Abstract:
Biochemical and microbiological changes that occur during fermentation
of Caryota urens phloem sap were studied with a view to conducting
basic research for later upgrading the local fermentation industry and to
developing new biotechnological processes by recognizing yeasts suitable
to local conditions. Sap, which was taken after keeping a sterilized pot for
10 hours was free of alcohol, showing that fermentation has not taken place
yet. Paper chromatographic studies done with this unfermented sap revealed
that the main type of sugar was sucrose while glucose and fructose were in
trace amounts. The content of reducing sugar of phloem sap at the time of
collection was very.low (0.14%). However this started to increase after 24
hours and reached a maximum value of (4.1 %w/v) after 24 hours. The
alcohol concentration, measured by ebulliometer, increased only after
appreciable quantities of reducing sugars was formed. Maximum alcohol
concentration of7% v/v was obtained on the fifth day. The unfermented sap
had a pH around 7. The pH value decreased substantially and reached a
constant value around 4 after the fourth day of fermentation. Decrease in pH
coincided well with increase of acidity. Microbial analysis of fermenting sap
revealed that the type of orgnisms present in the sap changed with time. At
the beginning of fermentation the sap contained mainly bacteria with a
colony count in the order of 107 cellsl ml. They were found to be mainly
Lactobacilli and Leuconostoc.
The yeast cells were very few in number initially but increased after
24 hours and reached a maximum of8x 107 cell/rnl after the third day. During
the latter stages of fermentation, there was a drop in the viable yeast cell
count, while the bacterial count increased again to 1()6cells/ml. A total of
eleven yeast strains were isolated from fermenting phloem sap.
Saccharomyces cerevisiae was found to be the most predominant yeast
species. In the early stages Candida tropicalis and Pichia membranifaciens
were found to be abundant.
