Skip to main content
ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Research Project #430368

Research Project: Characterization and Mitigation of Bacterial Pathogens in the Fresh Produce Production and Processing Continuum

Location: Environmental Microbial & Food Safety Laboratory

2018 Annual Report

4. Accomplishments
1. Spinach microbiota shifts following chlorine wash and storage at compliant and abusive temperatures. The microbial communities on fresh produce and in the processing environments could have profound effects on the growth and persistence of foodborne pathogens. Spinach samples were taken from a commercial fresh-cut processing facility and the microbiota compared before and after commercial washing in chlorinated water. Microbiota were also compared after storage in compliant (4 degrees Celsius) and abusive (10 and 15 degrees Celsius) temperatures. These analyses provided information regarding the dynamics of microbial populations during fresh-cut produce processing and storage. The information on the changes of the microbiota composition during chlorine washing and on microbiota restoration during storage is useful for developing antimicrobial intervention strategies and understanding the consequences of noncompliance with processing and storage standards.

2. Microbiological quality of spinach irrigated with reclaimed waste water and roof-harvest water. Water scarcity is a serious issue and alternative water, such as reclaimed (reused) wastewater and roof-harvest water, may help overcome the scarcity of water while maintaining food security and food safety. Spinach grown in a controlled environment chamber was irrigated with alternative water for four weeks, and then spinach samples were collected weekly and analyzed for bacterial populations. A single irrigation with alternative water containing higher populations of total and fecal coliform bacteria did not necessarily result in higher populations of the coliform bacteria on spinach leaves; however, repeated irrigation with reclaimed wastewater resulted in higher numbers of E. coli positive spinach samples. Pathogens were not detected from any water or spinach samples under this investigation. Irrigation waters containing higher populations of total and fecal coliforms did not necessary result in higher populations of these bacteria on the spinach leaves. Repeated irrigation with reclaimed wastewater resulted in higher numbers of (nonpathogenic) E. coli positive spinach samples. Roof-harvest water had higher microbial quality than the reclaimed wastewater. Roof-harvest water irrigation did not increase the populations of fecal bacterial indicators on the irrigated spinach plants. The results show the potential use of roof-harvest water for irrigation of spinach without affecting the microbiological quality of the spinach.

3. The microbial quality of alternative irrigation waters. The availability of water for crop irrigation is decreasing due to droughts, population growth, and pollution. Implementation of the Food Safety and Modernization Act governing irrigation water standards discourages growers from using poor microbial quality water for produce crop irrigation. A method was evaluated to determine the microbial quality of wastewater, rainwater, and creek water in comparison to the membrane filtration method. No significant differences were observed concerning bacterial populations and pathogens. Recovery of fecal coliform bacteria in wastewater was lower than that found in filtered water samples. The study provides the microbial quality of non-traditional irrigation waters.

4. Proteomic of Staphylococcus aureus exposed to plant-derived antimicrobials. Consumers’ preference for less chemicals in food has led researchers to explore natural antimicrobials to control foodborne bacteria. ARS scientists in Beltsville, Maryland, determined that punicalgins (plant derived antimicrobial substances) disrupted multiple bacterial cellular functions and inhibited bacterial growth of Staphylococcus aureus bacteria. This information is useful for understanding the functions of natural antimicrobials on potential foodborne pathogens.

5. Safe and effective water reuse. Reusing and reducing fresh-cut vegetable wash water is needed for sustained industry growth and a reduced environmental footprint. However, organic matter accumulated in reused wash water can lead to a loss of antimicrobial efficacy for chlorine disinfectant thus compromising the quality and safety of the washed products. ARS scientists in Beltsville, Maryland, identified that proteins and peptides are the major contributors to the loss of chlorine efficacy, and that sugars are important for developing effective wash water treatment and recycling programs. These findings will help vegetable processors develop safe, effective, and economical chlorine replenishment strategies and wash water reuse programs.

6. Essential oils control bacterial pathogens on fresh herbs. The demand for fresh herbs has increased in recent years due to health benefits and their distinct aroma in prepared food. Fresh herbs contaminated with shiga-toxigenic Escherichia coli and Salmonella bacterial species are associated with foodborne illnesses. Plant-based essential oils were evaluated on fresh herbs (basil, cilantro, dill, parsley, and tarragon) for their antimicrobial activities against Salmonella and E. coli. Treatments with specific concentrations of carvacrol or cinnamaldehyde killed E. coli and Salmonella on fresh herb leaves. There was no visual difference in herbs treated at lower concentrations of cinnamaldehyde or carvacrol. Results indicate use of novel, natural antimicrobials to kill E. coli and Salmonella without affecting the color attributes of fresh herbs.

