Crystallization Behavior of Diacylglycerol‐Rich Oils Produced from Rapeseed Oil

Abstract We examined the crystallization behavior of high‐melting fractions in liquid oil containing high concentrations of diacylglycerols (DAG >80%) (hereafter referred to as DAG‐rich oil). By differential scanning calorimetry and optical microscopy at moderate cooling rates, crystallization in the DAG‐rich oil was detected at around 6 °C. It was found that the crystallization extent increased with decreasing temperatures of crystallization below 0 °C. A gas chromatographic analysis was performed on the crystallized fractions, which were separated by filtration at different periods of isothermal crystallization at 3 °C. The results indicated that at earlier crystallization periods, the concentrations of 1,3‐disaturated DAG such as palmitic and stearic acid moieties (15 min) and 1,3‐saturated–unsaturated mixed‐acid DAG including oleic acid, palmitic, and stearic acid moieties (15 min–3 h) were predominant. However, the concentrations of 1,3‐diunsaturated DAG including oleic acid moiety increased after a crystallization period of 6 h. To clarify the sequential crystallization process of DAG, we examined the binary mixing behavior of principal DAG components occurring in the rapeseed‐based DAG‐rich oil. It was evident that 1,3‐disaturated DAG, 1,3‐saturated–unsaturated mixed‐acid DAG, and 1,3‐diunsaturated DAG exhibited immiscible behavior. From these data, basic information on the precipitation processes in DAG‐rich oils at chilled temperatures was obtained.