Sanitization of packaging and machineries in the food industry: Effect of hydrogen peroxide on ascospores and conidia of filamentous fungi

In the food industry, sterilization of packaging and filling machines by hydrogen peroxide (HP) is a widespread practice. Its effectiveness is usually tested by means of inactivation tests on selected test microorganisms that were any case chosen without taking into account that food products could be also spoiled by microorganisms presumably resistant to HP. For this reason, the aim of this work was to assess the resistance of different ascospore-forming moulds (Talaromyces bacillisporus, Aspergillus hiratsukae, Chaetomium globosum) to HP, in order to find the most resistant to this kind of chemical stress, and to compare their resistance with that registered for other moulds, including test microorganism Aspergillus brasiliensis ATCC 16404. Tests were carried out from 50 to 60 °C on spores or conidia, depending on the strain, either by immersing inoculated strips (aluminium, tin-plate, HDPE, PET) in HP, or by directly inoculating cells in the sanitizing medium. In both tests, T. bacillisporus proved the most resistant strain, followed by A. hiratsukae, C. globosum and A. brasiliensis at all temperatures tested. In test without a supporting material, D values of T. bacillisporus varied from 6 to 23 s. In test with metallic or plastic strips, D values of T. bacillisporus were higher on plastic materials, compared to those obtained on metallic ones up to 53 °C, whereas at higher temperatures D values proved similar. For A. hiratsukae, D values were similar if different materials were compared, except for D₅₀ on aluminium and HDPE, which proved slightly higher (3.1-3.4 s) than those obtained on tin-plate and PET (2.7-2.8 s). Analogously, ascospores of C. globosum behaved in a similar way if different materials were compared, except for D₅₀ values that varied in a wide range (from 2.9 s on tin-plate to 4.0 s on HDPE). A. brasiliensis was rapidly inactivated by the synergistic effect of heat and hydrogen peroxide, so for this strain it was not possible to calculate any D value. Based on the results obtained in this paper, tested ascospore-forming moulds proved to be sensibly more resistant to HP than other heat-sensitive strains tested, their D values always being significantly higher, regardless of the strain considered and the supporting material assessed. Ascospore-forming moulds could be furtherly investigated, as for practical purposes they seemed most suitable as target microorganisms than heat-sensitive microorganisms such as Aspergillus brasiliensis ATCC 16404, their use during bio-validations of sanitizing processes on machineries used for refrigerated products (pH > 4.5) or non-refrigerated acid products (pH ≤ 4.5) leading to more performing results.