Optimization of inulinase production by solid-state fermentation in a packed-bed bioreactor

BACKGROUND: This work is focused on inulinase production by solid-sate fermentation (SSF) using sugarcane bagasse, corn steep liquor (CSL), pre-treated cane molasses, and soybean bran as substrates in a 3-kg (dry basis) packed-bed bioreactor. SSF was carried out by the yeast Kluyveromyces marxianus NRRL Y-7571 and response surface methodology was used to optimize the temperature, air flow rate and initial mass of cells. RESULTS: The optimum inulinase activity (436.7 +/- 36.3 U g(-1) dry substrate) was obtained at 24 h at an inlet air temperature of 30 degrees C, air flow rate 2.2 m(3) h(-1) and 22 g of cells for fermentation. Inulinase productivity at these conditions was 18.2 U gds(-1) h(-1). Kinetic evaluation at the optimized conditions showed that the maximum inulinase production was verified at 24 h of fermentation. The carbon dioxide and the metabolic heat generation are directly associated with the consumption of total reducing sugars present in the medium. CONCLUSION: The high productivity achieved in this work shows the technical viability of inulinase production by SSF in a packed-bed bioreactor. (C) 2009 Society of Chemical Industry