Photocatalytic paint for phage inactivation in dairy industry: inactivation constants and efficiencies

A photocatalytic paint, formulated with commercial carbon doped anatase TiO2, was tested for the inactivation of sixteen bacteriophages infective to lactic acid bacteria. Phages were deposited on borosilicate glass plates coated with paint and subjected under radiation typically used for indoor illumination (λ = 360 - 720 nm). Inactivation assays for a total time of 20 h in a laboratory photoreactor at constant temperature and relative humidity were performed. Plaque Forming Units (PFU) as function of time were followed demonstrating that eight phages were completely inactivated in a short time (1.5 - 5 h, phage reductions higher than 2.79 log orders) whereas the eight remaining phages partially reduced their infectivity with varied log reductions and assay times (reductions of 2.33 - 5.88 log orders within 4 - 20 h). Apparent inactivation kinetic constant (kT) ranged from 0.30 to 7.52 1/h. The highest and lowest photonic inactivation efficiency were of 4.06×1012 PFU/Einstein and 3.00×109 PFU/Einstein, respectively; whereas the quantum inactivation efficiencies varied between 9.17×1012 PFU/Einstein and 6.00×109 PFU/Einstein. Results demonstrated the efficiency of photocatalytic paint to inactive phages in short times. Application of this paint on diverse surfaces of dairies using the own illumination system would contribute to the diminution of phage concentration in the environment, thus reducing the risk of phage attacks to bacterial strains belonged to starter cultures.