Combined effect of high-pressure treatments and bacteriocin-producing lactic acid bacteria on inactivation of Escherichia coli O157:H7 in raw-milk cheese.
The effect of high-pressure (HP) treatments combined with bacteriocins of lactic acid bacteria (LAB) produced in situ on the survival of Escherichia coli O157:H7 in cheese was investigated. Cheeses were manufactured from raw milk inoculated with E. coli O157:H7 at approximately 10(5) CFU/ml. Seven different bacteriocin-producing LAB were added at approximately 10(6) CFU/ml as adjuncts to the starter. Cheeses were pressurized on day 2 or 50 at 300 MPa for 10 min or 500 MPa for 5 min, at 10 degrees C in both cases. After 60 days, E. coli O157:H7 counts in cheeses manufactured without bacteriocin-producing LAB and not pressurized were 5.1 log CFU/g. A higher inactivation of E. coli O157:H7 was achieved in cheeses without bacteriocin-producing LAB when 300 MPa was applied on day 50 (3.8-log-unit reduction) than if applied on day 2 (1.3-log-unit reduction). Application of 500 MPa eliminated E. coli O157:H7 in 60-day-old cheeses. Cheeses made with bacteriocin-producing LAB and not pressurized showed a slight reduction of the pathogen. Pressurization at 300 MPa on day 2 and addition of lacticin 481-, nisin A-, bacteriocin TAB 57-, or enterocin AS-48-producing LAB were synergistic and reduced E. coli O157:H7 counts to levels below 2 log units in 60-day-old cheeses. Pressurization at 300 MPa on day 50 and addition of nisin A-, bacteriocin TAB 57-, enterocin I-, or enterocin AS-48-producing LAB completely inactivated E. coli O157:H7 in 60-day-old cheeses. The application of reduced pressures combined with bacteriocin-producing LAB is a feasible procedure to improve cheese safety.
Departmento Tecnología de Alimentos, INIA, Carretera de La Coruña km 7, 28040 Madrid, Spain.
Eva
E
Rodriguez
Juan L
JL
Arques
Manuel
M
Nuñez
Pilar
P
Gaya
Margarita
M
Medina
D000818:Animals; D001430:Bacteriocins / Q000378:metabolism* / Q000494:pharmacology; D002611:Cheese / Q000382:microbiology*; D015169:Colony Count, Microbial; D013293:Enterococcus faecalis / Q000254:growth & development / Q000378:metabolism; D016984:Enterococcus faecium / Q000254:growth & development / Q000378:metabolism; D019453:Escherichia coli O157 / Q000187:drug effects / Q000254:growth & development*; D005519:Food Preservation / Q000379:methods; D006874:Hydrostatic Pressure; D013294:Lactococcus lactis / Q000254:growth & development / Q000378:metabolism; D008892:Milk / Q000382:microbiology*; D013289:Streptococcaceae / Q000254:growth & development* / Q000378:metabolism
D001430:Bacteriocins