Sanitizers efficacy to inactivate E.coli O157:H7 on fresh-cut carrots

Fresh-cut produce is one of the most growing convenience foods because it offers freshness, nutrition, and convenience. However, the fresh produce contamination with human pathogens can occur anywhere during the chain, from farm to table.

Fresh-cut produce is marketed as pre-washed and read-to-eat, it is not subject to further microbial killing step, thus the use of effective sanitizers during produce washing is fundamental to ensure produce safety.

Chlorine has been widely used in the fresh produce industry as a sanitizer in spray and flume waters at concentrations of 50 to 200 ppm and a contact time of up to 2 minutes. However, chlorine efficacy on pathogens is limited because its activity rapidly decreases on contact with organic matter, increased temperature, exposure to light, and contact with metals.

The U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) have approved the use of acidified sodium chlorite for spray or dip sanitizing certain food products, including fruit and vegetables, at levels of 500 to 1,200 ppm. The acidified sodium chlorite is a combination of citric acid and sodium chlorite in aqueous solution, with an high oxidative action.

Researchers have compared the acidified sodium chlorite with chlorine, peroxyacetic acid, and stabilized chlorine dioxide. They have found that the acidified sodium chlorite has been the most effective to reduce both Escherichia coli O157:H7 and Salmonella Montevideo on inoculated strawberries. Peroxyacetic (peracetic) acid is a strong oxidizing agent that has been used widely to disinfect food processing equipments and has been approved by the FDA as a sanitizer for fruit and vegetables.

This acid is effective against Listeria monocytogenes, Salmonella spp., and E.coli O157:H7, achieving reduction of 97%, 92%, and 88%, respectively, at 10 ppm and as little as 30 seconds of immersion in a batch washing scheme with chilled water. Also, citric acid has been approved by FDA and EPA, but data on its performance are not available. Most sanitizers studies are conducted using pure lab water, whose conditions are significantly different from those of water used in the commercial processing.

The main objective of the study conducted by Gonzales et al. (2004) was to evaluate the efficacy of chlorine, citric acid, peracetic acid, and acidified sodium chlorite in reducing population of E. coli O157:H7, total aerobic bacteria, and yeasts and moulds from shredded carrots under tap water and simulated fresh-cut wash water conditions.

For the research, fresh carrots were purchased from a produce wholesale market and processed within 24 hours. The sanitizers were obtained directly from the manufacturers, and the concentration of the solutions tested were based on each manufacturer’s recommendation. For the inoculation, the carrots were immersed in the E. coli O157:H7 inoculum solution. After processing, the shredded carrots were stored for 14 days at 5 °C. The microbial analyses were performed at 0, 7, and 14 days.

Results showed that the organic matter in the fresh-cut processing water, sanitizer type, and their combination have significantly reduced E.coli at day 0. The organic matter in water has reduced the efficacy of sanitizers, mainly of chlorine. The acidified sodium chlorite was more tolerant to the organic loads presented in the processing water than the other sanitizers tested. By using acidified sodium chlorite, reductions of 4.5 log of pathogens, of 3.3 log of total microbial count, and of 0.7 of yeast and moulds were reached. In addition, the sanitizers are effective more against pathogens present in water than against those present on produce. Thus, it is fundamental to prevent cross-contamination of other produce with pathogens to ensure safety and quality of fresh-cut products.

Original study. Gonzales R.J., Luo Y., Ruiz-Cruz S., McEvoy J.L., "Efficacy of sanitizes to inactivate Escherichia coli O157:H7 on fresh-cut carrot shreds under simulated process water conditions". Journal of Food Protection, Issue No. 67(11), pagg. 2375-2380, 2004. For more details:

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