Survival of Escherichia Coli in Traditional Fermented Turnip Juice

Abstract

Turnip juice is a fermented traditional and popular Turkish soft drink. It is produced generally under the primitive conditions and sold without any heat treatment. So, the survival of any human-born contaminant becomes important from food safety reasons. In this study, survival of Escherichia coli in turnip juice was investigated at different pH and storage temperature combinations. Turnip juices pH were adjusted approximately to 3.0, 3.5, 4.0 and 4.5 and stored at 5, 20, 30 and 35 degrees C. Each pH/temperature combination was inoculated with 18 h old E. coli culture at the level of 10(7) - 10(8) cfu/ml. Turnip juices were sampled for cultural count at predetermined intervals. First order reaction kinetic was accepted for inactivation. Linear regression of log (survivals/initial count) vs time (h) was used for determining D-values (min) for each combination. Significant decrease in number of the survivals was either not observed or not confirmed statistically at pH 4.5 (4.47-4.54), pH 3.5-4.5 at 5 degrees C and pH 3.54 at 20 degrees C. In the other 9 temperature pH combinations (5 degrees C, pH 3.02; 20 degrees C, pH 3.01 and 4.00; 30 degrees C, pH 3.00, 3.50 and 4.00; 35 degrees C, pH 3.03, 3.50 and 4.03) the D-values decreased with the temperature, increased with the pH and changed between 11.98 and 225.23 min. 5D-values changed between 7.33 and 18.79 h for pH range 3.00-4.00 and at 20 degrees C storage temperature. If E. coli, and similar pathogens are the health risks in a food processing operation and the process causes 4D or 5D reduction in the number of these microorganisms (in the case of Clostridium botulinum 12D is necessary), then it is accepted as sufficient for the food safety purposes. Thus, according to the results of this study, turnip juice with pH < 4.0 did not pose any risk of E. coli contamination after storage for 19 h or more at ambient temperature. On the other hand, the time lapsed from production line to market shelves is higher than 19 h, this will further decrease survival of E. coli.