A procedure for reproducible measurement of redox potential (Eh) in dairy processes

The oxidoreduction potential (E (h)) is of growing interest in dairy research and the dairy industry. Lactic acid bacteria are able to decrease the E (h) to considerable reducing values, and it is an important feature of the technological characteristics of lactic starters and probiotics. Reducing E (h) is also necessary for the development of the characteristic flavour of certain fermented dairy products such as cheeses. Moreover, data comparisons and interpretations are often difficult due to an absence of standardised expression of the results. The objective of this work was to propose a complete procedure for the use of combined and half-cell platinum (Pt) sensors to obtain stable, repeatable and reproducible E (h) measurements and to standardise data. Three measurement systems, each made up of a sensor, cable and interface, were compared in tap water. A control chart was used to calculate a confidence interval (CI = 20 mV) to verify whether the process was under control. This complete procedure was then applied to the measurement of E (h) in milk samples to characterise both pure strains of lactic acid bacteria and complex mixed starters, to study the impact of a process parameter (oxygen) on starter activity, to follow E (h) during cheese making and to measure E (h) gradients in cheeses. This manuscript presents a procedure for the measurement of E (h) as well as the feasibility and interest of this procedure in the dairy chain.