Diriba MuletaMartha Yishak2025-08-172025-08-172024-10https://etd.aau.edu.et/handle/123456789/6890There is a high demand for baker’s yeast for various Ethiopian foods and bioprocess industries. Currently, the baker’s yeast for the country’s demand is fully imported from abroad, and a huge amount of foreign currency has to be spent for this purpose, which necessitates the need for alternative import substitution products. Therefore, the main objective of the current study was to screen indigenous yeasts and lactic acid bacteria isolates from Borde, Tella, and Teff dough having superior bread leavening abilities and evaluating their impact on bread’s sensory quality and shelf life investigation. A total of 230 yeasts and 42 lactic acid bacteria were isolated and purified. Out of which, 47 yeast and 20 lactic acid bacteria isolates were selected for further analysis based on their baking ability; carbon dioxide production, growth rate, hydrogen sulfide (H2S) production, temperature tolerance, flocculation, and ethanol tolerance, within 24 hours of incubation. Four yeasts and five lactic acid bacteria isolates were chosen to develop starter cultures for bread making. The combined effect of two selected yeast isolates was also tested. The findings demonstrated that the five most potent yeast isolates (Y3, Y1, Y2,Y4 and Y5) tolerated different values of temperature that ranged up to 45°C and alcohol concentrations up to 16%. The isolate from Tella (Y3), had a maximum leavening capacity of (251.67 ±7.6 ml) at 4 hours of fermentation, but the commercial strain had a maximum leavening capacity of (245.67 ± 5.9 ml) at 3 and 4 hours. There was no significant difference (p>0.05) between Tella and the commercial strain. Effect of the three co-inoculated isolates (Y3 + Y1 + Y2) was found the highest at 275 ml at 120 min, compared co-inoculation of two combinations (Y3+Y1) 261 ml at 120 min. The five screened lactic acid bacteria isolates (L1, L2, L5, L4 and L3) revealed very poor leavening capacity; none of the isolates were selected for further testing. A panel of judges assessed the bread's organoleptic quality based on its appearance, color, texture, flavor, and overall acceptability. A nine-point "Hedonic scale" was used to gauge consumer acceptability of the items, and the commercial strain scored the highest (6.18 ± 0.17), isolates from Tella (Y3) scored (5.70 ± 0.57) although there was no statistically significant difference (p>0.05) between the two isolates. The bread made with Tella isolates (BY3) had the highest shelf life of 5 days, compared the bread made with commercial yeast (BCY) 4 days. The results of the present study indicated that mixed cultures showed superior leavening potential than that of single cultures and commercial yeast, and the wild yeasts isolated from Ethiopian traditional fermented products can be used for the development of bakery yeast.en-USFermentationLeaveningMixed CulturesSensory QualityShelf LifeStarter Culture.Thesis