Acidulants and low pH

Abstract

The pH and organic acid content of foods are two significant factors that may determine not only the types of organisms that will survive during storage but also their activities as spoilage organisms. In general, growth of important food-spoilage and food-poisoning organisms occurs over the range pH 4–8, whereas spoilage yeasts and molds are able to grow and survive at lower pH. Although organisms do exist that grow outside these pH ranges they have not in the past represented a significant problem in food spoilage. The pH of a food can be lowered artificially by the addition of significant amounts of acid: for example, acetic, citric, and lactic acids are often added to foods to lower the pH and in this way to limit microbial growth. This approach may be complemented by the addition of low concentrations of specific lipid-soluble weak acids, for example, benzoic and sorbic acids. The combined effect of a low pH plus a high weak-acid concentration leads to acidification of the cytoplasm, which is usually sufficient to restrict microbial growth, but may also have other specific effects on cell activity. Over recent years, greater insights have emerged into the mechanisms employed by yeasts and bacteria to counter acid stress.