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United States Department of Agriculture

Agricultural Research Service

2007 Annual Report

1a.Objectives (from AD-416)
(1) Develop rapid and sensitive methods for detection of enteric human pathogens and spoilage bacteria from conventional and organically grown produce, (2) Develop effective postharvest sanitizing procedures providing improved antimicrobial activity while maintaining produce quality and shelf-life, (3) Understand the ecology and mechanisms that allow specific human and spoilage microorganisms to persist on fresh produce and develop control agents to reduce food safety risks.

1b.Approach (from AD-416)
We will design experiments to optimize rapid, real-time PCR-based microbial detection methods for enteric human pathogens and also assess the application of similar methods for spoilage bacteria on fresh and fresh-cut produce. Because of the high organic load in produce wash water, sanitizer applications approved for fresh and fresh-cut preparation often do not provide effective control of human pathogens or may cause adverse effects on produce quality and shelf-life. Sanitation and wash procedures that are more effective in the presence of a high organic load would be developed. We will identify gene families from human pathogens involved in resistance to sanitation agents as well as stress-tolerance which could be used as ‘targets’ to design novel food sanitation agents. We will develop effective Biocontrol agents such as bacteriophages, yeasts and lactic acid bacteria to enhance food safety by limiting human pathogens on fresh-cut produce without affecting its quality or shelf-life.

3.Progress Report
Optimization of a DNA preparation method suitable for real-time PCR. Detection of enteric human pathogens on produce at low levels (approaching ~ 1-10 cells per 25 g) can not be accurately and rapidly accomplished using current microbiological methods approved by the USDA. Molecular detection methods such as real-time PCR require high quality DNA preparations which are free of inhibitors of plant origin. We developed a simpler and better DNA isolation protocol in order to free bacterial DNA of plant phenolic and other inhibitory compounds, which facilitated the detection of pathogens at low levels. The protocol was optimized for DNA isolation especially for ‘in-field’ conditions, i.e., minimal laboratory equipment, less need for hands-on manipulation and ambient storage temperatures. Detection of Salmonella spp. and Listeria monocytogenes was possible in a high-throughput manner from a variety of produce such as broccoli, alfalfa sprouts, mixed salad and lettuce. The improved DNA isolation protocol will directly help Hazard Analysis Critical Control Point (HACCP) program development and monitoring human pathogens on fresh produce.

Analysis of fresh-cut preparation methods for potential microbial contamination. Coring iceberg lettuce in the field is a new technology that has significantly improved the production yield and reduced shipping cost. However, no scientific studies have been reported on the potential of E.coli O157:H7 contamination during field procedures and the effect of field conditions on the survival and growth of E.coli O157:H7 on pre-cored lettuce. We evaluated the potential for pathogen transfer during coring process and demonstrated that E.coli O157:H7 can be readily transferred from contaminated coring knives to the edible portion of lettuce; also, a 4-hour exposure of cored lettuce to 30 °C ambient environment significantly increased E.coli populations on lettuce. Our results provide critical information for the development and implementation of Good Agricultural Practice (GAP) and Hazardous Analysis and Critical Control Point (HACCP) by the FDA and produce industry.

Improved sanitizer efficacy for microbial safety of fresh-cut produce.

The control of the growth of disease-causing microorganisms and the enzymatic browning reaction on the cut-surface of apple slices is critical to maintaining the safety and quality of fresh-cut produce. We demonstrated and optimized the utility of a chemical compound, sodium chlorite, that has the potential to control both the browning reaction and pathogen growth for a variety of fresh-cut produce, including apples, pears, and lettuce, etc. This information is very useful for the development of dual control agents and to solve the current challenges facing the industry due to the incompatibility between browning inhibitors (reducing agents) and most sanitizers (oxidants) used commercially. We also found that an ultra sound technology significantly improved the efficacy of various sanitizers, including chlorine and acidified sodium chlorite, on pathogen reduction on spinach. Both the consumers and fresh-cut produce industry will benefit from the results of this research. This research fulfills a top ARS food safety research priority requested by the produce industry. This research is under National Program 108, Section 2.4.1.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of new CRADAs and MTAs1
Number of active CRADAs and MTAs3
Number of non-peer reviewed presentations and proceedings7
Number of newspaper articles and other presentations for non-science audiences3

Review Publications
Zhang, Y., Emily, Y., Cripe, J., Hall, G., Bhagwat, A.A., Meng, J. 2007. Characterization of listeria monocytogenes isolated from retail food. International Journal of Food Microbiology. 113:47-53.

Sharma, M., Kniel, K., Derevianko, A., Ling, J., Bhagwat, A.A. 2007. Sensitivity of Escherichia albertii, a potential foodborne pathogen, to food preservation treatments. Applied and Environmental Microbiology. 73(13):4351-4353.

Wang, H., Feng, H., Luo, Y. 2006. The effect of acidic electrolyzed water and peroxyacetic acid on reduction of escherichia coli o157:h7 populations on fresh-cut apples. Journal of Food Safety. 26:335-347.

Wang, H., Feng, H., Luo, Y. 2007. Control of browning and microbial growth on fresh-cut apples by sequential treatment of sanitizers and calcium ascorbate. Journal of Food Science. 72:M1-M7.

Kim, J., Lim, C., Luo, Y. 2007. Effect of ozonated water and chlorine water wash on the quality and microbial de-contamination of fresh-cut carrot shreds. Korean Journal of Food Preservation. 14(1):54-60.

Lu, S., Luo, Y., Turner, E.R., Feng, H. 2007. Efficacy of sodium chlorite as an inhibitor of enzymatic browning in apple slices. Journal of Food Chemistry. 104:824-829.

Zhu, B., Lu, J., Luo, Y., Tao, Y. 2007. Gabor feature-based apple quality inspection using kernel principal component analysis. Journal of Food Engineering. 81(4):741-749.

Ruiz-Cruz, S., Luo, Y., Gonzalez, R., Tao, Y., Gonzalez, G. 2006. Effect of acidified sodium chlorite applications on microbial growth and the quality of shredded carrots. Journal of the Science of Food and Agriculture. 86(12):188-1893.

Last Modified: 4/25/2014
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