Studies on the Antimicrobial Action of Sorbic Acid The Effect of Medium pH on its Inhibitory Power

• Published in: Nippon Nōgeikagaku Kaishi Vol. 29; no. 10; pp. 805 - 809
• Main Authors: NOMOTO, Masao, NARAHASHI, Yoshiko, NIIKAWA, Yasutaro
• Format: Journal Article
• Language: Japanese
• Published: Japan Society for Bioscience, Biotechnology, and Agrochemistry 1955
• ISSN: 0002-1407; 1883-6844
• DOI: 10.1271/nogeikagaku1924.29.805

The effect of medium pH on the inhibitory power of sorbic acid toward microörganisms was determined by the dilution method. The results are as follows: 1) Without distinction of the test strain, the medium pH did significantly influence the inhibitory power of free sorbic acid: i.e. in an acidic environment, below pH 4, sorbic acid prevented the growth of microorganisms even at the concentration of about 0.002 per cent. But proportional to the increase of pH value, the inhibitory action decreased, and at a neutral pH condition it disappeared (see Table 1 and Fig. 1). On the contrary, the inhibitory powers of esters of sorbic acid was invariable in any pH condition, and maintained the same level of inhibitory powers at about 0.002 per cent (see Table 2 and Fig. 2). 2) It may be understood that such a behaviour of sorbic acid is due to selective permiability of cell membrane toward nondissociative molecules of this agent; i.e. sorbic acid dissociates in proportion to the medium pH respectively, and, in case of such molecules, the nondissociative molecules penetrate into the cell injuring cell metabolism, but the ionized molecules cannot permeate the cell membrane and thus do not have. influence upon the physiology of microbes. Therefore, the inhibitory power of sorbic acid should depend on the concentration of nondissociativemolecules, and not upon that of the ionized molecules, and as the former is decided as a function of pH, so the inhibitory power varies as a function of medium pH. It was also found for the same reason that esters, nondissociable compounds, indicate the constant maximum inhibitory powers. 3) This information is neteworthy in the application of sorbic acid to beverage etc.