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Combining non-thermal techniques shows E.coli reduction potential - study

By Rory Harrington , 27-Apr-2011

Use of high intensity light pulses (HILP) and thermosonification (TS) is effective in cutting E.coli populations in orange juice, according to new research.

The preliminary study by J G Lyng et al said application of the non-thermal technologies - both individually and in combination – resulted in reduction of E.coli K12 DSM 1607 in commercial orange juice made from concentrate. The scientists found the decrease in bacteria was greater when the HILP and TS were used together.

The group said that while pasteurisation is successful in extending shelf life of fresh orange juice by killing pathogens such as E.coli 0157:H7 and Salmonella spp, the process can alter physical and chemical properties, as well as adversely affecting flavour.

“As a result non-thermal technologies may be a desirable alternative for juice processors in order to satisfy both consumer demands for a high quality product and ensure microbiological safety,” said the research.

HILP is a non-thermal technology which uses short light pulses (100-400 µs for microbial decontamination.

Results

The technologies were applied at two different energy settings – low (L) and high (H). For HILP the low setting was 4.03 J/cm2 while the high setting was 5.1 J/cm2 . TS(L) was 2.8 minutes residence time at 40ºC and TS(H) was set as five min residence time at 50ºC.

Both the individual technologies and their combinations (HILP&TS and TS&HILP) were studied

Results showed inactivation ranging from 1.10 log cfu/ml (TS(H)) to 2.42 log cfu/ml(HILP(H for the hurdles when applied individually. When applied in combination, the treatments produced reductions ranging from2.5 (HILP(L)&TS(H)) to 3.93 (HILP(H)&TS(L)) log cfu/ml.

The study, published in the journal Food Microbiology, noted similar reductions in E. coli populations were achieved in orange juice by all treatment combinations irrespective of the sequence in which they were applied.

Potential

When HILP was used on its own the maximum 2.42 log reduction did not meet US Food and Drug administration (FDA) recommendations of at least a 5 log reduction for fruit juices. However, other studies had found reductions of up to 5 log in apple juice using just HILP – with suggestions that the effectiveness of this process depends on the transparency of the media. The more transparent a liquid, the easier it is for the UV light to penetrate. Orange juice was found to be almost 14 times less transparent to UV light than apple juice.

The group highlighted the enhanced efficacy of applying the processes in tandem – stating that to their knowledge, this the first time the techniques had been used together in a continuous mode.

The research said the preliminary study had demonstrated the potential of HILP and TS combinations to reduce microbiological loads in orange juice but said further work was needed to optimise techniques to reach FDA-demanded 5 log reductions.

Combinations of High Intensity Light Pulses and Thermosonication for the Inactivation of E.coli in orange juice by A Munoz, I Palgan, DJ Morgan, DA Cronin, P Whyte, J G Lyng published in Food Microbiology

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