Year : 2017  |  Volume : 16  |  Issue : 3  |  Page : 138-143

Comparative studies of free and immobilized Aspergillus flavus onto functionalized multiwalled carbon nanotubes for soyasapogenol B production

1 Department of Chemistry of Natural and Microbial Products, National Research Centre, Dokki, Cairo, Egypt
2 Chemical Industries Research Division, National Research Centre, Dokki, Giza, Egypt

Correspondence Address:
Hala A Amin
Department of Chemistry of Natural and Microbial Products, National Research Centre, Dokki, Cairo, 12622
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/epj.epj_28_17

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Objective This research focuses on the microbial transformation of soybean saponins to soyasapogenol B (SB) by Aspergillus flavus cells producing saponin hydrolase (CSH) as a whole-cell biocatalyst. Multiwalled carbon nanotubes (MWCNTs) have been reported to have several properties that render them ideal support systems with the advantage of being further functionalizable at their surface. Materials and methods CSH was covalently immobilized onto carboxy-functionalized MWCNTs by different methods including direct immobilization as well as immobilization by glutaraldehyde or carbodiimide chemistry. Results and conclusion Results showed that direct immobilization of CSH onto oxidized MWCNTs was the best method accompanied by about an 80% immobilization yield. The optimum temperature was around 50°C for both the free and the immobilized CSH (MWCNTs–CSH conjugate). The apparent activation energy (Ea) was increased from 1.05 to 2.84 kcal/mol by immobilization. The immobilized enzyme also showed significantly improved thermal stability. The calculated half-life values of MWCNTs–CSH conjugate at 70, 80, and 90°C (55, 33.3, and 29.7 h, respectively) were higher than those of free CSH (36.1, 28.0, and 23.2 h, respectively). The MWCNTs–CSH conjugate showed higher Km (0.45 μmol) compared with the free CSH (0.41 μmol), whereas Vmax for the MWCNTs–CSH conjugate was smaller than that for free CSH. The MWCNTs–CSH conjugate morphology was examined using transmission electron microscope.

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