INHIBITION OF BACTERIA BY SOME VOLATILE AND NON-VOLATILE COMPOUNDS ASSOCIATED WITH MILK

Abstract

APT broth inoculated with Streptococcus lactis was dispensed into epoxy-lined aerosol cans. Twenty-five milk-associated volatile or non-volatile compounds were added individually to cans to give final concentrations of 1, 10, 100, and 1000 ppm of each compound. The compounds used were formic, acetic, butyric, hexanoic, octanoic, and decanoic acid; formaldehyde; acetaldehyde; propionaldehyde; glyoxal; acetone; 2-butanone; diacetyl; propyl- and hexylamine; furfurol; methanol; methylsulfide; methylsulfone; methanethiol; ethanethiol; acetonitrile; chloroform; ether; and ethylenedichloride. Bacteria were enumerated at intervals during incubation at 30 C. Fatty acids at 1000 ppm always significantly inhibited S. lactis. Decanoic acid was more active than other fatty acids at higher concentrations, whereas formic acid caused more inhibition of S. lactis when the acids were tested at a lower concentration (10 ppm). Formaldehyde was most inhibitory of the aldehydes tested. The lowest concentration of aldehydes was only marginally inhibitory. Diacetyl was more inhibitory than acetone or 2-butanone. Acetonitrile (100 ppm), chloroform (10 ppm), ether (10 ppm), and ethylenedichloride (10 ppm) always inhibited S. lactis. Lower concentrations of methylsulfone caused minimal growth stimulation early during the incubation, but later this changed to inhibition. Ethanethiol generally was more detrimental than methanethiol, and methylsulfide was less active against S. lactis than methanethiol. Amines were more inhibitory than alcohols.