Search results

(1 - 1 of 1)

Title

FACTORS AFFECTING THE SANITIZER EFFICACY IN PREVENTING SALMONELLA TRANSFER DURING POSTHARVESTWASHING OF CUT LETTUCE

Creator

Zang, Mingxia

Date

2014, 2014-07

Description

This study investigated the spread of Salmonella during postharvest washing of contaminated lettuce and determined the factors that affect the...
Show moreThis study investigated the spread of Salmonella during postharvest washing of contaminated lettuce and determined the factors that affect the efficacy of chlorine in preventing Salmonella cross-contamination. A bench-scale washing system was assembled. It consisted of a 15 gal tank equipped with a submersible pump and various probes to measure wash water properties including pl-l, temperature, chlorine level. oxidation reduction potential (ORP), turbidity, and total organic carbon (TOC) level. Eight grams of cut romaine lettuce inoculated with approximately 7 log CFU/g of Salmonella typhimurium expressing green fluorescent protein were added to 40 L of sterile tap water or spent wash water collected from a commercial produce processing facility together with 800 g of uninoculated lettuce and washed for 2 min. Washing trials were performed at 3°C under different levels of chlorine treatment (0. 5, 10, 20 and 30 ppm of sodium hypochlorite). Small-scale (100 mL) experiments were performed to determine the effects of organic matter (lettuce homogenate) and solids (play sand) on the efficacy of chlorine in wash water. Without chlorine treatment, the spread of Salmonella occurred during lettuce washing in both sterile tap water and in spent industry water. With 5 ppm ofchlorine. although no Salmonella was detected in the wash water, the pathogen was found in the uninoculated lettuce after culture enrichments. When the chlorine level increased to either 10 or 20 ppm of chlorine, no Salmonella was detected in the wash water or the uninoculated lettuce. Similar experiments were performed using the spent industry water. Salmonella transfer occurred at chlorine of 10 or 20 ppm. Transfer was prevented when the chlorine level was raised to 30 ppm. IX Data from the small-scale experiments indicated that the increase in organic contents resulted in a lower level of free chlorine and a greater survival of Salmonella. At 5 ppm of chlorine, the level of Salmonella increased from not detectable « 1 log CFU/ml) to completely unaffected (4.3 ± 0.4 log CFU/ml) when the TOC level increased from 10.6 ± 10.4 to 164.0 ± 21.2 mg/L. Also, the increase in solid contents led to a greater survival of Salmonella even though the free chlorine level remained unchanged. At 0.5 ppm of chlorine, the level ofSalmonella increased from not detectable « 1 log CFU/ml) to completely unaffected (4.2 ± 0.1 log CFU/ml) when the turbidity level increased from 0.7 ± 0.5 to 378.2 ± 53.5 NTU. In summary, the use of sufficient chlorine could prevent Salmonella cross-contamination but the effective chlorine level was affected by the organic load and solid content present in the wash water. Since the chlorine efficacy was the key to preventing cross-contamination and organic load was an important factor affecting the chlorine efficacy, measurements of the organic load was needed to determine the level ofchlorination needed in the wash water. However, current methods for measuring TOC took a few hours to perform. Turbidity measurements which could be done in a minute had been frequently used in the produce industry to determ ine wash water quality. In this study. it was found that a linear correlation could be established between turbidity and TOC suggesting that turbidity could be a good predictor of the organic load in produce wash water.
M.S. in Food Safety and Technology, July 2014
Show less