A new approach for measuring the redox state and redox capacity in milk

Milk is one of the most fundamental ingredients in our diet. It is a complex biological fluid, which contains numerous substances, ranging from metal ions to enzymes. There is a constant search for an improved way of monitoring its quality and freshness. These are highly affected by the redox state of milk, which is governed by different species. In this study, we investigated the redox state and capacity of milk. Specifically, milk was potentiometrically titrated using different redox mediators, which enabled facilitation of electron transfer between different oxidizable species and the electrode. We found that the iodine/iodide redox couple was superior for measuring the redox capacity of milk. These measurements revealed that milk is not a well-poised system due to the presence of at least two different oxidizable species, one of which is hydrophobic while the other is hydrophilic and therefore could be separated by phase separation of milk.