Synergistic effect of UV, laser and microwave radiation or conventional heating on E. coli and on some spoilage and pathogenic bacteria

Although laser sterilisation has been well studied in dentistry and medicine, there have been few studies within the food industry. UV radiation has been used for sterilisation of surfaces and water. The killing effect of microwave radiation has been investigated on many bacteria in food and there has been much controversy over its killing mechanism. In this study, the killing effect of laser, microwave and UV radiation was studied on E. coli and on some spoilage and pathogenic bacteria. The bacterial suspensions were exposed to the treatment processes in sequence and viable cell counts were made before and after each treatment. A difference in the reduction in viable counts was apparent when the sequential treatment was compared with the sum of the individual treatments alone. Similar results were obtained when conventional heating was used in place of microwave radiation. It was found that the order of the treatment processes had a significant influence on killing.Industrial relevanceSpoilage organisms often require treatment greater than the damage threshold of the substrate food, indicating that removal of these organisms with conventional meansmay lead to substrate damage. The present work develops protocols and experiments in liquid to investigate the combination of relatively low level treatments to reduce the effect of one treatment alone but with the added advantage of more severe degradation of the spoilage organisms. This technology is of interest to the foodprocessing or packaging industry where the presence of spoilage or pathogenic organisms are of concern.

Research Highlights
► Synergistic effect observed with UV, laser, microwave or conventional heating.
► The treatment order is important to maximise the synergistic effect.
► Optimal order was laser, heating then UV.
► Optimal order may be organism dependent.