INHIBITION OF LACTIC STREPTOCOCCI AND SOME PATHOGENIC BACTERIA BY CERTAIN MILK-ASSOCIATED VOLATILE COMPOUNDS AS MEASURED BY THE DISC ASSAY1

Abstract

Twenty-seven milk-associated volatile compounds were tested with the disc assay procedure for their ability to inhibit Streptococcus cremoris, Streptococcus lactis, Streptococcus diacetilactis, Leuconostoc citrovorum, Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus. Anisaldehyde, butyraldehyde, formaldehyde, glyoxal, diacetyl, butyric acid, decanoic acid, formic acid, hexanoic acid, octanoic acid, hexylamine, and propylamine inhibited all test cultures although frequently only at concentrations of 10,000 and 100,000 ppm. In addition, isobutyraldehyde (100,000 ppm) inhibited L. citrovorum, E. coli, S. typhimurium, and S. aureus and acetaldehyde (100,000 ppm) inhibited S. aureus. Compounds most active (inhibition at 1,000 ppm) against S. lactis, L. citrovorum, and S. aureus were formaldehyde, glyoxal, and decanoic acid; against S. cremoris were formaldehyde, butyric acid, decanoic acid, formic acid, and hexanoic acid; against one strain of S. diacetilactis were glyoxal, diacetyl, and decanoic acid; against another strain of S. diacetilactis were formaldehyde, decanoic acid, and formic acid; against E. coli were formaldehyde and formic acid; and against S. typhimurium were formaldehyde, diacetyl, butyric acid, formic acid, and hexanoic acid. At a concentration of 1,000 ppm formaldehyde inhibited all test cultures except the fast acid-producing S. diacetilactis and decanoic acid all but E. coli and S. typhimurium. The disc assay procedure was unsatisfactory for evaluating highly volatile compounds since they evaporated before adequate diffusion into the agar occurred.