Production of structured lipids by lipase-catalyzed interesterification in a 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 interesterification to produce specific structured lipids containing long-chain polyunsaturated fatty acids at the sn-2 position and medium-chain fatty acids (MCFAs) at the primary position in a packed-bed reactor. Diacylglycerols (DAGs) are important intermediate products in the production of structured lipids, both with regard to the yields of the products and the content of the by-products, but the levels of DAGs produced in lipase-catalyzed interesterification in a continuous process are not well-known. We examined the effects of the following interesterification parameters on the level of DAGs: reaction temperature, residence time, substrate ratio, and water content. Reaction temperature was the most critical factor, with elevated reactor temperatures (particular those above 60 °C) resulting in a considerable increase 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 and oil, as well as increasing the water content in the reacting substrate mixture affected the DAG content only slightly. The DAG content in the interesterification products had positive correlation with the migration of MCFAs, implying that a high level of DAGs is an indicator for partial acylglycerols and positional isomers, both are impurities in the products. On the other 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°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 incorporation and migration of MCFAs were 47% and 1%, respectively.