Abstract: Pichia stipitis yeast cells were immobilized by entrapment in marine alga manganese gel, the resulted gel beads with a diameter of 2-3 mm were further incubated to study the fermentation of ethanol under the condition of low pH value.The yeast cell immobilized gel beads were treated at low pH value(3.8, 2.8, 2.4) respectively for 2-3 h, followed by normal pH value 5.0.When pH value was 3.8, most bacteria were killed after such a treatment, while stabilization of immobilized cells was not affected significantly.When treated at pH value 2.4 or below, however, immobilized cells were injured under electronic microscopic observation, and it was difficult to recover the function, and shape of yeast cells changed into slim or irregular state from the original ellipsoid.

Key words: Pichia stipitis, manganese alginate, pentose, ethanol fermentation