Enterobacteriaceae species during manufacturing and ripening of semi-hard and soft raw ewe's milk cheese: Gas production capacity

The aim of this work was to identify the main species of Enterobacteriaceae present in two different varieties of raw ewe's milk cheese, to study their evolution during manufacturing and ripening, and to assess their potential to produce gas from lactose. Enterobacteriaceae activity may influence cheese ripening; it can even be responsible for some specific characteristics of artisanal cheeses. Nevertheles some of these microorganisms are potential pathogens. Enterobacteriaceae growth and disappearance were different between the soft and the semi-hard cheese variety, as well as the proportions of the species detected. Citrobacter freundii, Citrobacter braakii and Klebsiella oxytoca were the predominant species in milk and curd, whereas Hafnia alvei was predominant throughout ripening. The highest gas production was generated by Enterobacter nimipresuralis, C. braakii and Enterobacter cloacae strains, followed by Enterobacter aerogenes, H. alvei, K. oxytoca and C. freundii strains. According to the species found, their levels during the initial ripening stages and gas production ability, C. braakii, C. freundii, K. oxytoca and H. alvei can be considered as responsible for early blowing in soft and semi-hard ewe cheeses. The identification of the Enterobacteriaceae species most likely responsible for early blowing can lead to a better understanding of raw milk cheese ripening, and therefore, to the improvement of its quality.