Antimicrobial properties and mechanism of volatile isoamyl acetate, a main flavour component of Japanese sake (Ginjo-shu).

To evaluate the antimicrobial properties of the main Ginjo-flavour components of sake, volatile isoamyl acetate and isoamyl alcohol. Volatile isoamyl acetate and isoamyl alcohol both inhibited growth of the five yeast and 10 bacterial test strains. The minimum inhibitory dose and minimum bactericidal (fungicidal) dose of isoamyl acetate were higher than those of isoamyl alcohol. Escherichia coli and Acetobacter aceti were markedly sensitive to isoamyl acetate and isoamyl alcohol. In E. coli exposed to isoamyl acetate for 5 h, changes in expression were noted in proteins involved in sugar metabolism (MalE, MglB, TalB and PtsI), tricarboxylic acid cycle (AceA, Pfl and AcnB) and protein synthesis (EF-Tu, EF-G, and GlyS). Expression of acid and alcohol stress-response proteins was altered in E. coli exposed to isoamyl acetate. Esterase activity was detected in E. coli, suggesting that isoamyl acetate was hydrolyzed to acetic acid and isoamyl alcohol. Acetic acid and isoamyl alcohol damaged E. coli cell membranes and inactivated membrane proteins, impairing respiration. Volatile isoamyl acetate and isoamyl alcohol were effective in inactivating various micro-organisms, and antimicrobial mechanism of volatile isoamyl acetate against E. coli was clarified based on proteome analysis. To the best of our knowledge, this is the first report to examine the antimicrobial mechanism of volatile organic compound using proteome analysis combining two-dimensional difference gel electrophoresis with peptide mass fingerprinting.