Enzymatic preparation and purification of sn-1,3 diacylglycerols and their physicochemical properties

Abstract: Diacylglycerols (DAGs) are new functional lipids widely applied as emulsifier, crystallization regulator and healthy ingredients. The crudes n-1,3 DAG products were prepared by glycerol reacting with vinyl laurate and vinyl palmitate respectively under the catalysis of Lipozyme TL IM. Sn-1,3 lauric diacylglycerol (LDAG) with a purity of 97.67% was obtained by crystallization at 5℃ for 3 h in a mixed solvent of n-hexane ethyl acetate in a ratio of 92:8 (wt/wt) and 98.30% of sn-1,3 palmitic diacylglycerol (PDAG) was obtained by crystallization at 15℃ for 3 h in a mixed solvent of n-hexane: ethyl acetate in a ratio of 98:2(wt/wt) followed by methanol crystallization. The obtained sn-1,3 DAG was heated at 100℃ for different times to obtain LDAG and PDAG with different acyl migration degrees. The ratio of sn-1,3 DAG to sn-1,2 DAG eventually reached to 65:35 at the equilibrium. With the increase of acyl migration, the difference of crystallization and melting starting temperature of LDAG and PDAG decreased, and the morphology of DAGs changed from disordered needle crystals to more ordered Maltese cross. PDAG had a shorter melting range and better eutectic properties than LDAG. Then, the binary blending systems of sn-1,3 DAGs and DAGs were studied respectively. It was found that in the sn-1,3 DAGs blending system, it became eutectic when the X_{Sn-1,3 PDAG} was 0.2. In the DAGs blending system, the eutectic was reached when X_PDAG was 0.8. When the proportion of X_PDAG was relatively low, the blending system presented a continuous solid solution form.