Gamma irradiation for producing functional postbiotic ingredients from industrial probiotic biomass

The industrial application of postbiotics based on non-viable probiotic cells (paraprobiotics), requires robust inactivation technologies that ensure replicative death while preserving bioactive bacterial structures and functions. Here, we evaluated cobalt-60 gamma (γ) irradiation as an industrially scalable approach to produce functional postbiotics from freeze-dried biomasses of twelve probiotic strains packaged in sealed multilayer pouches. Viable counts of untreated biomasses ranged from 10.8 to 11.3 log₁₀ CFU g^-1. γ irradiation at 10, 15, or 20 kGy resulted in complete loss of culturability for all strains (below the detection limit), indicating that 10 kGy was sufficient for full inactivation under the tested conditions. Membrane integrity, assessed by flow cytometry according to ISO 19344:2015, was largely preserved immediately after irradiation and remained stable during storage at 4 °C up to 18 months, with strain-dependent but generally moderate declines in the active population. Intracellular functionality was probed via β-galactosidase activity, which remained detectable in irradiated biomasses and did not differ significantly from matched untreated controls. Moreover, the adhesion capacity of selected adhesive strains to differentiated Caco-2 monolayers was retained after γ irradiation. Using Bifidobacterium bifidum MIMBb23sg as a model, γ irradiation outperformed industrial pasteurization by preserving membrane integrity, adhesion, and β-galactosidase activity; both inactivation methods maintained comparable antioxidant responses in a Caco-2 cellular antioxidant activity assay. Overall, γ irradiation enables the production of non-culturable yet structurally and functionally competent bacterial biomasses, supporting its potential for next-generation postbiotic ingredients.