Predicting the behavioural pattern of Escherichia coli in minimally processed vegetables

Minimally processed (MP) vegetables are prepared to meet the demands of providing ready-to-eat (RTE) or ready-to-use products. In MP vegetables, contamination by foodborne pathogenic bacteria and their multiplication during storage is of serious health concern. Among the pathogenic bacteria, enterotoxigenic Escherichia coli is of prime concern to public health. Population curve fittings by multivariate analysis were derived from the growth data of an enterotoxigenic strain of E. coli D 21 in MP carrot, cucumber and tomato obtained with variables of initial inoculum (4.3, 5.3 and 6.3log10 CFU/g), storage temperature (2°C, 9°C and 16°C) and storage period (2, 6 and 10 d). Storage of MP vegetables at 2°C did not show any appreciable increase in the viable populations of E. coli. At 9°C and 16°C, there was a progressive increase in the viable populations of E. coli, which was more rapid at 16°C. Under the set of influencing factors, population curve fittings showed a good agreement with the experimental values, with majority of them being `fail-safeʹ. The values of statistical indices showed that the model fits ranged between extremely good and satisfactory fits. Response surface plots were generated to describe the quantitative effects of influencing factors on the population pattern of E. coli. Microbial safety of MP vegetables depends largely upon the initial population of microbial contaminant, followed by storage period and temperature.