Selective Quenching of Peracetic Acid by Sodium Dithionite Enables Rapid, Non-Thermal Sterilization for Euglena gracilis Cultivation

Peracetic acid (PAA) has strong biocidal activity against bacteria, fungi, and spores, even with short contact times. PAA-mediated sterilization is therefore an attractive method for sterilization of growth media that have heat-labile components or when polymer-based equipment is used. However, residual PAA and co-existing hydrogen peroxide (H2O2) can inhibit the growth of cultivated species, necessitating a fast and reliable quenching strategy that does not require rinsing. In contrast to Fe–EDTA-based catalytic decomposition that is strongly influenced by pH, buffers, and organic nitrogen, we demonstrate a fundamentally different, stoichiometric quenching strategy using sodium dithionite that enables instantaneous and selective removal of PAA. Na2S2O4 preferentially reduced PAA over H2O2 in a 0.03% PAA solution and achieved complete PAA reduction within 5 s, independent of pH and in the presence of nitrogen compounds. By adjusting the Na2S2O4 dose, PAA could be selectively removed while allowing a small fraction of H2O2 to remain. When applied to the cultivation of Euglena gracilis, which tolerates low levels of H2O2, the PAA–Na2S2O4-treated medium resulted in greater cell growth and higher paramylon production than autoclaved medium.