Production of structured lipids by lipase-catalyzed interesterification ina packed bed reactor: effect of reaction parameters on the level of diacylglycerols in the products

The 1,3-specificity of a lipase was utilized in lipase-catalyzed interester ification to produce specific structured lipids containing long-chain polyu nsaturated fatty acids at the sn-2 position and medium-chain fatty acids (M CFAs) at the primary position in a packed-bed reactor. Diacylglycerols (DAG s) are important intermediate products in the production of structured lipi ds, both with regard to the yields of the products and the content of the b y-products, but the levels of DAGs produced in lipase-catalyzed interesteri fication in a continuous process are not well-known. We examined the effect s of the following interesterification parameters on the level of DAGs: rea ction temperature, residence time, substrate ratio, and water content. Reac tion temperature was the most critical factor, with elevated reactor temper atures (particular those above 60 degrees C) resulting in a considerable in crease in the DAG content of the products. Longer residence times increased the level of DAGs in the products, and favoured the formation of 1,3-DAGs from 1,2-DAGs by acyl migration. Increasing the molar ratio between MCFAs a nd oil, as well as increasing the water content in the reacting substrate m ixture affected the DAG content only slightly. The DAG content in the inter esterification products had positive correlation with the migration of MCFA s, implying that a high level of DAGs is an indicator for partial acylglyce rols and positional isomers, both are impurities in the products. On the ot her hand, the content of DAGs correlated positively with the incorporation of MCFAs, suggesting that the DAGs are also important for the production of the structured lipids. Under optimized conditions (temperature, 60 degrees C; water, 0.03%; residence time, 4 h; substrate ratio, 6:1), the level of DAGs produced in the packed-bed reactor was less than 4%, and the incorpora tion and migration of MCFAs were 47% and 1%, respectively.