A comparative study on the inactivation of Penicillium expansum spores on apple using light emitting diodes at 277 nm and a low-pressure mercury lamp at 253.7 nm

Abstract

A comparative study was performed to assess the efficacy of UV-C light emitting diodes (UV–C LEDs) at 277 nm and a low-pressure mercury (LPM) lamp at 253.7 nm to inactivate Penicillium expansum spores on apple skin at 4 °C or 25 °C. In saline solution, the D value for the inactivation of spores using 277 nm at 25 °C was 6.62 mJ cm−2 and 7.19 mJ cm−2 at 4 °C, both of which were significantly lower than the D value at 253.7 nm (9.26 mJ cm−2). The UV-mediated inactivation of spores on the surface of apple skin followed non-linear kinetics with an initial linear phase followed by tailing. The calculated D values for spores on apple surface were significantly higher compared to within saline (14.49 and 18.80 mJ cm−2 with 277 nm at 25 °C and 4 °C, respectively, compared to 23.00 mJ cm−2 with 253.7 nm). This could be due to protective effects of apple peel constituents or the non-uniform energy distribution due to the uneven apple surface. Yet, the log reductions achieved (>2 log CFU) were equivalent to washing in hypochlorite solution (200 mg L−1 free-chlorine) which is the current industrial practice. UV-C light at 277 and 253.7 nm (500 mJ cm−2) was shown to prevent growth of blue mould and subsequent spoilage of inoculated and stored apples (28 days) if treated prior to damage. The UV-C treatments at doses corresponding to reduction of 2 log CFU of P. expansum did not impact apple physico-chemical quality parameters during 12 weeks of storage at 25 °C.