Assessment of the Potential for Listeria Monocytogenes in Alfalfa Sprouts

Assessment ofthe Potential for Listeria monocytogenes Survival and Growth duringAlfalfa Sprout Production and Use of Ionizing Radiation as a PotentialIntervention Treatment

Nicholas P.Schoeller; Steven C. Ingham; Barbara H. Ingham

Journal of FoodProtection      Volume: 65 Number: 8 Page: p1259 –p1266

InternationalAssociation for Food Protection

Abstract: Alfalfa seeds (Australian, nondormant,nonscarified) were treated with 20,000 ppm active chlorine, sprouted in canningjars for 5 days, and packaged and stored at 5°C for up to 9 days. Seeds orsprouts were inoculated with a three-strain cocktail of Listeriamonocytogenes at one of three points during the process – day 0 (before 24-haqueous seed soak), day 1 (after 24-h aqueous seed soak), or day 5 (aftersprouting, before prepackaging 10 ppm chlorine rinse) – or control (no inoculum),and the ability of the inoculum to survive and grow was evaluated. Totalbacterial numbers on uninoculated seeds increased dramatically during the first24 h the seeds were soaked; from 3.5 to ca. 8.0 log CFU/g, and remained at thislevel during refrigerated storage. When the seeds were inoculated with acocktail of L. monocytogenes (log 5 CFU/10 ml) on day 0 or 1, thepopulation of the pathogen increased dramatically, to within 1 to 2 logs of thetotal, and remained high during refrigerated storage. When sprouted seeds wereinoculated with L. monocytogenes later in the process (day 5), theinoculum survived but did not grow more than ca. 1 log CFU/g, regardless ofwhether the inoculation level in each jar was low (103) or high (105).Irradiation of sprouts with beta radiation at 3.3 or 5.3 kGy, but not 1.5 kGy,was effective at eliminating L. monocytogenes from inoculated sprouts (6log CFU/g) without causing noticeable changes in appearance or odor. In summary,L. monocytogenes can grow on sprouts during production, can survive onrefrigerated sprouts, and may be eliminated on sprouts with beta radiation.