Oxidation-Reduction Potential

Definition: Oxidation may be defined as the uptake of oxygen or the loss of hydrogen or the loss of electrons. Likewise reduction is defined as the loss of oxygen or the uptake of hydrogen or the gain of electrons. These process of oxidation and reduction go simultaneously in a system composed of more than onesubstance constituting the system which involve exchange of electrons simultaneously in the system.

Theory: Exchange of electrons generates an electromotive force i.e. emf in the system which indicates the direction in which processes proceeds. This is illustrated with the equation

Method of determining oxidation-reduction potential: Method of determining oxidation-reduction potential is based on the principle of oxidation-reduction.Substances giving or taking electrons in a solution creating potential difference can be measured using electrodes. Potential difference can be measured by platinum electrode (e.g., donating or accepting electrons) and a reference calomel electrode in the presence of a potentiometer. The voltage measured under these conditions gives the oxidizing or reducing capacity of the system. This is simply called as oxidation-reduction potential and is designated by the symbol E h . A positive potential involving loss of electrons from the platinum electrode is indicative of oxidizing properties, whereas a negative potential, which involves gain of electrons at the platinum electrode, gives reducing capacity.

The Oxidation-Reduction Potential of milk: Milk has a positive oxidation-reduction potential. It ranges between +0.2 and +0.3 volt for cow milk with an average value falling between +0.23 and +0.25 volt. This is primarily due to the presence of dissolved oxygen in milk. Flushing of oxygen of milk with nitrogen decreases the oxidation - reduction potential of milk. Heating of milk such as HTST Pasturization milk or preheating prior to making milk powder produces reducing substances in milk. This lowers E h values in heated milk or dried milk. Thus superior quality with higher storage capacity milk powders can be prepared by increasing reducing substances in it.

Bacterial contamination: of milk affects E h of milk. A lowering of E h occurs due to consumption of oxygen by microorganisms. Also reducing substances are formed during the course of bacterial metabolism. Methytane blue reaction is based on E h . A negative E h is obtained when the dye becomes colourless.

Presence of copper in milk also influences E h . Copper acts as an oxidizing agent with very strong electron acceptance. Presence of copper raises E h of milk.

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.


Most Reading