The blends were subjected to cooling from 80 to 0 °C (2°C /min), a subsequent 1 hr hold at 0 °C and heating from 0 to 50 °C (2°C /min), during which time the thermal and polymorphic behaviour of the blends were monitored. The solid fat content (SFC) of the blends was also measured. The blends containing 10 to 60 wt% AMF displayed delayed crystallization compared to bulk AMF with a decrease in crystallization enthalpy also observed. In most blends, CB and AMF crystallized independently with CB first crystallizing into the α form before the sub-α form appeared as the temperature approached 0 °C. In AMF, there first appeared the a form which later transformed into the b¢ form. In the blends with 10 to 20% AMF, the CB transformed to the b¢₂ form upon melting during the heating ramp whereas in the blends containing ³ 30% AMF, it transformed into the b¢₁ form. The iso-solids diagram revealed that AMF and CB formed a eutectic at AMF contents of > 30 wt%. The eutectic was most severe in the blends with 50 to 90 wt% AMF in the the 20 to 30 °C range, suggesting strong incompatibility between the two fats. The softening allowed CB in blends with > 30 wt% AMF to transform into b¢₁ form, as noted above. This study demonstrates the significant incompatibility that exists between CB and AMF.