Solvent-free synthesis of citronellyl acetate using Fermase: Optimization, kinetics and RSM studies

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Citronellyl acetate is a flavor ester with a fresh fruit aroma and a fruity, sweet flavor. The current study illustrates the synthesis of citronellyl acetate via a transesterification reaction of citronellol and vinyl acetate in a solvent-free system with the help of biocatalyst Fermase. The effect of various parameters affecting the reaction, including reactant mole ratio, enzyme loading, temperature, and agitation speed, was studied to obtain the maximum conversion of citronellol. Under optimized conditions with a 1:10 mole ratio of citronellol to vinyl acetate, 3% (w/w) enzyme loading with respect to citronellol, 300 RPM agitation speed, and 60 °C temperature, a maximum conversion of 99.8% was achieved in 2 h reaction time. The enzyme was reused for six reaction cycles, retaining 85% of its activity. Various kinetic models for enzymatic reactions were explored and validated. The ping-pong bi-bi model with both substrate inhibition gave the best fit for the experimental data. Optimization studies were also conducted using the response surface methodology to observe the interaction of various parameters.