Enzymatic ester synthesis with continuous measurement of water activity

Ester synthesis from aliphatic monoalcohols and organic acids was investigated by using a microbial lipase. The reaction medium only contained the substrates and the enzyme without addition of water or organic solvent. During the reaction, water was produced and the water activity (aw) increased. Batch reactors and continuous-flow reactors were used. In batch, the aw was 0.13 at the beginning of the reaction and increased to reach a plateau at 0.77, after which ester synthesis continued without modification of the aw. Different alcohols and acids were tried in solid-liquid reactors, and all cases synthesis occurred, leading to a significant increase in the water activity. For continuous-flow reactors, the use of silica beads retaining water inside the reactor where the enzymatic reaction took place resulted in some control of the enzymatic reaction by changing the aw.