Hydro peroxides
Most peroxides are odorless and tasteless per se, but they are further involved in the chain of reactions which produce the objectionable compounds Oxidation produces a number of different types of peroxides, some fairly stable, others so unstable that one cannot measure them by the normal iodometric method for peroxide value (PV) (AOAC Official Method 965.33). Such highly unstable peroxides tend to be formed from compounds that contain conjugated double bonds (R-CH CH-CH CH-R) such as fish oil, vitamin A, etc. In normal fats and oils containing methylene interrupted double bonds (R-CH CH-CH2-CH CH-R), the peroxides formed are primarily hydroperoxides which are stable for weeks or even months at room temperature. When one monitors the rate of oxidation of a refined oil using the Oil Stability Index Method (OSI) (AOCS Cd12 ), or the Active Oxygen Method (AOM), (AOCS Cd12) one can demonstrate that after the induction period, the PV increases quite rapidly This induction period is a time during which there is little change in the peroxide value measurements (often too small to measure) and can last for some time with high stability oils. As oxidation proceeds, the rate of peroxide decomposition with respect to formation increases. Eventually the peroxide values will actually begin to decrease because the formation slower than the decomposition. Some foods contain substances such as metal ions or enzymes that enhance the decomposition of the peroxides making the PV meaningless as a method of measuring rancidity. The PV test is most properly applied as a measure of the quality of fresh oils which should have a PV of one or less. Shortening with a PV of greater than 5 should not be used in the manufacture of mix products, as it will significantly decrease the shelf life of the product.