Immobilisation of yeast cells on carbon nanotubes

Carbon nanotubes are increasingly finding application in a wide range of industries. The focus of this study was to investigate the immobilisation of yeast cells onto carbon nanotubes, using a flocculation method, for possible use in fermentation processes. Carbon nanotubes, which are long thin cylinders of carbon, were used as artificial agents to induce flocculation of yeast cells. The immobilisation experiments on carbon nanotubes were conducted under different process conditions and compared with control experiments done on free cells. The resultant immobilised cells or flocs were recovered and freeze dried before analysis was performed. The flocculated cells were characterised by scanning electron microscopy to confirm that flocculation had occurred. Conditions that gave optimum flocculation on carbon nanotubes were found to be: a pH between 5.0 and 5.8, a temperature between 25 °C and 30 °C, an agitation speed of about 110 rpm, and a concentration of carbon nanotubes (in powder form) of between 44 mg/mL and 54 mg/mL. The addition of calcium ions and glucose decreased the rate of flocculation and delayed the onset of flocculation. Our study has demonstrated that carbon nanotubes have great potential to improve the flocculation capacity of brewer’s yeast.