Use of antibiotics to inhibit non-starter lactic acid bacteria in Cheddar cheese

The efficacy of Nisin, Penicillin G and Streptomycin at inhibiting the growth of the non-starter lactic acid bacteria (NSLAB) in Cheddar cheese was studied in cheeses treated with an antibiotic-salt mixture after milling. Nisin (500 U g^-1 curd) and particularly Streptomycin (12 μg g^-1 curd) did not effectively inhibit NSLAB. Penicillin G (12 U g^-1 curd) reduced NSLAB numbers but mixtures of antibiotics (250 U Nisin, 6 U Penicillin G, 6 μg Streptomycin g^-1 curd or 500 U Nisin, 12 U Penicillin G, 12 μg Streptomycin g^-1 curd) were more effective than any individual antibiotic. The higher level antibiotic mixture reduced NSLAB populations by 4-5 log cycles compared with the control after 100-160 days. Viable starter numbers (after 35 days) were not affected by the antibiotic treatments. Antibiotic- treated cheeses contained higher levels of free amino acids but no differences between the cheeses were indicated by urea-polyacrylamide gel electrophoresis or reverse-phase HPLC.