Effectiveness of citric acid to reduce pathogen surrogates in spinach leaves

Fresh vegetables are considered an important source of foodborne pathogens when not properly managed from farm to fork.
Washing and disinfection is a crucial step for reducing microorganisms of public health concern.
Furthermore, the most spread disinfection agent, sodium hypochlorite (SH), is very criticized due to the formation of carcinogenic byproducts.
Therefore the aim of this research is to test the effectiveness of citric acid (CA) at 0.5%, as an alternative to the traditional washing and disinfection of spinach, against surrogate markers at a high contamination load (≈10^8-9 cfu g^-1) and a lower and more realistic one, ≈10^5-6 cfu g^-1. Representing the typically found pathogens in leafy vegetables two strains of Escherichia coli (ATCC 3526 and 8739) and one of Listeria innocua (ATCC 33090) were evaluated through the plate count method.
Briefly, discs of spinach were sampled in duplicate, dipped for 2.5 min in SH 200 ppm (1:40 w:v) to reduce native microbiota and dried with tissue paper.
Next, samples were spot-inoculated simulating a postharvest contamination and incubated for 3 h at 22°C in order to allow bacterial attachment.
And finally, dip washings following the same procedure described before were carried out with distilled water (DW), SH 200 ppm (pH 6.5-7.0), and CA 0.5%. The results indicate that the mechanical effect of DW was very little, being insignificant (p<0.05) in some cases.
On the other hand, at a high load, SH and CA reduced significantly both strains of E. coli by 2.5-2.9 and 2.3-2.4 log cfu g^-1, respectively.
Regarding L. innocua, CA performed better and reduced their counts by 4.2 log cfu g^-1. At the lowest contamination load, surrogates were reduced below the detection limit (<2.3 log cfu g^-1). Thus, the performance of citric acid 0.5% demonstrated that it can effectively replace the sodium hypochlorite in the washing and disinfection of spinach leaves.

VIII International Postharvest Symposium: Enhancing Supply Chain and Consumer Benefits – Ethical and Technological Issues

G. Finten, M.V. Fernandez, M.V. Agüero, R.J. Jagus

Spinacia oleracea L., minimally processed vegetables, washing and disinfection

https://doi.org/10.17660/ActaHortic.2018.1194.127