Abstract:

The study was undertaken during the period 1991-
1994 to isolate and characterise yeasts associated
with surfaces of fruits, grains and fermented products
of the materials. The major aims of the study were to
isolate and characterise yeast strains focusing on
their habitats and to elucidate their physiological
and biochemical potential through experiments and
analysis.
Banana: The following yeast strains were isolated
from banana in Masaka/Rakai: Candida Y40, Candida Y60,
Candida pulcherrimin, Debaryomyces hansenii,
Saccharomyces cerevisiae, Hanseniaspora Y68,
Hanseniaspora Y20, Saccharomyces Y21, Saccharomyces
Y12, Schizosaccharomyces Y26, Cryptococcus Y37,
Debaryomyces Y13, Schizosaccharomyces pombe,
Saccheromyces pastorianus, Torulopsis Y29, Hansenula
Y49, Candida Y42, Hansenula Y62, Lodderomyces
elongisporus, Saccheromyces chevalieri, Dekkera
bruxellensis, Saccharomyces Y56, Debaryomyles Y10.
Tonto, Masaka/Rakai: Candida Y33, Candida Y6, Dekkera
bruxellensis, Hansenula Y1 7, Saccharomyces
pastorianus, Saccharomyces ellipsoides Y68,
Hanseniaspora Y68, Saccharomyces Y21, Saccharomyces
Y12, Schizosaccharomyces pombe, Schizosaccharomyces
Y26, Cryptoco^cus Y50, Saccharomyces Y25.
(Xiii)
Muramba, Mbarara/Rukunguri: Candida Y42, Hansenula
Y49, Hansenula Y62, Hansenula Y67, Saccharomyces Y30,
Saccharomyces Y68, Schizosacchoromyces Y56,
Debaryomyces Y40, Debaryomyces Y48, Saccharomyces
pastorianus.
Hansenula 2, Hansenula 32, Schizosaccharomyces 30M,
Saccharomyces 3 ON, Saccharomyces 30P ,
Schizosaccharomyces 44M, Schizosaccharomces 44M,
Schizosaccharomyces 44N, Saccharomyces cerevisiae,
Schizosaccharomyces pombe, Schizosaccheromyces 44T.
Apart from the study of biodiversity, the study
was also undertaken to study population density of
yeasts responsible for certain fermentation processes.
The fermented products of bananas, sorghum and millet
were tonto, muramba, kwete and amarwa (ajon) in
Masaka/Rakai, Mbarara/Rukungiri and Jinja/Tororo/
Mbale.
yeast units in tonto, the c.f.u. were 5.07 x 10
Muramba 5 x ml In
and amarwa 1.5x10 ml
some of the yeasts were preferentially anaerobic,
yielding ethanol and co2, potentially important in
brewing and bread industry.
Jinja/Tororo/Mbale
counts on banana were 2.5 cm'1 1
In Mbarara/Rukungiri the counts for banana were 76.6
cm'1; Muramba 5 x 107 m1'1
Amarwa from Jinja/Tororo/Mbale: Candida 2, Candida 11,
In Masaka/Rakai the mean count of colony forming
7 ml'1.
Experiments on selected strains of yeasts show that
(xiv)
Yield of ethanol under anaerobic conditions and
biomass production under aerobic conditions were
verified.
There was low pH change during controlled
fermentation PH 4.0 to pH 3.8. The PH shifted
significantly during uncontrolled fermentation typical
of local brewing conditions. This indicated high
level of acid production.
Ethanol is one of the products of the metabolism
of glucose in tonto. The amount produced was directly
related to the concentration of glucose in the medium.
Some yeasts were intolerant of ethanol in their
environment.
Yeasts have been discussed according to their
cultural, morphological and physiological
characteristics with the knowledge so obtained, it was
possible and fruitful to consider the relationship of
yeasts among themselves. Numerical analysis was
applied to give a more objective system of grouping of
the isolated and characterised yeasts. By studying
clusters, it was possible to determine the
characteristics the yeasts share as well as those in
which they differ. Cluster analysis was used to
identify the yeasts and their potential for biomass
and ethanol yield and carbon dioxide yield.