Purpose: This study was conducted as an evaluation of the influence of washing methods (time, temperature, NaClO concentration, water/produce ratio); wash water quality (organic matter, turbidity, conductivity, pH); and type of fresh-cut produce in bacterial cross-contamination during the washing step.
Methods: Physical-chemical characterization of fresh-cut produce wash water was carried out from effluents of a local fresh-cut processing industry. Fresh iceberg lettuce pieces (25 g) were inoculated with gentamicin-resistant Salmonella enterica (LFMFP 687) and washed in one liter of simulated wash water with stirring at 260 rpm for 2 min at 4 ºC; this was repeated twice with two subsequent washing cycles in reused water. Salmonella concentration was quantified in water and in the produce before and after the washing treatment. Similar experiments were conducted with fresh spinach.
Results: The main chemical properties of the prepared, simulated wash water can be summarized as 150 mg/L TOC, 100 NTU, 1000 µS/cm, pH of 6.2. Salmonella was transferred from the inoculated lettuce to the wash water and remained in the reused wash water, accumulating after each, subsequent, cycle of washing (reaching concentration values up to 105 CFU/mL). The produce to water transfer ratio was quantified for fresh-cut lettuce and spinach. The wash water became contaminated; with 99% of Salmonella present on the inoculated lettuce. For spinach, only 20-50 % of the Salmonella inoculated was transferred to the water. Spinach washing led to a notable increase in the concentration of suspended solids in the reused wash water.
Significance: Development of a solid understanding of the washing process and its effects on microbial growth is required to prevent cross-contamination, enhancing produce quality and safety.