Vegetables are an important source of dietary fiber, vitamins and minerals, have low energy density and provide a range of nutrients that are required to regulate the body’s metabolic functions. For these reasons, dietary guidelines recommend a high intake of vegetables (WHO/FAO, 2003).

However, due to their high surface/weight ratio and relatively high pH, salad vegetables host large microbial populations, particularly bacteria, which contribute to the natural decay of vegetative organs detached from the plant (Ragaert et al., 2007). Human pathogens such as Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7 can contaminate foodstuffs both during plant cultivation and processing (Francis et al., 1999; Brandl, 2006; Franz and van Bruggen, 2008).

Evidence of fresh produce-associated foodborne illnesses has been growing in recent decades and the description of such outbreaks is common in the United States and elsewhere (Berger et al., 2010), despite the prevalence of the main pathogens continuing to be low in fruit and vegetables (EFSA, 2015; Denis et al., 2016). However, outbreaks of illness associated with vegetables and juices have been increasing in recent years, rising from 4.4% in 2013 to 7.1% in 2014 (EFSA, 2015). Salmonella spp. and Listeria spp. are of major concern, due to the high number of cases and to the severity of the related harm, respectively (EFSA, 2015).

Salmonella enterica is an enteric, Gram negative pathogen which can contaminate fresh produce through various routes, including via use of organic waste as fertilizer, contamination of irrigation waters with fecal material, direct contamination by livestock and wild animals and hygiene errors in handling and processing (Heaton and Jones, 2008). L. monocytogenes is a ubiquitous Gram positive pathogen frequently isolated from food processing plants and recognized as an important agent of cross-contamination during food handling at both industrial and domestic levels (Lomonaco et al., 2015).

The risk derived from contaminated foodstuffs is increased for YOPIs (Young, Old, Pregnant, Immunocompromised) due to their high susceptibility and, thus, the possibility for disease to be more severe. The increased importance of fresh produce-associated foodborne illnesses has directed the attention of the scientific community toward the implementation of mitigation strategies able to prevent such cases (Chen and Jiang, 2014).

Despite the growing consumption of ready-to-eat vegetables, raw vegetables are still widely consumed in the European Union. This consumption pattern means the measures taken by consumers play a critical role in the prevention of foodborne diseases, as the consumption phase is the last step in the “farm to fork” chain and the only one beyond the official checks performed by the competent authorities involved in assuring food quality. However, according to the scientific literature, consumers are frequently unaware of their role in the prevention of foodborne diseases and underestimate the incidence and severity of such diseases (Losasso et al., 2012). Moreover, it has been shown that improved knowledge allows consumers to make informed choices regarding their actions and, consequently, the accuracy and the extent of information acquired by consumers could be of major significance in foodborne illness mitigation strategies (Losasso et al., 2012, 2013; Faccio et al., 2013).

Among mitigation strategies, sanitation treatments can play an important role in reducing pathogen levels on fresh vegetables. Application of a detergent before disinfection may help remove microbes from the surface of fresh produce (Gil et al., 2009). Most investigations concerning the efficacy of disinfectants for reduction of pathogenic bacteria have been conducted on inoculated fresh fruits (Liao and Sapers, 2000; Bastos et al., 2005; Sy et al., 2005) or vegetables (Hilgren and Salverda, 2000; Hellström et al., 2006). Among these studies, chlorine has proved to be one of the best candidate disinfectants, in association with surfactants.

In response to the current public health concerns associated with the microbiological safety of fresh produce, the aims of the present study were to: (1) assess vegetable sanitation strategies used by consumers, and; (2) determine the efficacy of identified common sanitisers at the consumer and industrial levels for reducing Salmonella and Listeria in fresh vegetables, taking Eruca vesicaria (rocket) as a case study.

