Rice husk (Oryza sativa) as support in the immobilization of yeast cells

The present study aims to evaluate the rice husk (Oryza sativa; RH), using H₂SO₄ and NaOH (concentration of 2% v/v, solid to liquid ratio 1:6 and temperature and reaction time of 121 °C and 40 min, respectively, for both treatments) as pretreatment to determine if this material can be used as support in the immobilization of Saccharomyces cerevisiae cells. Fermentation kinetics were evaluated in cell buffer solution solid to liquid ratio 1:20 and sampling was performed every 8 h for 32 h. The highest cellular retention of RH pretreated with H₂SO₄ (PretAcid) was at 24 h (98.35 mg g^-1), while RH pretreated with NaOH (PretAlka), was at 16 h (63.21 mg g^-1), having a cell count of 4.5 x 10⁷, and 1.2 x 10⁷, cell per mg of rice husk respectively, meanwhile, the treatment that was not subjected to chemical treatment (Control), was at 24 h (8.56 mg g^-1) and 0.6 x 10^6$ cell per mg of RH. On the other hand, the maximum support efficiency was reached at 36 h in the order of 44.99, 23.25 and 23.43 % for PretAcid, PretAlka and Control, respectively. These results indicate that due to the structural modification that RH underwent during chemical pretreatments, may be an ideal substrate for the adsorption of yeast cells.

Keywords: rice husk, cell immobilization, yeast cells, acid and alkaline pretreatment.