Muleta, Diriba (PhD)Kiros, Solomon (PhD)Tesfaye, Anteneh (PhD)Beyene, Elsa2019-05-242023-11-182019-05-242023-11-182017-08-02http://etd.aau.edu.et/handle/12345678/18321Ethiopia is a developing country with a high baker’s yeast demand for bread making and beverage industries. However, there is no baker’s yeast producing plant in the country. Therefore, the objective of this study was to assess bread leavening potential of wild yeasts from teff and wheat dough, shamita, tej, tella, molasses and honey samples, following standard methods. A total of 180 wild yeast isolates were, out of these isolates 23 isolates with high biomass yield (1.7 to 2.6 of 600 nm OD reading) and the efficient gas (CO2) producers in durum tube within 12 to 24 hours were selected for further analysis. Morphological, biochemical and molecular features were used to identify and characterize the yeasts. Isolates identified by biolog were belongs to genera Saccharomyces, Candida humilis and Kluyveromyces and found to utilize glucose, sucrose, raffinose, trehalose and maltose. Genetically, the sequence analysis of the ITS-5.8S rDNA region showed that the isolates belong to 5 species namely, Saccharomyces cerevisiae, Candida humilis (synonyms Candida milleri), Kazachstania bulderi, Pichia fermentans and Pichia kudriavzevii. All the test isolates were found to produce maximum cell mass at a temperature of 30oC, pH of 5.5 and 48 hours of incubation. Isolate AAUTf1 did not produce hydrogen sulfide. The isolates AAUTf5, AAUTj15 and AAUSh17 including commercial yeast produced light level of hydrogen sulfide, while AAUMl20 and AAUWt21 produced heavy level of hydrogen sulfide. The assessment of leavening performance of the yeasts indicated that, isolates AAUTf1 (Candida humilis) and AAUTf5 (Kazachstania bulderi) had higher leavening activity with raising dough by 131 cm3 and 128 cm3 respectively each within 120 min. Similarly, isolates AAUSh17 (Saccharomyces cerevisiae) and AAUTj15 (Saccharomyces cerevisiae), were found rising the volume of the dough by 127 cm3 and 125 cm3, respectively at 60 min compared to the commercial yeast that increased the volume to 117 cm3 within 90 min. The combined bread dough rising effects of AAUTf1 + AAUTf5 + AAUTj15, AAUTf5 + AAUTj15 and AAUTf1 + AAUTj15 + AAUSh17 caused volume increment to 143 cm3 at 90 min, 141 cm3 at 60 min and 140 cm3 at 60 min, in that order. Generally, mixed cultures showed superior leavening potential than that of single cultures and commercial yeast.enCommercial YeastDough FermentationInternal Transcribed SpacerLeavening ActivityThesis