Disinfection of Household Cutting Boards with a Microwave Oven

Used cutting boards with numerous knife marks, particularly those made of polymers, are difficult to disinfect manually. Plastic cutting boards have been preferred to wood because they can be washed in dishwashers and used in microwave ovens. Our study tested the microwave oven for disinfection of cutting boards. Surfaces of plastic and wooden cutting boards were inoculated with up to 10⁹ CFU of Escherichia coli or other bacteria in broth culture and later sampled by contact with agar medium for CFU assay or by swabbing for ATP bioluminescence assay. On wood, almost total elimination of vegetative cells occurred with exposure times of the 3 to 4 min at a high setting on typical 450 to 600 g wooden boards, depending on board size, bacterial load, and moisture level. On plastic, microwave energy had almost no lethal effect on bacteria: 12 min of exposure did not reduce the number of bacteria significantly. Increased moisture (wetness) enhanced killing efficiency on wood, but was negligible on plastic. Temperatures near the wood surface reached 95°C within the first 4 min, whereas plastic surfaces reached no more than 40°C. Our study indicates that brief "cooking" of wooden boards at a "high" setting in a microwave oven is an effective way to kill bacteria, and thus a very simple and cheap method to protect food against cross-contaminating pathogens. Because plastic is relatively inert to microwaves, disinfection of plastic boards in a microwave oven is impractical.