Benzyl propionate synthesis by fed-batch esterification using commercial immobilized and lyophilized Cal B lipase

In this work, a fed-batch approach was adopted to overcome propionic acid lipase inactivation effects in the benzyl propionate direct esterification mediated by lipases. The ester synthesis was performed using commercial immobilized (Novozym 435) and lyophilized form Candida antarctica fraction B lipase (Cal B) as biocatalysts of the esterification between benzyl alcohol and propionic acid in a solvent-free system. The reaction involved the propionic acid-controlled addition during the first 5 h ensuring an excess of alcohol to dilute the media. The biocatalyst Novozym 435 showed a good performance in the first cycle of the fed-batch esterification, ensuring 90 and 99% of conversion at substrates molar ratio of 1:1 and 1:5 (acid:alcohol), respectively. However, the enzyme lost the activity and the conversions were sharply reduced at the second cycle. A novel qualitative protein content analysis by optical microscopy showed that the lipase was desorbed from the support after the esterification, and this behavior was strongly related to the presence of propionic acid in the reaction medium. The lyophilized Cal B was also tested as biocatalyst of the benzyl propionate esterification and showed a similar performance (related to the Novozym 435) in ester conversion and initial reaction rates for all substrates molar ratios tested. Since the substrates affected the performance of the Novozym 435, the lyophilized Cal B is the most suitable catalyst to the benzyl propionate esterification with conversions above 90%, considering a the fed-batch approach in a solvent-free system.