Shimelis Admassu (Prof.)Hundessa Dessalegn (PhD)Eskindir Getachew2023-12-142023-12-142022-06http://etd.aau.edu.et/handle/123456789/921Traditional alcoholic beverages are widely produced and consumed in Ethiopia. Tej, Ethiopian honey wine, is one of Ethiopia's most popular spontaneously fermented traditional alcoholic beverages, usually made from honey and gesho (Rhamnus prinoides). However, this spontaneous way of fermentation increases the likelihood occurrence of suck and/or slow fermentation, making the process difficult to predict, control, and correct. Furthermore, it may also cause the product to have off flavor and inconsistent quality. As a result, the overall goal of this research is to create a direct fermentation system for Tej fermentation system, which is the assumed solution to the aforementioned problems. To achieve this goal, a physico-chemical and microbial ecological investigation, microbial isolation and strain selection, and kinetic study were carried out. Based on the honey production potential, Tej consumption culture, accessibility, and suitability for sample collection, study area for this research was selected to be Addis Ababa (AA), Debre Markos (DM), and Bahir Dar (BD), Ethiopia. The physicochemical properties of Tej samples collected from the aforementioned areas varied significantly from household to household and location to location. The alcohol and sugar contents ranged from 6.36 to 11.34 g/100 mL and 0.37 to 31.6 g/L, respectively. However, the microbial profiles were dominated by a few fermentative microorganisms. The bacterial community structure of Tej samples was dominated by the genera Lactobacillus (53.15%) and Zymomonas (38.41%). Similarly, the fungal community was exclusively dominated by the genus Saccharomyces (99.66%). Moreover, the microbial communities shifted to Lactobacillus and Saccharomyces dominance as Tej fermentation period progressed to the end. Furthermore, throughout these spontaneous fermentation period, the number of bacterial gene copies was half that of fungal gene copy numbers. After the intensive purposeoriented screening and genotypic identification the isolated strains were Saccharomyces cerevisiae, Pichia fermentans, Wickerhamomyces anomalus, Lactobacillus hilgardii, Lactobacillus paracasei, and Lactobacillus parabuchneri. These isolated microbial strains were then used to ferment honeymust in various combinations. The more mixed the microbial strains are, the more the fermented product resembles the control sample in terms of physicochemical properties and volatile compound profile. Moreover, to reduce the possibility of sluggish and stuck fermentation, the medium was supplemented by diammonium phosphate (DAP). Higher fermentation rate was observed for the medium supplemented with the nitrogen concentration greater than 140 mg/L. A predictive kinetic model for microbial growth, substrate utilization, and product formation rate was developed using two substrate limitation (Monod and Teissier) and product inhibition (Ghose and Tyagi) models.After simulation and parameter estimation, the Teissier model adequately described yeast assimilated nitrogen (YAN) utilization and ethanol production. Whereas Monod-Cheirsilp and Monod kinetic modes effectively described lactic acid bacteria (LAB) growth and sugar consumption rates. In general, the microbiological ecology analysis, isolation of dominant strains, and design of fermenting medium performed in this study yielded promising results for the modernization of Ethiopian honey wine, Tej. However, much more input from future research findings is required for the complete process upgrade, particularly in the areas of fermentation parameter optimization.en-USTej, Fermentation, Lactobacillus, Saccharomyces, antioxidant, physicochemical, Kinetic modelingThesis