In this work, the effectiveness of six washing procedures on S. enterica or L. monocytogenes artificially contaminated onto rocket was assessed. Among the sanitisers investigated, sodium hypochlorite, which has long been used to disinfect fresh produce (Beuchat et al., 1998), produced the largest reductions in microbial counts of both S. enterica and L. monocytogenes. However, a non-significant effect was obtained from trials involving rocket with low levels of contamination. This was the main limitation of the present study and raises some concerns about washing procedure effectiveness against Salmonella in naturally contaminated vegetables.

In the case of Salmonella, 200 mg/L sodium hypochlorite significantly reduced bacterial counts, whilst in the case of Listeria, all sanitisers significantly reduced the counts, with sodium hypochlorite and combined peracetic and perchloric acids being the most effective. A difference in the effect against Salmonella and Listeria was observed also in the case of heavy metals such as silver used as antimicrobial (Losasso et al., 2014; Belluco et al., 2016). This could probably be due to the different structure and physiology of Salmonella and Listeria, being Gram negative and Gram positive, respectively.

Due to its low cost and ready availability, sodium hypochlorite is the most commonly used water disinfectant specifically applied in the fresh-cut produce industry for wash, spray, or flume waters (Gil et al., 2009). However, many disadvantages have been identified when this chemical is used to treat fresh produce. Sodium hypochlorite is highly corrosive and can form carcinogens following reaction with organic matter, particularly at high concentrations (Rodgers et al., 2004). The commonly applied free sodium hypochlorite concentrations in vegetable washing processes range from 50 to 200 mg/L (WHO, 2000). In addition, the use of sodium hypochlorite at high concentrations could generate chlorine gas, which could be harmful for consumers via inhalation. Furthermore, the potential for trihalomethane formation by sodium hypochlorite, depending on dose and organic matter content, is well known (WHO, 2000). Evidence on the formation of sodium hypochlorite by-products has been obtained by testing concentrations and/or contact times that would have unacceptable effects on product quality, or could not be applied at industrial scale due to environmental effects and personnel safety issues (WHO, 2000).

The present study demonstrated that the effective concentration of sodium hypochlorite to reduce both L. monocytogenes and S. enterica contamination on E. vesicaria was 200 mg/L, suggesting potential harmful effects for consumers could occur. However, it is difficult to estimate the concentrations of sodium hypochlorite used in real life scenarios by consumers and, consequently, to exclude the risk deriving from consumer exposure to its by-products. Specifically, the amount of sodium hypochlorite added to water is often not measured, but it could exceed the safe level by an order of magnitude.

The current approach to ascertain the safety of foodstuffs is conceptually based on absence (or reduced presence) of foodborne pathogens in processed and unprocessed foodstuffs intended for human consumption, as legally required in the European Union Regulation (EC)2073/2005 (EC, 2005). However, sanitation practices applied to fulfill such safety criteria could change the microbial ecology of food matrices, thus resulting in potential positive and/or negative effects. In fact, due to the complexity of microbial metabolism and the interrelationships between various environmental factors, even apparently insignificant changes in the microbial environment can trigger food safety concerns or drive the evolution of pathogens. For example, the practice of rinsing foods with organic acids, with the aim of eliminating pathogens from the surface, could cause the evolution of acid-tolerant bacterial pathogens better able to survive in a host gastrointestinal tract (Cotter and Hill, 2003). The emergence of microorganisms with combined resistance to biocides and antimicrobial agents is a public health challenge. To date, much evidence has shown that biocides, used indiscriminately in an increasing number of applications, can also play a role in the development (or selection) and dissemination of biocide- and antibiotic-resistant pathogenic bacteria (Dancer, 2014; Tacconelli et al., 2014; Vergnano, 2015).

Correct vegetable washing practices, both at industrial and consumer levels, are critical to circumvent the phenomena described above. Clearly, this indicates the importance of proper communication campaigns targeting consumers on the correct and safe use of sanitation chemicals during vegetable washing for food safety purposes.

APe and SB conceived the experiments and conducted the experiments, CL analysed the results and wrote the manuscript, IP performed data analysis, APi conducted the experiments, DC, RM, and AR conceived the experiments and analysed the results. All authors reviewed the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.