Effect of salt concentration on acid- and salt-adapted Escherichia coli O157:H7 and Listeria monocytogenes in recombined nonfat cast cheese

Abstract

In Turkey, legislation reduced the salt content in fresh cheeses from 10% to 6.5% in dry matter (DM). This study investigated the effect of salt reduction on the fate of acid- and salt-adapted Escherichia coli O157:H7 and Listeria monocytogenes, as well as the textural quality of recombined nonfat cheese. The cheese was manufactured using milk protein concentrate (85% protein) and skim milk powder (35% protein). After pasteurization and addition of starter culture (0.1%), cheese milk was inoculated with acid- or salt-adapted pathogens (1 x 10(3) cfu/g). Following salting (4%, 6%, 8%, or 10% in DM) and fermenting (24 hr/30 degrees C), the microbiological and textural properties of the cheese were analyzed during 8 weeks of storage at 4 degrees C. Salt concentration did not affect E. coli survival during storage (p > .05). Acid-adapted L. monocytogenes and E. coli survived 1 week longer than the unadapted control. Cheese hardness was unaffected (p > .05) by the salt concentration. Practical applications The results of the present study can be used to assess the risk of survival of acid- and salt-adapted Listeria monocytogenes or Escherichia coli O157:H7 in nonfat cheese (with different salt concentration) produced from unpasteurized milk.