Redox potential (Eh) of food matrices

Among the various parameters that characterize an environment, redox status is a relatively recent development. The notion of oxidation has often been associated with the presence of oxygen, and the amalgam of oxygen and oxidation can reduce our understanding of redox processes.

The redox potential or E _h in the same way as pH, is an intrinsic parameter of all media, as soon as they contain a molecule that can change from one oxidation state to another. Whereas pH determines acid-base characteristics, E _h concerns redox properties (reducing medium, negative E _h = electron donor, oxidizing medium, positive E _h = electron acceptor).

The measurement of E _h has been the subject of various investigations since the development of sensors in biotechnology and the food industry, particularly in the 1980s, with more or less conclusive results. Problems have arisen with the reproducibility of measurements and the expression of redox potential values, making it difficult to interpret the results. There are few sensors available in these fields, and it would be regrettable to deprive ourselves of the information that a redox sensor can provide.

The last decade has shown a renewed interest in E _h measurement in the food industry, particularly through a rigorous metrological approach, which has helped to correct the variability of results.

The next step is to use the data collected. Like pH, E _h measurement does not generally provide precise information on the physico-chemical composition of the medium, as it is not a specific electrode. Using it to compare two media of similar physico-chemical composition can therefore prove tricky. On the other hand, it is a measurement that can be advantageously used in two fields:

• measurement of biological activity: living organisms, through their respiratory or fermentative metabolism, lead to a reduction in the surrounding environment, which can be advantageously used for both flora of interest and alteration flora;

• monitoring the redox state of a medium: applications have shown the value of fixing the redox state of a medium, or at least monitoring this redox state. Measuring the E _h then enables direct measurement and on-line monitoring.

This article sets out to detail these various aspects, highlighting the...