Abstract
Production of leafy vegetables for the “Ready-to-eat”-market has vastly increased the last 20 years, and consumption of these minimally processed vegetables has led to outbreaks of food-borne diseases. Contamination of leafy vegetables can occur throughout the production chain, and therefore washing of the produce has become a standard in commercial processing. This study explores the bacterial communities of spinach (Spinacia oleracea) and rocket (Diplotaxis tenuifolia) in a commercial setting in order to identify potential contamination events, and to investigate effects on bacterial load by commercial processing. Samples were taken in field, after washing of the produce and at the end of shelf-life. This study found that the bacterial community composition and diversity changed significantly from the first harvest to the end of shelf-life, where the core microbiome from the first to the last sampling constituted <2% of all OTUs. While washing of the produce had no reducing effect on bacterial load compared to unwashed, washing led to a change in species composition. As the leaves entered the cold chain after harvest, a rise was seen in the relative abundance of spoilage bacteria. E. coli was detected after the washing indicating issues of cross-contamination in the wash water.
Highlights
The consumption of leafy green vegetables, such as baby leaves of spinach, rocket, and other ready-to-eat, minimally processed vegetables, has increased over the last two decades
Numbers of colony forming units, from different bacterial groups, changed between the sampling occasions; in all cases an increase was seen in colony forming units per gram leaf (CFU g− 1) from sampling occasion O1 to O5 (Table 3)
Results showed that washing of the produce rather increased than decreased the bacterial load; a signifi cant increase only occurred for total aerobic counts at the production of spinach in spring, and for Enterobacteriaceae in rocket produced in the autumn
Summary
The consumption of leafy green vegetables, such as baby leaves of spinach, rocket, and other ready-to-eat, minimally processed vegetables, has increased over the last two decades. Consumption of minimally processed leafy greens has been known to cause outbreaks of food-borne illnesses through contamination with human pathogens, such as Escherichia coli O157:H7, Listeria and Salmonella. With or without addition of sanitizing agents, is the main intervention step for removal of microorganisms, wash water has been identified as a source for cross-contamination of human enteric pathogens (Allende et al, 2008; Holvoet et al, 2012). With process water being reused for several hours in commercial washing and packaging establishments this shows a clear potential for cross contamination between different batches of leafy greens processed during the same day. At a lower initial load of bacteria (3 log CFU/g), the efficiency of the washing procedure was at best 1 log, but for many washing procedures the effi ciency was negligible (Pezzuto et al, 2016)
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