Postprocessing cross-contamination of cheese can lead to both food safety issues and significant losses due to spoilage.
PL treatment, consisting of short, high-energy, broad-spectrum light pulses, has been proven effective in reducing the microbial load on cheese surface.
As PL treatment effectiveness is limited by light-cheese interactions, the authors looked at the possibility of improving its effectiveness by combining it with the antimicrobial nisin.
The effect of natamycin, which is added to cheeses as an antifungal agent, on PL effectiveness was also investigated.
Slices of sharp white Cheddar cheese and white American singles were cut in rectangles of 2.5 × 5 cm. For cheese slices receiving antimicrobial treatment before PL, slices were dipped in natamycin or nisin, spot inoculated with 100 μL of bacterial suspension, and then treated with PL.
Cheese slices receiving PL treatment before antimicrobials were spot inoculated, treated with PL, and then treated with antimicrobials.
Results discussed – the order matters
Treatment with nisin or natamycin before PL decreased the effectiveness of PL for all bacteria tested. The authors said this is because both nisin and natamycin have the ability to absorb light in the UV range, which diminished the effective fluence in the bactericidal range of PL, and thus diminished the antimicrobial potential of PL.
Increased inactivation was obtained when antimicrobials were applied after PL.
Even under these circumstances, PL in combination with nisin and natamycin offered only a marginal increase in microbial reduction compared with PL alone.
Besides the observed antagonistic effects, the authors said questions arise regarding the possibility of degradation of antimicrobials by PL and formation of by-products, which should be monitored in the future.
They added interactions between the individual treatments need to be verified before any such treatments are used in commercial applications.
The project was supported by the Dairy Research Institute.
Pulsed light and antimicrobial combination treatments for surface decontamination of cheese: Favorable and antagonistic effects
Source: Journal of Dairy Science, March 2017
Authors: J. Proulx, G. Sullivan, L.F. Marostegan, S. VanWees, L.C. Hsu, C.I. Moraru