Biotransformation Of CIS/TRANS 3, 7-Dimethyl-2, 6-Octadien-1-Ol Mediated By Saccharomyces Cerevisiae
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Date
2011-08
Authors
Khor, Guat Kheng
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Publisher
Universiti Sains Malaysia
Abstract
Biotransformation of geraniol and nerol mediated by Saccharomyces cerevisiae was performed. Linalool and geraniol were mainly obtained from nerol using growing cells but only isomerisation to geraniol occurred using resting cells. Reductive biotransfomation of geraniol to citronellol was apparently more effective with resting cells system. Combination of full factorial design with response surface methodology (RSM) was applied in order to evaluate the effects of cell density, substrate concentration and biotransformation time on product concentrations. The productivity increased proportionally with cell density. However, inhibition was observed at higher substrate concentrations. The optimum conditions for biotransformation of geraniol were found to be 1.36 g/L substrate concentration and 60 g/L cell density at 38 h, with 2.21 g/L citronellol and 1.03 g/L nerol formed. Linalool and α-terpineol achieved their optimums at concentrations of 0.568 g/L and 0.209 g/L respectively, using 1.98 g/L of substrate nerol and cell density of 35.8 g/L after 8.5 days. Kinetic studies assumed a two-site model (productive ES and non-productive SE) and revealed that a non-competitive substrate inhibition was involved in the biotransformation processes. The corresponding values of Michaelis-Menten constant, Km, and maximum biotransformation rate, vmax were obtained. Ki represents the dissociation constant for non-productive SE complex. Increase in substrate concentration leads to the increase in the proportion of SE and SES (ternary) complexes in the enzyme, causing inhibition even though the inhibitory sites has poor affinity for the substrate (Ki >Km).
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Biotransformation of geraniol and nerol mediated , by Saccharomyces cerevisiae was performed