Evaluation of a GRAS Sanitizer for Enhanced Microbial Safety and Shelf-life of Whole Tomatoes for ISS and Planetary Outpost 2004-01-2560

The successful incorporation of fresh fruit and vegetables in the diet of astronauts in space would require that these products are free of foodborne pathogens and retain desirable quality characteristics during storage. This study evaluated 200 or 500 ppm sodium hypochlorite, 5% (w/v) hydrogen peroxide (H₂O₂); and 1% (w/v) PRO-SAN™, a biodegradable foodgrade sanitizer, for inactivating pathogenic bacteria on whole tomatoes and improving the shelf-life of these products. Tomatoes were inoculated with a 5-strain mixture of nalidixic-acid-resistant Escherichia coli O157:H7 or Salmonella spp ( ∼ 10⁸ CFU/tomato) to facilitate selective isolation of the pathogens from inoculated tomatoes without interference from the natural microflora. The inoculated tomatoes were immersed for 4 min in distilled water (control) or in each sanitizer at ambient temperature (23°C) then rinsed for 5 s in fresh distilled water. Some of the treated tomatoes (non-rinsed) were stored at 23°C for 8 days. Viable pathogens on tomatoes were evaluated immediately after treatment and at set intervals during storage. Non-inoculated tomatoes were exposed to basically the same treatments then subjected to visual, chemical, and physical analyses at set intervals during storage at ambient temperature.

PRO-SAN consistently reduced initial populations of each pathogen on tomatoes by more than 3 log cycles. Log reductions from washing tomatoes with water, sodium hypochlorite and H₂O₂ ranged from 1.60 to 2.37 for Salmonella and 1.07 to 2.79 for E. coli O157:H7. Populations of Salmonella survivors on tomatoes remained relatively constant during storage; however, significant decreases in E. coli occurred only on PRO-SAN-treated tomatoes at day 8 of storage (P<0.05). PRO-SAN decreased the percentage of tomatoes spoiled during storage compared to water, H₂O₂, and sodium hypochlorite. There were no significant differences in color of tomatoes treated with water or with the sanitizers tested in this study (P≥ 0.05). The use of 1% PRO-SAN at 23 °C seems to have good potential for enhancing the microbial safety and shelf-life of tomatoes.