Crystallization behaviors of milk fat by seasons

In this study, thermal profiles (heating-cooling curves, isothermal crystallization), rheological properties (flow curves), crystal size and shape, crystal polymorphic type and solid fat content of milk fats produced at each season were investigated. Two different cooling rates (2 and 10°C/min) and different crystallization temperatures (5, 10, 14, 17 and 20°C) were studied by using differential scanning calorimetry (DSC), X-ray diffractometer (XRD), rhemometer, polarized light microscope (PLM), nuclear magnetic resonance (NMR). Fatty acid composition and color properties were determined by using gas chromatography (GC) and spectrocolormeter.Fatty acid compositions and color values revealed that seasonal differences had significant effect on these parameters of milk fat. Milk fat had the highest value of stearic acid and oleic acid at summer. Higher values for saturated fatty acids were recorded in autumn and winter. It was found that cooling rate affected the crystallization and melting behavior, size and morphology of the milk fat crystals. In contrast to that, type and formation time of polymorphs were not affected by cooling rate and seasonal difference. It was shown that, at 0°C, highest solid fat content (SFC) belonged to autumn milk fat and all of the milk fat melted at about 35°C.Keywords: Milk fat, isothermal crystallization, rheology, XRD, polymorphic type.