title: Survival, growth, and thermal resistance of Listeria monocytogenes in products containing peanut and chocolate.
abstract: Outbreaks of listeriosis associated with the consumption of ready-to-eat foods have raised interest in determining growth, survival, and inactivation characteristics of Listeria monocytogenes in a wide range of products. A study was undertaken to determine the thermal tolerance of L. monocytogenes in a peanut-based beverage (3.1% fat), whole-fat (3.5%) milk, wholefat (4.0%) and reduced-fat (1.0%) chocolate milk, a chocolate-peanut spread (39% fat), and peanut butter (53% fat). The D60 degrees C value (decimal reduction time at 60 degrees C) in peanut beverage (3.2 min) was not significantly different (P > 0.05) than the D60 degrees C value in whole-fat milk (3.3 min) or whole-fat chocolate milk (4.5 min) but significantly lower (P < or = 0.05) than the D60 degrees C value in reduced-fat chocolate milk (5.9 min). The pathogen was significantly more resistant to heat when enmeshed in chocolate-peanut spread (water activity [aw] of 0.46; D60 degrees C = 37.5 min) and peanut butter (aw of 0.32; D60 degrees C = 26.0 min) than in liquid products. At 10 degrees C, the pathogen grew most rapidly in whole-fat chocolate milk and slowest in peanut beverage. At 22 degrees C, populations increased significantly within 12 and 16 h in whole-fat milk and reduced-fat chocolate milk, respectively, and within 8 h in whole-fat chocolate milk and peanut beverage. Initial populations (3.37 to 4.42 log CFU/g) of L. monocytogenes in chocolate-peanut spread and peanut butter adjusted to an aw of 0.33 and 0.65 declined, but the pathogen was not eliminated during a 24-week period at 20 degrees C. Survival was enhanced at reduced aw. Results indicate that a pasteurization process similar to that used for full-fat milk would be adequate to ensure the destruction of L. monocytogenes in peanut beverage. The pathogen survives for at least 24 weeks in chocolate-peanut spread and peanut butter at an aw range that encompasses that found in these products.
authors.affiliation: Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Kenney
authors.forename: Larry R
authors.initials: LR
authors.lastname: Beuchat
mesh_terms: D010367:Arachis / Q000382:microbiology*; D002099:Cacao / Q000382:microbiology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004196:Disease Outbreaks / Q000517:prevention & control; D005506:Food Contamination / Q000032:analysis; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000254:growth & development* / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water