UV light tested to kill E.coli in apple juice

By Joseph James Whitworth

- Last updated on GMT

Related tags Escherichia coli

Inactivating E.coli O157:H7 in apple juice
Inactivating E.coli O157:H7 in apple juice
Inactivation and potential reactivation of E.coli in apple juice has been studied using different ultraviolet (UV) light exposure wavelengths. 

Objectives were to compare inactivation efficacies of monochromatic UV lights with the wavelengths of 222, 254 and 282nm on pathogenic E. coli O157:H7, and examine potential reactivation in dark incubation phases following exposure to these three UV light sources in apple juice.

The inactivation of E. coli O157:H7 following exposure to Far UV light at 222nm was higher than that following the irradiation of UVC at 254nm and Far UV+ lights at 282nm in apple juice.

UV light applicability

UV light irradiation at 254nm is considered as a novel non-thermal method for decontamination of foodborne pathogenic bacteria.

However, lower penetration depth of UV light at 254nm in apple juice resulted in higher UV dose consumption during decontamination.

Two novel monochromatic UV light sources (222 and 282nm) were tested for inactivation of E.coli O157:H7 in apple juice.

The length for Far UV, UVC and Far UV+ lamps were 20, 29 and 20cm, respectively.

In 2000, the US Food and Drug Administration (FDA) approved UV-light as alternative treatment to thermal pasteurization of fresh juice products.

The E. coli O157:H7 strain used was acid-resistant, and up to 99.5% survived in apple juice (pH = 3.5) at 20 °C for 24 hours.

Researchers said previous findings revealed inactivation of E. coli O157:H7 is UV fluence-dependent; the higher the fluence is, the lower the pathogen survives.

The reduction of E. coli O157:H7 following exposure to Far UV light at 222nm (0.55 Log) was higher (P​ < 0.05) than that following Far UV+ light (0.34 Log) at 282nm at the fluence of 5 mJ/cm2

With the increase of UV fluence up to 75 mJ/cm2​, the reduction of E. coli O157:H7 following exposure to Far UV light (2.81 log) was significantly higher (P​ < 0.05) than that following UVC light (1.95 Log) and Far UV+ light (1.83 Log).

Potential reactivation

The apple juice is held for a long time for production, distribution and selling prior to reaching the consumer, the storage time at refrigerated conditions at 4 °C in the dark or at the ambient temperature on the shelf at 20 °C with light.

During this period, UV light treated microorganisms may undergo photo and dark reactivation to potentially re-grow within the system.

No reactivation potential was observed for E. coli O157:H7 in apple juice in dark incubation.

Survival of E. coli O157:H7 followed by dark incubation at 37°C was lower after exposure at 222nm compared to 254 and 282nm.

Thermal processing has been used for juice pasteurization but as heating may cause changes in nutritional composition and flavor, there is a need to explore non-thermal alternatives for mild decontamination of foodborne pathogenic bacteria.

To stabilize the temperature and prevent overheating, the Far UV and Far UV+ lamps were air-cooled during their operation. The sample was transferred into a sterile Petri dish stirred and placed directly below each UV lamp for irradiation.

Source: Food Microbiology, volume 46, April 2015, pages 329-335

Online ahead of print, DOI: 10.1016/j.fm.2014.08.015

“Inactivation and potential reactivation of pathogenic Escherichia coli O157:H7 in apple juice following ultraviolet light exposure at three monochromatic wavelengths”

Authors: Fugui Yin, Yan Zhu, Tatiana Koutchma, Joshua Gong

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