Adaptation fermentation of Pichia stipitis and combination detoxification on steam exploded lignocellulosic prehydrolyzate

Abstract

Yeast Pichia stipitis CBS 5776 was developed through adaptation fermentation step by step in steam exploded corn stover prehydrolyzate because high concentration of weak acids and other inhibitors present in the prehydrolyzate could degrade the fermentability. However, the adaptability of Pichia stipitis CBS 5776 in the prehydrolyzate was so limited that steam strip-ping and overliming were applied to remove these inhibitors from it. Corn stover was steam exploded; the filtrate of steam exploded corn stover was hydrolyzed with dilute sulfuric acid, and then the acid hydrolyzate was detoxified and fermented by Pichia stipitis CBS 5776. Steam stripping could remove volatile com-pounds from the acid hydrolyzate and the fil-trate. At a steam stripping time of 120min, 81% acetic acid and 59% formic acid were removed from the acid hydrolyzate, 77% acetic acid and 45% formic acid were removed from the filtrate, while furfural was stripped off completely from the acid hydrolyzate and the filtrate. Overliming could reduce the contents of furfural and phe-nolics present in the acid hydrolyzate, however, sugars, especially pentoses, were also removed partially. It was necessary to detoxify the acid hydrolyzate in order to ferment the sugars to ethanol. Acid hydrolyzate detoxified with a combination of steam stripping for 120 min and overliming at pH11 and 60℃ for 90 min, its fer-mentability was significantly improved. Xylose was consumed nearly completely in 24h with an ethanol yield of 15.92g/l, 80.34% of theoretical.