Ultraviolet-C light inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on organic fruit surfaces

• Published in: International journal of food microbiology 2015-10, Vol.210, p.136-142
• Main Authors: Adhikari, Achyut, Syamaladevi, Roopesh M., Killinger, Karen, Sablani, Shyam S.
• Format: Article
• Language: English
• Subjects: Colony Count, Microbial; Contact angle; Escherichia coli O157 - radiation effects; Food Microbiology - methods; Fruit - microbiology; Hydrophobic; Listeria monocytogenes - radiation effects; Microbial Viability - radiation effects; Surface energy; Surface roughness; Ultraviolet Rays; Weibull model
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2015.06.018

This study investigated UV-C light inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on the surface of organic apples, pears, strawberries, red raspberries and cantaloupes. Fruit surfaces spot inoculated with cocktail strains of E. coli O157:H7 and L. monocytogenes were exposed to UV-C doses up to 11.9kJ/m2 at 23°C. Fruit surface roughness, contact angle, and surface energy were determined and correlated with UV-C inactivation kinetics. Results demonstrate that bacterial pathogens on fruit surfaces respond differently to UV-C light exposure. E. coli O157:H7 on apple and pear surfaces was reduced by 2.9 and 2.1logCFU/g, respectively when treated with UV-C light at 0.92kJ/m2 (60s). For berries, the reduction of E. coli O157:H7 was lower with 2.0 (strawberry) and 1.1logCFU/g (raspberry) achieved after UV-C treatment at 7.2kJ/m2 (8min) and at 10.5kJ/m2 (12min), respectively. Similarly, a higher reduction of L. monocytogenes was observed on apple (1.6logCFU/g at 3.75kJ/m2) and pear (1.7logCFU/g at 11.9kJ/m2) surfaces compared to cantaloupe and strawberry surfaces (both achieved 1.0logCFU/g at 11.9kJ/m2). L. monocytogenes shows more resistance than E. coli O157:H7. Inactivation rates were higher for less hydrophobic fruits with smoother surfaces (apples and pears) as compared to fruits with rougher surfaces (cantaloupe, strawberry and raspberry). Findings indicate that UV-C light can effectively reduce E. coli O157:H7 and L. monocytogenes populations on fruit and berry surfaces. However, surface characteristics influence the efficacy of UV-C light. •L. monocytogenes showed more UV-C resistance than E. coli O157:H7.•UV-C inactivation of pathogens was more effective on smoother surfaces.•E. coli and L. monocytogenes reduced by 2.9 and 1.6logCFU/g, respectively on apple.•A maximum of 1.1logCFU/g reduction of E. coli was observed on raspberry.•L. monocytogenes reduced by maximum 1.0logCFU/g on strawberry and cantaloupe.