Progress 10/01/97 to 09/30/03
Tests with a simulated, scale model flume confirm that chlorinated water (150 to 200 ppm, pH 6.0 to 7.0, 24 C) will prevent cross contamination (movement of bacterial cells or fungal spores from a source to potential infection courts such as wounds). Hydrogen peroxide (27 ppm), peroxyacetic acid (80 ppm) and solutions of chlorine dioxide (5 ppm) did not prevent cross contamination. Gas phase chlorine dioxide was more effective in preventing decay development at inoculated wounds than were 30-sec washes in chlorinated water (100 ppm, pH 6.5). The cardboard of standard tomato boxes was a significant sink in gas phase chlorine dioxide treatments.
Water chlorination remains the best way to achieve sanitation in water handling systems in tomato packinghouses. The proposed alternatives to chlorine were not effective.
- Lukasik, J., Bradley, M. L., Scott, T. M., Dea, M., Koo, A., Hsu, W.-Y., Bartz, J. A., and Farrah, S. R. 2003. REDUCTION OF POLIOVIRUS 1, BACTERIOPHAGES, SALMONELLA MONTEVIDEO, AND ESCHERICHIA COLI O157:H7 ON STRAWBERRIES BY PHYSICAL AND DISINFECTANT WASHES. J. Food Protection 66:188-193.
- Bartz, J. A. 1999. Washing fresh fruits and vegetables: lessons from treatment of tomatoes and potatoes with water. Dairy, Food and Environmental Sanitation. 19:853-864.
- Vigneault, C.*, Bartz, J. A. and Sargent, S. A. 2000. Postharvest decay risk associated with hydrocooling tomatoes. Plant Dis. 84:1314-1318.
- Bartz, J. A., Eayre, C. G., Mahovic, M. J., Concelmo, D. E., Brecht, J. K., and Sargent, S. A. 2001. Chlorine concentration and the inoculation of tomato fruit in packinghouse dump tanks. Plant Dis. 85:885-889. Bartz, J. A., Mahovic, M., and Concelmo, D. 2001. Rapid movement of inoculum into wounds on tomato fruit. (Abstract) Phytopathology 91:S6.
- Bartz, J. A. 2002. Chemical control of foodborne human pathogens. (Abstract) Phytopathology 92:S99
- Bartz, J. A., Schneider, K., Sargent., S. and Felky, K. 2002. Addressing microbial hazards in tomato fruit after harvest. Proc. 2002 Florida Tomato Inst. p. 21-23.
Progress 10/01/01 to 10/01/02
Dry chlorine dioxide produced within an enclosed chamber prevented the development of bacteria soft rot at inoculated wounds on tomato fruit. Most treated wounds were free of viable soft rot bacteria. When similar wounds were washed for 2 min in 100 ppm free chlorine at pH 7.0, nearly 80% became diseased. The chlorine dioxide also reduced sour rot development when wounds were inoculated with Geotrichum candidum and Rhizopus rot when wounds were inoculated with Rhizopus stolonifer. Peroxycetic acid at 80 ppm killed G. candidum spores (4 log reduction) within 30 sec when solutions were warmed to 40 C, but were not completely effective within 2 min when solutions were at room temperature.
Completion of the project is expected to lead to two additional hurdles for controlling fruit contamination, e.g. wash with peroxyacetic acid or acidified sodium chlorite and then treat packaged fruit with dry chlorine dioxide gas.
- No publications reported this period
Progress 10/01/00 to 10/01/01
When a water-soluble dye was placed on fresh wounds on tomatoes (section of peel removed with a scalpel), color framed cells at the wound surface within seconds. At edges of the treated area, dye was observed in intercellular areas below the wound surface. The dye could not be completely removed from the tissues by rinse with tap-water or 1% sodium hypochlorite. When wounded tomatoes were immersed briefly in a suspension of Erwinia carotovora subsp. carotovora and then immediately washed for 2 min in water or 100 ppm free chlorine (pH 6.0, 27 degrees C), the incidence of bacteria soft rot averaged 77, 48, or 20% in the control, tap water or chlorine treatments, respectively. When wounded tomatoes were moistened by immersion in a suspension of E. carotovora subsp. carotovora, allowed to drip dry for 30 min and then washed for 2 min with up to 800 ppm free chlorine (pH 6.0, 27 degrees C), incidence averaged 67 % among the control fruit and 57% among the chlorine treated
fruit. Wound surfaces that were mechanically rubbed or brushed during the chlorine wash developed as much decay as those not mechanically treated. When fresh wounds on tomato fruit contact soft rot bacteria, inoculum quickly moves into intercellular spaces, which includes areas that are physically inaccessible to a surface sanitizer.
