The Toxicity of Sulphur Dioxide towards Certain Lactic Acid Bacteria from Fermented Apple Juice

摘要

This paper describes a method for testing the effect of various concentrations of SO2on lactic acid bacteria from ciders. The media and methods were devised to minimize loss of SO2due to oxidation or binding with carbonyl compounds. Exposure of laboratory or freshly isolated strains to various concentrations of free SO2at pH 4·0 did not readily kill them even at high concentrations of free SO2(c.150 p/m or 0·97 p/m molecular SO2) yet they were suppressed at low concentrations (c.5 p/m or 0·032 p/m molecular SO2). Reducing the pH to 3·4 reaffirmed how much more effective SO2is against lactic acid bacteria at lower pH levels because more is present as molecular SO2. As a result of this the idea of quoting SO2values as p/m molecular SO2is advocated. Addition of hydrogen peroxide or acetaldehyde to a test system containing 142 p/m free SO2showed that they had a similar effect in nullifying its antimicrobial properties and allowing the test bacteria to grow. There was no indication that acetaldehyde bisulphite was toxic to the test bacte