Lactic Acid Bacteria of Fermentlng Tef Dough and Fermented Kocho and Their Inhibitory Effect on Certain Food -Borne Pathogens or Spoilage Organisms
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Date
1992-06
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Addis Ababa University
Abstract
Lactic acid fermentation is the commonest and inexpensive traditional
household food manufacturing method.
"Injera" and "Kocho" are two major Ethiopian lactic acid fermented
foods.
Injera is a pancake-like bread baked from "Tef" (Eragrostis tef) or
other cereals' flour fermented for two to three days.
Kocho is a product of "Ensete" plant (Ensete ventricosum) pitfermented
for few weeks to several months. It is then baked and
consumed Members of the Enterobacteriaceae family initiate tef dough
fermentation. They lower the pH from about 6.3 to 4.7. Lactic acid
bacteria(LAB)- Leuconostoc, Lactobacillus, streptococcus and
Pediococcus species succeed and further lower the pH to or below
4.00. Species of Bacillus degrade the starch.
Kocho fermentation was found to be initiated by Leuconostoc spp. and
the other LAB follow to lower the pH. A properly fermented kocho has
a pH of 4-4.5 and contains a large number of LAB. Yeasts and molds
were also common at lower pH values in both foods.
Lactic acid bacteria were known to prevent food-borne pathogens and spoilage bacteria from growing in fermenting foods using their
antibiotic metabolites.
Nevertheless, inhibitory effect of fermenting tef or fermented kocho
on such undesirable organisms was not known.
Hence, in this study effect of these two acidic foods and also their
components in broth on certain disease-causing and spoilage bacteria was determined.
The results showed that tef dough began inhibition after 30 h of
fermentation (pH 4.7). This period had maximum nutrient availability
and best inhibitory activity among all fermentation periods in tef.
Fermented kocho (pH 4.3) was inhibitory except for B. cereus. It also
inhibited best at lower concentrations but higher pH values among all
agents employed.
Spent media from the LAB inhibited growth of most test bacteria where
Streptococcus spp. did the best amongst the group.
The pH decline as a result of introducing acetic and/or lactic acid
to broth was much higher than anyone of the other agents. Therefore,
the inhibitory activity of the foods or the LAB was due to
antibiotics elaborated-by the LAB and some species of Bacillus.
Heat treatment of tef dough or kocho extract also seemed to have a
promotion effect on antimicrobial potency of the extracts.
Sporeforming bacteria, yeasts and molds survived baking temperature,
but much lowered to low populations.
Furthermore, tef dough fermented upto
properly fermented kocho (to about pH
30-48
4.3)
h (pH 4. 1-4 • 7 ) and
both baked before
consumption were found as safe foods from food-borne infections and
spoilage bacteria.
Further studies on these two foods and their micro flora were
recommended.
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Biology