Pathogen inhibition, surrogate validation and microbiome analysis during biltong processing

Abstract

Biltong is a South African dried beef product that is made from beef that is marinated in a mixture of spices, vinegar and salt and then dried at ambient temperature and humidity. USDA-FSIS dried beef processing guidelines require beef jerky products to be cooked in excess of 90% humidity and 145℉. Since biltong processing deviates from these requirements, processors must demonstrate to the USDA-FSIS that their process can achieve a sufficient microbial reduction. There is limited data demonstrating sufficient reduction of foodborne pathogen of interest (Salmonella) for biltong manufacturing. The objective of this study was to identify approaches to control Salmonella in biltong processing. Validation studies were conducted using beef pieces (1.9-cm x 5.1-cm x 7.6-cm) inoculated with a four-serovar mixture of Salmonella, vacuum-tumbled in a marinade comprised of spices, 4% 100-grain red wine vinegar, and 2.2% NaCl and dried in a humidity-controlled oven for 8 days (25℃/75℉; 55% relative humidity). Microbial enumeration of surviving surrogate bacteria and evaluation of intrinsic factors (water activity, pH, salt concentration) were performed post-inoculation, post-marinade, and after 2-, 4-, 6-, and 8 days of drying. Separate validation studies were conducted using potential surrogate organisms (commercially available starter culture lactic acid bacteria and isolates obtained from biltong-processed beef) for in-plant validation of biltong processing. Further microbiome analysis of biltong manufacturing was also done to evaluate changes in the microbiome during processing. Samples were taken at each step of the biltong process. DNA extraction was performed prior to 16S rRNA sequencing and bioinformatic analysis. A 5-log reduction was achieved in all validation studies. Carnobacterium sp. was the only tested bacteria with similar activity to pathogens during processing and is recommended as a surrogate for biltong processing. During processing, there was an increase in observed diversity on the raw beef which diminishes after marination and drying, resulting in primarily Latilactobacillus sp. on the beef. We believe this is the first published report of a biltong process achieving >5.0 log10 reduction of Salmonella which is a process validation recommendation by USDA-FSIS for the sale of dried beef in the USA and helps to fill USDA-FSIS knowledge gaps in air-dried, shelf-stable dried beef.