Thermal behavior of binary mixtures of palm kernel oil (PKO), cocoa butter (CB), and anhydrous milk fat was used to study mixed-lipid crystallization. This study was related to the physical properties of compound coatings made with these fats. Phase behavior was studied by evaluating changes in melting behavior with composition and time, by creating isosolid diagrams, and by monitoring polymorphic behavior. For binary mixtures, multiple melting peaks and eutectic formation were observed for 30-50% addition levels of CB to PKO, but not for addition of milk fat to PKO. For compound coatings and binary mixtures, made with the same fat composition, hardness of compound coatings increased as solid fat content (SFC) at 25°C of binary mixtures increased. Also, as SFC at 25°C of the binary mixtures increased, induction time for bloom formation and time to fully bloom for compound coatings decreased. Observation of eutectic behavior for binary mixtures indicated softness in a compound coating with the same fat composition, but the converse was not necessarily true. JAOCS 74, 357-366 (1997). KEY WORDS:Compound coatings, fat bloom, hardness, mixed lipids, phase behavior.It is desirable to enhance flavor and texture of palm kernel oil (PKO)-based compound coatings with addition of fats, such as cocoa butter (CB) or milk fat. The use of milk fat in confections is advantageous because of its abundance and flavor attributes (1). It is also known to inhibit bloom formation in dark chocolate (2). However, use of CB and milk fat in PKObased coatings is limited. This is due to incompatibilities between these fats, which result in increased bloom formation and/or excess softening of the final product.Phase behavior of mixed lipid systems has been extensively studied (3-5), although it is not well understood. Eutectic and diluent interactions in fat mixtures have been investigated by using solid fat content (SFC) diagrams by several researchers (5-9). From these diagrams, one can readily determine compatibility of two fats. If two fats are perfectly compatible and exhibit similar melting behavior, the lines of constant SFC lie on straight horizontal lines that connect the melting temperatures of the individual fats. Two fats can also be compatible in phase behavior but have different melting behavior. In this case, lines of constant SFC are straight and connect points for the two pure fats, but decrease in temperature from the harder fat to the softer fat. In this case, diluent softening of the hard fat occurs by addition of the softer fat. For extreme incompatibility between fats, eutectic crystallization effects cause significant depressions in SFC for mixtures of two fats. On the isosolid diagram, this is seen as a compression of the lines of constant SFC and melting temperatures below each of the individual fats. Thus, isosolid diagrams can be used to rapidly distinguish compatibility of two fats.Timms (9) found that mixtures of milk fat and CB exhibit detrimental eutectic effects at moderate levels of milk fat addition. Eutectic...

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