The rapid movement of bacteria into the intercellular spaces of cells below the surface of fresh wounds on tomatoes indicates why surface sanitizers such as chlorine are ineffective when used after the wound is inoculated. Therefore, wound contamination much be prevented.
- Bartz, J. A., Eayre, C. G., Mahovic, M. J., Concelmo, D. E. Brecht, J. K., and Sargent, S. A. 2001. Chlorine Concentration and the Inoculation of Tomato Fruit in Packinghouse Dump Tanks. Plant Dis: 85:885-889.
- Bartz, J. A., Mahovic, M. and Concelmo, D. 2001. Rapid movement of inoculum into wounds on tomato fruit. (Abstr) Phytopathology 91:S6.
Progress 10/01/99 to 09/30/00
Tomatoes hydrocooled with a cell suspension of Erwinia carotovora subsp. carotovora containing 50 to 200 ppm free chlorine (10 C, pH 7) remained disease free during a 10-day storage at 20 C. Sporadic disease (5 to 20% incidence) developed among similarly stored fruit that had been cooled in a suspension of spores of Rhizopus stolonifer. By contrast, control fruit cooled in the pathogen suspensions alone developed 50 to 100% disease. Fruit shower hydrocooled with stem scars upward absorbed more water than those similarly cooled with stem scars oriented downward. Tomatoes may be shower hydrocooled without risking postharvest decay if 150 to 200 ppm free chlorine is maintained in the water. These chlorine concentrations were not associated with phytotoxicity and did not affect fruit quality.
Addition of chlorine to the water enables use of hydrocooling, the most efficient method of cooling tomatoes. The cooling fruit absorbed some water but did not internalize viable decay pathogens.
- Vigneault, C., Bartz, J. A., and Sargent, S. A. 2000. Postharvest decay risk associated with hydrocooling tomatoes. Plant Dis. 84:1314-1318.
Progress 10/01/98 to 09/30/99
When several postharvest pathogens including Erwinia carotovora, Rhizopus stolonifer, Geotrichum candidum, and Penicillium digitatum, were exposed to two oxidizing chemicals, hypochlorous acid and acidified sodium chlorite, determination of efficacy was complicated by significant recovery from injury. The exposed microbes would grow out 24 or 48 hrs after the untreated checks, evidence for recovery from injury. The recovered cells were fully pathogenic in host fruits. Kasugamycin, an antibiotic used for crop protection, delayed or prevented the development of bacterial soft rot in freshly injured potato tuber tissues.
Optimization of the sanitation of dump tanks,flumes, and packing lines is necessary to prevent postharvest decays as well as to reduce biological hazards in products normally consumed raw. Kasugamycin could help prevent seed-piece decay in potatoes when warm wet soils are planted.
- Bartz, J.A. 1999. Suppression of bacterial soft rot in potato tubers by application of kasugamycin. Amer. J. of Potato Res. 76:127-136.
- Bartz, J.A. 1999. Washing fresh fruits and vegetables with emphasis on tomatoes and potatoes. Dairy, Food and Environmental Sanitation 19:(December issue)
Progress 10/01/97 to 09/30/98
Treatment of freshly injured potato tubers with kasugamycin immediately prior to or after inoculation with Erwinia carotovora delayed the onset of bacterial soft rot by up to 4 days depending on tuber temperature. The delay was longer than that resulting from immersion in 500 ppm free chlorine. Treatment efficacy was reduced by the addition of a nonionic surfactant either to the injured surface or antibiotic solution. The treatment was not effective when used on whole tubers from storage. Increased initial inoculum decreased treatment efficacy. However, pretreatment of tubers with chlorine did not reliably inhance the efficacy of kasugamycin. Forced-air cooling of freshly harvested and then washed tubers from 30 to 18 C prevented soft rot for up to 4 days, whereas up to 30% of the tissues on control tubers were decayed within 24 hrs. Treatment with 200 ppm chlorine or 80 ppm peroxyacetic acid acid reduced by half the amount of decay that developed on control tubers.
- Bartz, J. A. 1998. Suppression of bacterial soft rot in potato tubers by application of kasugamycin. Am. Potato J. (accepted for publication).