Manuel Michel, the board's executive director, said the mango industry provided financial support because it is always looking for more effective and efficient water disinfectants.
"This study will generate new knowledge and should provide science-based results that mango operations can incorporate right away," he said. "Food safety and quality are top priorities for the mango industry, and the information generated from this study will help improve the best management practices in the areas of washing and post-harvest handling of mangoes. Any research that enhances food safety and quality is beneficial to consumers and the produce industry."
Amalaradjou, who enjoys eating mangoes but admits she knew little about all the steps involved in mango processing before starting the research, praised Mango Board representatives for their extreme helpfulness.
"It's been a pleasure working with the National Mango Board - they are very interested in my work," she said.
In fact, the board flew Amalaradjou to a state-of-the-art packinghouse in Puerto Rico so she could see first-hand the steps the fruit goes through from when it arrives until it is shipped out. She said that was extremely important because she is trying to replicate the processes on a small scale using 30-gallon containers in her laboratory. Amalaradjou also was able to collect water samples so she could simulate the same ratios of soil and organic matter in her laboratory treatments.
In addition, the mango board continues to ship her freshly harvested fruit that has not been through a packinghouse for her laboratory trials.
Mangoes actually come in contact with water three times in a packinghouse - initially in a dump tank, where they are briefly washed; in a hot-water dip used to address USDA APHIS quarantine requirement; and in a hydrocooler used to quickly reduce fruit temperature after the hot-water treatment.
Amalaradjou's project is looking at chlorine (100 ppm), the most commonly used water disinfectant, as well as chlorine dioxide (5 ppm) and peracetic acid (80 ppm), also known as PAA.
Organic matter is a big concern, especially with chlorine and chlorine dioxide, because in large enough volumes it can significantly reduce those disinfectants' effectiveness. Based on her packinghouse water sample analysis, she used mango wash water that contains latex (the main organic matter found in mango dump tank water) as well as clay-loam soil to simulate organic contamination that can be encountered in the dump tank.
Amalaradjou also inoculated the dump tank water with a known quantity of
Salmonella (7 log CFU/ml of wash water).
Then she added the mangoes and pulled out samples at 30-second intervals up through 2 minutes. Although fruit typically is washed for only about 30 seconds, it can sit in the wash water for longer periods if the packing line backs up.
In those trials, chlorine and PAA proved more effective than chlorine dioxide.
"Basically in my dump tank trials, chlorine and peracetic acid worked - we didn't detect any
Salmonella on the mangoes," Amalaradjou said. "With chlorine and PAA (at the levels used), we don't recover any
Salmonella from the water or mangoes or the dump tank.
"With chlorine dioxide up until 30 seconds, it's still positive (for
Salmonella). But after that it becomes negative."
The next two steps, which she will complete in 2016, will look at the three disinfectants during the hot-water treatment as well as hydrocooling.
During the hot-water dip, mangoes are subjected to 46°C water (115°F) for 65 to 115 minutes, depending on the fruit size, to kill insect larvae that may be present.
Then the mangoes quickly undergo hydrocooling, which involves being immersed in water at 21 to 22°C (70 to 72°F) water for 30 minutes, to bring down the fruit's internal temperature.