In this work, the capacity to produce ethanol of auxotrophic strains belonging to the CEN.PK family of the yeast Saccharomyces cerevisiae has been investigated. Shake flask experiments were set up to study the ethanol production by the auxotrophic S. cerevisiae CEN.PK strains in terms of biomass and ethanol yield, the latter was evaluated on both glucose and biomass. The test was carried out in a rich-complex medium with 2 and 15 % w/v initial glucose concentration. The results obtained, compared with those of the prototrophic CEN.PK strain, indicated that the fermentative capacity of the auxotrophic strain in 2 % glucose was comparable at all to the prototrophic one, whereas using 15 % initial glucose, the auxotrophic CEN.PK strain exhibited a more than doubled ethanol yield on biomass. The fermentative capacity of both the prototrophic and the auxotrophic strain was also tested after having refreshed the exhausted medium with glucose to restore the initial 15 % concentration. In these conditions, the amount of ethanol produced by the auxotrophic strain per mass unit, resulted to be double with respect to the prototrophic one. In the light of these results, yeast culture based on auxotrophic CEN.PK, strains could be taken into consideration as culture capable to produce ethanol with a low amount of microbial cells and so potentially suitable to be used for ethanol production by immobilized system.
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