Effects of ultraviolet irradiation on the growth of micro‐organisms on chilled beef slices

Summary Continuous ultraviolet irradiation (0.‐2–24 μW/cm2) of psychrophilic micro‐organisms growing on muscle slices at 0°C and an equilibrium relative humidity (ERH) of 99–3% resulted in an extension of the lag phase of Pseudomonas sp. and of the moulds Thamnidium sp. and Penicillium sp., but not of the yeast Candida scottii. While both reduction in growth rates and in levels of the stationary phase of bacteria significantly increased with u.v. intensity only the levels of the stationary phase of the yeast were reduced significantly. With intensities of > 2.1 μW/cm2 growth rates of the moulds were significantly less than those of controls and no aerial mycelium appeared. Lower ERH did not substantially increase u.v. effects. The relative extension of storage life at 10°C was comparable to that obtained at 0°C. Simultaneous use of u.v. (0.2 μW/cm2) and ozone (0.5 mg/m3) produced synergistic effects with moulds, but not with bacteria. The results suggest that the application of u.v. light with an intensity not lower than 2 μW/cm2 is necessary to obtain a substantial inhibition of microbial growth.