Evaluating Environmental Monitoring Protocols for Listeria spp. and Listeria monocytogenes in Frozen Food Manufacturing Facilities

J Food Prot. 2020 Jan;83(1):172-187. doi: 10.4315/0362-028X.JFP-19-190.


Food processors face serious challenges due to Listeria monocytogenes contamination. Environmental monitoring is used to control L. monocytogenes from the processing environment. Although frozen foods do not support the growth of L. monocytogenes, the moist and cold conditions in frozen food production environments are favorable for growth of L. monocytogenes. The purpose of the study was to determine the current state of awareness and practices applied across a variety of frozen food facilities related to environmental monitoring for Listeria. A survey tool was created to elicit information on existing environmental monitoring programs within the frozen food industry. The topics included cleaning and sanitizing applications and frequency, microbiological testing, and environmental areas of concern. The survey was reviewed by academic and industry experts with knowledge of microbiology and frozen food processing and was field tested by industry personnel with extensive knowledge of environmental monitoring. The survey was distributed and analyzed electronically via Qualtrics among 150 frozen food contacts. Data were gathered anonymously with a response rate of 31% (n = 46). The survey indicated that facilities are more likely to test for Listeria spp. in environmental monitoring zones 2 to 4 (nonfood contact areas) on a weekly basis. The major areas of concern in facilities for finding Listeria-positive results are floors, walls, and drains. At the time of the survey, few facilities incorporated active raw material and finished product testing for Listeria; instead, programs emphasized the need to identify presence of Listeria in the processing environment and mitigate potential for product contamination. Recognition of environmental monitoring as a key component of a comprehensive food safety plan was evident, along with an industry focus to further improve and develop verification programs to reduce prevalence of L. monocytogenes in frozen food processing environments.

Keywords: Environmental monitoring; Frozen food; Listeria monocytogenes; Listeria spp; Manufacturing facility.

MeSH terms

  • Environmental Microbiology
  • Environmental Monitoring
  • Food Contamination / analysis*
  • Food Microbiology
  • Food-Processing Industry
  • Frozen Foods / microbiology*
  • Listeria monocytogenes / isolation & purification*
  • Manufacturing and Industrial Facilities*