Peroxide value

The peroxide value is defined as the amount of peroxide oxygen per 1 kilogram of fat or oil. Traditionally this was expressed in units of milliequivalents, although in SI units the appropriate option would be in millimoles per kilogram (N.B. 1 milliequivalents = 0.5 millimole; because 1 mEq of O2 =1 mmol/2 of O2 =0.5 mmol of O2, where 2 is valence). The unit of milliequivalent has been commonly abbreviated as mequiv or even as meq. ==Method==

The peroxide value is determined by measuring the amount of iodine which is formed by the reaction of peroxides (formed in fat or oil) with iodide ion. : The base produced in this reaction is taken up by the excess of acetic acid present. To measure the iodine, a redox titration is performed using sodium thiosulfate. : The acidic conditions (excess acetic acid) prevents formation of hypoiodite (analogous to hypochlorite), which would interfere with the reaction. A starch indicator solution is used, for which amylose forms a blue to black solution with iodine and is colorless when the iodine is converted to iodide titrated. ==Taste==

Peroxide values of fresh oils are less than 10 milliequivalents/kg; when the peroxide value is between 30* and 40 milliequivalents/kg, a rancid taste is noticeable. ==See also==