Effect of purification methods on the physicochemical, thermodynamic properties and crystallization kinetics of medium chain, medium-long chain and long-chain diacylglycerols.

Medium chain diacylglycerol (MCD), medium-long chain diacylglycerol (MLCD) and long chain diacylglycerol (LCD) were prepared through enzymatic esterification using different conditions at temperatures of 55-70°C, reaction time of 1.5-5 h and in the presence of 5-6% of Novozym® 435. Subsequently, purification was performed using three different techniques, namely, molecular distillation (MD), deodorization (DO) and silica gel column chromatography (SGCC). Variations in terms of the physicochemical and thermodynamic properties, crystallization properties and kinetics of the diacylglycerols (DAGs) before and after purification were determined. Irrespective of the DAG chain lengths, SGCC was able to produce samples with high DAG purity (96-99 wt.%) followed by MD (58-79 wt.%) and DO (39-59 wt.%). Higher 1,3-DAG to 1,2-DAG ratio was recorded for all samples with the highest ratio recorded for SGCC purified samples. Regardless of the purification techniques used, the solid fat content (SFC) profiles of crude samples with steep curves were altered post purification, showing gradual increment in SFC along with increasing temperature. Modification of the Avrami constant and coefficient suggested the modification of the crystal growth mechanism post purification. Crystallization and melting temperatures of products with higher DAG purity were shifted to higher temperature region. Variations were also reflected in terms of the crystal polymorphism whereby the α and β' crystals transitioned into the more stable β form in purified samples accompanied with modification in the microstructures and crystal sizes. However, there was insignificant change in the crystal's morphology of the MLCD after purification except for the decreased in crystal sizes. In conclusion, synthesis of MCD, MLCD and LCD comprising of different DAG purities had distinctive SFC profiles, thermodynamic properties, crystallization kinetics and crystal morphologies, which can further be incorporated into the preparation of a variety of fat products to obtain end products with desired characteristics.