Kinetics and mechanism of lipase catalyzed monoacylglycerols synthesis

• Monostearin was synthesized from stearic acid and (R,S)-1,2-O-iso-propylidene glycerol (solketal).
• The reaction was catalyzed by CaL B immobilized in water in oil microemulsions.
• A yield of 80% in 30 min was obtained with very low amount of biocatalyst.
• The kinetic analysis indicated that the reaction followed the ordered bi–bi mechanism with dead-end inhibition by stearic acid.

Monoacylglycerols are increasingly used in several industrial applications as effective and cheap emulsifiers. In the present work monostearin synthesis has been studied, using lipase as a biocatalyst of the esterification reaction of stearic acid with (R,S)-1,2-O-iso-propylidene glycerol (solketal). The lipase from Candida antarctica (CaL B) was immobilized in AOT/isooctane water in oil microemulsions. Optimization of the reaction conditions have shown that the highest production (80% in 30 min) could be achieved at 40 °C, in microemulsions with relatively low water content (wo = 8). Kinetic studies have shown that the esterification reaction of stearic acid with solketal catalyzed by CaL B occurs via the ordered bi–bi mechanism, in which inhibition by the acid was identified. Moreover, at high fixed solketal concentrations a negative cooperativity is pronounced, which means that binding of the alcohol lowers the affinity of the enzyme for binding of the acid. Values of all kinetic parameters have been determined.

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