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| | Detection and Elimination of Salmonella
Mbandaka from Naturally Contaminated Alfalfa Seeds by Treatment with Heat or
Calcium Hypochlorite
March 2002
Journal of Food Protection: Vol. 65, No. 3, pp. 452458.
Travor V. Suslow and Jiangchun Wu, Department of Vegetable Crops, One Shields
Avenue, University of California, Davis, California 95616; William F. Fett, U.S.
Department of Agriculture, Agricultural Research Service, Eastern Regional
Research 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
Abstract
Salmonella Mbandaka led to a multistate outbreak of salmonellosis. In this
study, the implicated alfalfa seed lot (no. 8119) was confirmed to be
contaminated with Salmonella Mbandaka at a detection frequency of approximately
72% per replicated 100 g of seed. The sensitivity of detection was improved by a
combination of nonselective and selective enrichment of 5.0 ml of germination
effluent, followed by immunomagnetic separation. Detection of low levels of
viable cells with nonselective enrichment, employed to enhance the recovery of
stressed or injured cells, was facilitated by the application of
Salmonella-specific polymerase chain reaction (PCR). With PCR assays, Salmonella
Mbandaka was detectable on seed stored at 5°C for at least 11 months, but at an
increasingly diminishing frequency. Using conventional techniques, viable
populations were detected in the seed germination effluent from seeds stored for
up to 8 months. Seed treatments with buffered (to pH 7) and unbuffered solutions
of calcium hypochlorite, providing approximately 2,000 and 20,000 ppm of free
chlorine, for 10 min were equally effective in eliminating viable populations of
Salmonella Mbandaka. However, aqueous heat treatments at up to 85°C for 1 min
did not eliminate the naturally occurring contaminant from the seed. Reductions
of >15% in germination were observed following heat treatments of 65°C for 6
min or 70°C for 4 min. On the basis of these results, aqueous heat treatments
alone do not appear to be a viable alternative to hyperchlorination as an
effective method to eliminate Salmonella from alfalfa seed.
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