Pentose fermentation of normally toxic lignocellulose prehydrolysate with strain of Pichia stipitis yeast using air

A process for the preparation of a strain of the yeast Pichia stipitis NPw9 comprising:

• a) growing a Pichia stipitis strain of yeast on toxic prehydrolysate of agricultural residues, grain processing intermediates and residues, softwoods, hardwoods or mixtures thereof;
• b) maximizing the number of cell generations and using all generated cells by splitting and transferring culture progeny into additional cultures while said yeast have active mitochondria;
• c) reducing nutrient concentration in an amount sufficient to obligate yeast dependency on oxygen;
• d) gradually substituting for yeast extract a lesser amount of corn-steep liquor, or the equivalent;
• e) replacing a nitrogen source of peptone with a lesser amount of ammonium sulfate, or the inexpensive nitrogen source;
• and
• f) collecting cells of a strain of Pichia stipitis NPw9 yeast.

A process for the preparation of a strain of the yeast Pichia stipitis NPw9 comprising:

• a) growing an NREL strain of Pichia stipitis yeast, derived from, for example, the Northern Regional Research Lab (NRRL), Agricultural Research Service, USDA, on toxic prehydrolysate of a blend of whole tree softwoods, hardwoods agricultural residues, grain processing intermediates and residues, or mixtures or blends thereof;
• b) maximizing the number of cell generations and using all generated cells by splitting and transferring culture progeny into additional cultures while said yeast have active mitochondria;
• c) reducing nutrient concentration in an amount sufficient to obligate yeast dependency on oxygen;
• d) gradually substituting for yeast extract a lesser amount of corn-steep liquor, or equivalent;
• e) replacing a nitrogen source of peptone with a lesser amount of ammonium sulfate, or similar;
• and
• f) collecting cells of a strain of Pichia stipitis NPw9.