7. Contamination of Listeria monocytogenes on cantaloupes at the packinghouse. Listeria monocytogenes is a bacterial pathogen which caused a large outbreak in 2011 was associated with contaminated cantaloupes. Research showed that packing house surfaces and equipment (nylon brushes, conveyor belts, foam pads) with cantaloupe juice on their surfaces supported increased survival of L. monocytogenes. Surfaces were also assessed for their ability to contaminate multiple cantaloupes. Foam surfaces contaminated more cantaloupes than conveyor belt surfaces (polyvinyl chloride, polyurethane, nitrile rubber). The study highlights the importance of plant sanitation and equipment design in controlling L. monocytogenes.

8. Rapid method to determine free chlorine levels in wash water during commercial-scale washing of fresh-cut produce. Substances released into the water during washing of the cut produce with the chlorine, sanitizer and reduce its efficacy. Maintenance of the level of free chlorine, a form that can interact with contaminants, is critical to avoid cross-contamination from bacteria during commercial-scale washing of fresh-cut produce. Controlling the sanitizer levels needed in fresh-cut produce wash water could improve if the chlorine demand is known in real-time. ARS scientists in Beltsville, Maryland, developed a rapid method using ultraviolet light absorbance to estimate chlorine demand for produce wash conditions. Ultraviolet light absorbance of the wash water was measured at two wavelengths. Based on these measurements, a predictive model for chlorine demand was developed and tested. The method shows promise for real-time application during commercial-scale washing of fresh-cut produce.

Review Publications
Luo, Y., Zhou, B., Van Haute, S., Nou, X., Zhang, B., Teng, Z., Turner, E.R., Wang, Q., Millner, P.D. 2017. Association between bacterial survival and free chlorine concentration during commercial fresh-cut produce wash operation. Food Microbiology. 70:120-128.

Park, E., Luo, Y., Marine, S.C., Everts, K.A., Micallef, S.A., Bolten, S.J., Stommel, J.R. 2018. Consumer preference and physicochemical evaluation of organically grown melon. Postharvest Biology and Technology. 141:77-85.

Mei, L., Teng, Z., Zhu, G., Liu, Y., Zhang, F., Li, Y., Guan, Y., Luo, Y., Chen, X., Wang, Q. 2017. Advanced materials interfaces. ACS Applied Materials and Interfaces. 9(40):3529-3530.

De Frias, A.J., Luo, Y., Zhou, B., Turner, E.R., Millner, P.D., Nou, X. 2018. Minimizing pathogen growth and quality deterioration of packaged leafy greens by maintaining optimum temperature in refrigerated display cases with doors. Food Control. 92:488-495.

Lu, Y., Dong, W., Yang, T., Luo, Y., Wang, Q., Chen, P. 2017. Effect of preharvest CaCl2 spray and postharvest UV-B radiation on storage quality of broccoli microgreens, a richer source of glucosinolates. Journal of Food Composition and Analysis. 67(1):55-62.

Gu, G., Ottesen, A., Bolten, S.J., Ramachandran, P., Reed, E., Rideout, S., Luo, Y., Patel, J.R., Brown, E., Nou, X. 2018. Shifts in spinach microbial communities after chlorine washing and storage at compliant and abusive temperatures. Food Microbiology. 73:73-84.

Teng, Z., Luo, Y., Alborzi, S., Zhou, B., Chen, L., Zhang, J., Zhang, B., Millner, P.D., Wang, Q. 2017. Investigation on chlorine-based sanitization under stabilized conditions in the presence of organic load. International Journal of Food Microbiology. 67:150-157.

Zhou, B., Luo, Y., Bauchan, G.R., Feng, H., Stommel, J.R. 2017. Visualizing pathogen internalization pathways in fresh tomatoes using MicroCT and confocal laser scanning microscopy. Food Control. 85:276-282.

Cooper, B., Isalm, N., Xu, Y., Beard, H.S., Garrett, W.M., Gu, G., Nou, X. 2018. Quantitative proteomic analyses of Staphylococcus aureus treated with punicalagin, a natural antibiotic from pomegranate that disrupts iron homeostasis and induces SOS. Proteomics. 18:1700461.

Patel, J.R., Keelara, S., Green, J.A. 2018. Inactivation of Escherichia coli O157:H7 and Salmonella on fresh herbs by plant essential oils. Foodborne Pathogens and Disease. 15(6):1-7.

Hsin-Bai, Y., Patel, J.R. 2018. Comparison of methods to determine the microbial quality of alternative irrigation waters. Agricultural Water Management. 201:38-45.

Hsin-Bai, Y., Nou, X., Patel, J.R., Gu, G. 2018. Microbiological quality of spinach irrigated with reclaimed wastewater and roof-harvest water. Journal of Applied Microbiology.