Effect of fermentation on the growth of Escherichia coli - NG7C in gruels made from whole grain flours of wheat and tef

The effect of fermentation on the production of lactic acid, pH-development an on the growth of Escherichia coli strain NG7C in gruels made of whole grain wheat and whole grain tef under different conditions was studied. The results show that the number of E. coli decreased rapidly in both 1% and 10% back-slopping quicker than in control that was fermented without back-slopping. The growth of E. coli in the gruels was found to depend not only on the amount of lactic acid and pH but also on the amount of undissociated lactic acid both in whole wheat gruel and whole tef gruel. At the lowest pH (3.5) obtained in all fermentation experiments, the number of E. coli was found to be reduced to > 6-log-unit. The initial pH of the slurry was adjusted to different levels by adding lactic acid alone or by adding hydrochloric acid. It shows that the lower pH have an effect on the growth of E. coli. However a lower pH caused by the addition of lactic acid is more effective in reducing the number of E. coli than addition of HCl. The sample with the highest amount of undissociated lactic acid had the fastest reduction of viable E. coli during fermentation.