Lipase-Catalyzed Synthesis of Saccharide-Fatty Acid Esters Utilizing Solvent-Free Suspensions: Effect of Acyl Donors and Acceptors, and Enzyme Activity Retention

摘要

The effect of acyl donor (oleic, caprylic, lauric and myristic acids) and acceptor (fructose, sucrose, glucose and xylose) for synthesis of saccharide-fatty acid esters was conducted using solvent-free (50–200 μm sized) suspensions of saccharide crystals in a mixture of fatty acid/fructose oleate (90 wt% monoester and 10 wt% diester) at a ratio of 75/25 w/w initially, and a bioreactor system containing a packed bed bioreactor filled with immobilized Rhizomucor miehei lipase (Lipozyme®IM, Novozymes, Franklinton, NC, USA) at 53 °C or a stirred tank bioreactor (STBR) at 65 °C. A nearly linear relationship between initial saccharide concentration and initial rate of reaction and final ester concentration was achieved which was independent of acyl donor or acceptor type. Slightly lower reaction rate and yield were obtained for operation in STBRs. Suspensions containing the highest saccharide concentration coincided with saccharide crystals of the smallest average size, since large-sized crystals sedimented out during the workup for formation of the suspensions. The best performance was achieved using fructose and oleic acid as substrates (92.3 wt% ester, consisting of 92 wt% monoester) in a packed-bed bioreactor (PBBR). The activity of RML did not decrease appreciably after four successive runs for solvent-free fructose-oleate esterification, or equivalently, a 22 day reaction period.