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United States Department of Agriculture

Agricultural Research Service

2009 Annual Report

1a.Objectives (from AD-416)
Develop more effective means for decontaminating organic and conventionally grown fresh and minimally processed fruits and vegetables including sprout seed containing human pathogens to ensure food safety and security by assessing the efficacy of new and/or improved intervention technologies. Determine effectiveness of treatment combinations (multiple hurdle approach). Assess factors that might limit treatment efficacy. Transfer effective decontamination technology to the produce industry in order to reduce the risk of foodborne illness.

1b.Approach (from AD-416)
A variety of chemical, physical and biological intervention technologies will be evaluated. Physical and chemical treatments include the use of hot water pasteurization, ultrasound, gaseous chlorine dioxide, cold plasma, hydrogen peroxide vapor, and ionizing radiation alone or in combination. Conduct studies on the use of single or multiple isolates of antagonistic bacteria for inhibiting the outgrowth of bacterial human pathogens on sprouting seed and on sprouts postharvest. Determine the mode of action of effective antagonists. Scale up studies of effective interventions from laboratory scale to pilot plant scale. Investigate changes in composition and structure of indigenous microbial communities in relation to shelf life and hygienic quality of produce while in storage. Study the formation of biofilms by pathogens alone or in combination with native microflora on the surface of selected produce. Evaluate the effects of the various interventions on sensory and nutritional quality attributes, yield, physiology, and shelf-life to ensure acceptable quality of treated foods.

3.Progress Report
Project research determined that Salmonella can be effectively inactivated on sliced tomatoes with low doses of irradiation. It is also found that furan generation in fruits treated with irradiation is negligible for a wide range of fruit commodities. For certain acidic, high-sugar fruits such as pineapple and grape, furans were generated at only parts-per-billion levels when treated with exceptionally high irradiation doses (5 kGy). Research data generated by the Project was cited extensively by the US-FDA in an August 2008 regulatory action to allow the use of irradiation to improve the safety and shelf-life of iceberg lettuce and spinach. As a result, this ARS research was featured prominently in tech transfer media outreach activities via television, podcasts, radio, internet and newspaper articles. On May 27, 2009, Project scientists conducted a high-level briefing on ARS food irradiation research for a team of analysts from the Government Accountability Office, pursuant to a Congressional request.

Acidified sodium chlorite (ACS) is significantly more effective and safer than industry standard treatments. Improved protocols for ACS were able to reduce Salmonella by 99.9% on seeds used for sprouting. A biocontrol agent, Pseudomonas fluorescens 2-79, was successfully combined with ASC treatment, enhancing the suppression of Salmonella over either treatment alone. Together, the combination of chemical and biological treatments can suppress Salmonella to a level of clinical insignificance.

A new cold plasma generation technology has been developed which has the potential for in-package reductions of produce contaminating pathogens. Technological improvements have significantly enhanced the power and uniformity of the plasma fields. The pinboard corona discharge (PCD) system achieved 4 log reductions of Salmonella and E. coli O157:H7 with 10 second treatment times in vitro. Tests are ongoing with contaminated produce. This technology has the potential to be adapted to a conveyor-belt food processing system. Project research and leadership in the field of cold plasmas has resulted in two separate CRADAs (currently being finalized) with manufacturers of commercial plasma machinery.

Hot water surface pasteurization of artificially inoculated tomatoes was capable of reducing pathogenic bacteria by 6 logs. Results indicated that this process will enhancing the microbiological safety of tomatoes with no adverse effect on maturation process, and will extend the shelf life of this commodity as well

Chlorine dioxide gas treatment inactivated internalized pathogenic bacteria by at least 4 logs on tomatoes and at least 3 logs on mangoes within one hour of exposure. Optimization of this gaseous treatment for enhancing the microbial safety while maintaining sensory qualities is underway. Gaseous treatments will enhance the microbiological safety of these commodities. Reproducible inoculation protocol of mangoes with human pathogens is being finalized.

1. Irradiation improves produce safety: An antimicrobial process (a “kill step”) is urgently needed for fresh produce. Project research shows that low doses of irradiation can effectively inactivate Salmonella on sliced tomatoes. Furthermore, the generation of furan (a potential carcinogen) is shown to be negligible in most fruits treated with irradiation. For certain acidic, high-sugar fruits such as pineapple and grape, furans were generated only at low parts-per-billion levels, even when treated with exceptionally high irradiation doses (5 kGy). Project research data was cited repeatedly by US-FDA in a 2008 regulatory action approving irradiation as an effective means to improve the safety and shelf-life of iceberg lettuce and spinach. Extensive technology transfer of ARS research was accomplished via associated print and broadcast media outreach activities. This technology is one of the only true kill steps that can be applied to produce, and has the potential to dramatically reduce pathogen contamination of fresh fruits and vegetables.

2. New sanitizers made even more effective: Acidified sodium chlorite was shown to reduce Salmonella on sprouting seeds by 3 log units, significantly more effective than calcium hypochlorite. Optimized treatment protocols included extending treatment times up to 45 minutes and employing 800ppm concentrations. Significant advantages of acidified sodium chlorite are that it does not generate toxic (carcinogenic) compounds and its antimicrobial activity remains unaffected when making contact with organic materials. Combination treatments of acidified sodium chlorite plus exposure to a biological control agent (Pseudomonas fluorescens 2-79) for 2 min suppressed the growth of salmonellae to a level of clinical insignificance.

