Crucial role of support and water activity on the lipase-catalyzed synthesis of structured triglycerides

The synthesis of structured triglycerides (MLM) containing medium-chain fatty acids (e.g. caprylic acid) in the 1- and 3-positions and a long-chain fatty acid (e.g. oleic acid, linoleic acid) in the 2-position of glycerol has been investigated. Special emphasis was given on the influence of support, organic solvent, and water activity on the lipase activity. Water adsorption isotherms for different lipase preparations were determined. In the interesterification between triolein and caprylic acid, best results (up to 45% CyOCy and 46% CyOO) were found with Celite-immobilized lipases from Rhizopus sp. and Rhizomucor michei at low water activity (0.11 < a(w) < 0.33) in n-hexane. V-max/K-m-values were similar using caprylic acid or the corresponding methyl or ethyl esters. Alternatively, a two-step reaction was investigated, where 2-monoglycerides (2-MG) were produced with a 1,3-regiospecific lipase from Rhizopus delemar from pure triglycerides (triolein, trilinolein) or cottonseed oil. The 2-MG were isolated and then esterified with caprylic acid using the same lipase immobilized on polypropylene (EP 100). In the presence of activated molecular sieves, highly pure structured triglycerides were formed within short reaction times (< 5 h). For instance, the structured triglyceride derived from cottonseed oil contained >95% caprylic acid in the 1- and 3-positions and 80% of linoleic acid and 19% stearic acid in the 2-position of glycerol.