IngentaConnect Assuring Growth Inhibition of Listerial Contamination during Proc...

Authors: Samelis, John¹; Giannou, Eleni²; Lianou, Alexandra²

Source: Journal of Food Protection®, Volume 72, Number 11, November 2009 , pp. 2264-2271(8)

Publisher: International Association for Food Protection

Abstract:

The current microbiological regulatory criteria in the European Union specify a maximum Listeria monocytogenes population of 100 CFU/g allowable in ready-to-eat foods provided the product will not exceed this limit throughout its shelf life. The aim of this study was to validate the manufacturing method for traditional Greek Graviera cheese produced from thermized milk. Initial challenge experiments evaluated the fate of inoculated L. monocytogenes (ca. 4 log CFU/ml, three-strain cocktail) in thermized Graviera cheese milk (TGCM; 63°C for 30 s) in the presence and absence of a product-specific starter culture (SC) in vitro. Milk samples were incubated for 6 h at 37°C and then for 66 h at 18°C. Experiments were conducted to evaluate the fate of a cocktail of three nonpathogenic L. monocytogenes and L. innocua indicator strains inoculated (ca. 3 log CFU/g) in Graviera cheeses commercially manufactured from TGCM+SC. Cheeses were brined, ripened at 18°C and 90% relative humidity for 20 days, and stored at 4°C for up to day 60 under vacuum. In TGCM, L. monocytogenes increased by ca. 2 log units, whereas in TGCM+SC L. monocytogenes growth was retarded (P < 0.05) after a ca. 1-log increase within 6 h at 37°C. Populations of Listeria indicator strains did not grow in TGCM+SC cheeses at any stage; they declined 10-fold in fresh cheeses within 5 days and then survived with little death thereafter. Thus, growth inhibition but not inactivation of potent natural Listeria contaminants at levels below 100 CFU/g occurs in the core of traditional Greek Graviera cheese during fermentation, ripening, and storage.

Document Type: Research article

Affiliations: 1: National Agricultural Research Foundation, Dairy Research Institute, Katsikas, 45221 Ioannina, Greece;, Email: jsam@otenet.gr 2: National Agricultural Research Foundation, Dairy Research Institute, Katsikas, 45221 Ioannina, Greece

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Assuring Growth Inhibition of Listerial Contamination during Processing and Storage of Traditional Greek Graviera Cheese: Compliance with the New European Union Regulatory Criteria for Listeria monocytogenes