Five longissimus muscles from USDA Select carcasses were used in preliminary research to determine an optimal air pressure of 25 psi for needle-free injection. An additional 15 strip loins were inoculated with generic E. coli at a target level of 105-6 CFU/cm2. After 1 hour of microbial attachment, matching halves were allocated to needle-free or needle injection with a phosphate and salt solution. Immediately after injection, two cores were taken aseptically from each half and cross-sectional slices were taken at the inoculated surface and at depths of 0.4, 1.2, and 2 in. to determine translocation of generic E. coli. Two steaks were displayed 5 days for retail color life evaluation, and a third steak was cooked for slice shear force determination. The objective of this experiment was to compare the effects of needle-free injection and traditional needle injection on microbial translocation of generic Escherichia coli into subsurfaces of beef strip loins and determine effects on tenderness and color.

Samples taken from the surface of needle-injected muscles had lower (P<0.05) microbial counts than needle-free injected muscles (2.79 vs. 3.23 log CFU/g, respectively). Also, the 1.2- and 2.0-in. depth samples from needle injection had the least (P<0.05) microbial contamination (1.69 and 2.12 log CFU/g, respectively). Traditional needle injection resulted in approximately 0.5 log CFU/g less microbial contamination at all depths. Both treatments resulted in acceptable tenderness; however, needle-free injection improved (P<0.05) tenderness more than needle injection. Needle injection posed fewer microbial risks but resulted in less tender steaks compared with needle-free injection.

Bottom Line…. Needle-free injection enhancement might be expected to slightly increase microbial translocation into the muscle interior by as much as 0.5 log10 CFU/g compared with needle injection but improve tenderness compared with needle controls and have no effect on color display life. View the complete research report at For more information, contact Michael Dikeman and Liz Boyle, Kansas State University Extension