| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 81 === In this work, immobilized invertase was added into the
fermenter in order to compete with microorganims for the
hydrolysis of sucrose, the accumulation of monosccharides in
the broth was thus controlled and the ethanol yield was
enhanced. Results from batch fermentations of Z. mobilis showed
that the formations of by-products; i.e., sorbitol and levan,
were associ- ated with an higher sucrose concentration in the
medium.The for- mation of by-products was suggested to be the
reason for low ethanol yields from sucrose. As the sucrose
concentration in the feed was 200g/l, the ethanol yield became
only 57％ of its thro- retical value. In a combined Z. mobilis/
immobilized invertase system with 200 g/l sucrose as
substrates. It was found when 0.2g immobilized invertase
(activity 2100Ｕ/g)was added to a 1.2 liter batch fermenter,
the ethanol yield was increased from 0.29 to 0.40 g/g (80％ of
the theoretical value). High ethanol yields we also obtained
from continuous cultures.When 0.2 g immobilized invertase was
added, the dilution rate for the maximum ethanol productivity
(10.5g/l/h) was determined as 0.2. Experimenal data showed that
increasing the addition of immobilized invertase led to a low
concentration of sucrose in the culture and lower rate of levan
formation and sucrose hydrolysis,both were catalyzed by the
extracellular exzyme levansucrase.It could be concluded that
the levansucrase secreted by Z. mobilis is a sucrose inducible
enzyme. In this work,the kinetic models of Z. mobilis
fermentation and combined Z. mobilis/immobilized invertase
system were also developed. Parameters used for model
simulation were estimated from fitting the experimental data
with these kinetic models.
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