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

Lean and adipose beef carcass tissues inoculated with Brochotrix thermosphacta (BT) (approx. 4.50 log₁₀ cfu cm^-2) were left untreated (U) or treated with 100 μg ml^-1 nisin (N), calcium alginate (A) or 100 μg ml^-1 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 log₁₀ cfu cm^-2 by day 7) while treatments of lean and adipose tissues with AN suppressed bacteria (> 2.42 log₁₀ 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.