Redox properties of milk

Oxidation-reduction (redox) reactions involve the transfer of an electron from an electron donor (reducing agent) to an electron acceptor (oxidizing agent). The species that loses electrons is said to be oxidized while that which accepts electrons is reduced. Since there can be no net transfer of electrons to or from a system, redox reactions must be coupled and the oxidation reaction occurs simultaneously with a reduction reaction. 

The tendency of a system to accept or donate electrons is measured using an inert electrode (typically platinum). Electrons can pass from the system into this electrode, which is thus a half-cell. The Pt electrode is connected via a potentiomenter to another half-cell of known potential (usually, a saturated calomel electrode). All potentials are referred to the hydrogen half-cell  

becomes more positive as the concentration of the oxidized form of the compound increases. is influenced by pH since pH affects the standard potential of a number of half-cells. The above equation becomes  

The concentration of dissolved oxygen is the principal factor affecting the redox potential of milk. Milk is essentially free of O2 when secreted but in equilibrium with air, its Oj content is about 0.3 mM. The redox potential of anaerobically drawn milk or milk which has been depleted of dissolved oxygen by microbial growth or by displacement of O2 by other gases is more negative than that of milk containing dissolved O2. 

of milk is influenced by exposure to light and by a number of processing operations, including those which cause changes in the concentration of O2 in the milk. Addition of metal ions (particularly Cu ) also influences the redox potential. Heating of milk causes a decrease in its 

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Although whey protein concentrates possess excellent nutritional and organoleptic properties, they often exhibit only partial solubility and do not function as well as the caseinates for stabilizing aqueous foams and emulsions (19). A number of compositional and processing factors are involved which alter the ability of whey protein concentrates to function in such food formulations. These include pH, redox potential, Ca concentration, heat denaturation, enzymatic modification, residual polyphosphate or other polyvalent ion precipitating agents, residual milk lipids/phospholipids and chemical emulsifiers (22). 

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