Study of Enterobacteriaceae throughout the manufacturing and ripening of hard goats' cheese

Abstract

The evolution of the counts and the species of Enterobacteriaceae as well as some physico-chemical parameters (pH, aw and NaCl and moisture contents) during manufacturing and ripening of a hard Spanish goats' cheese of the Armada-Sobado variety were studied. Enterobacteriaceae (mean log counts 4.45 g-1 in milk) increased 0.71-2.18 log units in curd and afterwards decreased until they disappeared after 2-4 weeks of ripening. This premature disappearance seems to be due to the decrease in aw values and in moisture contents. However, the low pH values, reached from the beginning of the ripening process, could also contribute to this phenomenon. The most abundant species in milk was Serratia liquefaciens (57.5% of isolates), followed by Morganella morganii (27.5%), Hafnia alvei (5%), Klebsiella oxytoca (5%) and Yersinia enterocolitica (5%). Yersinia enterocolitica was not subsequently isolated from either curd or in cheese. Hafnia alvei numbers increased in curd and in 1-week-old cheese where this micro-organism was the most abundant (47.5% and 75% of the isolates respectively). Escherichia coli, which was not isolated from milk, curd or 1-week-old cheese, was the predominant organism in 2-week-old cheese (57.8% of isolates). This confirms the finding of other authors who have shown that it is one of the most resistant species in ripening cheeses.