Evaluation of Listeria challenge testing protocols: A practical study using cooked sliced ham

A comparison was made of two approaches to microbiological challenge testing. Sliced cooked ham was challenge tested with Listeria monocytogenes using the protocol detailed in the Technical Guidance Document on shelf life studies for L. monocytogenes in ready-to-eat foods produced by Agence Française de Securité Sanitare des Aliments (AFSSA now known as ANSES) which required testing of three batches of product, an inoculum level of no more than 100 cfu/g, cultures pre-adapted to chill conditions and a storage regime of 7 d at 8 °C followed by 14 d at 12 °C. This was compared to a more standard industry type of approach using a single batch of product, an inoculum level of between 100 and 1000 cfu/g, cultures grown overnight at optimal temperature and a storage regime of 21 d at 8 °C. The results of the trial showed that the standard Industry approach gave similar results to that of the more complex AFSSA approach with regards to growth potential, lag time and time for a 2 log increase.