MINIMIZING SALMONELLA CONTAMINATION IN SPROUTS BY CONTROLLING THE GERMINATION TEMPERATURE

Since 1990, contaminated sprouts have been linked to at least 46 outbreaks and over 2,500 cases of illness in the US [13]. Unlike other ready-to-eat produce, sprouts pose a particular concern as the conditions that promote germination of their seeds also facilitate the growth of pathogens [6]. To address sprout’s propensity to microbial contamination, the U.S. Food and Drug Administration (FDA) has recommended that seeds destined for sprout production be disinfected with chemical sanitizers such as 20,000 ppm of calcium hypochlorite, Ca(OCl)2 [29]. However, this disinfectant often cannot completely eliminate pathogen that may be present in seeds [4, 23]; in which case, the surviving bacteria can re-grow to significant numbers during germination and cause severe illness upon consumption [45]. Therefore, maintaining control of the germination conditions to present the proliferation of pathogens is a crucial step in the overall approach to reduce microbial hazards in finished sprouts. This study examines the effects of temperature on the proliferation of Salmonella during germination, and how this temperature effect is influenced by factors such as pathogen load, seed-lot, and the presence or absence of chemical treatment with Ca(OCl)2 was also evaluated. Alfalfa seeds artificially inoculated with ~3 log CFU/g of Salmonella were used as the contaminated seeds. They were mixed at different levels (0.01, 0.1, 1.0, or 10.0% by weight) with 200g of non-contaminated seeds and then were allowed to germinate in glass jars for 3 or 5 days at 10, 20, or 30°C. The same experiment was repeated for the spiking seeds that were treated with 20,000 ppm Ca(ClO)2 for 15 min prior to sprouting. Sprout samples were taken from each jar daily and analyzed for the level of Salmonella ix by either plating on XLD plates or the three-tube most probable number method as described in the FDA BAM. The level of Salmonella increased during sprouting at all three temperatures and reached the highest level at 48h. Sprouting at 10°C yielded the least number of Salmonella when all other factors were controlled. At all spiking levels, or the percentage of seeds contaminated before sprouting, level of Salmonella increased during sprouting, and at 20°C and 30°C, the level of Salmonella reached to a similar level of 5 log CFU/g and 7 log CFU/g respectively. At 1.0% spiking level, the level of Salmonella increased by approximately 1.5, 4.0, and 6.0 log CFU/g in sprouts grown at 10, 20, and 30°C respectively. Difference in the level of microflora background between different seed lots did not appear to affect Salmonella proliferation during sprouting. Treatments with 20,000 ppm free chlorine in some cases lowered the levels of Salmonella to undetectable levels, while in other cases, it caused an approx. 3 log reduction in Salmonella count on seeds. The surviving ones could still proliferate during sprouting although with a delay and a much slower rate, and did not reach the maximal level at 48 h of sprouting. However, Ca(OCl)2 did not prevent the re-growth of Salmonella during germination. In conclusion, these results showed that sprouting temperatures do affect Salmonella proliferations. We recommend lowering the sprouting temperature in conjunction with chemical treatment of prior to sprouting seeds to reduce microbial hazards in sprouts.M.S. in Food Safety and Technology, December 201