Browsing by Author "Weldesemayat Getachew"

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    Screening and Characterization of Thermostable Alpha- Amylase from Bacteria Isolated from Hot Environments
    (Addis Ababa University, 2025-02) Weldesemayat Getachew; Fitsum Tigu; Asnake Desalegn (PhD)
    Alpha-amylase is one of the most important enzymes for undergoing in starch saccharification and liquefaction to results simple sugar. Despite there were numerous resources to isolate thermostable alpha-amylase producing bacteria however little research was conducted in our country. The objective of this study was to screen, and characterize thermostable alpha-amylase producing bacteria. A totally of 35 samples were gathered from selected hot environments around Addis Ababa. A total of 188 bacterial isolates were screened for alpha- amylase production through starch hydrolysis test. Of which, 161 isolates were obtain to be positive for starch hydrolysis test. Sixty-six isolates with amylolytic index (AI ≥ 1.5+0.3 mm) were selected for submerged state fermentation and the enzyme assay was conducted through DNSA method. Based on their fermentation performances, 6 isolates, FBW2-3A, FHW5-1A, KS1-1A, SJS1-4A, KHW2-2A and SAS1-2A were selected for further amylase production optimization process. All the six bacterial isolates were phenotypically and molecularly characterized into species level. They belonged to Bacillus cabrialesii (FBW2-3A), Acinetobacter haemolyticus (FHW5-1A), Enterobacter quasiharmachei (SJS1-4A), Bacillus cereus (KHW2-2A) and Pseudomonas plecoglossicida (SAS1-2A) while KS1-1A isolates was not identified. The effect of temperature, pH, incubation period, carbon and nitrogen sources, starch and salt concentration, metal ions and inoculum size were optimized based on one factor at a time approach. For all isolates the optimal growth temperature, pH and incubation time was obtained at 50oC, pH 7 and 24 h, respectively. Crude alpha-amylase was optimally active at 55oC with pH 7. The crude enzyme was thermally stable above 90% at 55oC for 30 min incubation. Partially purified amylase from Bacillus cabrialesii (FBW2-3A) has a specific activity of 10.12U/mg, which is 1.8-fold than the crude enzyme with molecular weight lies approximately 20kDa. The food industrial efficiency of the alpha amylase was investigation by applying of crude alpha-amylase into wheat flour fermentation and it showed a good dough raising capacity.