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To investigate the impact of butter production on growth of listeria monocytgenes

Project Code: B12007

31/05/2006

Campden BRI
Voysey, P

SUMMARY

Butter has recently been implicated in a small but significant number of listeriosis outbreaks, including an outbreak that occurred in England in 2003. This has raised a number of questions about the growth and survival of L. monocytogenes in relation to the formulation and structure of butter and how subsequent storage and handling practices influence the behaviour of this organism.

Butter is a water-in-fat emulsion comprising water droplets of varying size and number, depending on the formulation and manufacturing conditions. While some studies have shown little or no growth of L. monocytogenes in butter, other studies have reported growth at both refrigeration and ambient temperatures.

This research project investigated the ways butter and butter-containing spreads are formulated, manufactured and handled and it determined how these factors affect the growth and survival of different strains of L. monocytogenes, particularly outbreak strains. Following practical work in butter production, the project derived conclusions about the safety of butter and butter-containing spreads with respect to L. monocytogenes.

Laboratory experiments showed that water droplet size, salt content and temperature cycling may affect the rate and/or total amount of growth of L. monocytogenes in butter.

Click here to see a related, peer reviewed paper, in the Journal of International Dairy Technology.

Final Report

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