Water Activity Effects on Geranyl Acetate Synthesis Catalyzed by Novozym in Supercritical Ethane and in Supercritical Carbon Dioxide

• Published in: Journal of agricultural and food chemistry 2003-03, Vol.51 (7), p.1884-1888
• Main Authors: Peres, Célia, Gomes da Silva, Marco D. R, Barreiros, Susana
• Format: Article
• Language: English
• Subjects: acetates; Acetates - metabolism; acetic acid; Acetic Acid - metabolism; Biological and medical sciences; Carbon Dioxide; enzyme activity; enzymes; Esterification; Ethane; Food additives; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; Handling, storage, packaging, transport; Lipase - metabolism; temperature; Terpenes - metabolism; Water - metabolism; water activity
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf026071u

The esterification reaction of geraniol with acetic acid catalyzed by Novozym was studied in supercritical ethane (sc-ethane) and in supercritical carbon dioxide (sc-CO2). Water activity (a W) had a very strong effect on enzyme activity, with reaction rates increasing up to a W = 0.25 and then decreasing for higher a W. Salt hydrate pairs could not prevent changes in a W during the course of reaction but were able to control a W to some extent and had a beneficial effect on both initial rates of esterification and conversion in sc-ethane. The enzyme was more active in sc-ethane than in sc-CO2, confirming the deleterious effect of the latter already observed with some enzymes. Temperatures between 40 and 60 °C did not have a strong effect on initial rates of esterification, although reaction progress declined considerably in that temperature range. For the mixture of 50 mM acetic acid plus 200 mM geraniol, 100% conversion was achieved at a reaction time of 10 h at 40 °C, 100 bar, an a W of incubation of 0.25, and a Novozym concentration of 0.55 mg cm-3 in sc-ethane. Conversion was below 50% in sc-CO2 at otherwise identical conditions. With an equimolar mixture of the two substrates (100 mM), 98% conversion was reached at 10 h of reaction in sc-ethane (73% conversion in sc-CO2). Keywords: Novozym 435; Candida antartica lipase B; enzymatic esterification; supercritical fluids; geranyl acetate; geraniol; water activity