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Seven different brands of commercial baker's yeast commonly found in Nigerian markets were evaluated for their acidity, viability and leavening activity. The baking and staling qualities of bread produced using the yeasts were also determined. Acidity and viability of yeast cells in the samples ranged from 2.09 to 2.78 and 89.42 to 95.09%, respectively, while leavening activity in lean and rich doughs varied from 70.46 to 90.06 mlh g and
55.8 to161.6mlh g , respectively. Bread baked from different baker's yeasts were not significantly different (p>0.05) in their crumb structure and texture. However, significant differences were found in terms of crust color, loaf symmetry and overall acceptability. The staling rate of bread samples correlated positively with yeast's leavening activity (r=0.382, p=0.486). The leavening activity and crumb staling process were modeled by a power law (r = 0.76- 0.93) and an exponential equation (R = 0.92-0.97), respectively. The study highlights the need to control the quality of yeast leavened products such as bread by appropriate choice of commercial baker's yeast.
Key Words Baker's yeast, viability, acidity, dough leavening, baking properties, bread staling