Food and Nutritional Sciences

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Browsing Food and Nutritional Sciences by Author "Abate Dawit (PhD)"

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    Growth Inhibition of Grain Spoilage Fungi by Some Herb and Spice Essential Oils Grown in Ethiopia
    (Addis Ababa University, 2009-06-05) Chewaka Diriba; Abate Dawit (PhD)
    Microbial food contamination is an on-going limiting factor in crop production that can determine the shelf life of processed and unprocessed foods. Spice plants and herbs are commonly used as food flavoring and seasoning agents. Their antimicrobial properties as food preservatives are also well documented. In this study, essential oils of seven spice plants were tested for their antimicrobial properties against Aspergillus flavus and A. niger, two of the most important food and feed spoilage organisms. Agar disk diffusion assay was used for screening of the most effective essential oils, agar dilution assay was used to determine Minimum Inhibitory Concentration (MIC) of the essential oils and broth dilution assay was employed to the spore germination inhibition assay. Tests were also conducted to examine the effects of the essential oils for sorghum kernel protection against the tested fungi, and the optimal protective dosages on the sorghum grains were also determined. From the preliminary tests, essential oils of Cinnamomum zeylanicum (Cinnamon) and Thymus schimperi (thymus) were found to be the most effective. However piper nigrum (black pepper) had no effect on the test organisms. In MIC, spore germination inhibition and grain protection assay, cinnamon essential oil was found to be superior where its MIC on the isolates was found to be 0.0156% and its optimum protective dosage on the grain was 5%. It inhibited spore germination at a concentration of 3 _L/ml. The effect of thymus oil was also very much comparable to these results (no significant difference at P < 0.05). Finally, it could be concluded that some plant essential oils can be a useful source of antifungal agents for protection of grain spoilage by fungi.
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    Isolation and Characterization of Rennin Enzyme from Mucor Species and Utilization for Cheese Making
    (Addis Ababa University, 2006-01-31) Getu Abebe; Abate Dawit (PhD)
    Microbial milk-clotting enzymes are valued as calf rennet substitutes in the cheese industry. Rennet, a microbial coagulant, can be obtained from Mucor species isolated from cow dung. The aim of this work was to extract milk-clotting enzyme from Mucor species by submerged fermentation and to produce cheese. Among the physico-chemical parameters tested, the best results were obtained in a medium having initial pH of 7.0 and incubated at 25oC for 5 days, using glucose and peptone as carbon and nitrogen sources respectively. A partial purified extract of the enzyme was obtained by fractional precipitation with (NH4)2SO4 and its maximum activity were obtained at pH 5.5 and 550C. The clotting activity of the purified enzyme was stimulated with increasing CaCl2 concentration up to 0.05%.The enzyme was completely inactivated by heating for 5 min at 70oC. This enzyme was stable at pH 4.5–6 and below 45 °C, and this was convenient for storage and transportation. The result showed that the enzyme from Mucor was a promising microorganism for industrial milk-clotting enzyme production in Ethiopia.