From farm to fork: Fungal and bacterial contaminants and their diagnostics in the production steps of ready-to-eat salads

Ready-to-eat leafy greens are vegetable plants marketed already washed in sealed bags and intended to be eaten raw. Packaged fresh salads represent a very fast-growing market. The most crucial requirement for these products, typically consumed without cooking, is adequate microbiological quality to ensure health and safety. Their quality depends on the conditions and methods of cultivation, washing, bagging, storage, transport, and distribution, as well as any other operation that can select or favour microbial growth. Some microorganisms can cause premature product spoilage, while others are hazardous to humans. There is, in fact, evidence in outbreaks, recalls, and survey results that foodborne pathogens can be found in leafy greens. However, they are usually not in a high proportion of samples and are generally hard to detect. The different stages of bagged salad production are examined, and the microbiological aspects are also analysed in light of current food hygiene legislation. The methods used to study individual contaminants and the microbiome of bagged salads are reviewed, including the protocols described in ISO standards and the technologies based on high-throughput sequencing methods. This review paper aims 1) to highlight the critical points of the salad production process in terms of the origin of microbiological contamination and 2) to discuss the solutions available for monitoring the microbiological quality and safety of ready-to-eat salads. Zeroing microbiological risk in ready-to-eat salads is statistically unrealistic because contamination can occur throughout the production chain. However, the ready-to-eat salads market can benefit from new sustainable technologies that might support risk management decisions before salads reach consumers.