Study of diverse conditions on the inactivation of dairy phages using photocatalytic paint

JACOB, M.F.; MERCANTI, D.; QUIBERONI, A.; BALLARI, M. M.; BRIGGILER MARCÓ, M.

Congreso; 32 Congresso Brasileiro Microbiología 2023; 2023

Phage infections constitute the main cause of failure of lactic acid bacteria used as starter cultures during manufacture of fermented dairy products. In previous research, our group demonstrated the efficiency of a photocatalytic paint formulated with carbon-doped TiO2 anatase, for the inactivation of 16 dairy phages using typical indoor radiation (λ= 360-720 nm). The aim of this work was to analyze the effect of the incident radiation flux (18, 56 and 100%; λ= 360-720 nm) and the effect of relative humidity (30, 50 and 100%) on the inactivation of two dairy phages (J-1 and M13-G1b), utilizing photocatalytic paint. Besides that, the impact of the irradiation source was also evaluated, calculating the photonic and quantum inactivation efficiencies for an UV-A source (λ= 300-420 nm) and comparing those with the obtained previously with a different source (λ= 360-720 nm). Inactivation assays were carried out under the diverse conditions explained before in a laboratory scale reactor for a total time of 16 h. Phages were placed on borosilicate glass plates coated with photocatalytic paint. Phage enumeration (Plaques Forming Units per mL, PFU/mL) was performed by the double-layer plaque titration method on diverse times and results were plotted against time. Apparent kinetic constants (kT) were obtained fitting the data with a first order kinetic equation. As results, kT slightly increased when relative humidity was modified from 30% to 50% (from 0,43 to 0,58 1/h) and markedly increased when relative humidity reaches the value of 80% (3,30 1/h). As expected, kT decreased when the incident radiation flux was reduced (3,30, 1,96 and 1,74 1/h for 18%, 56% and 100% radiation, respectively). Under UV-A radiation (100% radiation flux and 80% relative humidity), photonic and quantum efficiencies were 1.16×1012 and 1.72×1012 PFU/Einstein for phage M13-G1b and 2.29×1012 and 3.41×1012 PFU/Einstein for phage J-1, being higher in comparison with those obtained under typical indoor radiation. Results showed the significant effect on photon absorption and relative humidity in the photocatalytic paint efficacy. As demonstrated previously, the application of this paint on diverse surfaces of dairy industries will contribute to the phage concentration reduction in the environment, decreasing the risk of phage attacks on bacterial strains employed as starter cultures.