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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/34

Authors: Esayas, Assefa
Keywords: Lactic acid bacteria
Fermented milk
S. typhi
S. flexineri
Discdiffusion assay
Date Added: 31-Aug-2007
Abstract: “Ergo” is a traditional Ethiopian fermented milk produced by spontaneous fermentation using traditional utensils under non-hygienic environment. To produce microbiologically safe and chemically defined product; study on the production, processing, utilization and handling of ‘Ergo’ under different agro-ecological zones as well as the isolation and characterization of potential lactic acid bacteria strains with the potential production of inhibitory factor should be the first essential step. In this study ninety-smallholder farmers from the three districts (Lumme, Fentale, Adami Tulu), thirty from each district, who produced and processed milk were purposeively selected and individually interviewed using a semi-structured questionnaire to asses the production, processing, utilization and handling of traditional fermented milk, “Ergo”. Milk fermentation takes relatively longer period (3.57 + 1.04 days) in Lumme district than the two districts Fentale and Adami Tulu (1.03+ 0.183). All households (100%) in Fentale consume unboiled milk; rather they utilize it in its fermented or raw state, where as only 40% and 46.6% of households in Lumme and Adami Tulu areas, respectively, used fermented milk for consumption. Even though milk is fermented and consumed in all these areas a very limited hygienic care is practiced, 93.4% of the households do not heed for the sanitary aspect of the milk and milk products. To evaluate the antimicrobial activity of the lactic acid bacteria (LAB), 112 strains of LAB, belonging to Lactococcus, Lactobacillus, Entorococcus, Streptococcus, Leuconostoc and Pediococcus were isolated from Ethiopian traditional fermented milk, “Ergo”. Moreover the culture filtrates of all the isolates were examined for antimicrobial activity on some food born pathogens Salmonella thyphi, Shigella flexineri , Staphylococcus aures (ATCC-25923) and x Escherchia coli (ATCC-25922) using disc diffusion assay method. Inhibition diameters obtained with the inhibitory substance of 2mm and above inhibition zone over the control were considered as positive. Twelve strains of lactic acid bacteria that produced the greatest antimicrobial substance were selected. These strains were identified as species of Lactobacillus acidophilus(2) , Lactobacillus plantarum(2), Lactococcus lactic spp crimoris(2) , Lactococcus lactic spp lactic(3), Leuconostoc lactic (1) , Pediococcus pentosaceus(1) and Pediococcus sp.(1). All the inhibitory substance-producing strains were tested for their temperature and pH stability. The antimicrobial activity of the culture filtrate of isolated strains were completely inactivated when treated at 121oC for 15 minutes, where as at 30, 60 and 80oC there were no Significant (P>0.05) difference in diameter of inhibition compared to untreated (control). The entire culture filtrate were stable with in a wide range of pH (2-10) and no significant (P>0.05) difference was observed between the treated filtrate and the untreated (control). However treating the culture filtrate at pH 12 has significantly (P<0.05) decreased the inhibition diameter.
Description: A Thesis presented to the School of Graduate Studies of the Addis Ababa University in partial fulfillment of the Degree of Master of Science in Biology (Applied Microbiology)
URI: http://hdl.handle.net/123456789/34
Appears in:Thesis - Biology

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