Validation of Predictive Models for the Growth of Listeria monocytogenes in Indian Cottage Cheese (Paneer) By Challenge Testing Under Homemade Preparation Scenario

Introduction:   There is an increasing food safety concern regarding the consumption of fresh cheese due to Listeria monocytogenes. Paneer is a cottage cheese, popular among Asian and Middle Eastern countries. Listeria monocytogenes is the major cause of foodborne illness associated with consumption of fresh, soft cheese. Several outbreaks and recalls have been reported.

Purpose:   The goal of this work was to validate predictive growth models for L. monocytogenes, based on challenge test data performed in paneer under a homemade preparation scenario.

Methods:   The paneer cheese was prepared in the laboratory. Three different pathogen contamination scenarios were simulated: i) contamination during the coagulum preparation stage; ii) contamination from the water during immersion of the coagulated milk; and iii) post-processing surface contamination. Each trial was conducted using three batches with two replicates each. The initial concentration of L. monocytogenes was ca. 500 cfu/g. Results of challenge testing were compared with Combase and FSSP, predictive modeling software for L. monocytogenes growth.

Results:  The results showed that the models predicted the growth of L. monocytogenes, if contamination occurred at the surface or immersion stage. There was an increase of more than two log cfu/g, during 10 days storage at 4°C. The models were unable to predict the growth, if contamination occurs during coagulum preparation stage. It was found that there was no growth of L. monocytogenes and the presence of L. monocytogenes/25 g was, only, detected occasionally.

Significance:   This work is the first validation of predictive models used to assess the growth of L. monocytogenes in the paneer (Indian cottage cheese). Results indicate that the models are valid, only, if L. monocytogenes contamination occurs after coagulum preparation.