Geranyl Butyrate Production by Candida antarctica Lipase B-Displaying Pichia pastoris

Abstract

Enzyme-displaying whole-cell yeast is becoming an alternative to immobilized enzyme. Here, a recombinant Pichia pastoris displaying Candida antarctica lipase B (CALB) was used to catalyze the synthesis of geranyl butyrate with geraniol and butanoic acid as substrates in n-heptane. Response surface methodology (RSM) with a four-variable five-level central composite design (CCD) was applied when biocatalyst concentration, geraniol concentration, butanoic acid/geraniol molar ratio, and water activity were taken as influential factors to improve the production of geranyl butyrate. The results indicated that both substrates molar ratio and water activity affected significantly the geranyl butyrate yield (p < 0.05). Biocatalyst concentration 20.9 g/L, geraniol concentration 0.57 mol/L, butanoic acid/geraniol molar ratio 1.21:1, and water activity 0.53 were the optimum of the ester synthesis. Under the above conditions, the geraniol conversion rate was 98.5 % in 10 mL reaction after 9 h reaction, which was equivalent to 126 g/L geranyl butyrate. When the esterification reaction was scaled up in batch stirred reactors, 97.87 % of geraniol conversion rate in 200 mL as well as 97.56 % in 500 mL could be obtained.