Study On Inulinase Overproduction And Ethanol Fermentation By A Mutant Of Marine Yeast Pichia Guilliermondii

Inulin is present as a reserve carbohydrate in the roots and tubers of plants such as Jerusalem artichoke, chicory, dahlia, and yacon. The yields of the roots and tubers are very high. It is a good renewable raw matetial for fructose syrup, oligofructan, and ethanol production.The inulinases are classified among the hydrolases and target on theβ-2, 1 linkage of inulin and hydrolyze it into fructose and glucose (EC.3.2.1). We used the marine yeast Pichia guilliermondii, strain 1, as parent strain; its ascospores were treated by using UV light and LiCl. The mutant M-30 with enhanced inulinase production was obtained and was found to be stable after cultivation for 20 generations.Surface response methodology (SRM) was used to optimize the medium compositions and cultivation conditions for inulinase production by the mutant M-30 in liquid fermentation. Inulin, yeast extract, NaCl, temperature, pH for maximum inulinase production by the mutant M-30 were found to be 20.0 g/l, 5.0 g/l, 20.0 g/l, 28oC and 6.5, respectively. Under the optimized conditions, 127.7 U/ml of inulinase activity was reached in the liquid culture of the mutant M-30. Under the same conditions, its parent strain only produced 48.1 U/ml of inulinase activity. We also found that inulin could be actively converted into monosaccharides by the crude inulinase.On the basis of results obtained above, we took advantage of the inulinase produced by M-30 to hydrolyse inulin and Jerusalem artichoke tubers, further; the hydrolysate was fermented into ethanol by Saccharomyces cerevisiae W-0. Finally, the ethanol concentrations obtained were 12.93±0.30% (v/v) from inulin and 7.03±0.21% (v/v) from the ground tubers after 120h of the fermentation.