Crystallization Behavior And Compatibility Of Diacylglycerol-based Plastic Fat

Diacylglycerol(DAG) has good nutritional value and great market potential because of its health benefits such as reducing body weight, lowering serum triacylglycerol level and adjusting postprandial glucose level. In this paper, some DAGs were enzymatically prepared and their crystallization behaviors were studied. The crystallization behaviors and compatibilities of DAGs and DAG-based plastic fat were also studied. The results are as follows:(1) DAG was synthesized through Lipozyme 435-catalyzed glycerolysis of soybean oil in a solvent-free system using a bubble column reactor. The selected conditions by single factor experiments were established as being enzyme load of 4 wt%, glycerol/soybean oil mole ratio of 20:1, reaction temperature of 80 °C, gas flow of 10.6 cm/min, and a reaction time of 2.5 h, obtaining the DAG content of 49.4 wt%. The reusability of Lipozyme 435 was good in 10 consecutive runs. After purified by molecular distillation, the DAG content of 63.5 wt% was achieved in soybeen oil-based diacylglycerol(SO-DAG). The fatty acid composition had no significant difference from that of soybean oil(SO). However, the thermal properties of SO-DAG and SO had considerable differences. Polymorphic form of SO-DAG were mainly the β form and minor amounts of the β′ form. Granular aggregation and round-shaped crystals were detected in SO-DAG.(2) DAG was prepared through Lipozyme 435-catalyzed esterification from stearin acid, oleic acid and glyceol using a bubble column reactor. After purified by molecular distillation, a DAG content of 78.4 wt% was achieved. The effect of polyglycerol fatty acid esters(PGFE) on crystallization behaviors of DAG was investigated by differential scanning calorimetry and pulsed nuclear magnetic resonance. The results shown that polyglycerol stearic acid ester(PGFE1) promoted the crystallization of DAG, polyglycerol linoleic acid ester(PGFE2) inhibited the crystallization of DAG, and the inhibition effect grew when its addition increased from 2% to 10%. The results of X-ray diffraction indicated that the presence of PGFE1 stabilized the β’ crystals. The addition of PGFE1 made the crystal of DAG smoother as observed by polarized light microscopy.(3) DAGs were synthesized through Lipozyme 435-catalyzed glycerolysis of soybean oil,camellia oil and palm olein using a bubble column reactor. After purified by molecular distillation, the DAG contents of 63.5 wt%, 73.0 wt% and 82.6 wt% were achieved in SO-DAG, camellia oil-based diacylglycerol(CO-DAG) and palm olein-based diacylglycerol(POL-DAG). The crystallization behavior and compatibility of the three DAGs were studied. The results showed that both the crystallization onset and the melting point decreased when the contents of CO-DAG and SO-DAG increased from 0% to 33.33%, 66.66% and 100%, while POL-DAG shown opposite results. Compatibility was best when CO-DAG, SO-DAG and POL-DAG were mixed in 1:4:1 ratio, but worse when in 1:0:1 and 1:1:1.(4) Isothermal crystallization process of the three DAGs was studied by DSC. The result showed that the isothermal crystallization curves of CO-DAG, SO-DAG and POL-DAG at different temperatures were S-type. The crystallization speed became faster with the decrease of crystallization temperature. And the isothermal crystallization kinetics of the three DAGs were analyzed. The results showed that the Avrami constants(n) of DAGs at different temperatures were between 2 and 3, and the crystallization rate constants(k) decreased with increasing temperatures, while crystallization half times(t1/2) increased with increasing temperatures.(5) The crystallization behavior and compatibility of the plastic fat composed of camellia oil(CO), palm stearin(PS) and POL-DAG was analyzed by DSC and p NMR. Both the crystallization onset, the melting point and cooling enthalpy decreased when the contents of CO increased from 0% to 33.33%, 66.66% and 100%, while PS and POL-DAG shown opposite results. Compatibility was best when CO, PS and POL-DAG were mixed in 4: 1: 1 ratio, but worse when in 0:1:1 and 1:1:1.