Effect of different marinade treatments on survival and morphology of pathogens in beef jerky

In the early fall of 2003, the Food Safety and Inspection Service (FSIS 2004) found that producers of meat and poultry jerky were not adequately processing the meat to achieve the lethality required to kill or reduce the number of microorganisms. In this project, ground beef jerky was prepared with four different treatments i.e. traditional marinade (TM), modified marinade (MM), acetic acid-traditional marinade (AATM), Tween 20-traditional marinade (TWTM), along with a control.;The jerky strips were individually inoculated with four different bacterial strains i.e. E. coli O157:H7, S. Typhimurium, L. monocytogenes and S. aureus and 30 minutes were allowed for bacterial attachment. The strips were then individually vacuum packaged and stored at ambient temperature for analysis at 7 day intervals up to 28 days. The parameters studied were pH, water activity and enumeration of microbial count.;The pH ranged from 5.78 for control to 4.45 for MM. The water activity ranged from 0.923 for control to 0.533 for MM. For microbial count, in case of E. coli O157:H7, a decline of 2.59 log, 2.96 log and 2.79 log was observed for MM, AATM and TWTM respectively. Even TM was able to manifest a reduction of 2.89 log units. The bacterial count reduction was significantly different (P < 0.05) between MM and other three treatments i.e. TM, AATM and TWTM at the starting point of Day 1. The same pattern was observed during the middle of observation period i.e. Day 14. However, by the end of Day 28 all four treatments i.e. TM, MM, AATM and TWTM were significantly different from control but not from each other. For S. Typhimurium, a decline of 3.47 log, 3.72 log and 3.74 log was observed for MM, AATM and TWTM respectively. However, TM was the most effective of all four treatments resulting in a reduction of 4.17 log units. The bacterial count reduction was significantly different (P < 0.05) between MM and other three treatments i.e. TM, AATM and TWTM at the starting point of Day 1. It continued until Day 7, however by the end of Day 28, all four treatments i.e. TM, MM, AATM and TWTM were significantly different from control but not from each other.;In the case of S. aureus, a decline of 2.31 log, 1.85 log and 2.44 log was observed for MM, AATM and TWTM respectively. TM resulted in a reduction of 2.05 log units. The bacterial count reduction was not significantly different between any of the treatments in the beginning i.e. Day 1. However, by the end of Day 14, MM, AATM and TWTM were significantly different (P < 0.05) from TM. By the end of Day 28, MM was significantly different (P < 0.05) from all the other treatments i.e. TM, AATM and TWTM, with TM and AATM overlapping with each other, TWTM overlapping with MM and AATM.;For L. monocytogenes, a decline of 2.77 log, 2.76 log and 2.73 log was observed for MM, AATM and TWTM respectively. TM resulted in a reduction of 2.22 log units. The bacterial count reduction was not significantly different between any of the treatments until Day 21. However, by the end of Day 28 MM was significantly different (P < 0.05) from TM but overlapping with both AATM and TWTM.;Therefore, the results confirmed efficacy of all the treatments in controlling postprocessing contamination of ground beef jerky which was evident by low microbial count in treated jerky samples compared to control. However, the effect of four different marinade treatments used i.e. TM, MM, AATM and TWTM varied greatly with respect to four bacterial strains used. AATM was the most effective treatment against E. coli O157:H7, TWTM against S. aureus, MM against L. monocytogenes and TM against S. Typhimurium.;Scanning electron microscopy was performed to confirm the results of microbiological evaluation by visual observation of pathogens on the surface of beef jerky strips. In general, the cells from all the four bacterial populations treated with the marinade treatments appeared wrinkled and, unlike the control, some fibrils connecting the cells to each other or attaching to the membrane filter began to appear. These fibrils were believed to be from cytoplasmic leakage. It is also possible that exoploysaccharide material on the outer membrane of the cells were untangled and released due to marinade treatments (Slavik and others 1994).;The response of E. coli O157:H7, S. Typhimurium, S. aureus and L. monocytogenes to marinade-induced stress as observed from Transmission Electron Microscopy (TEM) micrographs was in agreement with the results of microbiological evaluation, and enhanced the understanding of behavior of bacterial cells under marinade-stress conditions and assisted in analyzing the data obtained via quantitative techniques.