Microbial validation for Biltong processing to achieve 5-log reduction of Listeria monocytogenes, E. coli O157:H7 and Staphylococcus aureus

Abstract

Biltong' is a South African style dried beef product that is marinated and dried at moderate heat but still must accommodate USDA-FSIS safety concerns for process validation by demonstrating a 5-log pathogen reduction. Our objective was to achieve a 5-log reduction of Listeria monocytogenes, E. coli O157:H7 and Staphylococcus aureus without a heat lethality step and evaluate the individual contribution of marinade components (spice, salt, vinegar) to the overall reduction on inoculated beef. Beef was cut into small 'steaks' (0.75-in x 2-in x 3-in) and inoculated with a 4-serovar mixture of acid-adapted L. monocytogenes, E. coli O157:H7 or S. aureus and spread on the surface of the beef. Beef pieces were vacuum tumbled with either a mixture of spice, salt and vinegar, or just individual marinade components, and marinated for 30 minutes. Beef was then dried in a temperature-controlled humidity oven for 10 days (75 degrees F/23.9 degrees C; 55% RH). All trials were performed in duplicate replication (with triplicate samples at each time point; n=6) and RM one-way ANOVA to determine significant differences (p < 0.05). The combination of spice, salt, and vinegar resulted in (>5-log) reduction for L. monocytogenes with drying period of 8 days. The greatest reduction of L. monocytogenes from individual marinade components was exhibited by vinegar (>5-log) followed by salt (4.68-log) and spice (4.1-log). Combined ingredients of marinade also resulted in reduction of (>5-log) with drying period of 4 days for E. coli O157:H7. Salt and vinegar when treated individually lead to similar reduction of (5.48-log) and (5.49-log) followed by spice (4.11-log) for E. coli O157:H7. S. aureus achieved (>5-log) reduction using combined components of the marinade after 8 days of drying and staphylococcal enterotoxin (SEA, SEB) was not produced in the meat through 10 days of drying. Water activity for 10-days of drying was 0.79. This is the first published work achieving (>5-log) reduction of L. monocytogenes, E. coli O157:H7 and S. aureus with biltong, thereby validating this process for USDA-FSIS approval that is sought by many upscale food stores to ensure product safety.