Browsing by Author "Nigatu Ayele"

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    Lactic Acid Bacteria of Fermentlng Tef Dough and Fermented Kocho and Their Inhibitory Effect on Certain Food -Borne Pathogens or Spoilage Organisms
    (Addis Ababa University, 1992-06) Nigatu Ayele; Abegaz Berhanu (PhD)
    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.