Inactivation of Escherichia coli by a combination of nisin, pulsed electric fields, and water activity reduction by sodium chloride.
The effect of nisin combined with pulsed electric fields (PEF) and water activity reduction by sodium chloride (NaCl) on the inactivation of E. coli in simulated milk ultrafiltrate media was studied with a Doehlert design and a response surface method. The reduction of water activity from 0.99 to 0.95 by the addition of NaCl (without any other hurdle) did not affect E. coli viability of approximately 10(8) CFU/ml. A reduction in PEF effectiveness occurred when the NaCl concentration was increased because of an increase in conductance, which reduced the pulse decay time. In cells submitted to PEF nisin activity was decreased, probably as a consequence of the nonspecific binding of nisin to cellular debris or the emergence of new binding sites in or from cells. However, the lethal effect due to nisin was reestablished and further improved when water activity was reduced to 0.95. A synergistic effect was evidenced when low-intensity PEF were applied. Decreasing water activity to 0.95 and applying PEF at 5 kV/cm (a nonlethal intensity when no other hurdle is used) with the further addition of nisin (1,200 IU/ml) resulted in a 5-log cycle reduction of the bacterial population.
Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad de Buenos Aires, Ciudad Universitaria, Argentina.
M
M
Terebiznik
R
R
Jagus
P
P
Cerrutti
M S
MS
de Huergo
A M R
AM
Pilosof
D000818:Animals; D000900:Anti-Bacterial Agents; D015169:Colony Count, Microbial; D004558:Electric Stimulation; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D008892:Milk / Q000382:microbiology; D009561:Nisin / Q000494:pharmacology*; D011673:Pulsatile Flow; D012965:Sodium Chloride / Q000494:pharmacology*; D014867:Water
D000900:Anti-Bacterial Agents; D014867:Water; D009561:Nisin; D012965:Sodium Chloride