Detection and Elimination of Salmonella Alfalfa Seeds by Treatment with Heat or Calcium Hypochlorite

Detection and Elimination of SalmonellaMbandaka from Naturally Contaminated Alfalfa Seeds by Treatment with Heat orCalcium Hypochlorite

March 2002
Journal of Food Protection: Vol. 65, No. 3, pp. 452­458.
Travor V. Suslow and Jiangchun Wu, Department of Vegetable Crops, One ShieldsAvenue, University of California, Davis, California 95616; William F. Fett, U.S.Department of Agriculture, Agricultural Research Service, Eastern RegionalResearch Center, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038; Linda J.Harris, Department of Food Science and Technology, One Shields Avenue,University of California, Davis, California 95616, USA

Salmonella Mbandaka led to a multistate outbreak of salmonellosis. In thisstudy, the implicated alfalfa seed lot (no. 8119) was confirmed to becontaminated with Salmonella Mbandaka at a detection frequency of approximately72% per replicated 100 g of seed. The sensitivity of detection was improved by acombination of nonselective and selective enrichment of 5.0 ml of germinationeffluent, followed by immunomagnetic separation. Detection of low levels ofviable cells with nonselective enrichment, employed to enhance the recovery ofstressed or injured cells, was facilitated by the application ofSalmonella-specific polymerase chain reaction (PCR). With PCR assays, SalmonellaMbandaka was detectable on seed stored at 5°C for at least 11 months, but at anincreasingly diminishing frequency. Using conventional techniques, viablepopulations were detected in the seed germination effluent from seeds stored forup to 8 months. Seed treatments with buffered (to pH 7) and unbuffered solutionsof calcium hypochlorite, providing approximately 2,000 and 20,000 ppm of freechlorine, for 10 min were equally effective in eliminating viable populations ofSalmonella Mbandaka. However, aqueous heat treatments at up to 85°C for 1 mindid not eliminate the naturally occurring contaminant from the seed. Reductionsof >15% in germination were observed following heat treatments of 65°C for 6min or 70°C for 4 min. On the basis of these results, aqueous heat treatmentsalone do not appear to be a viable alternative to hyperchlorination as aneffective method to eliminate Salmonella from alfalfa seed.