Evaluation of 405-nm monochromatic light for inactivation of Tulane virus on blueberry surfaces.

AIM

The study aim was to evaluate the potential of 405-nm light as a virus intervention for blueberries.

METHODS AND RESULTS

Tulane virus (TV)-inoculated blueberries were treated with 4·2 mW cm of 405-nm light for 5-30 min. To mitigate thermal heating due to the intense light, a dry ice-chilled, nitrogen-based cooling system was utilized. Blueberries were rotated to ensure exposure of all surfaces to 405-nm light. Five-, 15- and 30-min treatments resulted in little or no inactivation of TV on blueberries (average log reductions of -0·18; -0·02; and +0·06 respectively). Since 405-nm light's inactivation mechanism may involve singlet oxygen, two singlet oxygen enhancers, riboflavin and rose bengal, were used to coat the blueberries prior to 405-nm light treatment. 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-s 405-nm light pulses with 2-min ambient cooling periods without the dry ice nitrogen cooling system did not inactivate TV, suggesting that oxygen limitation by the nitrogen CO mixture was not the cause of limited inactivation.

CONCLUSIONS

Overall results indicate that 405-nm light has some potential to inactivate viruses if singlet oxygen enhancers are present.

SIGNIFICANCE AND IMPACT OF THE STUDY

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.