Mary Ann Liebert, Inc. DOl: 10.1089/fpd. ... Enteritidis by approximately 4.8 and 6.0 logo CFU/mL, respectively. ... pressure-resistant mutants of E. coli in apple.
FOODBORNE PATHOGENS AND DISEASE Volume 5, Number 2, 2008 Mary Ann Liebert, Inc. DOl: 10.1089/fpd.2007.0055
Effect of Hydrostatic Pressure Pulsing on the Inactivation of Salmonella Enteritidis in Liquid Whole Egg M.L. Bari,' D.O. Ukuku, 2 M. Mon, 3 S. Kawamoto, 1 and K. Yamamoto'
Abstract Eggs and egg-containing foods contaminated with bacterial human pathogens have been implicated in numerous foodhorne outbreaks leading to costly recalls. Research was undertaken to investigate the use of high pressure-pulse treatment to inactivate Salmonella Enteritidis inoculated in liquid egg. Liquid egg was inoculated with Salmonella Enteritidis (8.0 log colony-forming units [CFU]/mL) and exposed to hydrostatic pressures (300-400 MPa) and pressure (350 MPa) pulsing at 25 C, 40C, and 50 C for up to 40 minutes to determine the maximum allowable pressure that can inactivate the Salmonella with minimal injury. Pressure treatments (350 and 400 MPa) at 25C for up to 40 minutes reduced the population of Salmonella Enteritidis by approximately 4.8 and 6.0 logo CFU/mL, respectively. High pressure (350 MPa) treatment at 50C and 2-minute pulses at four cycles for a total of 11.4 minutes, including the come-up and come-down times, led to a significant (17 C',
3.00 2.00 1.00 0.00
10 20 30 40
10 20 30 40
Treatment time (mm)
FIG. 1. Effect of selective and nonselective media on recovery of injured and surviving Salmonella in treated liquid whole egg at 25 C. Values are means ± SD of three experiments with duplicate determinations.
SALMONELLA IN
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LIQUID WHOLE EGG
was 1.0 log higher than that of 400 MPa treated samples. Although, we observed a slight decrease in microbial populations in samples recovered on BSA compared to TSA, there was no significant (p > 0.05) difference in terms of populations recovered per media. Ponce et al. (1999) reported similar findings on selective and nonselective media. The influence of HPPprocessing temperatures (25 C, 40 C, 50 C) on inactivation of Salmonella in liquid egg was monitored at 350 MPa pressure up to 40 minutes. Highest inactivation of Salmonella Enteritidis in the liquid egg was observed at 50 C which resulted to a 6.0 log CFU/mL reduction (Fig. 2). It has been reported that a high-pressure processing at moderate temperature could retain product functionality and maximize microbial inactivation (Lee et al., 2003; Ponce et al., 1999; Tewari et al., 1999). Since liquid egg is a sensitive product, we therefore hypothesized that a lower HPP treatment at 25C to 50C with pressure pulsing might be appropriate for microbial reduction without causing coagulation. Therefore a pressure of 350 MPa was determined and confirmed to be the optimum pressure treatment that can achieve significant microbial reduction with no or minimal coagulation of liquid whole
egg (data not shown). The 350 MPa pressure treatments were repeated at 25 C to 50 C for 10 minutes and results showed no coagulation of liquid whole egg. Again the microbial population recovered on BSA after 350 MPa pressure treatments of liquid egg samples at 40C for 40 minutes was lower than the numbers on TSA. High pressure 350 MPa treatment at 25 C for 10 to 20 minutes treatment time did not result in significant (p > 0.05) log reduction of Salmonella Enteritidis. But when temperature was increased from 25-C to 40 C, a significant (1) 0.05) different at 30 and 40 minutes (Fig. 3). Percent injury for Salmonella Enteritidis was not found in sample treated at 25 C until 40 minutes. At 350 MPa pressure and treatment temperature of 50C for up to 40 minutes led to approximately 0.58% injury of the pathogen at 10 minutes,
10.00 9.00 8.00
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6.00
0
0 U)
5.00 4.00
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3.00
U)
2.00 1.00 0.00 0 10 20 30 40
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Treatment time (mm)
FIG. 2. Effect of temperature and 350 MPa pressure on surviving Salnwtu'I/a in treated liquid whole egg. Values are means ± SD of three experiments with duplicate determinations.
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BARI ET AL. 1.4
-r
1.2 E U- 1
0
0
0)
.9 0.8 C 0.6
0.4 .0 U)
0.2
0 0
10
20
30
40
Treatment time (mm)
FIG. 3. Effect of temperature on recovery of injured and surviving Salmonella in treated liquid whole egg at 350MPa. Values are means ± SD of three experiments with duplicate determinations.
3% injury at 20 minutes, and was below detec- four cycles at 50C for the inactivation of Saltion at 30 and 40 minutes, respectively. mane/la Enteritidis in liquid egg is shown in Fig. 4. A total of 11.4 minutes (including the come-up and come-down pressure times) for the Effect of pressure-pulse treatment 2-minute 350 MPa pressure-pulse treatments of The results of 350 MPa hydrostatic pressure the liquid egg inoculated with Salmonella Enpulsing at 2-, 5-, and 10-minute treatments for teritidis resulted to a complete inactivation of 10 9 8 E7 U. C.) 6 0
C)
05 0)
04 3 2
0
0 2 4 6 8 0 5
10 15 20 0 10 20 30 40
Treatment
time (mm)
FIG. 4. The effect of repeating hydrostatic pressure (2 minutesx4 cycles, 5 minutes>
