Abstract: Objective To evaluate the effects of varying riboflavin concentrations and visible light intensities on E. coli in plasma, based on which to propose alternative methods for reducing bacterial contamination in plasma. Methods Fresh frozen plasma that failed the glutamate aminotran sferase (ALT) test was randomly selected and divided into control, light, and experimental groups after being differently treated. Plasma mixed with E. coli was added to each group. The control group did not undergo any treatment, the light group was subjected to irradiation without addition of riboflavin, and the experimental group received irradiation with addition of riboflavin at a working concentration of 50~300 µM. The light and experimental groups were placed in a pathogen reduction device and irradiated with 420 nm visible light with 50 mW/cm², 75 mW/cm², and 100 mW/cm², respectively. The duration of the light treatment was 55 minutes. The study evaluated the effects of different riboflavin concentrations and visible light intensities on E. coli in plasma. Bacterial culture was performed at the end of light exposure to assess the outcomes. Results After treatment with 420 nm visible light for 55 minutes, the concentration of E. coli decreased by 1.7~3.5 log (50 mW/cm²),2.8~≥4.4 log (75 mW/cm²),and 4.0~≥4.7 log (100 mW/cm²) respectively. Treatment with high-intensity light (100 mW/cm²) and high riboflavin concentration (150 and 300 µM) reduced over 4 logs of E. coli in plasma. Increased light intensity and riboflavin concentration both enhanced the reduction effect on E. coli. The two factors were also found to be in positive correlation with E. coli reduction efficacy. Conclusion At the wavelength of 420 nm, light intensity of 75 mW/cm², riboflavin concentrations of 150 µM and 300 µM, riboflavin visible light irradiation method has the best treatment effect on E. coli in plasma, and could effectively reduce the concentration of E. coli contaminated in plasma.

Key words: Pathogen reduction, Riboflavin, E. coli, Bacterial contamination, Blood safety