Effect of the fatty acid composition of monoglycerides and shear on the polymorphic behavior in a water-in-oil (W/O) emulsion semi-solid fats blend was investigated. The bulk fat blend and the W/O emulsion fat blend with added either unsaturated or saturated monoglycerides were prepared using a rapid cooling heat exchanger, and the polymorphic transitions from b 0 to b-form during storage were compared by X-ray diffraction. The peak intensity of the b-polymorph of the samples with added saturated monoglycerides was stronger than that of unsaturated monoglycerides, and the peak intensity of the b-polymorph of the W/O fat blend emulsions was stronger than that of the bulk fat blends. The polymorphic transition to the b-form during storage of the W/O emulsion fat blend was promoted by the applied shear. In contrast, that of the bulk fat blend was retarded by shear. These results suggested that fatty acids, which combined to monoglycerides on the surface of water droplets, influenced the polymorph transformation of the fat crystal network in a continuous semi-solid fat phase because of the acyl-acyl interactions between the fatty acid residues of the monoglycerides and triacylglycerols in the fat crystal network.

The effect of shearing on the polymorphic behavior of palm oil-based fat blends with low (LT-Fat) and high (HT-Fat) trans-fatty acid contents during storage was investigated. A shear stress was applied to fat blends at 5℃ or 10℃ by the flat-crush method or after rapid or slow cooling by the syringe-extrusion method. The fat networks were evaluated by cryo-scanning electron microscopy (SEM), polarized light microscopy, and solid fat content measurement, and the polymorphic transition from the β′-form to the β-form under thermal thawing between 5℃ and 20℃ was investigated by X-ray diffraction. Transition to the β-form of LT-Fat with shearing was retarded compared with that without shear. SEM revealed that with shearing, LT-Fat built complex networks involving both fine reticulation and a tight structure, whereas without shearing, the structure was nearly uniform. These results suggest that the non-uniformly network achieved by shearing could suppress the localization of specific triacylglycerides, preventing transformation into the β-form.