Flash pasteurisation and antimicrobial combo hailed as effective Listeria hurdle

22 May 2012

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Using flash pasteurization in tandem with antimicrobial lauric-arginate-ester (LAE) can curb the growth of Listeria monocytogenes (LM) on frankfurter sausages for up to 12 weeks, according to new US Government research.

The study from the Agricultural Research Service, part of Department of Agriculture, proposed using the technologies in combination because only when used together did they provided an effective hurdle process for decontamination.

Employing each method individually did inhibit LM development for relatively short periods of time after which the bacterium were able to bounce back and resume growth, said ARS researchers Christopher Sommers et al.

The paper - Inactivation of Listeria innocua on Frankfurters by Flash Pasteurization and Lauric Arginate Ester – was published earlier this year in the Journal of Food Processing Technology.

High mortality rate

LM is capable of growth at refrigerated temperatures and in high salt environments, which allows it to proliferate during long-term cold storage and is able to grow in RTE meats such as deli products and frankfurters.

While control of the pathogen has improved in recent years, the fact that outbreaks continue and the high mortality rate they provoke means the US federal regulators have imposed a zero tolerance approach to the pathogen.

The researchers said LM contamination generally occurs post-processing and prior to packaging.

Methodology and results

Flash Pasteurization (FP) uses short pulses of steam 120°C, 1.5s) to decontaminate the surface of precooked sausages. The antimicrobial LAE has also been shown to cut levels of LM and its nonpathogenic surrogate L. innocua on frankfurters.

The study noted there were numerous technologies available to combat pathogen growth – such as infrared light, in-package thermal treatments, ionizing radiation UV and pulsed light – but that “those actually in commercial use are relatively few because of the need for effectiveness, low cost, and the ability to use the technology at commercial processing line speeds”.

The team not only wanted to measure the efficacy of the FP/LAE partnership but also to do so at a pilot plant environment.

The frankfurters were inoculated with L. innocua and then and loaded into open preformed trays before being treated with FP steam at 120C for 1.5 seconds. LAE was then added immediately before the packages were then vacuum-sealed. Separate frankfurters were also subject to the treatments individually as a control.

All single layer packages of frankfurters were held at 10°C for 12 weeks and tested three times for LM growth.

The team found that LM inhibition on individually treated frankfurter lasted up to10 weeks by which time the bacterium levels measured >106 CFU/g at 10°C.

The group found the most effective approach for control of Listeria was by application of both FP and LAE, with the bacterial growth being inhibited for the full 12 week storage period.

The dual methods also had little effect on the colour and texture of the frankfurter.

Sommers concluded: “Both processes, FP and application of LAE, have been commercialised. However, the use of FP in combination with LAE improved the inactivation of Listeria over that of the processes used individually. In conclusion, FP in combination with LAE is an effective hurdle process that can be used to control Listeria in pre-cooked sausages such as frankfurters.”

Source: Journal of Food Processing & Technology