Comparison of different reducing agents for enhanced detection of heat-injured Listeria monocytogenes

xThe effect of different reducing agents (L-cysteine, Oxyrase, and Enteroco ccus faecium) and their combinations on the detection of heat-injured (62.8 degrees C, 7.5 min or 10 min) Listeria monocytogenes was examined. The inc orporation of L-cysteine (0.5 g/liter) yielded higher percentage detection than any of the other reducing agents (P < 0.05). The combination of Oxyras e (10 U/ml) and E. faecium (10(3) CFU/ml) synergistically enhanced the dete ction of L, monocytogenes heat-injured for 10 min at 62.8 degrees C (P < 0. 05). Simultaneous addition of L-cysteine (0,5 g/liter) and Oxyrase (10 U/ml ) significantly lowered the recovery of heat-injured L. monocytogenes (P < 0.05). Higher activities of Oxyrase (50 U/ml) inhibited the detection of he at-injured L. monocytogenes (P < 0.05). The rates of depletion of relative percentage O-2 were in the order: L-cysteine (0.5 g/liter; 6.63%/min) > Oxy rase (10 U/ml; 5.00%/min) > E. faecium (10(8) CFU/ml; 1.66%/min) > E. faeci um (103 CFU/ml; 0.20%/min). The final levels of redox potential (Eh) achiev ed were -110.5 mV, -100 mV, -83.5 mV, and -25 mV for E, faecium (108 CFU/ml ), L-cysteine, Oxyrase, and E. faecium (10(3) CFU/ml), respectively.