Acid-Adaptation Leads to Sensitization of Salmonella Challenge Cultures During Processing of Air-Dried Beef (Biltong, Droëwors)

US food regulatory agencies have adopted a preference for researchers and testing labs to use ‘acid-adapted challenge cultures’ when performing inoculated validation studies of food processes that involve acidic treatments to accustom the cultures to acidic pH so that they will not be easily affected during processing. We evaluated acid adaptation in regard to the processing of South African style air-dried beef notably, biltong and droëwors, using a mixture of five serovars of Salmonella. Acid adaptation was obtained by growing cultures in tryptic soy (TS) broth containing 1% glucose. Non-adapted cultures were obtained by growth in TS broth without glucose or, in TS broth with 1% glucose but buffered with 0.2M phosphate buffer. Processes included biltong (dried solid beef) and droëwors (ground, sausage-style). Each trial was performed twice and triplicate samples were examined at each sampling point (i.e., n = 6). Statistical analysis was applied using analysis of variance (ANOVA) or one-way repeated measures (RM-ANOVA) and the Holm–Sidak test for pairwise multiple comparisons to determine significant differences (p < 0.05). We observed that in all processes examined, treatments using acid-adapted cultures were more sensitive to the biltong and droëwors processes, giving greater reductions than when non-adapted cultures were used. We conclude that acid-adaptation leads to stressed conditions in Salmonella resulting in sensitization to the multiple hurdles found in biltong/droëwors processing (acid/vinegar, salt, desiccation) and the use of non-adapted cultures could actually lead to more robust bacterial conditions for testing process effectiveness.