Efficacy of chlorine and heat treatment in killing Salmonella stanley inoculated onto alfalfa seeds and growth and survival of the pathogen during sprouting and storage

Abstract

The efficacy of chlorine and hot water treatments in killing Salmonella stanley inoculated onto alfalfa seeds was determined. Treatment of seeds containing 102 to 103 CFU/g in 100-μg/ml active chlorine solution for 5 or 10 min caused a significant (P ≤ 0.05) reduction in population, and treatment in 290-μg/ml chlorine solution resulted in a significant reduction compared with treatment in 100 μg of chlorine per ml. However, concentrations of chlorine of up to 1,010 μg/ml failed to result in further significant reductions. Treatment of seeds containing 101 to 102 CFU of S. stanley per g for 5 min in a solution containing 2,040 μg of chlorine per ml reduced the population to undetectable levels (<1 CFU/g). Treatment of seeds in water for 5 or 10 min at 54°C caused a significant reduction in the S. stanley population, and treatment at ≤57°C reduced populations to ≤1 CFU/g. However, treatment at ≤54°C for 10 min caused a substantial reduction in viability of the seeds. Treatment at 57 or 60°C for 5 min appears to be effective in killing S. stanley without substantially decreasing germinability of seeds. Storage of seeds for 8 to 9 weeks at 8 and 21°C resulted in reductions in populations of S. stanley of about 1 log10 and 2 log10 CFU/g, respectively. The behavior of S. stanley on seeds during soaking, germination, sprouting, and refrigerated storage of sprouts was determined. An initial population of 3.29 log10 CFU/g increased slightly during 6 h of soaking, by about 103 CFU/g during a 24-h germination period, and by an additional 10 CFU/g during a 72-h sprouting stage. A population of 107 CFU/g of mature alfalfa sprouts was detected throughout a subsequent 10- day storage period at 5°C. These studies indicate that while populations of S. stanley can be greatly reduced, elimination of this organism from alfalfa seeds may not be reliably achieved with traditional disinfection procedures. If S. stanley is present on seeds at the initiation of the sprout production process, populations exceeding 107 CFU/g can develop and survive on mature sprouts exposed to handling practices used in commercial production and marketing.