PASTEURIZATION OF FOOD BY MICROWAVE IRRAD IATION

Bacteria in frozen shrimp (4.1 x 10(3)/g), refrigerated thick custard (1.2 x 10(2)/g) and frozen pilaf (1.2 x 10(2)/g) were killed by microw ave irradiation for 40 seconds, 60 seconds and 4 minutes, respectively . The temperatures at the center of the foods at that time were 55 deg rees C, 25 similar to 30 degrees C and 80 degrees C, respectively. E. coli (4.2 x 10(3)/ml), S. aureus (7.0 x 10(3)/ml) and B. cereus (1.6 x 10(5)/ml) in saline were also killed by microwave irradiation. The pa steurization time for killing of E. coli and S. aureus was about 30 se conds and the temperature at that time was about 50 degrees C. The pas teurization time of B. cereus was 90 seconds and the temperature was 1 00 degrees C. But spores (2 x 10(2)/ml) survived when B. cereus in sal ine was heat-treated at 100 degrees C for 30 minutes. Microwave irradi ation was shown to result in the release of proteins from E. coli, as detected by gel electrophoresis of cell-free supernatants using sensit ive silver staining. The above results suggest that the mechanisms of killing of bacteria depend not only on temperature, but also on other effects of microwave irradiation.