Evaluation of 405 nm monochromatic light for inactivation of tulane virus on blueberry surfaces

Authors: Kingsley, David; PEREZ, RAFAEL - Former ARS Employee; Boyd, Glenn; Sites, Joseph; Niemira, Brendan

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2017
Publication Date: 4/23/2018
Citation: Kingsley, D.H., Perez, R.E., Boyd, G., Sites, J.E., Niemira, B.A. 2018. Evaluation of 405 nm monochromatic light for inactivation of tulane virus on blueberry surfaces. Journal of Applied Microbiology. 124:1017-1022.

Interpretive Summary: The aim of this investigation was to develop a new, dry, nonthermal technology to inactivate virus on the surface of produce, such as blueberries. Visible violet or blue light (405 nm) has been shown to have the potential to inactivate pathogenic bacteria. Results indicate only limited inactivation of a norovirus surrogate-coated blueberries exposed for up to 30 min to intense 405 nm light. Since the mechanism by which 405 nm light is thought to inactivate pathogens involves reactive oxygen, the effect of the dry ice-nitrogen cooling system was evaluated and determined not to be the cause of the lack of inactivation observed. However addition of two singlet oxygen enhancers, riboflavin and rose bengal, compounds that can interact with light and oxygen to produce reactive oxygen species, indicate that inactivation does occur when blueberries are coated with these compounds. Rose bengal is a common food coloring while riboflavin is known as vitamin B2. Use of food grade singlet oxygen enhancer compounds in combination with visible spectra light may offer means to inactivate foodborne viruses.

Technical Abstract: The aim of this study was to evaluate the potential of 405 nm light as an intervention for virus contaminated blueberries. Tulane virus-contaminated-blueberries were treated with 4.2 mW/sq cm of 405 nm light for 5 to 30 min. To mitigate thermal heating due to the intense light, a dry ice-chilled nitrogen-based cooling system was utilized. Blueberries were manually rotated with forceps to ensure exposure of all surfaces to 405 light. Five, 10, and 30 min treatments resulted in little or no inactivation of Tulane virus on blueberries (average log reductions of -0.18; -0.02; and +0.06 respectively). Since the mechanism by which 405 nm light inactivates pathogens is thought to involve singlet oxygen and other reactive oxygen molecules, two singlet oxygen enhancers, riboflavin and rose bengal, were used to coat the blueberries prior to 405 nm treatment. More substantial inactivation was observed, when 0.1% riboflavin or rose bengal was added, resulting in an average PFU reduction of - 0.51 and -1.01 logs, respectively. However it was noted that the addition of riboflavin and rose bengal in the absence of 405 nm light treatment produced some inactivation. Average untreated log reductions for riboflavin and rose bengal were -0.13 and -0.66, respectively. Also 60-30 second 405 nm light pulses with two minute ambient cooling periods without the dry ice-nitrogen cooling system did not inactivate Tulane virus, suggesting that oxygen limitation by the nitrogen CO2 mixture was not the cause of limited inactivation. Overall results indicate that 405 nm light may have some potential to inactivate viruses if singlet oxygen enhancers are present. The potential of visible monochromatic violet/blue light (405 nm) as a nonthermal intervention for viruses on foods, such as berries that are prone to norovirus contamination, had not been previously evaluated. Use of food grade singlet oxygen enhancer compounds in combination with visible spectra light may offer a means to inactivate foodborne viruses.