Survey pinpoints listeria weak points at fish plants

The regions include drains, skinning machines, brine injection units and fish slicers. Plant workers could also spread the germ from area to area via their hands or equipment, the research found.

The study derived its information through interviews with businesses and enforcement officials and scrutiny of available literature relating to L. monocytogenes contamination in the smoked fish sector.

The analysis was carried out by Hutchison Scientific, the School of Natural and Computing Sciences, University of Aberdeen, and Chilled Food Associates.

Information and guidance​

The research suggested that the following areas required additional information and guidance:

• environmental sampling and process monitoring
• sourcing of high quality raw ingredients
• verification of cleaning and sanitation of food contact surfaces and the plant environment
• use of the ‘hurdle approach’ to reduce the potential of final product contamination. (This involves using a number of barriers to growth, which on their own are not sufficient to prevent or reduce growth, but are effective when used in combination.)
• shelf life determination studies
• improved knowledge of hygiene and safety regulations
• prevention of post processing contamination during storage

Techniques such as irradiation, high pressure processing and pulsed light technology are examined as ways to remove L. monocytogenes contamination.

Sound microbiological advice​

The researchers said larger smoked fish processing plants had expert technical staff who were well-briefed on tackling L. monocytogenes, but most smaller plants did not have ready access to sound microbiological advice.

FSAS said it would consider the recommendations made in the report and anticipated that more information gathering would be needed to ensure subsequent advice was risk-based and proportionate.

The findings arise from a critical review of the literature relating to L. monocytogenes contamination of raw and finished fish during hot and cold smoking processes.

The review was undertaken to identify key production and processing practices that could potentially influence L. monocytogenes prevalence.

Mitigation strategies​

Visits were made to fish farms and commercial smokers. FSAS surveyed environmental health officers to secure information on mitigation strategies used by the sector in controlling listeria contamination and perceived barriers in controlling listeria to identify areas where further information was required.

An analysis of available information indicated that fish entering processing plants could have listeria present on their skin. Prevalence rates were low, but variable.

FSAS said some L. monocytogenes biotypes could persistently colonise plant processing environments, becoming resident in plants. However, these were more likely to be isolated from the final products.

A copy of the full study is available here​.