Inactivation of Listeria innocua in UHT milk by thermosonication and PEF
Special Symposium - Innovations in Food Technology (LMC Congress)
Hygiene, Hygienic Design & Unit Operations (Food-5a)
Keywords: Thermosonication, pulsed electric fields, Listeria innocua, HTST, milk
In recent years there has been increased interest in the use of novel non-thermal preservation techniques due to growing demand from consumers for safe, minimally processed products. The objective of this study was to investigate the potential of two such technologies, thermosonication (TS) and pulsed electric fields (PEF), for the inactivation of Listeria innocua. Experiments were designed to evaluate the survival of this organism in UHT low fat milk following individual and combined sequential exposure to these treatments. The product was exposed to two forms of TS treatment (TS1 and TS2). TS1 involved increasing product temperature from 25ºC to 55ºC during an 80 s exposure to ultrasound, while TS2 consisted of a pre-heating step to 55ºC followed by sonication during which the temperature was maintained constant. Square-wave PEF pulses were applied at 30 and 40 kV cm-1 for a total treatment time of 50 µs. Immediately after TS or PEF treatments milk was cooled to 5ºC. TS1 resulted in a maximum inactivation of 0.6 log cycles when the milk was processed for 80 s at the maximum power output (85 W cm-2), while TS2 caused a 3.3 log cycle reduction. The application of PEF alone at 30 and 40 kV cm-1 led to a maximum reduction of L. innocua of 1.1 and 3.3 log cycles, respectively. When TS1 was combined sequentially with PEF at the highest electric field strength (40 kV cm-1) a 6.8 log reduction was observed, indicating a synergistic effect between both treatments. Similarly, when TS2 was combined with PEF the overall microbial reduction was 4.5 and 6.3 log cycles for 30 and 40 kV cm-1 respectively. The results obtained by combining TS1 or TS2 with PEF at 40 kV cm-1 showed no significant difference (P≥0.05) from the control HTST treatment (72ºC for 26 s) which produced a 7.0 log cycle reduction. Based on these results the combination of TS and PEF may represent a thermally milder alternative for the inactivation of microorganisms of L. innocua in milk. Further studies will focus on the effect of the applications of these technologies on the overall quality of the milk, as well as establishing its safety of the product over the intended shelf life.
*Communicating author: e-mail: james.lyng@ucd.ie Tel: +353-1-7167710, Fax: +353-1-7161147.
Presented Saturday 15, 11:15 to 11:30, in session Hygiene, Hygienic Design & Unit Operations (Food-5a) Continued.
