title: Inactivation and potential reactivation of pathogenic Escherichia coli O157:H7 in apple juice following ultraviolet light exposure at three monochromatic wavelengths.
abstract: Ultraviolet (UV) light irradiation at 254 nm is considered as a novel non-thermal method for decontamination of foodborne pathogenic bacteria. However, lower penetration depth of UV light at 254 nm in apple juice resulted in higher UV dose consumption during apple juice decontamination. In addition, no studies are available on the reactivation of pathogens following exposure to UV light in drinks and beverages. Two novel monochromatic UV light sources (λ = 222 and 282 nm) have been developed for bacterial disinfection. However, the inactivation of pathogenic Escherichia coli O157:H7 following exposure to these UV wavelengths is still unclear. Therefore, the present study was conducted to determine the inactivation and reactivation potential of pathogenic E. coli O157:H7 in apple juice following exposure to UV light at three monochromatic wavelengths: Far UV (λ = 222 nm), Far UV+ (λ = 282 nm) and UVC light (λ = 254 nm). The results showed that E. coli O157:H7 is acid-resistant, and up to 99.50% of cells survived in apple juice when incubated at 20 °C for 24 h. Inactivation of E. coli O157:H7 following exposure to Far UV light (2.81 Log reduction) was higher (P < 0.05) than the inactivation caused by UVC light (1.95 Log reduction) and Far UV+ light (1.83 Log reduction) at the similar levels of UV fluence of 75 mJ/cm(2). No any reactivation potential was observed for E. coli O157:H7 in dark incubation phases after exposure to UV light as determined by the regular plating method. In addition, the exposure to Far UV light at 222 nm followed by incubating at 37 °C significantly decreased (P < 0.05) the survival of E. coli O157:H7 during dark incubation phase compared to that of UVC and Far UV+ light.
authors.affiliation: Key Laboratory of Agri-Ecological Processes in the Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, People's Republic of China; Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, N1G 5C9, Canada.
authors.forename: Fugui
authors.initials: F
authors.lastname: Yin
authors.affiliation: Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, N1G 5C9, Canada.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, N1G 5C9, Canada. Electronic address: Tatiana.Koutchma@agr.gc.ca.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Koutchma
authors.affiliation: Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, Ontario, N1G 5C9, Canada.
authors.forename: Joshua
authors.initials: J
authors.lastname: Gong
mesh_terms: D001628:Beverages / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000254:growth & development / Q000528:radiation effects*; D005514:Food Irradiation / Q000379:methods*; D027845:Malus / Q000382:microbiology* / Q000528:radiation effects; D050296:Microbial Viability / Q000528:radiation effects*; D014466:Ultraviolet Rays
keywords: Apple juice; Escherichia coli O157:H7; Far UV light; Far UV+ light; Inactivation; Reactivation; UVC light