Kathryn Fontenot, Adhikari, Achyut, Janes, Marlene E.
Jose L. Brandao Delgado, Kathryn K. Fontenot, Achyut Adhikari and Marlene Janes
The Louisiana strawberry industry, which contributed $13.6 million to the state’s economy in 2017, according to the LSU AgCenter Ag Summary, is one of the most popular industries in the state. This industry now faces new regulations with the introduction of the Food Safety Modernization Act Produce Safety Rule that requires farmers to comply with higher microbial water quality standards than before. This rule aims to guarantee that the water used for pre- and post-harvest activities with produce should be of adequate sanitary quality. To address this new regulation for farmers who use surface water, LSU AgCenter researchers developed a new filtration system.
The new method uses a surfactant-modified zeolite, an aluminum-silicate mineral. The modified zeolite allows bacteria to attach to the surface, and the surfactant kills the bacteria. The modification is carried out by heating a mix of zeolite with a surfactant and then drying it.
To test the surfactant-modified zeolite’s ability to remove bacteria from irrigation water, a field test was conducted at the LSU AgCenter Botanic Gardens at Burden in Baton Rouge. The treatments were a control with no filtration system, a sand filtration system using agricultural sand and a sand filtration system with surfactant-modified zeolite. Surface irrigation water inoculated with generic E. coli was passed through a filter filled with 50 pounds of sand or through a surfactant-modified zeolite filter system composed of two filters, one with 50 pounds of sand and the other with 25 pounds of surfactant modified zeolite. The treated water was used to irrigate strawberries.
Once a month the water was spiked with the generic E. coli during the harvesting season of February, March and April for two years. Water samples were collected before and after each monthly treatment and tested for generic E. coli. Three samples were taken at each sampling point. Fruit samples were harvested when matured and tested for generic E. coli levels the first year.
The surfactant-modified zeolite filtration system significantly reduced the E. coli in the pond irrigation water compared to the control and sand treatment (Figure 1). The initial generic E. coli counts inoculated into the pond water were about 5 Log CFU E. coli counts per milliliter of irrigation water, and after filtration through the surfactant-modified zeolite filtration system, the E. coli counts ranged from 1.31 Log CFUI E. coli counts per milliliter of irrigation water to nondetectable levels over the two-year growing season. Generic E. coli counts for the inoculated irrigation water filtered through the sand were not significantly different from the control. After irrigation with the surfactant-modified, zeolite-treated pond water, E. coli counts on the strawberries were not significantly different from the control.
LSU AgCenter researchers developed a surfactant-modified zeolite filter system capable of reducing the risk associated with foodborne pathogens from irrigation water. Currently, most growers do not treat their surface irrigation water. The results from the on-farm study will provide growers with information to assess the potential benefits of using the surfactant-modified zeolite filtration system for pathogen risk reduction and comply with the proposed FSMA produce safety rule agricultural water requirements.
Jose L. Brandao Delgado is a former graduate student in the School of Nutrition and Food Sciences; Kathryn K. Fontenot is an associate professor and extension specialist in the School of Plant, Environmental, and Soil Sciences; Achyut Adhikari is an assistant professor and Marlene Janes is a professor in the School of Nutrition and Food Sciences.
(This article appears in the fall 2019 issue of Louisiana Agriculture.)
The Louisiana strawberry industry contributed $13.6 million to the state's economy in 2017, according to the LSU AgCenter Ag Summary.
Figure 1. E. coli counts of inoculated pond water after filtered through sand or surfactant-modified zeolite during field testing on strawberry plants.