School of Chemical and Bio Engineering

Permanent URI for this college

http://etd.aau.edu.et/handle/12345678/127

Browse

Browsing School of Chemical and Bio Engineering by Author "Abate, Dawit (PhD)"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Aflatoxin Content of Peanut (Arachis hypogaea) in Relation to Shelling and Storage Practice of Ethiopian Farmers
    (Addis Ababa University, 2010-06) Legesse, Eshetu; Abate, Dawit (PhD)
    The threat of aflatoxin contamination in food commodities and its association with health risks in both animals and humans continues to raise increasing concern over years. In this research, A. flavus species found in association with peanuts in storage and their potential to produce aflatoxin in collected samples was determined. About 11 to 87% of collected peanut samples were infected with various moulds including Rhizopus sp., Fusarium sp., Aspergilus flavus, A. niger, other Aspergillus sp., Penicillium sp., and other undefined sp. Aspergillus flavus is known to be the most patent aflatoxigenic strains infects 80.69 % of the total samples analyzed. Eighty five percent of the tested isolates of A. flavus were capable for the production of aflatoxins. From the total of 52 peanut (Arachis hypogaea) samples analyzed, 38 (73.06 %) were positive for aflatoxin. The average levels of aflatoxins detected in the seed samples were between 0.57(from Babile new harvest sample) to 447.02 ppb (from Babile three month stored in pp bag). The higher level of toxicity is more than twenty times greater than the acceptable dosage (20 ppb: US Standards) in peanuts of three month stored after wet shelling. This research pointed out that the storage and shelling practice of farmers have effects in aflatoxin contamination in peanut despite enormous efforts to control this mycotoxin. Keywords: Peanuts (Arachis hypogaea), A. flavus, aflatoxins, shelling and storage practice
  • No Thumbnail Available
    Item
    The Effect of Natural Fermentation on Some Antinutritional Factors, Minerals, Proximate Composition and Sensory Characteristics in Sorghum Based Weaning Food
    (Addis Ababa University, 2009-06) Kassa, Mihiret; Abate, Dawit (PhD)
    The effect of natural fermentation of two sorghum cultivars on antinutritional factors (tannin and phytate), minerals (Ca, Fe, Zn and P), proximate analysis and sensory characteristics were investigated. Flours from both cultivars were fermented at room temperature (20- 230 C) for 0, 12, 24, 36 and 48h at a concentration of 1:3 dilutions (w/v). TTA and pH were determined immediately at the end of each fermentation period and the samples were dried at 70o C in air oven drier for 36h. Fermentation caused an increase in the protein, TTA, energy content and improved mineral bioavailability and decrease in fat, carbohydrate, ash, crude fiber, viscosity, antinutritional factors, phytate: mineral molar ratios and pH of sorghum flour. The bioavailability of zinc (phytate: zinc molar ratio <15) after 24-48h fermentation of Gobiye cultivar was found to meet the critical limit. The bioavailability of calcium and iron was below the critical limit in all the samples analyzed; phytate: calcium molar ratio >0.24 and phytate: Fe molar ratio > 0.15. However calcium had no effect on the absorption of zinc ([Calcium x Phytate]: [Zinc] <0.5 millimolar).When the samples were subjected to sensory evaluation, there was no significant difference (p<0.05) in the appearance and aroma of the unfermented and gruel samples fermentation for 12h. The panelists however noted that appearance, aroma, texture, taste and overall acceptability of the gruel prepared from sorghum flour that was subjected to 48h fermentation differ from others and least acceptable. Taste and overall acceptability decreased significantly (p<0.05) along with period of fermentation. Ethiopian weaning mothers should be encouraged to prepare 12 to 24h fermented sorghum based weaning gruels that may blend with either legumes or milk powder by adding some amount of sugar. Further research on cereal based fermented weaning foods needs to be conducted in Ethiopia. Researchers should also take into consideration the incorporation of phytase enzymes into cereal plants to enhance the nutritional value in addition to yield improvement by the application of biotechnology.
  • No Thumbnail Available
    Item
    Improvement of Shelf Life of ‘Injera’ Using Chemical Preservatives
    (Addis Ababa University, 2009-06) Zewdu, Ashagrie; Abate, Dawit (PhD)
    Injera is staple Ethiopian fermented bread which can be made from different types of cereals, particularly from tef (Eragrostis tef). About two-third of Ethiopian diet consists of injera and it accounts for about two-third of the daily protein intake of Ethiopian population. It has a very high nutritional value, as it is rich in calcium and iron. Unfortunately, injera has a short shelf life of 3-4 days essentially due to mould spoilage. The use of weak organic acid as preservatives is allowed in acidic foods, primarily as mould inhibitor. In this study, the influence of some commonly used chemical preservatives, benzoic acid, sodium benzoate, potassium sorbate and calcium propionate was investigated by isolation of moulds before and during its ambient storage for 12 days. The preservatives were added immediately before baking at the concentration of 0.1% of benzoic acid/ sodium benzoate, 0.2 % of potassium sorbate, 0.3 % of calcium propionate and 0. 2 % blend of the four (wt/wt) as recommended by Food and Drug Administration. Three fungal species: Aspergillus niger, Penicillium sp and Rhizopus sp found to be responsible in injera spoilage. Penicillium and Rhizopus are more dominant at the temperature of between 16-200c, while Aspergillus niger is more dominant at higher temperature of between 25-320c. Injera samples had a pH and moisture content of 3.38- 3.45 and 62-65%, respectively. Antimicrobial activities of the preservatives investigated prolong the shelf life of injera up to12 days. The effectiveness of preservation was ranked as sodium benzoate>benzoic acid>potassium sorbate>blend >calcium propionate showing that benzoates and benzoic acid are the most effective. The incorporation of benzoic acid and its salt while preparing injera at home or in larger scale processing should be practiced so as to save a significant amount of injera that is lost due to mould spoilage.