1. Fate of Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes during the manufacture of dry cured Westphalian-style Ham
S. Balamurugan1, Carlos G. Leon-Velarde2, Saleema Saleh-Lakha2
1Guelph Food Research Centre, Agriculture & Agri-Food Canada, Guelph ON 2Laboratory Services Division, University of Guelph, Guelph ON
INTRODUCTION
ANALYSIS
RESULTS & DISCUSSION
Treatments
Schedule of sampling
For sampling, cm2 area cores (Fig. 4) were taken from each ham, homogenized and bacteria enumerated by plating on selective media.
Westphalian ham is a dry cured, ready-to-eat product that is manufactured without a lethal heat treatment. Hams are preserved by a process that involves: curing with salts and spices; fermentation; smoking; and drying. These processes have to be validated to successfully control the growth of pathogens.
Treatment
Inoculated
Bioprotective Culture (CHR Hansen) P1
Inoculum Cocktail
C-P-77
P1 Control No P2
C-P-77 and B-SF-43
P2 Control
MATERIALS & METHODS
Process Steps
Time point (day)
Enumeration of inoculated strains aw
Presence of Target Organism
Total Viable Count
Raw Ham
Inoculated Raw Ham
Uninoculated Raw Ham
Salting 3
P1/P2 14 28
P1/P2 Controls
Smoking 35
Drying 63 70
D0: Surface Inoculate ham
Cocktail (108 CFU cm-2)
4°C overnight
D1: Salting Ham
Starter culture and dry rub mixed together
Dry rub amount ≥4.3% start weight of meat
Material rubbed until all sides are covered
See Fig. 1
Strain (ATCC #)
Source
E. coli O157:H
Human
L. Monocytogenes 19115
S. enterica sp. Berta 8392
Unknown
Salmonella spp. and E.coli O157:H7 decreased by at least 5-log cm-2, regardless of starter culture.
L. monocytogenes decreased 4.41 and 5.36-log cm-2 for C-P-77 and C-P-77/ B-LC-48, respectively.
Greatest decrease for all pathogens occurred during first 28 days
Total viable count of uninoculated hams
Initial count was 2.83-log cm-2;
Slow increase to 5.01-log cm-2 after 28 days;
Under high salt conditions and 4°C.
Rapid increase to 7.73-log cm-2 by day 35;
Increased temperature in smoking chamber.
Final count was 9.04 log cm-2 after 70 days.
aw dropped from 0.98 (day 1) to between 0.93 & 0.90 (day 70, P1 & P2 respectively).
D128: Pressing
Hams placed into bins,
4°C
Bins stacked 4 high
Rotated top to bottom each week
D2935: Smoking
Hams removed from bins, placed onto racks in the smoke chamber (Fig. 2)
Temp: varied between
18-27°C
RH: varied between 70-88%
Smoke injected into chamber
Bacteria
Growth Media
Appearance
E. coli O157:H7
BBL™ CHROMagar™ O157
Mauve colonies w/ translucent borders
L. monocytogenes
ALOA® Listeria monocytogenes Chromogenic agar (bioMerieux SA)
Blue colonies w/ opaque halo
Salmonella spp.
Oxoid™ Brilliance Salmonella Agar
Purple colonies on white agar
Total viable counts
3M™ Petrifilm™ Aerobic Count Plates
Red colonies 1
Fig. 1: Raw ham in dry rub 2
Fig. 2: Hams in smoke chamber 3
Fig. 3: Final Product (cross section)
12.5 cm2 core 4
Fig. 4: Ham showing sample core
D3670: Drying
Placed into drying chamber
Temp: 13°C
RH: 75%
70 days
See Fig. 3
Conclusion
The process for the manufacture of dry cured Westphalian-style Ham is adequate for the reduction of Salmonella spp., E. coli O157:H7, and L. monocytogenes by at least 4.4 to 5.4-log regardless of the bioprotective/fermentation culture used.