The objective of our study was to evaluate the effects of various levels (0%, l%, 2%, 3%) of sodium lactate on selected physical, sensory, and microbiological characteristics of fresh pork sausage stored at 4°C for 28 davs. Samules containing 0% and 1% SL reached 10s CFU/z after 10 days refrigerated storage. Addition of 2% or 3% SL to fresh .pork sausage delayed microbial deterioration, pH decline, and development of sour-and off-flavors 7 days at 4°C. Samples containing 2% SL did not reach total plate counts of 108 CFU/g until 24 days storage. SL appeared to protect red color, and to "enhance" porkand salty-flavors in sausage. TBA, L-, a-, and b-values were unaffected by SL level.

Four strains of Listeria monocytogenes were examined for catalase (CA) and superoxide dismutase (SOD) activities. The two strains having the highest CA activities (LCDC and Scott A) also possessed the highest SOD activities. The CA activity of heated cell extracts of all four strains examined decreased sharply between 55 and 60°C. SOD was more heat labile than CA. Two L. monocytogenes strains demonstrated a decline in SOD activity after heat treatment at 450C, whereas the other two strains demonstrated a decline at 50°C. Sublethal heating of the cells at 55°C resulted in increased sensitivity to 5.5% NaCI. Exogenous hydrogen peroxide was added to suspensions of L. monocytogenes; strains producing the highest CA levels showed the greatest H202 resistance.

Beef bologna, containing 0, I , 2, or 3% sodium lactate (SL), was vacuum packaged and stored at 4C for 0, 2 , 4 , 6, 8, and 10 weeks. Color was assessed using L*, a*, b* measures, and fade (7% reflectance 570 nm/650 nm). A trained sensory panel evaluated flavor and color intensity. Total aerobic plate counts (TPC), pH, and TBA values were determined. Addition of SL had no effect on initial pH. Pink color was correlated with a* values, fade, and TPC (r = 0.74, -0.70 and -0.54, respectively; p < 0.05). Salty-flavor intensity was highest for bologna containing 3 % SL and lowest in controls. Beefy fEavor was inversely correlated with TPC (r = -0.45, p < 0.05). Sour-flavor scores were inversely correlated with pH (r x -0.51) and directly with P C (r = 0.33, p < 0.05).Afer 10 weeks TPC for control product was highest, while that for bologna containing 3% SL was lowest. 5Correspondence should be sent to: M. Susan Brewer,

The activities of catalase, superoxide dismutase, and a thiol-activated hemolysin produced by four strains of Listeria monocytogenes propagated in media containing various concentrations of sodium chloride were examined. L. monocytogenes 7644 showed an increase in catalase, superoxide dismutase, and thiol-activated hemolysin activities when grown in a medium containing 2.5% (wt/vol) NaCI followed by a decrease in activities when propagated in media containing salt concentrations higher than 2.5%. L. monocytogenes LCDC 81-861 demonstrated enhanced catalase activity when grown in media containing NaCI ranging from 1.5 to 4.6% and increased superoxide dismutase activity when propagated in media containing 1.5 to 3.5% NaCl. L. monocytogenes LCDC 81-861 did not exhibit any detectable hemolysin activity under the conditions tested. After growth in various NaCI-containing media, both strains were subjected to sublethal heat injury for 30 min at 55°C. L. monocytogenes LCDC 81-861 showed increased sensitivity to the heat treatment when grown in media containing 4.6 and 6.5% NaCI, whereas L. monocytogenes 7644 did not exhibit enhanced heat lability.

Virulence, as determined in a mouse model, and the virulence factor activities of catalase, superoxide dismutase, and listeriolysin 0 were examined in a parental strain (10403S) and in a nonhemolytic mutant strain (DP-L224) of Listeria monocytogenes. The cells were propagated in media containing various concentrations of sodium chloride or potassium chloride. Strains 10403S and DP-L224 exhibited significant increases in catalase activity and listeriolysin 0 activity when grown in medium containing either salt at 428 mM. The superoxide dismutase activities for both strains increased when they were grown in medium containing either salt. The superoxide dismutase activity was significantly increased only when cells were propagated in medium containing no salt compared with that when they were propagated in medium containing either salt at 1,112 mM. In addition, the listeriolysin 0 activity was highest for cells propagated in medium containing KCI at 428 mM, while the activity was significantly less for cells propagated in medium containing NaCl at an equal concentration. Virulence was examined in mouse livers and spleens after intravenous infection, and approximate 50%o lethal doses were determined after intragastric and intraperitoneal infection. Each method of infection indicated that listeriolysin 0 is required for virulence, while growth in salt-containing medium or the production of higher levels of catalase, superoxide dismutase, and listeriolysin 0 do not appear to enhance the virulence of L. monocytogenes.