Microbiological hazards involved in fresh-cut lettuce processing

BACKGROUND: The increasing consumption of produce all over the world has resulted in increasing concern by the regulatory agencies with respect to the level of safety performed by the processors. The objective of the present study was to investigate the hazards involved in the various steps of fresh-cut lettuce processing (reception/selection of raw material, washing, rinsing, sanitisation and final product) by means of microbiological analyses of microbial groups used as indicators of hygienic conditions and of pathogens. RESULTS: High microbial loads of mesophilic and psychrotrophic bacteria and Pseudomonas spp. were found in the ram reception (similar to 6 log colony-forming units (CFU) g(-1)), which were reduced by a single logarithmic cycle for the last two microbial groups after the sanitisation step (P < 0.05), the latter being ineffective against the first microbial group (P > 0.05). Lower counts of yeasts and moulds, total coliforms (35 degrees C) and faccal coliforms (44 degrees C) were observed in the initial step (3.49-4.53 log CFU g(-1), 0.65-1.55 log most probable number (MPN) g(-1) and 0.50-0.90 log MPN g(-1) respectively), these values increasing significantly after the sanitisation step for yeasts and moulds (similar to 5 log CFU g(-1)) but remaining unaltered for coliforms (P > 0.05). Salmonella spp. were not found in any of the experiments carried out, while the presence of Escherichia coli was observed in the final product. CONCLUSIONS: Practices compromising the hygienic quality of the final product during commercial storage were observed and corrective measures suggested. To the best of the authors' knowledge, these are the first data on microbiological safety in Brazilian fresh-cut processing plants. (c) 2008 Society of Chemical Industry.