Effect of organic solvents on the yield and specificity of cyclodextrins by recombinant cyclodextrin glucanotransferase (CGTase) from Anaerobranca gottschalkii

Abstract

Cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) is an enzyme that degrades starch and starch related glucans into cyclodextrins (CDs) by intramolecular transglycosylation reaction. The biochemical activity of recombinant CGTase from Anaerobranca gottschalkii for the yield and product specificity of cyclodextrins was investigated in the presence of organic solvents. Compared with the control of starch bioconversion, addition of various organic solvents generally increased the total CD and product specificity by affecting product inhibition and/or intermolecular transglycosylation reaction. The highest conversion (45 %) of starch to CDs was obtained in the presence of ethanol, while the simultaneous addition of two organic solvents, decanol-ethanol, comparatively showed a reduced total yield of 39 %. Despite this, the highest product ratio of 91 % α-CD, and 64 % β-CD was obtained in the presence of decanol and cyclohexane respectively. The effect of organic solvents on the yield and specificity of CD was attributed mainly to their effect on product inhibition and transglycosylation reaction. Although the use of two organic solvents showed almost a significant increase in total yield of CDs, it resulted in a comparatively lower specific product yield compared to their respective individual effect. Generally, normal enzyme activity was favoured at higher temperature of 65 °C, but the addition of organic solvents, in most cases, was found to decrease the bioconversion. Thus, the preferred optimal condition was reduced to 40 °C, where the maximal conversion of starch to CDs in general and α-CD in particular was achieved.