Inhibition of Staphylococcus aureus on beef by nisin-containing modified alginate films and beads

Nisin, a bacteriocin, was immobilized into palmitoylated alginate-based films or in activated alginate beads. Sterile beef muscle slices or ground beef were inoculated with Staphylococcus aureus at a level of 104 CFU/g. Sliced beef was then coated with palmitoylated alginate-based films containing 0, 500 or 1000 IU/mL of nisin. Also, ground beef was mixed with 0, 500 or 1000 IU/mL of nisin covalently linked to activated alginate beads in order to evaluate the effect of nisin concentration on S. aureus level. The content of S. aureus in beef was determined during storage at 4 °C. Results demonstrated that after 7 days of storage, a reduction of 0.91 and 1.86 log CFU/cm2 was observed on sliced beef covered with film containing 500 or 1000 IU/mL of nisin, respectively. After 14 days of storage, when nisin solution (500 or 1000 IU/g) was mixed with ground beef, 2.2 and 2.81 log CFU/g reductions of S. aureus counts were respectively observed. However, when nisin (500 or 1000 IU/g) was linked into activated alginate beads, 1.77 and 1.93 log CFU/g reductions of S. aureus counts were respectively observed (P ⩽ 0.05). These results suggest that sterile, hydrophobic and biodegradable films or beads incorporating various amounts of nisin could be used efficiently to control the growth of pathogens or microorganisms responsible of spoilage at the surface of round beef or other meat products