Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2012
Publication Date: 7/1/2012
Citation: Sheen, S., Huang, L., Sommers, C.H. 2012. Survival of Listeria monocytogenes, E.coli 0157:H7 and Salmonella spp. on catfish fillets exposed to microwave heating in a continuous mode. Journal of Food Science. 77(8):E209-E214. Interpretive Summary: The survival of Listeria monocytogenes, E. coli O157:H7 and Salmonella spp. in microwave oven using a continuous power output mode has demonstrated microwave cooking can be a usual and effective tool in foodborne pathogen reduction (5 log CFU/g reduction). This modified microwave control system and added phosphates (e.g. sodium tripolyphosphate or STPP) in foods further provide the industrial microwave application potentials with enhanced food quality and microbial safety which are the two major issues of microwave cooking.
Technical Abstract: Microwave (MW) heating using continuous power output with feedback control and a modified ingredient formulation, may provide better and consistent cooking of foods. Currently, household units with build-in inverter power supply units are available. These new generation microwave ovens provide continuous, adjustable output and cooking, in contrast to the traditional rectifier-based ovens that rely on the on-off mechanism for control. This study attempted to apply a feedback power control (termed as the modified MW) and phosphate treatment to further improve heating uniformity and enhance food quality and safety. Listeria monocytogenes (Lm, 4-strain cocktail), Escherichia coli O157:H7 (Ec, 5-strain cocktail), and Salmonella spp. (Sal, 6-strain cocktail), surface-inoculated onto catfish fillets (75 x 100 x 15 mm; weight 110g), were heated using the modified MW oven to study the inactivation of the pathogens. The sensitivity of these three bacteria to microwave heating was in the order of Ec (most), Lm, and Sal (least). Greater than 4-5 log reductions in the counts of Ec, Lm or Sal on catfish surfaces were inactivated within 2 min with full power of 1250 watts, and the surface temperature of fillets increased from 10-20 deg C to 80-90 deg C. Microwave heating caused degradation of catfish fillet texture, which was noticeable as early as 10-15 s after the heating started, as evidenced by bumping sounds. Texture further degraded by uneven heating. Negative effect of microwave heating on the products was significantly reduced by cooking in the modified MW in combination with the phosphate treatment. The results of this study successfully demonstrate the feasibility of applying MW energy for elimination of foodborne pathogens on fish fillets.