Microbiological Quality of Leafy Green Vegetables Grown in the Toluca Valley

Abstract

The intake of fresh fruits and vegetables has increased in recent years, as have outbreaks of foodborne illnesses associated with these products. The risk of microbiological hazards in vegetables can occur from the field to the table. The main sources of contamination are agricultural soil and irrigation water, which can affect product quality and be a reservoir of foodborne pathogenic bacteria. This research analysed the microbiological quality of green leafy vegetable crops: spinach (Spinacia oleracea L.), lettuce (Lactuca sativa L.) and coriander (Coriandrum sativum L.), grown in the valley of Toluca. The presence of microorganisms indicating microbiological contamination (mesophilic bacteria, total coliforms, faecal coliforms and Escherichia coli, Salmonella and Listeria) was evaluated in plants, water and soil. Sampling, processing, isolation and bacterial identification were performed in accordance with Mexican Official Standards and the FDA Bacteriological Analytical Manual. The recovered bacteria were subjected to biochemical tests, serotyping and PCR. Microbial counts were present in 100 % of the samples tested. The spinach culture had higher recovery of mesophilic bacteria and total coliforms, while the lettuce culture presented higher values for the faecal coliform group. The results indicated higher microbiological contamination in water and soil > 250 CFU for mesophilic bacteria, total coliforms and faecal coliforms, respectively. The microbiological counts of the three cultures were found within the maximum limits established by Mexican regulations. However, the presence of faecal coliforms, which included E. coli bacteria of serotype O105 ab flagellar, compromises the quality of the product and poses a risk to the health of the consumer.