Summary
Foodborne outbreaks associated with consumption of raw mangoes have been traced back to the use of contaminated wash water. This highlights the critical role of wash water disinfection in mango processing, affecting its quality, and safety. While investigations on the efficacy of disinfectants to reduce pathogens on other fruits have been performed, no studies have been conducted on mangoes. Therefore, this study will investigate the efficacy of different disinfectants (chlorine, peracetic acid and FIT fruit and vegetable wash solutions) for killing Salmonella on mangoes and prevention of water–to-mango cross contamination. The study will be performed under conditions that simulate dump tank washing, hot water treatment and hydrocooling. Additionally, the study will investigate the efficacy of trans-cinnamaldehyde, a GRAS status antimicrobial for use as a natural, alternative disinfectant in mango wash water. It is expected that this study will provide insight into the efficacy of disinfectants to inactivate Salmonella in mango packing facility water operations. Furthermore, this proposal will help understand the role of organic load in mango wash water on disinfectant efficacy. In conclusion, the proposed research is expected to help develop best practices regarding post harvest washing and disinfection of mangoes to control Salmonella and other potentially pathogenic organisms.
Technical Abstract
Mangoes have been associated with foodborne outbreaks involving different serovars of Salmonella, including S. Oranienburg (1998), S. Newport (1999) and S. Saintpaul (2001 and 2003). A common theme in these outbreaks was the source of contamination which was traced back to wash water used in hydrocooling. In order to reduce mango flesh temperature following hot water treatment, mango producers practice hydrocooling. However, it has been shown that cooling of fruit following heat treatment can lead to potential pathogen internalization into mangoes. Since there are no available technologies to inactivate internalized pathogens, wash water disinfection is a critical processing step in mango production, affecting its quality, safety and shelf-life. Although several commercially available chemical disinfectants are approved for use in wash water, chlorine is the most commonly used chemical sanitizer in the fresh produce industry. Besides chlorine, other commercially used wash solutions include peracetic acid based disinfectants and natural alternatives such as FIT vegetable and fruit wash. Although investigations on the efficacy of disinfectants to reduce pathogens on other fruits such as cantaloupe, berries, and apples have been performed, no studies have been conducted on mangoes. Additionally, most studies have not examined the effect of organic matter on the antimicrobial efficacy of disinfectants. Furthermore, there are several unique differences in the post-harvest management practices for mangoes when compared to other fruits. Therefore, these reasons warrant the need for an investigation into the efficacy of different disinfectants on pathogen inactivation on mangoes and in mango wash water operations. Hence this study will be undertaken to evaluate the antimicrobial activity of water disinfectants on pathogen inactivation in presence and absence of organic matter. In order to simulate the mango packing facility water tank operations, the effect of disinfectants on Salmonella transfer from water-to-mango and its control on mango surface will be done in three different stages to mimic washing in the dump tank, hot water treatment and hydrocooling. Additionally, the study will also investigate the efficacy of trans-cinnamaldehyde, a GRAS status antimicrobial for use as a wash water disinfectant in the mango industry. Trans-cinnamaldehyde was selected as a potential candidate based on its antimicrobial effect on other produce as established in scientific literature. Through these objectives, the proposed research will provide insight into the efficacy of disinfectants for pathogen inactivation during mango washing operations and the role of organic matter on disinfectant effectiveness. This in turn will help develop best management practices regarding post-harvest washing of mangoes and yield potential water disinfection treatments for application in the mango industry.
Research Objectives
1. To determine the efficacy of water disinfectants to eliminate water-to-mango cross contamination with Salmonella in the presence and absence of organic matter.
Objective 1 will be accomplished through the following experiments:
- Investigating the efficacy of disinfectants to inactivate Salmonella in wash water
- Investigating the efficacy of disinfectants to prevent and eliminate Salmonella transfer to mangoes from contaminated wash water
2. To determine the efficacy of water disinfectants on inactivating Salmonella on the surface of artificially inoculated mangoes in the presence and absence of organic matter.
