Reduction of Brochothrix thermosphacta on beef surfaces following immobilization of nisin in calcium alginate gels

Lean and adipose beef carcass tissues inoculated with Brochothrix thermosphacta (BT) (approx. 4.50 log(10) cfu cm(-2)) were left untreated (U) or treated with 100 mu g ml(-1) nisin (N), calcium alginate (A) or 100 mu g ml(-1) nisin immobilized in a calcium alginate gel(AN). Tissue samples were refrigerated after treatments and bacterial populations and nisin activity were determined at 0, 1, 2 and 7 d. U, A and N treatments of lean and adipose tissues did not suppress bacterial growth (>6 log(10) cfu cm(-2) by day 7) while treatments of lean and adipose tissues with AN suppressed bacteria (> 2.42 log(10) cfu cm(-2) by day 7). Bacteriocin titres from both tissues were higher in AN vs N samples after the 7 d incubation. This study demonstrates that immobilization of nisin in a gel may be a more effective delivery system of a bacteriocin to the carcass surface than direct application.