High yields of ascorbyl palmitate by thermostable lipase-mediated esterification

High yields of ascorbyl palmitate (6-O-palmitoyl L-ascorbic acid) were obtained by lipase-mediated esterification using Bacillus stearorhermophilus SE 1 lipase. The final yield was greatly influenced by the initial water content of the system, quantity of enzyme, and molar ratio of palmitic acid to L-ascorbic acid. Reaction rates increased directly with temperature from 40 to 100 degrees C. Maximum conversion (97%) was achieved after 30 min at 100 degrees C (solvent-free), 1 h at 80 degrees C (solvent-free), and 2 h at 60 degrees C (solvent/hexane). The synthesis was scaled up to l-L volume with 95% conversion using 50 mmoles of ascorbic acid and 250 mmoles of palmitic acid in hexane. Similar yields of ester were obtained in five repetitive cycles using 5 g enzyme immobilized on Accurel. The present B. stearothermophilus SE 1 lipase was a more efficient catalyst for the synthesis of ascorbyl palmitate than other commercial lipases.