Objective 2 will be accomplished through the following experiments:
- Investigating the efficacy of disinfectants to inactivate Salmonella on mangoes
- Investigating the efficacy of disinfectants to prevent and eliminate Salmonella transfer from contaminated mangoes to wash water
Findings & Recommendations
Key project findings:
• Dump tank wash water had the highest level of organic load, which is usually made up of latex, leaves and soil, with a COD of 317 ppm.
• Hot water (30 ppm) and hydrocooling (17 ppm) tanks were found to contain lower levels of organic contamination.
• Mango variety had no influence on the antimicrobial efficacy of the disinfectants tested.
• There are two likely scenarios for contamination of mangoes with Salmonella, namely (i) contaminated irrigation water, and (ii) contaminated fruit. Under both these scenarios, chlorine (200 ppm) and PAA (80 ppm) were found to be most effective in inactivating Salmonella in contaminated wash water and on contaminated mangoes. Furthermore, washing with chlorine and PAA prevented water-to-mango and mango-to-water cross contamination, both in the presence and absence of organic matter.
• Internalization studies revealed that the use of chlorine and PAA significantly reduced bacterial uptake into mangoes, by greater than 7 log. However, in the presence of organic contamination, treatment with chlorine dioxide did not inhibit Salmonella internalization; ~2 log CFU of Salmonella/fruit was recovered from the chlorine dioxide treated mangoes.
• Among the three disinfectants used, chlorine dioxide was found to be the least effective due to an observed loss in its effective concentration over time. In the hot water tank in the presence of organic contamination, chlorine dioxide levels fell below the detection limit (0.8 ppm) within 2 min of addition to the wash water.
• Over time (72 h), there was a significant reduction in the effective concentration of all three disinfectants and this effect was more pronounced in the presence of organic contamination.
• In addition to being effective in controlling Salmonella in wash water and on mangoes, all three disinfectants did not adversely affect fruit color. Recommendations: Results from this study provide information to producers and mango processing facilities to develop better management practices, with particular reference to washing of mangoes. Wash water has been shown to be a major source of Salmonella at the packinghouse. Furthermore, contaminated mangoes, originating either at the farm or along the processing line, can also contribute to contamination of wash water and other fruits in the lot. This project demonstrated that in either of these scenarios the use of 200 ppm chlorine or 80 ppm PAA would help reduce the risk for contamination of the fruit. As observed in the case of the dump tank wash, hot water treatment and hydrocooling, both these disinfectants demonstrated immediate efficacy (>7 log reduction in Salmonella populations as early as 30 seconds or less). At these levels, chlorine and PAA also effectively prevented cross contamination and pathogen internalization. Hence for instantaneous treatment, use of sodium hypochlorite (200 ppm) and PAA would be recommended. This result is particularly relevant to the mango industry since chlorine or sodium hypochlorite is the most commonly employed disinfectant at the packinghouse. Additionally, to prevent pathogen carryover from one wash tank to the other, we endorse the inclusion of disinfectants in the hot water and hydrocooling tank besides the dump tank. Although these compounds are effective, it is important to note that their antimicrobial effect is highly dependent on their effective concentration in water. Therefore, it is highly recommended that constant monitoring and detection of the effective disinfectant concentrations and replenishment with these compounds is necessary to obtain a sustained and effective antimicrobial activity. In summary, considering the high inoculum load that we used in the study and the low population densities that may be routinely encountered in the field, all three tested disinfectants would be effective for wash water disinfection. Albeit the use of simulated packinghouse conditions, further studies would be necessary to investigate the effect of these disinfectants in large-scale commercial fruit washing operations using larger tanks and fruit volumes. National Mango Board collaboration and support: We appreciate the support from Dr. Leonardo Ortega and Wanda Ramos for helping us understand the mango production process and coordinating mango procurements throughout the study. We also thank Mr. Veny Martex, Martex Farms, for hosting the PI at his farm and providing the team with water samples towards organic load determination.