Purpose: Examine whether the contamination level on seeds affects the extent of Salmonella proliferation during sprouting of seeds treated with 20,000 ppm Ca(OCl)2, and determine how pathogen proliferation may be minimized by adjusting sprouting conditions (irrigation frequency, sprouting temperature, and irrigation with chlorinated water).
Methods: 1200 g of alfalfa seeds spiked with 1 % of inoculated seeds that contain ~ 1 - 5 log CFU/g of Salmonella were treated with 20,000 ppm Ca(OCl)2 for 15 min. The treated seeds were germinated either in a glass jar or in an automatic sprouter (EasyGreen®) for 3-5 days at room temperature (~22°C) or 30°C, and irrigated with tap water or water containing 100 ppm of sodium hypochlorite at different frequencies (once every 2, 4 or 24 hours). Sprouts samples were taken daily and analyzed for Salmonella, either by plating on XLD or by the three-tube MPN method described in FDA BAM.
Results: For seeds with a low contamination level (~ -1 log CFU/g), treatment with 20,000 ppm Ca(OCl)2 lowered the level of Salmonella by > 2 log units to an undetectable level. No Salmonella growth was observed during 5 days of sprouting, regardless of whether the sprouts were irrigated with tap water or chlorinated water. For seeds with a high contamination level (~1 log CFU/g), the Salmonella level was also reduced by ~2 logs after seed treatment; however, the level in sprouts increased significantly under all sprouting conditions. Germination in glass jars at 30°C resulted in the greatest Salmonella growth (by ~5 log CFU/g). For sprouts grown at room temperature, irrigation with chlorinated water did not prevent Salmonella proliferation.
Significance: Seed treatments with 20,000 ppm Ca(OCl)2 have the potential to reduce pathogen load on seeds to levels low enough such that re-growth does not occur. Adjusting sprouting conditions especially temperature could reduce pathogen proliferation during sprouting.