The increasing demand for fresher and natural food is driving consumers towards minimally processed fruits and vegetables. However, such products are common hosts to pathogens, including salmonella, l. monocytogenes and Escherichia coli O157:H7.
Recent outbreaks of pathogens in spinach and tomatoes, which led to some deaths and caused illness to hundreds of people across the US, has knocked public confidence in fresh food.
Scientists at the University of Sao Paulo collected salads from retailers in the city and found that minimally processed produce had poor microbiological quality.
A total of 181 samples of minimally processed leafy salads were taken and tested for coliforms, fecal coliforms, enterobacteriaceae, psychrotrophic microorganisms, and Salmonella in 133 samples.
L. monocytogenes was assessed in 181 samples using the BAX System, a DNA-based test.
Tests found populations of psychrotrophic microorganisms above the Brazilan standard in 51 per cent of the 133 samples, and enterobacteriaceae populations were found in 42 per cent of the samples.
Suspected Listeria colonies were submitted to classical biochemical tests, which found fecal coliform concentrations higher than the Brazilian standard in 97, about 73 per cent, of the samples. Salmonella was detected in concentrations above the standard in four samples, about three per cent of the total, while a another two tested positive but were below the standard.
L. monocytogenes was detected in only 1, or 0.6 per cent, of the 181 samples examined.
The other Listeria species identified by plating were L. welshimeri in one sample of curly lettuce and L. innocua in two samples of watercress.
"The results indicate that minimally processed vegetables had poor microbiological quality, and these products could be a vehicle for pathogens such as Salmonella and L. monocytogenes," the study stated.
In the US an estimated 76 million cases of foodborne illnesses occur each year, causing about 325,000 hospitalizations and 5,000 deaths, according to CDC statistics for 2005.