3. New anti-browning agent improves and quality and safety of fresh-cut apples: Fresh-cut apples are an increasingly popular snack food, but preparation can cause discoloration to apple tissues. Conventional anti-browning solutions can become contaminated with human pathogens such as Listeria monocytogenes, creating a health risk. Sodium acid sulfate (SAS) was compared with conventional anti-browning agents on Granny Smith apple slices. Project research showed that SAS was the most effective compound tested in inhibiting browning. SAS also suppressed microbial growth for 14 days. The information is useful for the fresh-cut produce industry to enhance microbial safety of fresh-cut apples while minimizing browning, and providing a healthy anti-obesity snack-food for consumers. This research is conducted under CRADA project 1935-41420-011-07N.

4. Thermal treatment yields safer tomatoes: Numerous outbreaks of salmonellosis have been associated with the consumption of fresh tomatoes contaminated with Salmonella. Commercial washing processes for tomatoes are limited in their ability to inactivate and/or remove this human pathogen. Development of hot water surface pasteurization process for enhancing microbiological safety of tomatoes is needed. Reductions in S. Poona populations on artificially inoculated tomatoes following treatments in water at 70C and 20 ppm chlorine solution were 99.999% and only 90%, respectively. These results indicate that surface pasteurization will enhance the microbiological safety of tomatoes with no adverse effect on maturation process, and will extend the shelf life of this commodity as well.

5. Gas-phase Chlorine Dioxide kills Salmonella on tomatoes: Previous reports from this laboratory indicated that gas-phase chlorine dioxide treatment of surface inoculated cantaloupes with Salmonella Poona was capable of inactivating in excess of 99.99% of the pathogen population. This led to the development and evaluation of chlorine dioxide gas treatment of artificially inoculated tomatoes. This gas treatment yielded in excess of 99.99% reductions in natural microflora and internalized pathogenic bacteria, maintained sensory qualities of this commodity. Currently, experimental protocols with industrial cooperator are being developed for validating this process under commercial production conditions.

6. Antimicrobial packaging for inactivation of E. Coli O157:H7 in apples: Apples can occasionally become contaminated by the pathogen E. coli O157:H7, leading to product recalls and foodborne illness outbreaks. Precision-formulated coatings were used to inactivate E. coli O157:H7 on the surfaces of apples. Antimicrobial compounds, singly and in combinations, were incorporated into coatings and applied as micro-droplets to the apple surface. The coatings inactivated more than 99.99 percent of E. coli O157:H7 on apples. The antimicrobial coating has the potential to reduce product recalls and foodborne illness outbreaks due to contamination by E. coli O 157:H7.

6.Technology Transfer

Number of Active CRADAs2
Number of Other Technology Transfer3

Review Publications
Keskinen, L.A., Todd, E., Ryser, E. 2008. Impact of bacterial stress and biofilm forming ability on transfer of surface-dried listeria monocytogenes during slicing of delicatessen meats. International Journal of Food Microbiology. 127:298-304.

Liao, C. 2009. Control of foodborne pathogens and soft-rot bacteria on bell pepper by three strains of bacterial antagonists. Journal of Food Protection. 72(1):85-92.

Annous, B.A., Fratamico, P.M., Smith, J.L. 2009. Quorum Sensing in Biofilms: Why Bacteria Behave the Way They Do. Journal of Food Science. 74(1):R24-R37.

Niemira, B.A. 2008. Irradiation Compared with Chlorination for Elimination of Escherichia Coli O157:H7 Internalized in Lettuce Leaves: Influence of Lettuce Variety. Journal of Food Science. 73(5):M208-M213.

Fan, X., Sokorai, K.J. 2008. Retention of Quality and Nutritional Value of Thirteen Fresh-cut Vegetables Treated with Low Dose Radiation. Journal of Food Science. 73(7):S367:S372.

Fan, X., Huang, L., Sokorai, K.J. 2008. Factors Affecting Thermally Induced Furan Formation. Journal of Agricultural and Food Chemistry. 56:9490-9494.

Keskinen, L.A., Burke, A.M., Annous, B.A. 2009. Efficacy of chlorine, acidic electrolyzed water and aqueous chlorine dioxide solutions to decontaminate Escherichia coli O157:H7 from lettuce leaves. International Journal of Food Microbiology. 132:134-140.

Liao, C. 2009. Acidified sodium chlorite as an alternative to chlorine for elimination of Salmonella on alfalfa seeds. Journal of Food Science. 74(4):M159-164.

Niemira, B.A., Fan, X. 2006. LOW-DOSE IRRADIATION OF FRESH AND FRESH-CUT PRODUCE: SAFETY, SENSORY AND SHELF LIFE. IN: Sommers, C., Fan, X., editors. Food Irradiation Research and Technology. Blackwell Publishing. p. 169-184.

Niemira, B.A., Zhang, H.Q. 2009. Advanced Technologies for Detection and Elimination of Pathogens. In: Sapers, G., Solomon, E., Matthews, K., editors. The Produce Contamination Problem — Causes and Solutions. Elsevier. 425-443.

Rajkowski, K.T. 2009. Percent Moisture and Seed Coat Characteristics of Alfalfa Seeds After Artificial Inoculation. Journal of Food Safety. 224-235.

Last Modified: 12/1/2015
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