Processing of green leaf produce: microorganisms associated with process water and produce

Bacterial colonisation of a green leaf product (rocket) was studied before processing and after packing and raw and process water quality at different stages during processing under commercial conditions was analysed. “Raw water” denotes fresh water of potable water quality used to fill the washing line, whereas “process water” describes water sampled from the prewash and the main wash unit in the washing line. Samples were collected on four events, with three replicates per event. Leaf and water samples were both analysed for heterotrophic plate counts (HPC) at 22 °C, slow-growing bacteria (SGB), total coliform bacteria (TC), Escherichia coli (EC), intestinal enterococci (IE), Listeria monocytogenes (LM), Salmonella spp. and Campylobacter spp. The bacterial load in the process water increased substantially after produce came in contact with raw water. HPC exceeded 300,000 CFU mL-1 and SGB 50,000 CFU mL-1. IE were also very abundant, but not TC and EC. The microbial reduction rate was log 0.5. From these specimens, microorganisms were grown on semi-selective media (0.1x Tryptic Soy Agar, King agar B, Enterococci agar and Violet Red Bile Dextrose Agar) and five randomly selected colonies were identified using Biolog GenIII panels. Various Pseudomonas species and Pantoea agglomerans were frequent in the process water. The phyllosphere microbiota before washing was also dominated by P. agglomerans. After washing, P. agglomerans, Rahnella aquatilis and Pseudomonas spp. were abundant. Pseudomonas fluorescens and Enterobacter cloacae resisted washing procedures in the washing line and under laboratory conditions.