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INJURY OF ESCHERICHIA-COLI AND DEGRADATION OF RIBOFLAVIN DURING PASTEURIZATION WITH MICROWAVES IN A TUBULAR FLOW REACTOR

1992-01-01
AKTAS, SN
OZILGEN, M
Injury and death of Escherichia coli by microwaves in a tubular pasteurization flow reactor was detected by using nutrient and violet red bile agars with reactors of length 100, 150 and 195 cm and average flow velocities of 159, 211, 233 and 247 cm/min. Under these conditions, generally 15 to 25% of the surviving micro-organisms were injured. The fraction of the injured microorganisms increased drastically near total sterilization conditions. In a typical experiment with 150 cm of reactor length, 159 cm/min of average velocity, 1 × 105 cfu/mL of initial microbial load, 8.3 × 104 cfu/mL of the micro-organisms were destroyed, 1.7 × 104 cfu/mL ssurvived and 1.5 × 104 cfu/mL of the survivors were injured. Cells injured during pasteurization may escape detection and are still capable of repair and producing toxins, therefore they might be potentially more hazardous than uninjured cells. Damage by the pasteurization process on nutrients was assessed with reference to riboflavin. When an inoculum with 105 cfu/mL was pasteurized to reduce the viable microbial concentration to less than 1% of the initial population, 25 to 40% of riboflavin was degraded. Ratios of the maximum to minimum values of the pre-exponential constant of the Arrhenius expression were about 36 times larger with E. coli than those of riboflavin obtained under the same conditions. The large variation of this ratio may imply that the death mechanism varies with the experimental conditions in the microwave field.