Effect of citric acid at different pH on the survival of <i>Escherichia coli</i>

Abstract

Microorganisms are included among the major spoilers of food, they achieve this by using the nutrients present in food material. Susceptibility of microorganisms to the most currently used preservatives has been decreasing. Organic acids have been considered as valuable food preservatives. This study aimed to isolate, identify and determine the effect of citric acid at different pH levels on the survival of E. coli. The E. coli was isolated and a pure culture was obtained after series of sub-ulturing on Eosine Methylene Blue agar. The biochemical tests known as IMViC were performed to confirm the presence of the organism. The organism was also identified using polymerase chain reaction (PCR) in which the DNA was extracted, amplified and viewed by gel electrophoresis. The organism was then inoculated in nutrient broth containing citric acid at pH levels of 3.0, 4.5 and 6.0 in different test tubes. Negative controls were included. Results were analyzed using one way ANOVA to compare the means obtained. Results obtained was positive for indole and methyl red tests but negative for Voges
Proskauer and citrate tests which confirmed the organism. After 24 hours of inoculation, the results of spectrophotometry showed that at pH level of 3.0, the absorbance was lower than the results obtained at pH level of 4.5 and 6.0. This is an indication of higher reduction in the count of the organism at pH of 3.0. There was significant difference between the control and the test groups (p<0.05) but the difference obtained between the test groups were not significant (p>0.05). Results from this study showed that citric acid could not eliminate the whole organism but was effective in inhibiting the growth of the organism dependent on pH level. This indicates that a pH dependent citric acid can be used as a good preservative.